SOP CONFERENCE PROTOCOLS FOR BEGINNERS

1. SOP ON STEREOTAXY
Compiled By
MAHATMA GANDHI CANCER HOSPITAL
AND RESEARCH INSTITUTE
VISAKHAPATNAM
INDIA

2. Editors In Chief
Dr. Voonna Murali Krishna
Dr. Kanhu Charan Patro
Editors
Dr. Chitta Ranjan Kundu
Dr. Partha Sarathi Bhattacharyya
Dr. Venkata Krishna Reddy
Dr. Palla Madhuri
Mr. A C Prabu
Ms. Subhra Das
Mr. Aketi Srinu
Dr. Anil Kumar

3. BOOK CONTRIBUTORS
S.No. TITLE AUTHOR
1. Need of SOP in stereotactic radiotherapy Dr. B. Ravi Shankar
2. Protocols in stereotaxy Dr. P. Madhuri
3. Motion management Dr. Anish Bandyopadhyay
4. DIBH [ABC] Dr. David K Simson
5. DIBH[RPM] DR. Rima Pathak
6. Delivery of stereotaxy-review of technologies Dr. Vibhay Pareek
7. Frame to frameless Dr. Kaustav Talaptara
8. Plan evaluation SRS/SRT/SBRT Dr. Maruthu P
9. Radiobiology of SRS/SBRT Dr. Vibhay Pareek
10. Functional SRS/SBRT Dr. Pradeep
11. AVM Dr. Sayan Paul
12. Meningioma Dr. Vibhay Pareek
13. Brain metastasis Dr. Rashmi Shukla
14. Brain metastasis- post op cavity Dr. Udaya Krishna
15. Acoustic Neuroma Dr. Suman Das
16. Head and neck SBRT Dr. Trinanjan Basu
17. Spine SABR Dr. Deepak Gupta
18. Lung SBRT Dr. Naveen Mummudi
19. Stereotaxy in lung metastasis Dr. Ritika Harjani Hinduja
20. Breast SBRT Dr. Vibhay Pareek
21. Liver SBRT Dr. Karishma George
22. SBRT For Liver Metastasis Dr. Ritika Harjani Hinduja
23. Portal vein thrombosis Dr. Ashu Abhisek
24. Pancreatic SBRT Dr. Arun Verma
25. Prostate SBRT Dr. Rushi Kumar Panchal

5. WHY SOP NEEDED IN STEREOTAXY
Dr B RAVISHANKAR
SRS is strictly defined as radiation therapy
delivered via stereotactic guidance with
approximately 1-mm targeting accuracy to
intracranial targets in 1 to 5 fractions.
Stereotactic body radiation therapy (SBRT) is an
external beam radiation therapy method that very
precisely delivers a high dose of radiation to an
extracranial target. SBRT is typically a complete
course of therapy delivered in 1 to 5 sessions
(fractions). Specialized treatment planning results
in a high dose of radiation to the target with a much
lower dose to the immediate surrounding normal
tissues.
SRS and SBRT requires stereotactic target
localization and improved delivery precision over
those required for conventional 3-D treatment
delivery.Strict protocols for quality assurance (QA)
must be followed. SBRT requires levels of
precision and accuracy that surpass the
requirements of conventionally fractionated
radiation therapy or intensity-modulated delivery
because of the high radiation doses used per
fraction.

6. Standard operating procedures
Site-specific SOPs should address the components
essential to the patient review, simulation, planning,
treatment, and follow-up. Patient safety should be
the primary consideration when developing any SOP.
1. Safety
a. The roles and responsibilities of each member of
the clinical team should be clearly described.
b. Mechanical tolerances will be established
during commissioning and should be well
documented. Additional tolerances for clinical
operation should be considered for each SRS-
SBRT service
.
c. The SOP should establish certain process
expectations for safe implementation such as
appropriate time intervals from simulation to
treatment with critical points along the path allowing
for reconsideration or rescheduling.
d. Every team member has the right and
responsibility to halt a case and/or a particular
procedure based on safety imperatives.

7. 2. Patient selection
a. Patient selection criteria should initially be
determined using data available from clinical
protocols or published guidelines
Maximum target size should be documented along
with standard prescription dose and fractionation
schemes.
b. Where possible, a multidisciplinary review or a
peer review of proposed cases should be
completed prior to simulation. If the patient is
enrolled in a clinical trial, the rules and guidelines
of the clinical trial must be followed.
3. Simulation
a. Reproducible immobilization techniques should be
developed for each treatment site.
b. The reference imaging study to be used for
treatment planning should cover the target and
all relevant organs at risk. A typical scan length
should extend at least 10 cm beyond the
treatment field borders. For non-coplanar
treatment techniques, the scan length may need
to be further extended to adequately model the
beam paths and resultant scatter dose and
extend beyond the entrance path and clinically
relevant exit path of every beam.

8. c. For SBRT applications, tomographic slice
thickness of 1–3 mm should be used. For SRS
applications, slice thickness should not exceed
1.25 mm and scan field of view should be
optimized for maximum in-plane spatial resolution
while including all necessary anatomy and
immobilization hardware in the field of view.
d. Respiratory motion management should be
considered in thoracic and abdominal sites.
4. Treatment planning
a. The treatment planning system must have the
capability of accurately calculating the predicted
dose for the scope of
SRS-SBRT services to be offered.
b. Each treatment site should have a defined
list of critical structures to evaluate and
stereotactic fractionation based tolerances
should be defined based on clinical protocol
data or peer-reviewed literature.The planning
target volume margins should be clearly
documented.
c. Image fusion requirements for target
definition should be defined and target
margins should be clearly described. Target
margins should be based on data from
current literature along with knowledge of the
limitations of in-house localization
capabilities.

9. d. Planning strategies and techniques should be
described for each treatment site, such as
conformal arcs, intensity-modulated radiation
therapy, and volumetric-modulated arc therapy.
These technique definitions should include clinical
limitations based on the findings from
commissioning. If noncoplanar techniques are
included, potential collision should be considered
in determining overall beam configuration.
e. In cases of re-irradiation, the cumulative
dose should be evaluated by the treating
physician. A description of the method used
and the outcome of the evaluation should be
documented.
f. The use of an isotropic calculation grid size of 2
mm or finer is recommended. The use of a gridsize
>3 mm is discouraged. 10 For very small targets, a 1
mm calculation grid size may be necessary.
g. Target dose coverage, dose fall-off beyond the
target, dose conformity metrics, and compliance
with critical structure dose objectives should be
clearly reported and signed by the radiation
oncologist to confirm that the chosen treatment
technique is clinically acceptable.
h. An independent dose calculation check must be
performed prior to treatment.

10. 5. Treatment delivery
a. A clearly defined pretreatment QA check
should be performed and may depend on the
technique used(e.g., frameless cranial, frame-
based cranial, cone-based SRS or SBRT). This
should include a collision check where the
potential for collision exists.
b. The SOP should clearly describe the
professional supervision requirements for each
SRS-SBRT treatment type.
c. The SOP should clearly describe the image
guidance method to be used, including target
anatomy, critical organ avoidance, and localization
tolerance. Pretreatment verification of target
localization should always be performed; the
criteria for intratreatment image guidance should
be clearly Described.
d. If motion management is used, the SOP
should clearly describe the process,
tolerances,and professional supervision.

11. 6. Patient follow-up
The SOP should clearly describe the follow-up
schedule and clinical tests for each treatment
site. “There should be follow-up of all patients
treated, and appropriate records should be
maintained to determine local control, survival,
and normal tissue injury.
7. Checklists
Effective checklists support human thinking, allow
constructive team member interactions, and facilitate
a systematic care delivery by reducing process
variability.

12. RESPONSIBILITIES OF PERSONNEL
A. Radiation Oncologist
1. Participating in initial treatment decision making
and obtaining informed consent
2. Overseeing radiation therapy management of the
patient
3. In concert with the neurosurgeon,
neuroradiologist, or other physicians, specifying the
target volume and relevant critical normal tissues
4. Participating in the process of plan
development and approving the final treatment
plan and dose prescription
5. Ensuring that patient positioning on the treatment
unit is appropriate
6. Attending and directing the radiosurgical treatment
delivery
7. Following the patient and participating in the
monitoring of disease control and complications

13. B. Neurosurgeon
1. Participating in initial treatment decision making
and obtaining informed consent
2. Placement of stereotactic head frame, where
necessary
3. Locating and specifying the target volume
and relevant critical normal tissues in concert
with the radiation oncologist and
neuroradiologist or other physicians
4. Participating in the iterative process of plan
development and approving the final treatment
plan and dose
5. Ensuring that patient positioning on the treatment
unit is appropriate
6. Attending and directing treatment delivery
7. Following the patient and participating in
the monitoring of disease control and
managementof treatment complications

14. Medical Physicist
1. Acceptance testing and commissioning of the
radiosurgery system to assure its initial geometric
and dosimetric precision and accuracy. This
includes:
a. Localization devices used for accurate
determination of target coordinates
b. The treatment-planning system
c. The radiosurgery external beam delivery unit
d. The precision of the imaging device, such as
the MRI scanner, used for target and normal
tissue identification
2. Implementing and managing a QA program
for the radiosurgery system to monitor and
assure its proper functioning
a. The radiosurgery external beam delivery unit
b. The treatment-planning system PRACTICE
PARAMETER Stereotactic Radiosurgery
c. The precision of the imaging device, such as
the MRI scanner, used for target and normal
tissue identification
3. Initiating and maintaining a comprehensive
QA checklist that acts as a detailed guide to the
entire treatment process

15. 4. Directly planning, supervising, or overseeing the
treatment-planning process, including verification of
dosimetric calculations using monitor unit double-
check software
5. Consulting with the radiation oncologist and/or
medical dosimetrist to determine the optimal
patient plan
6. Using the plan approved by the radiation
oncologist and an appropriate patient-specific
measurement technique, performing checks of the
appropriate beam-delivery parameters
7. Supervising the technical aspects of the
beam-delivery process on the treatment unit
to assure accurate fulfillment of the
prescription of the radiation oncologist

16. E. Radiation Therapist
1. Preparing the treatment room for the stereotactic
radiosurgery procedure
2. Assisting the treatment team with patient
positioning/immobilization
3. Operating the treatment unit after the clinical and
technical aspects of beam delivery areapproved

17. QUALITY ASSURANCE OF THE TREATMENT
UNIT
1. Radiation-beam alignment testing to assure the
beam can be correctly aimed at the targeted
tissues (see section IV for a complete list of the
references describing this test
2. Calculation of radiation dose per unit time (or per
monitor unit) based on physical measurements for
the treatment field size at the location of the target

18. QUALITY CONTROL OF IMAGES
All salient anatomical features of the SRS/SBRT
patient, both normal and abnormal, are defined with
computed tomography (CT), magnetic resonance
imaging (MRI), angiography, and/or other applicable
imaging modalities. Both high 3-D spatial accuracy
and tissue-contrast definition are very important
imaging features if one is to utilize SRS to its fullest
positional accuracy.
Images are used for localizing target boundaries as
well as generating target coordinates at which the
treatment beams are to be aimed. They are used for
creating an anatomical patient model (virtual patient)
for treatment planning, and they contain the
morphology required for the treatment plan
evaluation and dose calculation.The chosen image
sets should also allow optimal definition of target(s)
and normal tissue(s).

19. QUALITY ASSURANCE FOR STEREOTACTIC
RADIOSURGERY TREATMENT-PLANNING
SYSTEMS
A. System Log Maintain an ongoing system log
indicating system component failures, error
messages, corrective actions, and system
hardware or software changes.
B. System Data Input Devices Check the input
devices of image-based planning systems for
functionality and accuracy. Devices include
digitizer tablets, input interfaces for medical
imaging data (CT, MRI, angiography, etc), and
video digitizers. Assure correct anatomical
registration: left, right, anterior, posterior,
cephalad, and caudad from all the appropriate
input devices.
C. System Output Devices Assure the functionality
and accuracy of all printers, plotters, and graphical
display units that produce, using digitally
reconstructed radiographs or the like, a beam’s-
eye-view rendering of anatomical structures near
the treatment beam isocenter. Assure correct
information transfer and appropriate dimensional
scaling.
D. System Software Assure the continued integrity
of the RTP system information files used for
modeling the external radiation beams. Confirm
agreement of the beam modeling to currently
accepted clinical data derived from physical
measurements. Similarly, assure the integrity of the
system torender the anatomical modeling correctly.

20. VALIDATION OF THE TECHNIQUE AS
IMPLEMENTED
Once the individual components of the planning and
treatment technique are commissioned, it is
recommended that the QA program include an
“operational test” of the system before clinical
treatment begins or whenever a plan modification is
implemented for a fractionated treatment schedule.
This testing should mimic the patient treatment and
should use all of the same equipment used for
treating the patient. The testing is given the name
“patient-specific end-to-end testing”

21. FOLLOW-UP
There should be follow-up of all patients treated
and maintenance of appropriate records. The data
should be collected in a manner that complies with
statutory and regulatory guidelines to protect
confidentiality

22. SUMMARY
The quality of a SRS or SBRT program depends on
the coordinated interactions of a team of skilled
health care professionals. A high degree of spatial
accuracy is necessary in the treatment planning and
delivery process. Since SRS or SBRT uses either
single-fraction treatment or a hypofractionated
regimen, there is little chance for adjustment once
treatment has been initiated. This demands
considerable time for planning and treatment
verification by the radiation oncologist and medical
physicist.

23. PROTOCOLS IN STEREOTAXY
Dr. KANHU CHARAN PATRO, Dr CHITTA RANJAN KUNDU, Dr. Partha Sarathi Bhattacharyya, Dr. VENKATA
KRISHNA REDDY, Dr. PALLA MADHURI, Mr. A C PRABU, Ms. SUBHRA DAS, Mr. AKETI SRINU, Dr. ANIL KUMAR
1. BRAIN METASTASIS  RTOG 9508
 JROSG 99-1
2. BRAIN METASTASIS RERT  RTOG 9005
3. PITUITARY  IRSA
4. MENINGIOMA  NHS PROTOCOL
5. ACOUSTIC NEUROMA  IRSA
 ISRS
6. AVM  IRSA
 ISRS
7. TRIGEMINAL NEURALGIA  IRSA
8. HEAD AND NECK RERT  MIRI PROTOCOL
9. SKULL BASE TUMORS  MARCO KRENGLI, REPORTS OF
PRACTICAL ONCOLOGY AND
RADIOTHERAPY,2015
10. LUNG CENTRAL  RTOG 0813
11. LUNG PERIPHERAL  RTOG 0915
12. LUNG METASTASIS  NRG BR001
13. LIVER METASTASIS  RTOG0438
 AAPM
14. LIVER HCC  RTOG 1112
 AAPM
15. PANCREAS  ALLIANCE
 AAPM
16. BILLIARY  ANAND MAHADEVAN, JOURNAL OF
CANCER.2015
17. PROSTATE  PRIME STUDY TMH
 ONE SHOT
18. NODAL RECURRENCE  ROSANNA YEUNG,RADIATION
ONCOLOGY, 2017
19. SPINE METASTASIS  RTOG 0631
20. SBRT BONE METASTASIS  GILLIAN BEDARD, ANNALS OF
PALLIATIVE MEDICINE,2016
21. PLANNING  TG 101

24. MOTION MANAGEMENT IN STEREOTAXY
AnisBandyopadhyay, KanhuCharanPatro, Souransu Sen.
Introduction
Image guided radiation therapy (IGRT) is defined as imaging in the treatment room, with
positional adjustments for geometric deviations, and represents an advanced quality assurance
tool for successful radiation therapy. Image guidance helps in reducing errors or uncertainties in
radiation planning and delivery, mostly uncertainty of margin from CTV to PTV. As per ICRU
(International Commission on Radiation Units and Measurements) report 62, the two major
components of this margin are the ITV margin and setup error, that is the uncertainty due to
intrafraction movement and interfraction setup error respectively. Respiratory motion affects all
tumour sites in the thorax and abdomen (even the pelvis), though the disease of most prevalence
and relevance for radiotherapy is lung cancer. Thus in thoracic and abdominaltumours motion
management is of utmost importance and rapid strides have been made in developing systems to
tackle the same in the last decade. With the increasing use of increasingly conformal
radiotherapy, with intensity modulation techniques, using reduced irradiation fields, and
especially with stereotactic hypo-fractionated radiotherapy, adapting radiotherapy to respiratory
movements is becoming the more and more standard in the radical treatment of lung and
abdominal cancers.
The Need for motion management
Image-guided radiotherapy (IGRT) implies the use of imaging to localize the target with the aim
of guiding the treatment beam to an accurate aim. Image guided radiotherapy aims at reducing
margins of the target. With the evolution of conformal to high precision radiotherapy, radiation
oncologists have been able to progressively reduce the margins needed around targets and also
reduce the normal tissue dose, thereby increasing the therapeutic window. However, a major
block in theseefforts to reduce the margin is the uncertainty involved in accurately defining,
targeting, computing, aligning, and finally delivering a prescribed radiotherapy treatmentto

25. tumours that move, with an additional dimension of uncertainty; that is temporal. Thus forlung
tumours, sub diaphragmatictumours and intra-thoracic normal tissue, respiratory motion can
have a significant impact on RT planning and delivery. Though the respiratory motion is mostly
periodic and predictable, it varies from time to time in short term and also in long termand at
times can be extremely unpredictable.Tumour motion is also variable and takes place in all three
orthogonal directions, with most prominent in the cranio-caudal direction. It also varies
according to the site and the size and relation with mediastinal and thoracic structures and also
impacted by hysteresis (a phenomenon by which tumours can exhibit paradoxical motion on
inspiration and expiration). The lung tumour respiratory displacement varies from few
millimeters in the apical regions to few centimeters in the lower lobes near the diaphragm.
Primary tumour motion does not have a direct relationship to involved or high-risk nodes, which
can affect subsequent motion management. Moreover, individual characteristics of breathing in
an individual patient produce different tumour motions and displacements. Cardiac movement
can also influence tumour motion, particularly in left lower lobe tumours. Thus the respiratory
movement of each individual patient should be assessed prior to treatment.
This motion can cause severe geometrical and volumetric distortion in conventional computed
tomography (CT) scanning. These distortions along the axis of motion could either lengthen or
shorten the target length depending on the complex interplay of the magnitude and speed of
organ motion, gantry rotation speed and pitch. The technical term for thisdistortion is temporal
aliasing. These temporal aliasing artefacts are also frequently observed in diagnostic thoracic
scan, where in coronal multiplanar reconstruction of a thorax scanned in the helical mode, one
can see the lung/diaphragm discontinuity artefacts.
Effect of motion artefacts in treatment planning:
For radiotherapy treatment, margins needed to be added all around the target to ensure coverage.
Thus as per ICRU (International Commission on Radiation Units and Measurements) report 62,
the margin around the Gross tumourshould be added to form the CTV to account for the
suspected microscopic spread. Beyond CTV an additional margin to form the Planning Target
Volume is added which accounts for the intrafraction motion (respiratory motion), the
interfraction motion and the setup error. For lung tumours and other thoracic and abdominal

26. tumours the margin for intrafarction motion can be substantial, leading to formation of a large
volume of PTV. Without quantifying this range of intrafarction motion individually, to put
angeneric margin for PTV would result in either too tight a margin, leading to missing of the
target, or too big a margin, leading to unnecessary radiation to a large volume of normal tissue.
Hence proper imaging of the motion or motion encompassment is of utmost importance to
reduce intrafraction motion uncertainties and define the actual desired PTV.
Options available for motion management
1. Imaging motion or motion encompassment– relates to processes that encompass or
capture the motion while imaging so as to reduce uncertainties in tumour margin due to
motion.
2. Motion freezing or dampening- relates to processes that reduce the tumour motion
during imaging as well as during treatment delivery.
3. Gating- relates to the process of acquiring image and delivering radiation within a
particular period or ‘gate’ of the respiratory cycle.
4. Tracking- relates to the process oftracking the target during intrafraction period while
simultaneously delivery of radiation.
A. Motion management - Imaging strategies
There are various methods developed to circumvent these motion artefacts by acquiring images
at various stages of the radiotherapy chain and with high degrees of temporal and spatial
resolution.The integration of respiratory motion has been made with “passive” techniques based
on reconstruction images from 4DCT planning, or “active” techniques adapted to the patient's
breathing. The earlier studies and strategies for motion management incorporated fluoroscopy
based methods, wherein CT scan images were acquired in both free breathing and during breath
holding, and the tumour motion was screened by fluoroscopy, thus enabling additional margins
in PTV for motion. The problem of imaging with conventional 3DCT is that the scan time is
typically much faster than the normal respiration cycle time of 3-5 seconds thus producing

27. artefacts. There are various ways of solving this issue and they are described below.When
motion is present in the treatment region of the patient, this needs to be accounted for both in
treatment preparation and in treatment delivery. The past 15 years of development has made it
possible to do so on an individual basis and even in real time.
Figure 1: Options available for motion management during imaging
1. Slow CT
One easy way of respiratory motion encompassment, thereby obtaining representative CT scans,
is the use of slow CT, or slow scanning. The idea is to make CT image acquisition time for a
particular slice thickness longer (~ 4 sec) encompassing the full respiratory cycle, so that
multiple CT scans areaveraged. This means the scanner scans at a particular couch position
longer and hence the image of the tumour should show the full extent of the respiratory motion
that occurred during scanning of that particular slice/ anatomic position of the thorax. Thus it
yields atumour –encompassing volume. While the plus points of this technique includes the fact
that conventional CT scanners can be employed without the addition of any software or
hardware, more accurate anatomic delineation and dose calculations are more representative of
Imaging for
motion
mangement
Flouroscopy conventional CT
slow CT
breath holding
(not practical)
4DCT
Retrospective
ITV generation
method
Mid Ventilaton
method
Prospective
Breath holding
Full expiration
/Ful inspiartion
method

28. the real life situation. The down sides are lack or loss of clarity or resolution leading to blurring
of images, variation of respiratory motion from imaging to treatment and applicability to
peripheral tumours only. In fact, this method is only recommended for lung tumoursand also for
those that are not involved or close to the mediastinum or the chest wall. Another disadvantage is
the increase in dose compared with conventional CT scanning.
2. Inhale and exhale breath hold CT scans
A simple way of obtaining tumour encompassing volume using a standard CT scanner is to
acquire both inhale and exhale gated or breath hold CT scans. This method will double the CT
acquisition time and will depend on the patients ability to accurately hold breath. Moreover,
since two image sets are available, image fusion and extra contouring will be required. The
Maximum intensity projection (MIP) tool may be used to create the tumour encompassing
volume, provided there is no mediatinaltumour involvement. The advantage of this method over
slow CT is the reduction in the blurring caused by the respiratory motion during free breathing.
3. 4D-CT or Respiration-correlated CT scan
4DCT scanning allows correlation of patients breathing with CT image acquisition. This requires
two independent systems, one that senses and monitors the patient’s respiratory movement by
help of external surface/ abdominal motion surrogates or by spirometry. This can be performed
through many different techniques—optical recording of reflective optical markers or light-
emitting diodes positioned on the surface of the patient, spirometry for volume measurement of
air flowing in and out of the lungs, measurement of the temperature of in- and out flowing air
with a thermocouple placed under the nose, measurement of pressure produced by chest
expansion with piezoelectric ceramics placed in an elastic abdominal strap or patient surface
rendering by use of lasers. The other system is correlated CT image acquisition, wherein multiple
CT slices are taken for a particular couch position, so as to acquire a full set of axial images of
that slice for the full respiratory cycle. This is called ciné axial method where the CT scanner
scans continuously for the duration of at least one breathing cycle with the CT couch being

29. stationary. Usually, 8 to 25 CT datasets are generated. The images from 4D CT scans can be
reconstructed to create inhale, exhale or slow CT scans.
The integration of respiratory motion has been made with “passive” techniques based on
reconstruction images from 4DCT planning, or “active” techniques adapted to the patient's
breathing. The quality and representativeness of a 4DCT scan depends highly on the regularity of
the patient’s breathing. The more irregular the breathing, the more artefacts will be present in the
4DCT scan.
Prospective gated Imaging
In this form of gated imaging the CT scanner uses the RPM (Real-time PositionManagement)
trigger signal to synchronise image acquisition with respirations. The therapist determines the
gating thresholds before the scan, and the scanner acquires images when the marker block
(tumour) is within the defined thresholds . The result is a single gated volumetric data set.
Retrospective gated Imaging
In retrospective image acquisition, the CT scanner acquires images continuously, and the scan is
acquired for at least one respiratory cycle at each couch position. Following image acquisition,
the CT image set is synchronized with the RPM/external monitoring reference motion file. The
images are sorted into the corresponding phase bins of the respiratory cycle, and are then are
evaluated to determine the optimum phase for treatment. The selected phase bin images are then
sent for treatment planning.
When 4DCT is available, two common methods are used to apply individualized tumour margin
by encompassing the motion or the range of motion. These are the ITV or Internal Target
Volume based method or the Mid Ventilation Method. In the ITV based method all the images of
the 4DCT scan are overlayed and a maximum or minimum intensity projection of the phases and
the combined volume of the target in all the phases are outlined in the ITV. Maximum intensity
projection is generally used when the tumour is denser than the surrounding tissue (e.g., lung)
and minimum intensity projection is used when it is less dense or hypodense (as in liver). On
ITV further margins are then added to get the final PTV volume. In the Mid ventilation
approach, the phase at which the target is closest to the mean position in the trajectory is

30. identified and term as mid Ventilation phase. The target is delineated in this phase and further
margin is added by measuring the extent of motion of the target through all phases.
B. Motion freezing or dampening methods:
1. Breath holding
Breath-hold during simulation and treatment is another option for respiratory management and
requires active patient participation and trained therapists to coach and advise the patients during
treatment. Breath-hold is a well-known and early technique used in diagnostics for achieving CT
images with reduced artefacts, and CT images obtained during a breath-hold are of a better
quality than those obtained in a 4DCT scan. Self-Breath hold imaging can be obtained with a
conventional CT scanner with or without respiratory monitoring. For breath-hold, the stability of
tumour position and reproducibility of patient setup during each breath-hold need to be accurate
and verified. The most commonly used breath hold techniques are Deep Inspiration Breath Hold
technique, Mid Inspiration Breath Hold technique and Active Breath Hold techniques. Deep
inspiratory breath hold (DIBH) is where a patient attempts a maximum reproducible inhalation
during simulation and treatment. DIBH can be implemented using spirometric devices or non-
spirometric methods such as chest wall movement.
Commercially three products are available that interact directly with the patient’s airflow through
the mouth or nose, namely the Active Breathing Coordinator (ABC) device (Elekta AB,
Stockholm, Sweden), the SDX (Dyn’R, Toulouse, France) and the VMAX Spectra 20C
(VIASYS Healthcare Inc, Yorba Linda, CA). The ABC is a spirometer device dedicated to the
practice of semi-voluntary breath-hold. It is connected to a balloon valve that blocks the patient
air flow in severe DIBH until the field is delivered, usuallyrequiring two or three breath holds for
the entire delivery. The advantages of breath-hold over free breathing are: decreased requirement
for fluoroscopy, decreased motion of internal structures, less time required for CT acquisition,
shortened treatment time and improved patient compliance.However, the major disadvantageis
that the system can only work is the patient is compliant enough to hold breaths, which is at
times difficult for elderly patients or patients with compromised pulmonary capacity. Moreover,

31. simultaneous reduction in lung density associated with increase in lung volume may lead to
overestimation of dosimetric coverage by certain treatment planning systems.
2. Forced shallow breathing with abdominal compression:
Abdominal compression plates can be used with immobilisation frames to reduce tumour motion
by forcing the patient to shallow breathe and therefore can lead to a reduction in margins. The
technique employs a stereotactic body frame with an attached plate that ispressed against the
abdomen. The applied pressure to the abdomen reduces diaphragmatic excursions, while still
permitting limited normal respiration. However this technique is unusable for patients with poor
respiratory function, for obese patients and for some this may lead to errartic breathing patterns.
C. Gating
Respiratory gating involves both imaging and treatment delivery within a particular portion of
the patient’s breathing cycle, commonly referred to as the “gate.” The gated RT technique is a
noninvasive, synchronized system of imaging and respiratory motion that allows for imaging and
treatment of lung, breast, and upper abdominal sites. With respiratory gating approaches, the
patient continues to breathe normally. The position and width of the gate are determined by
monitoring the patient’s respiratory motion using either by an external respiration signal or by
monitoring internal fiducial markers
Gating using an external respiration signal
The commercially available solutions are the Varian Real-time PositionManagement (RPM)
system (Varian Medical Systems, Palo Alto, CA); the Siemens Medical Systems (Concord, CA)
linear acceleratorgating interface and an Anzai belt (used for CT) and the BrainLab (Heimstetten,
Germany) ExacTrac Gating/Novalis Gating.
In these systems some sort of external markers is used to monitor the respiratory motion.
During CT simulation a respiration gating system sends a trigger to the CT scanner once per
breathing cycle, to acquire a CT slice. CT scanparameters (slice thickness, scanner rotation time,
index, etc.) remain the same as those used for standard CT scans. Note that the CT image is not
gated in a strict sense, but is initiated by thetrigger.

32. During treatment, after initial setup the patient is asked to relax andbreath normally. Once a
stable respiration trace has been established and gating thresholds are verified, gated radiation
delivery is initiated. The position of the patient’s internal anatomy is verified using gated
radiographs or portal images and comparing them with digitallyreconstructed radiographs
(DRRs) from the gated planning CT
Gating using an internal fiducial markers
In this system fiducials (usually gold) are implanted in or near the tumour using a percutaneous
or bronchoscopy method. The positions of these fiducials are tracked in all three dimensions
several times a second by stereotactic KV imaging with automatic detection software. Then the
linear accelerator delivers the radiation when the fiducials are within the desired range of
position or gate.
Phase based versus amplitude based gating
Respiratory motion can be characterized by two variables that are recorded as part of the
respiration signal or the motion of the tumour/target. These variables are (a) displacement or
amplitude and (b) phase. Accordingly, the method of gating is referred to as either amplitude
based gating or phase based gating.In amplitude-based gating, the user definesminimum and
maximum limits between which the CTacquisition or radiation is delivered, dependent on the
absoluteposition of the marker regardless of the phase ofbreathing. In phase-based gating, the
system calculatesa running estimate of the breathing cycle and imaging and radiation delivery is
done on a specific phase of respiration as specified by the clinician.

33. Figure2 : Respiratory gating (A) and Breath hold technique (B)
Time in seconds
A
B
Beam on windows
Beam on windows
Breath Hold periods

34. D. Real time Tracking
Real time tracking involves tracking of the target during intrafraction period while
simultaneously delivery of radiation. This tracking of the tumour is generally achieved by
continuous monitoring of some internal or external surrogate of tumour/target motion. This is the
ultimate solution for accounting the target motion during treatment by aiming the treatment beam
continuously and dynamically at the moving target. The major advantage of this strategy is that it
can significantly reduce the required margins without compromising the treatment time. Since
there is no beam off during treatment, the treatment delivery time is markedly reduced compared
to gating. However, it is, by far, the most technologically demanding solution as it comprises of
three simultaneous processes. First it involves continuos tracking of the external or the internal
fiducials or surrogates, second process involves establishing a mathematical correlational model
between the target motion and the motion of the surrogate. Third is the final process of directing
the beam dynamically to the target with the help of the correlation motion model.

35. Fluoroscopy based RTT
The Cyberknife and Vero hasan X-ray based system, where in-room orthogonal x-rays and
fluoroscopy mode continuously tracks the surrogate markers. The robotic arm of the Cyberknife
is programmed to move synchronously with the breathing cycle, in a trajectory following the
projected 3D motion of the target. The target motion is not monitored directly, but before
treatment is started, a sequence of orthogonal radiographic images is recorded from which the
target breathing motion is derived in three dimensions. They rely on the high contrast of
implanted internal fiducials. In addition to that, optical tracking of external markers are done
simultaneously for both cyber knife ( by LED) and Vero system (infrared markers ). The real
time tumour tracking is done either by the robotic arm in Cyberknife or by gantry mounted on
gimbal system of the Vero. The BrainlabExactrac Adaptive Gating system is a device used for
patient positioning and intra-treatment tumour motion monitoring.Its principle is similar to the
Cyberknife and Vero as it takes advantage of a kV imaging system and chest motion to build a
correlationmodel. However unlike the above two systems it monitors the tumour position and
irradiates at a particular position during freebreathing.
Tumour
Surrogate
marker
Interceptive Radiotherapy – Gating Pursuing Radiotherapy – Tracking

36. Electronic transponder based tracking
This is a non-imaging based motion management technique that makes the use of
electromagnetic transponders for lung tumour tracking. This system uses non-ionising alternating
current electromagnetic radiation to locate and continuously track small devices inserted/
locatedclose to the tumour, percutaneously or through bronchoscopy. These are detected
wirelessly by a detector placed over the chest in the treatment room. Thus real time tumour
tracking is done. It is mainly used for prostate cancer, but has the potential to be used in lung
cancer as well. These beacons can be tracked and beam is thus adapted by using dynamic MLC
tracking.
Summary of Motion management strategies during treatment
Methods Strategies Examples
1. Encompassing treatment
margin
ITV generation
Mid ventilation
2. Motion freezing
or
dampening
Motion mitigation Abdominal compression
 Paddle
 Pneumatic belt
 Full body
Breath holding Breathing control
 ABC
 SDX
 CPAP
3. Gating Optical  RPM

37.  C-Rad
Respiratory belt  Anzai belt
 Philips bellows
Spirometry  ABC
Surface monitoring  Align RT
4. Tracking KV image based  Exact Trac
 Cyberknife
 Gymbal based KV imaging
and tracking-Vero
Optical based  Synchrony –Cyberknife
Electromagnetic beacon
based
 Calypso
 Micropos
Conclusion
The potential therapeutic benefit of motion monitoring and management techniques that are
being increasingly used in modern radiotherapy are widely published and deliberated upon.
However very few literature is available till date on its role in improving clinical outcomes like
progression free or overall survival. Whether patients treated with motion management
techniques have better clinical outcome in terms of reduced toxicity or better tumour response
due to dose escalation is matter of research. There is wide disparity in the practice of various
motion quantification, immobilization, motion encompassment, margin determination and finally
intervention for stereotactic body radiotherapy for lung and abdominal tumours within the
country and internationally. Also there is a whole gamut of choices for available hardware and
software solutions for motion management as per varying need and requirements of particular
institution. Hence cross comparison between various solutions utilized by different institution is

38. difficult. All systems have their advantages and disadvantages which needs to be accounted for
while adopting a particular solution.
Apart from the equipment, patient selection is also of utmost importance, as motion management
is more beneficial for reducing irradiated volumes for tumours with significant motion and with
smaller grosstumour volumes. Moreover motion management is resource intensive which
escalates cost of treatment along with increased planning and treatment times. Many challenges
persist in interpreting pretreatment imaging, capturing real-time data and predicting motion
patterns for individual tumours. Thus the balance of resource implications coupled with patient
selection should hold key in routine implementation of motion management of lung tumours. .

39. Table 2: Comparison of available motion management strategies/ techniques
Abdominal
compression
Slow CT Breath Hold Gating MIP Tracking
4D CT required No No No Yes ( but
can be done
without )
Yes Yes
Patient compliance
required
Very much Not much Very much Very much Not much Not much
Patient in free
breathing during
RT
Yes (but
restricted)
Yes No Yes Yes Yes
Treatment time Not affected
much
Not
affected
Increased Increased Slightly
increased
Slightly
increased
(Adapted from Munshi, et al.: Tumour motion in lung cancers.Asian Journal of Oncology;
Volume 3 Issue 2 :July - December 2017)

40. Deep Inspiration Breath Hold (DIBH) using Active
Breathing Coordinator (ABC)
simulation to execution
DR DAVID K SIMSON
1. Introduction
Radiotherapy to patients with left-sided breast cancer may result in increased
cardiac morbidity. Darby et al. compared the cardiac mortality ratio amongst
breast cancer survivors who had received radiotherapy to the left side to that
of right.1
He found that the cardiac mortality ratio was high in those survivors
who had received radiotherapy to the left side. In a separate paper, he
demonstrated that the relative risk for ischemic heart disease was increased
by 7.4% for every 1Gy increase in the mean heart dose.2
To minimize this
problem, various techniques were tried. The most successful and popular
amongst these was the ‘Deep Inspiration Breath Hold’ (DIBH) technique. In
this technique, the patient is asked to take a deep inspiration and hold the
breath for a few seconds. This causes the left lung to inflate and insinuate
between the heart and the chest wall, pushes the heart away from the
radiation field, and thereby reduces the radiation exposure of the heart. Apart
from reducing the dose to the heart, this technique also helps to minimize the
radiation exposure of the lungs, especially the ‘low dose volume’ regions of
the lung. As a result, it lowers the chances of radiation-induced pneumonitis
and second malignancies.
The DIBH technique can be done using various modalities. The two most
commonly available modalities in the market are ‘Real-Time Position
Management’ (RPM) by Varian and ‘Active Breathing Coordinator’ (ABC) by
Elekta. In this chapter, we will review the processes involved in treating a left-
sided breast cancer patient using the ABC technique.
2. Case selection
The DIBH technique, even though it is aninnovative idea, should be done in
carefully selected patients. A few points to consider during patient selection
are as follows:

41. 1. The patient’s understanding of this technique and compliance are
crucial for its execution.3
Even though most patients will ultimately be
able to undergo this technique, some patients might need intense and
repeated training, making this technique labor-intensive and time-
consuming.
2. All those patients who have lung disease, which restricts them from
holding their breath for a meaningful period of time during radiotherapy,
may not benefit from this technique.4
3. The patient’s chest wall and thoracic anatomy are equally important. In
those patients with a deformed chest wall, such as phthisis chest,
pectus excavatum or pectus carinatum, the DIBH technique does not
necessarily reduce the dose to the heart. The same holds true for
those patients who have cardiomegaly, in which the heart fails to
separate from the chest wall, even after deep inspiration due to its
large size. Therefore, a free-breathing CT scan of the chest can be
performed prior to the selection processto roughly assess the anatomy,
so that the oncologist can select the right candidate who is likely to
benefit from the DIBH technique.5
4. Age is not a criterion for selecting patients for this technique, even
though one study recommends the use of this technique in patients
less than 60 years.6
As long as patients of any age meet the above-
listed criteria, they will benefit from the DIBH technique.
3. The ABC system
The ABC system comes with external hardware equipment along with a
laptop connected to it. This equipment has a mouthpiece (Figure 1; A) which
is connected to a spirometer (Figure 1; B) through which the patient breathes.
The spirometer measures the volume of air in liters which is inhaled and
exhaled by the patient through the mouth. A nose clip is used to pinch the
nostrils so that the patient breathes only through the mouth. The volume thus
measured by the spirometer, is displayed in a simple graphical form,
simultaneously on two screens. One screen is kept beside the radiation
technologist (Figure 2) and the other one displayed in front of the patient
(Figure 1; C). The patient can view the screen which is kept next to her using
special goggles (Figure 1; D).

42. Figure1: ABC setup. A – Mouthpiece, B – Spirometer, C – Screen next to the
patient, D – Special goggles through which the patient can see the screen, E
– Breast board, F – Emergency button and G – Cable that connects the ABC
system to the Linac and to the outside laptop which is controlled by the
radiation technologist.
Figure 2: Laptop screen which is kept at the console.
4. Patient setup on the ABC system and training

43. Fit the mouthpiece snugly between the teeth and the lips of the patient, and
instruct her to hold it in tightly so that there won’t be any air leak. The nose
clip is placed on the nostrils to ensure that she breathes only through the
mouth. After placing this nose clip, ask her to take a deep breath, and note
the maximum volume of air and the time for which she can hold it comfortably.
On average, a patient can inspire 1 to 1.8 liters of air and hold the breath for
20 to 25 seconds.7
This volume would be roughly 75% to 80% of the vital
capacity of the patient.
The next step is to enter and set the following values on the computer screen
- the volume of air that the patient holds comfortably and time which she can
hold it. Now, when the patient takes a deep breath, a broad green bar
appears on the top of the screen (Figure 1; C, Figure 2 and 3), which denotes
the set target air volume. The patient should aim to take a deep breath so that
the graph climbs up and touches the lower line of the broad green bar. As
soon as the graph crosses the lower line of the broad green bar, the valve
inside the spirometer shuts preventing further inspiration.
Instruct and train the patient to take just enough inspiration, so that the graph
just touches the lower line of the broad green bar and doesn’t overshoot it as
shown in the figure 3. If the graph overshoots the line, during image
verification at the beginning of each treatment, the planning CT scan and the
CBCT will notmatch.
At the same time when the graph touches the green bar, a countdown starts
at the lower right portion of the screen, which is equal to the set breath-hold
time fed into the computer before. At the end of the countdown, the valve in
the spirometer opens allowing the patient to exhale. Before starting the next
breath-hold cycle, she should be given a few seconds to relax, during this
time she breathes freely. She can see the graph and the countdown on the
screen, which is kept next to her, using the special goggles she wears.
Repeat the breath-hold cycles until the patient becomes confident. For most
patients, the planning CT scan can be taken on the same day. A few patients
might need practice training for a day or two before performing the planning
CT scan.

44. Figure 3: A case where the graph overshoots the lower border of the broad
green bar present on the top of the screen.
5. Positioning and immobilization
The patient is positioned on a breast board (Figure 1; E) with or without
Vacloc. Orfit cast is generally not preferred as it hinders the chest expansion.
6. Imaging
The planning CT scan is taken whilst the patient is on breath-hold. Usually,
the scan finishes in a single breath-hold cycle. However, if the scan time
exceeds the time for 1 breath hold cycle, the scan acquisition should be
manually paused at the end of one breath hold cycle and resumed at the
beginning of the next cycle.
As a backup, it would beprudent to take a free-breathing planning CT scan,
just in case the DIBH plan is unsuccessful.
7. Target delineation
The targets and the organs at risk (OAR) are contoured on the CT scan as
per standard guidelines. Whilst contouring the heart, draw the left anterior
descending (LAD) coronary artery and right coronary artery (RCA) separately.
This is because, one of the major purposes of the DIBH technique is to
reduce the incidence of coronary artery disease amongst long-term survivors.
To account for intrafraction movement, a 5 mm margin around boththese
arteries should be made as a ‘planning organ at risk volume’ (PRV).8,9

45. 8. Doses
The doses to the planning target volume are prescribed as per the standard
guidelines and institutional protocol, either conventional fractionation or
hypofractionation.
9. Planning and plan evaluation
To achieve the least mean dose to the heart, the preferred planning
techniqueis 3D-CRT with field-in-field.10,11,12
However, a few patients who
have deformed chest wall anatomy, pendulous breast or extended surgical
scars, would benefit fromIMRT technique. This is because in these patients, it
would be difficult to control the lung doses using the 3D-CRT technique.
Amongst different studies which utilized DIBH technique, the mean dose to
the heart varied between 0.7 Gy and 5Gy.13
However, in routine clinical
practice whilst using DIBH, a mean dose of less than 3 Gy to the heart should
be achievable.
The dose constraint to the LAD is still an unsettled topic. The mean dose to
the LAD varied considerably amongst different DIBH studies (0.8 Gy to 23.7
Gy). It is also seen that the mean and maximum doses to the LAD structure
are reduced when the DIBH technique is used along with IMRT rather than
3DCRT.11
10. Treatment delivery - setup and image verification.
The patient is set up for the treatment in the exact same way on the day of the
simulation and training. After the setup, the image verification must be done,
either by CBCT or 2D matching. The frequency at which the image verification
is done is similar to that of a case without DIBH technique, according to the
institutional protocol. For hassle-free treatment, in some linear accelerators
(linac) the ABC system and linac software are synchronized. Therefore, the
need to manually pause and resume the treatment at the beginning and end
of each breath-hold cycle is no longer required. However, this automated
feature is not available while taking CBCT image verification. Depending upon
the complexity of the plan and the duration for which the patient holds the
breath, 5 to 10 breath-hold cycles are required to complete the whole
treatment.
Whilst the patient is on the treatment couch, an emergency button (Figure 1;
F) is given to her, which she must press continuously throughout the entire
course of the treatment. The patient is instructed to release the button in case
of an emergency which stops the treatment, opens the valve in the
spirometer, and allows free breathing.

46. References
1
Darby SC, McGale P, Taylor CW, Peto R. Long-term mortality from heart disease
and lung cancer after radiotherapy for early breast cancer: prospective cohort study
of about 300,000 women in US SEER cancer registries. Lancet Oncol. 2005;6:557–
65.
2
Darby SC, Ewertz M, McGale P, et al. Risk of ischemic heart disease in women
after radiotherapy for breast cancer. N Engl J Med. 2013;368:987–98.
3
Borst GR, Sonke JJ, den Hollander S, et al. Clinical results of image-guided deep
inspiration breath hold breast irradiation. Int J Radiat Oncol Biol Phys.
2010;78:1345–51.
4
Swanson T, Grills IS, Ye H, et al. Six-year experience routinely using moderate
deep inspiration breath-hold for the reduction of cardiac dose in left-sided breast
irradiation for patients with early-stage or locally advanced breast cancer. Am J Clin
Oncol. 2013;36:24–30.
5
Wang W, Purdie TG, Rahman M, Marshall A, Liu FF, Fyles A. Rapid automated
treatment planning process to select breast cancer patients for active breathing
control to achieve cardiac dose reduction. Int J Radiat Oncol Biol Phys.
2012;82:386–93.
6
Nissen HD, Appelt AL. Improved heart, lung and target dose with deep inspiration
breath hold in a large clinical series of breast cancer patients. Radiother Oncol.
2013;106:28–32.
7
Remouchamps VM, Vicini FA, Sharpe MB, et al. Significant reductions in heart and
lung doses using deep inspiration breath hold with active breathing control and
intensity-modulated radiation therapy for patients treated with locoregional breast
irradiation. Int J Radiat Oncol Biol Phys. 2003;55:392–406.
8
Wang X, Pan T, Pinnix C, et al. Cardiac motion during deep-inspiration breath-hold:
implications for breast cancer radiotherapy. Int J Radiat Oncol Biol Phys.
2012;82:708–14.
9
Munshi A, Khataniar N, Sarkar B, et al.Spatial orientation of coronary arteries and
its implication for breast and thoracic radiotherapy—proposing “coronary strip” as a
new organ at risk. Strahlenther Onkol. 2018;194:711.
10
D Trifiletti, K Wijesooriya, G Moyer, et al. A comparative analysis of 3D conformal
and intensity modulated radiation therapy during deep inspiratory breath hold for left-
sided whole-breast irradiation. Int J Radiat Oncol Biol Phys. 2014;90:S266.
11
Sripathi LK, Ahlawat P, Simson DK, et al. Cardiac dose reduction with deep-
inspiratory breath hold technique of radiotherapy for left-sided breast cancer. J Med
Phys. 2017;42:123-7.
12
Smith BD, Bellon JR, Blitzblau R, et al. Radiation therapy for the whole breast:
Executive summary of an American Society for Radiation Oncology (ASTRO)
evidence-based guideline. Pract Radiat Oncol. 2018;8:145-152.
13
Bergom C, Currey A, Desai N et al. Deep Inspiration Breath Hold: Techniques and
Advantages for Cardiac Sparing During Breast Cancer Irradiation. Front Oncol.
2018;8:87.

47. DEEP INSPIRATORY BREATH HOLD (DIBH) WITH REAL-TIME POSITIONING MANAGEMENT (RPMTM
)
DR RIMA PATHAK
Deep inspiratory breath hold technique is now commonly used for treating patients with radiation
therapy especially left sided breast cancer[1]. There is enough literature to suggest that use of DIBH
technique for these patients not only reduces the heart doses significantly but also decreases the
ipsilateral lung doses due to chest expansion[2–7]. These are thought to potentially reduce the long
term toxicities to the heart in a dose dependant manner. DIBH can be implemented by various
methods and RPMTM
by Varian is one of techniques developed by Varian for the same. This,
completely non-invasive technique, utilizes the principles of reflected infrared light to identify the
position of the marker. It also relies on the assumption that the surrogate marker correctly
synchronizes with the waveform of the breathing cycle and thus accurately and objectively allows
manipulation of the organ motion associated with the breath cycle.
The components of RPMTM
Infrared light is emitted from the bulbs which are assembled all around the camera circumferentially
as shown in figure 1a. The camera embedded at the centre receives all the reflected infrared light
also seen in figure 1a. A light weight, nearly air-equivalent, marker box seen in figure 1b and 1c is
placed externally on the body part which can act as a surrogate for internal organ motion. This
marker box has multiple reflector dots which reflects the infra-red light back onto the camera. This
varying position of this reflected light dotsis captured and translated into a continuously moving
point in 2 dimension (figure 1b marker) or 3 dimension (figure 1c marker) depending upon the
marker type used. The continuously moving dot’s trajectory is recorded and traced as a line or a
curve and in free breathing it shows a sinusoidal waveform as shown in figure 1d.
Figure 1: Components of RPMTM

48. 1a shows the infrared camera and the display of the captured camera image of the reflective marker
box. 1b and c are 2D and 3D marker boxes and 1d shows a typical free breathing waveform captured
using RPMTM
The RPMTM
monitor display
Figure 2 shows the typical components visible on the RPMTM
monitor when the motion is being
captured (also available on the downloadable brochure from Varian) The labelled photograph in
figure 2 depicts the treatment delivery of a patient using gating during specific part of the breath
cycle. For DIBH, breath cycle gating is amplitude based.
Figure 2: Labelled photograph of the RPM monitor display during gated treatment
Typical DIBH Waveform
The figure 3 shows a typical waveform captured using the infrared camera with the reflector marker.
The waveform is plotted in a graphical manner where the x-axis of the graph shows the time in
seconds and the y-axis shows the amplitude of the marker. At the beginning we allow patient’s free
breathing motion to be captured. After this the patient is instructed to take a deep breath and hold
in the same deep-inspiratory position as taught to them during the coaching session. As the patient
takes a deep breath ideally the wave ascends to a higher amplitude and the sinusoidal wave plateaus
to a straight line (figure 3). The consistency of the breath hold is established by repeating the breath
hold at least 3 times using both skin marks and the amplitude depicted on the y-axis.
Once the desirable deep and consistent inspiratory breath hold is established, the threshold bars are
set. Ideally a phantom can produce the exact same breath hold every time, however, in real life a
few millimetre variation would be seen in the amplitude of the DIBH and the plateau also may not
be an exact straight line. Therefore, the threshold bars are used to make the model more
degenerate for practical implementation. The threshold bars should be placed within ± 2mm of the
recorded plateau (seen in figure 3 from 1.1 mm to 1.5 mm). Literature review and personal
experience suggests that threshold bars which are more liberal (>± 2mm) can lead to significant
internal organ changes leading to inconsistencies in the target and organs at risk leading to
dosimetric uncertainties.

49. Figure 3: Atypical DIBH waveform display on the RPMTM
monitor during simulation and treatment
A DIBH Scan is acquired in the DIBH position once the patients’ breath is within the gated thresholds.
A yellow hue over the graph depicts that the marker box is within the desirable threshold and
therefore the target too is in the desired position. This feedback is then provided to the linac and
acts as a go ahead signal for beam on. Similarly when the patient exhales, the waveform descends to
go out of the threshold bars from the DIBH position, which automatically via feedback turns the
beam off in real time. The time delay for this feedback from the patient to the RPMTM
is a small
fraction of a second and is considered clinically not significant[8,9]. Therefore, it is considered real-
time position and thus the term RPMTM
.
Treatment planning with DIBH:
Treatment planning is similar to planning on the non-gated free breathing scan. The only things that
are different as compared to the regular bitangents are as follows.
The dose rate: This is usually selected as 600MU/min instead of the standard doserate of
400MU/min, to minimize time taken to deliver the treatment with every field.
The treatment technique: At our centre mono-isocentric technique is used for planning to minimize
the uncertainties of the gap between the bi-tangents and the supraclavicular fields with every breath
hold especially given the fact that our threshold window is ≤ 4mm.
Free breathing plan is usually acquired and the reduction in cardiac and lung doses are recorded to
ascertain the clinical utility of the performed breath-hold.
Merging Sub-fields: This is done for patients planned with field-infield intensity modulated radiation
therapy. This allows to again economize on the time taken to complete the treatment and also avoid
patient fatigue while treating with DIBH.

50. On-board Imaging with RPMTM
:
This is also synced and performed using the RPMTM
with the patient in DIBH position. The scan’s
beam on is also similar to the treatment beam on and is triggered only when the patients’ position is
within the desired threshold limits. Volumetric or 2 dimensional imaging can be acquired in this
desired position to ascertain the position reproducibility of the patient for treatment as well as
visualize the separation of the heart from the chestwall as seen in the planning scan as seen in figure
5a and 5b.
Figure 5: On Board imaging with DIBH technique for breast cancer patient
5a showing matching of volumetric imaging while 5b shows matching of the 2D imaging both in DIBH
position using the RPMTM
Treatment Delivery:
This is also performed using DIBH technique after reproducing the desired patient position.
Treatment time can be anywhere between 12 -30 minutes depending upon the complexity of
treatment position, plan and patient co-operation.
Audio and video feedback of the patient’s breath hold within the threshold is provided to improve
patients’ adherence and consistency reducing the planning and treatment time [10].
References:
[1] Desai N, Currey A, Kelly T, Bergom C. Nationwide Trends in Heart-Sparing Techniques Utilized
in Radiation Therapy for Breast Cancer. Adv Radiat Oncol 2019;4:246–52.
doi:10.1016/j.adro.2019.01.001.
[2] Hayden AJ, Rains M, Tiver K. Deep inspiration breath hold technique reduces heart dose from
radiotherapy for left-sided breast cancer. J Med Imaging Radiat Oncol 2012;56:464–72.
doi:10.1111/j.1754-9485.2012.02405.x.
[3] Lee HY, Chang JS, Lee IJ, Park K, Kim YB, Suh CO, et al. The deep inspiration breath hold
technique using Abches reduces cardiac dose in patients undergoing left-sided breast
irradiation. Radiat Oncol J 2013;31:239. doi:10.3857/roj.2013.31.4.239.
[4] Joo JH, Kim SS, Ahn S Do, Kwak J, Jeong C, Ahn S-H, et al. Cardiac dose reduction during
tangential breast irradiation using deep inspiration breath hold: a dose comparison study
based on deformable image registration. Radiat Oncol 2015;10:264. doi:10.1186/s13014-015-
0573-7.

51. [5] Al-Hammadi N, Caparrotti P, Naim C, Hayes J, Rebecca Benson K, Vasic A, et al. Voluntary
deep inspiration breath-hold reduces the heart dose without compromising the target
volume coverage during radiotherapy for left-sided breast cancer. Radiol Oncol 2018;52:112–
20. doi:10.1515/raon-2018-0008.
[6] Kim A, Kalet AM, Cao N, Hippe DS, Fang LC, Young L, et al. Effects of Preparatory Coaching
and Home Practice for Deep Inspiration Breath Hold on Cardiac Dose for Left Breast Radiation
Therapy. Clin Oncol 2018;30:571–7. doi:10.1016/j.clon.2018.04.009.
[7] Zhao F, Shen J, Lu Z, Luo Y, Yao G, Bu L, et al. Abdominal DIBH reduces the cardiac dose even
further: a prospective analysis. Radiat Oncol 2018;13:116. doi:10.1186/s13014-018-1062-6.
[8] Goharian M, Khan RFH. Measurement of time delay for a prospectively gated CT simulator. J
Med Phys 2010;35:123–7. doi:10.4103/0971-6203.62196.
[9] Guan H. Time delay study of a CT simulator in respiratory gated CT scanning. Med Phys
2006;33:815–9. doi:10.1118/1.2174129.
[10] Cerviño LI, Gupta S, Rose MA, Yashar C, Jiang SB. Using surface imaging and visual coaching to
improve the reproducibility and stability of deep-inspiration breath hold for left-breast-
cancer radiotherapy. Phys Med Biol 2009;54:6853–65. doi:10.1088/0031-9155/54/22/007.

52. Delivery of Stereotaxy – Review of Technologies
associated with SRS and SBRT
DR VIBHAY PARREK
Introduction:
Stereotactic radiation therapy in the form of radiosurgery (SRS) or stereotactic body
radiation therapy (SBRT) need high accuracy and precision for treatment delivery and improve
upon the therapeutic ratio by delivering conformal dose to target and sparing surrounding critical
organs. Radiosurgery a high dose, single fraction treatment technique has role in both malignant
and benign neurological conditions and was first described by Lars Leksell in 1951. Gamma
Knife is a well-known modality to deliver such treatment and thereafter many advancements
have been seen. Similarly, Cyberknife system has revolutionized branch of stereotactic radiation
and has been used for both SRS and SBRT. Initially developed in late 1990s, it has seen major
advancements in the design and functional changes with latest Cyberknife M6 series released in
2014. Imaging, planning, quality assurance, and treatment delivery needs tobe accomplished in a
single day, making stereotactic procedures resource intensive.Brada and Laing from Royal
Marsden hospital identified four requirements for SRT which included precise patient fixation,
accurate targetdelineation, target localization, and means of delivery.Image guidance in
combination with appropriate patientimmobilization has made stereotactic treatment possible for
extracranial sites as well. Recently, Linear accelerator-based delivery of stereotactic radiation
therapy has seen major improvement after the reports from the Royal Marsden experience. An
ideal system is essential for delivery of highly precise and accurate treatment and includes the
following characteristics:
 High dose rate – Minimize treatment time and thus reduce uncertainties
 Sharp dose fall of to allow for delivery of high dose to target without compromising
adjacent normal tissues
 High mechanical accuracy for treatment delivery
 On Board Imaging (OBI) – identify exact positioning of target within body
 Monitoring and adjustment for patient movement
 Radiation output stability related to gantry rotation, collimator movement and dose rate
variation
This chapter gives an overview of traditional systems for SRS and SBRT delivery and newer
alternatives available. The systems that would be discussed include:
1. Gamma based delivery systems
2. Cyberknife image guided hypofractionated stereotactic radiotherapy (IG-HSRT)
3. Linac based IG-HSRT
A. Gamma based Delivery systems:
They are commonly referred to as Leksell gamma knife or gamma units and have been
used for intracranial SRS and use Cobalt -60 as radiation source which is shielded and collimated

53. with different aperture sizes. Beam arrangement for given target is called ‘shot’. The technique
requires a rigid frame which helps provide a fixed localization and coordinate system. A newer
alternative, LGK Perfexion is an extended system and allows immobilization with head frame
and dental suction system in place of screws. Another advancement called Icon has 3D OBI with
patient monitoring capabilities and uses a thermoplastic mask.
LGK models included U, B and C/4C types which constituted 201 Co-60 sources
arranged in hemisphere with internal fixed collimator and collimator helmet. The collimators are
available as 4 different diameters – 4,8,14,18 mm. The source to focus distance (SFD) is 40 m
and provide a mechanical accuracy of 0.3 mm. Models U and B are set manually whereas C and
4C have automated positioning system with patient docking indicator.
Leksell gamma knife Perfexion is a newer advancement and includes 192 Co-60 sources
and provides conical geometric arrangement and thus different SFD can be achieved depending
on the source position along the cone. The SFD ranges from 37.4 – 43.3 cm. It thus, helps
provide higher dose rates. The system does not have collimators and do not use collimator
helmets. It constitutes 12 cm thick tungsten collimator array and these smaller collimator arrays
help provide increased treatment position range. They are provided with a new patient
positioning robotic treatment couch which positioning speed between coordinates of 10 mm/s.
However, they lack method to visually confirm coordinates of each isocenter. Another system
associated is the Extend system which helps provide multifraction treatment with Perfexion. It
uses the patient dental impression and vacuum and fixes over the palatal region. The level of
vacuum is based on patient control unit and if the vacuum pressure drops, the treatment is
paused. Patient positioning is checked using repositioning check tool. The advantages associated
with Perfexion include: more optimal dose distribution, faster treatment times and safer, more
efficient and more accurate treatment delivery. The latest advancement in LGK is LGK Icon. It
has on board imaging and monitoring tools and does not use frames. It is compatible with
thermoplastic masks and equipped with intrafraction motion management. The system is
equipped with infrared reference tool with 4 infrared reference markers. The system has both
active and passive modes.
Immobilization of patient involves use of local anesthesia or light sedation and 4 pins are
inserted in systems which use pinsfor fixation. Leksell coordinate system is used and includes
positions including origin superior, posterior and right of patient head and measures the
increments towards left (+x), anterior (+y) and inferior (+z). Image guidance is done with use of
either MR, CT or biplane angiography. It includes the use of fiducial markers as part of modality
specific imaging boxes. These indicator boxes are filled with copper sulphate and appear bright
on MR images.
Gamma Knife IG-HSRT involves the use of two types of frame systems:
1. Removable frame system: This includes TALON cranial fixation system. This system
is well tolerated however, it has side effects of developing infection at screw site and
loosening of screws.
2. Relocatable frame system: This includes bite blocks, head straps, thermoplastic masks
and optical tracking
eXtend frame system:
This system includes carbon fiber front plate with dental impression or mouthpiece,
Baseplate with front piece and a vacuum cushion where the patient heads fits. The system
involves the following steps of setting up:

54. 1. Selection of mouthpiece and creation of dental mold; Dental impression created with
vinyl polysiloxane; Plastic spacer between mold and hard palate which allows for
airspace. However, this may not be suitable for edentulous or patients with inadequate
dentition
2. Setup at Gamma knife and construction of eXtend framesystem using completed
mouthpiece; Supine position with head on vacuum cushion and head frame removed;
Head elevation and angle is given, leg position in flexion, ambient temperature of
treatment room is set and introduction to team members; Dental mold connection with
spacer and vacuum tubing completed and abutted to hard palate and maxillary dentition;
Vacuum is set at 30-40% of atmospheric pressure and has bacterial filter; There is a
safety alarm which detects loss of suction (10% change)
3. Frame creation: Head frame secured by attaching front piece to mold and then locking
front piece to docking area
4. Vacuum cushion creation – Rigid cushion with firm impression of dorsal aspect of scalp
maintained for each fraction and defines stereotactic alignment of patient head with
couch
5. Test measurements and measurement hole selection –Daily measurements using
Repositioning tool (RCT) and compared to measurements taken at time of simulation
imaging; RCT uses 4 plastic panels that surround patient head in extend frame; Electronic
linear measurement probes measure distance between holes in RCT and scalp; Each
aperture chosen and distance to head are recorded
6. Ancillary setup information and patient instruction: Measuring distance from
earlobe laterally to side of frame and from frame inferiorly to shoulder;
Measuring height of cushion and avoid any dental manipulation and cutting or
braiding of hair
Simulation (CT) imaging:
1. Simulation imaging setup and reference RCT measurements
2. Simulation stereotactic CT imaging: CT indicator – Transparent box with implanted
fiducial markers which act as rigid points; CT images obtained from vertex to midframe;
IV contrast is used
3. Post T Measurements: Verify that patient did not shift during CT imaging; If there is
more than 0.5 mm difference then there is a need for reposition, remeasure and
reobtaining the images; afterwards the images are transferred to planning system
4. Thereafter, integration of non-stereotactic scans and later treatment planning undertaken
Treatment Procedure:
 Entering reference measurements during first fraction
 Repositioning measurements – Using electronic probe and guided by GK eXtend console
 During treatment, each position is maintained for dwell duration and patient has a call
button
 Intrafraction position monitoring done using vacuum surveillance system and loss of
>10% of vacuum level interrupts the treatment
Limitations of eXtend system:

55.  Complicated workflow – Mouthpiece creation, application and RCT measurement
system
 Vacuum as proxy for motion
 Patient contraindication (Dentition/ Performance status/ Gag)
B. CyberKnife system
This system constitutes a Linear Accelerator mounted on robotic arm. The robotic arm
delivers radiation from hundreds of noncoplanar, non-isocentric beams. CyberKnife provides the
novelty of nonisocentric treatment delivery, flexibility of robotic arm and integrated image
guidance. The treatment delivery is in entire body without need of any rigid fixation devices. In
2014, M6 series of CyberKnife (CK)were introduced which had the feature of micro multileaf
collimator (MLC) which significantly reduce treatment time and improving treatment quality.
System Specification:
CK constitutes of X band cavity magnetron and side coupled standing wave LINAC
mounted on robotic manipulation. LINAC produces an unflattened 6MV photon beam with dose
rate up to 1000 Gy/min and field size (SAD) of 800 mm. CK comprises of Iris collimation
system which has 2 hexagonal banks of tungsten with 12 sided apertures and iris field sizes of
0.2 mm. Planes are generated with multiple apertures which help provide better dose
conformality and heterogeneity and require lesser monitor units (MU). The micro MLCs
constitute 41 pairs of tungsten leaves (2.5 mm thick and 100 mm wide at 800 mm SAD allowing
maximum field size of 120 mm x 100 mm) and allows to treat larger lesions (>6 cm) and
fractionate dose regimens. Each beam is defined by source point known as a node and complete
set of nodes form the path set (Range from 23 - 133). Image guided system associated with CK
contains 2 diagnostic x-ray sources mounted in ceiling and 2 amorphous silicon flat panel
detectors in floor. Multiplan is the integrated planning system with CK and helps in contouring,
treatment planning, optimization and image guidance structure definition. Newer CK units have
multiple collimation options including standard fixed circular collimator, Iris variable aperture
collimator and InCise MLC
Patient setup and Treatment simulation:
For treating a brain lesion, thermoplastic head mask with head rest is used. For spinal
lesions, especially cervical lesion, head and shoulder mask is used whereas in thoracic or lumbar
lesions, vacuum bag or foam cradle is used. CT simulation in supine position with slice thickness
of 1-1.5 mm is used with higher resolution DRR and better tracking accuracy. Scan is centered
on target exceeding 10-15 cm above and below superior and inferior border of target and
encompasses all organs at risk (OAR). Primary CT for treatment planning should be a non-
contrast CT as contrast agents would distort DRR quality and impact tracking accuracy
Volume definition and Treatment planning:
Multiplan software provides autosegmentation feature for cranial structures using atlas-
based approach, that is, non-rigid registration algorithm. Brain lesion contouring is
donegadolinium enhanced T1 and T2 weighted FLAIR MRI sequences. CK can be used to treat
primary brain lesion, post-operative resection cavity, single or multiple brain metastases or
benign diseases. The patient specific residual target motion has been reported to be 2 mm.

56. Plan optimization and Dose calculation:
Optimization involves three methods – isocentric, conformal or sequential and the
segment shapes could be eroded, perimetric or random. Eroded segment includes the fraction of
entire PTV seen from beam eye view, perimetric includes narrow fields around perimeterof
target which help achieve highly conformal dose distribution and random, as the name suggests,
within the PTV hosen automatically by treatment planning system (TPS). Beam parameters are
chosen and define the maximum, minimum and mean dose objectives, dose volume upper and
lower limits, optimal coverage or homogenous dose to specific volumes. Isocentric plans are
useful in small spherical brain lesions. Sequential planning is most commonly undertaken as it
loosely mimics decision making process of clinician. Ray tracing and Monte Carlo are the dose
calculation algorithms used with fixed or iris collimator. Dose is calculated from irregularly
shaped fields by dissolving fields into subset of Finite size pencil beam (FSPB)
Treatment delivery and image guidance:
 Fiducial tracking: Radio-opaque markers are used for positioning and 6D corrections (3
rotational and 3 translation) are made. They are especially useful in prostate and liver
lesions. Alternatively, screws or pins could be fixed to vertebral body
 6D skull tracking: Used in intra cranial cases or sites considered fixed with respect to
skull. 6D transformation best aligns current skull position to original planning CT skull
position
 Xsight spine tracking: Used in spine lesions. Image registration is based on differential
contrast between bony features in vertebral body
 Xsight spine tracking in prone position: The advantage is decreased dose to anterior
organs with this position but has significant problem in terms of breathing movements.
Synchrony (Accuray) is a motion management system accounting for breathing motion
 Xsight Lung: It provides global aligning and useful for tumor tracking
C. LINAC based system:
Linear accelerators have been optimized for SRS/ SBRT by having finer resolution MLC,
higher dose rates,greater mechanical accuracy, and robust integratedimage guidance for patient
positioning and intrafractionalmonitoring and modern designs now offer flattening filter beams
(FFF) which provide higher dose rates. The FFF beams in association with noncoplanar or arc
beams provide high dose delivery to target volume, sharp dose gradient, normal tissue sparing
and reduced motion likelihood of patients during treatment. Tertiary collimators have been
developed which are in the form of fixed circular collimators or coneswhich attach to the LINAC
and provide smaller field sizes with sharper penumbra. These are useful for treatment of smaller
brain lesions and provide field size of 5-40 mm and height of 12 cm. The m3 micro-MLC
(BrainLab) is a popular add on compatible with LINACs which can be manually mounted when
gantry is at 180 degrees. The MLC have 26 pairs of leaf which travel perpendicular to central
axis of beam and the internal MLC of LINAC need to be fully retracted.
Respirator motion management options of SBRT include Elekta Active BreathingCoordinator
(ABC) and the Real-Time Position Management(RPM) system by Varian.The ABC is a
spirometer-based systemthat measures the patient’s inhaled volume ofair during respiration. In
case of RPM, there is tracking of motion of the IR marker boxthat is placed on the patient’s

57. torso. This motionprovides the breathing trace for the patient. Novalis and Edge platforms by
Varian are exclusively available for SRS and SBRT treatment delivery. Novalis Tx system is
developed by both Varian and BrainLab and constitutes high definition ML (HDMLC) and
ExacTrac system. HDMLC constitutes 32 inner leaf pairs and 14 outer leaf pairs on either side.
The addition of the ExacTrac system inthe platform allows for accurate patient setup
andintrafraction monitoring on the basis of two x-rayimaging panels mounted on the ceiling with
theircorresponding sources built into the floor. Theseallow for imaging at any couch angle, even
duringtreatment. It also has an optical tracking device forIR markers. Predefined marker arrays
are availableor markers can be manually placed on the patientfor position monitoring and precise
couch motion. TrueBeam STx offers both FFF and flattened beams. The maximum dose rate for
6 MV FFF is 1,400 MU/min and that of 10 MV FFF is 2,400 MU/min thus providing faster
treatment delivery. Edge radiosurgery system is a new variant used for SRS/ SBRT and has been
equipped with optical surface monitoring system (OSMS) which tracks the surface of the patient
for positioning and monitoring and is similar to AlignRT. It is equipped with PerfectPitch 6
degree of freedom (DOF) couch and also offers Calypso system for extracranial real time
tracking. Calypso tracks the target using the electromagnetic signalfrom the beacon transponders
implanted in thepatient, and it can interface with the machine toadjust the couch position or gate
the beam on thebasis of the received signal. Similarly, Elekta offers VersaHD and Synergy S
models for SRS/ SBRT delivery. VersaHD is useful for both conventional and SRS/ SBRT
treatment and equipped with both FFF and flattened beams and has Agility collimator which
improves treatment for dynamic treatments. Real time tumor tracking can be done with Agility
MLC and OBI and thus improve the therapeutic ratio.
Besides the above-mentioned systems, there are other systems which have been used for
delivery of SBRT/ SRS treatment. These include the TomoTherapy systems, VERO (devised by
BrainLab and Mitsubishi) and View Ray. The latter two systems are still being investigated for
their efficiency and ease of treatment delivery.
Conclusion:
Radiosurgery has evolved remarkably compared to previous decades, led by advances in
existingsurgical delivery platforms including the GK platform.Future advancements to GK will
give it true image-guided HSRTcapabilities without sacrificing the precision and accuracy that
have established GK as the “goldstandard” for radiosurgery.The future promises further
developments. Knowledge-based planning systems have thepotential to reducethe expertise
required to deliver high-quality radiosurgery.We have provided a thorough overview of the more
commonly available. Options and future developments in the setup and monitoring of thepatient.
Each platformhas its unique characteristics with commongoal of delivering highly accurate and
precisetreatments with improved image guidance. No one treatment platform has allthe ideal
characteristics and decision are made on the basis ofthe relative importance of factors such as
treatmenttime length.A successful SRS/SBRTprogram will also need reliable and well-thought-
outprotocols, careful patient selection on the basis ofthe technology available for treatment,
appropriatetreatment planning tools and algorithms, and awell-designed quality management
program.

58. Figure 1: Leksell Gamma Plan (Courtesy Elekta.com)

59. Figure 2: Leksell Gamma Knife Perfexion (Source: Elekta.com)

60. Figure 3: Accuray CyberKnife

61. Figure 4: TrueBeam STX (Source: Varian.com)

62. 1
Frame to frameless
Authors: Talapatra Kaustav, Vadgaonkar Rohit.
Department of Radiation Oncology, Kokilaben Dhirubhai Ambani Hospital, Mumbai.
Various retrospective studies and prospective randomized trials have established stereotactic
radiosurgery (SRS) as method of treating intracranial tumors with advantage of minimizing radiation
dose to normal brain parenchyma1,2
. Evolution of this highly précised and accurate method of treatment
has demonstrated a perfect correlation between medical science advancements and technological
progress.
The first stereotactic frame was developed by Horsley and Clarke in 19063
. They developed a
method of locating deep-seated brain lesions by assigning coordinates in three planes to
neuroanatomical structures, based on cranial landmarks3
.
In 1947 Spiegel and Wycis introduced frame-based stereotaxy using a plaster head cap known as
a stereoencephalatome, and a 3-D coordinate system relative to this4
.Later on, Lars Leksell, a Swedish
Neurosurgeon, introduced the term “Radiosurgery” in 19515
. He described this technique including the
concept of “center of arc”. He used a invasive head frame for rigid immobilization.
The technique initially employed superficial low energy x-rays, but in 1967 Leksell developed
first Gamma Knife prototype.The initial models of gamma knife used 179 Cobalt-60 sources which were
modified into advancements with 201 Cobalt-60 sources. Again he used a rigid metal stereotactic head
frame to localize small intracranial targets and radiation was delivered in a single high-dose
fraction5
.Since then, Gamma Knife has become widely used for intracranial SRS, with sub-millimetre
accuracy6
.The 1980s saw the adaptation of linear accelerators for intracranial SRS, using rigid

63. 2
stereotactic head frames, and specialist dosimetry software. Soon over the next two decades, Linac
based radiosurgery was widely used all across the world as it allowed more flexibility than Gamma knife.
Accumulated robust data on frame based SRS has validated the technique and established as a
standard of care for intracranial radiosurgery. Though frame-based methods reliably immobilize
patients, they also present several limitations. Invasive fixation to the skull may be painful. It may
provoke patient anxiety. It requires the patient to remain in the department for prolonged time. This
techniques put immense pressure on department for simulation, designing treatment and quality
assurance because of time constraints7
.
Now, modern frameless techniques provide a non-invasive alternative option for patient
immobilization and repositioning when used in conjunction with proper image guidance and precision
delivery8
. Framelesstechniques in contrast to frame based technique also provide more time for
planning which can increase safety and flexibility.
No randomized trials have compared both these techniques. However, few studies have
analyzed both techniques and have demonstrated comparable physical, dosimetric and clinical
outcomes7,9
.
A study fromIndia has shown that set up accuracy of frameless SRS is as comparable with frame-
based SRS. With availability of verification methods such as CBCT and hexapod couch, an accurate and
precise treatment delivery is feasible with frameless techniques9
.
Image guidance is very critical while using frameless stereotaxy as a retrospective study of 44
patients treated with both these techniques have shown errors in terms of Sub millimeter and the
estimated CTV to PTV margins of both these techniques were comparatively similar10
. Though there was
a statistical significant difference in the mean shift of Y (0.000) and Z (0.013) axis between the two
techniques, authors concluded that the integration of image guidance in traditional SRS can improve set-

64. 3
up accuracy and has the potential to reduce or avoid the PTV margin if a strict on-line IGRT protocols are
in place.10
Bennion, N. et al has analyzed a data of 98 patients (170 lesions). Patients were immobilized
with either an invasive stereotactic frame [34 patients (61 lesions)] or frameless SRS mask [64 patients
(109 lesions)]. At median radiologic and clinical follow-up of 6.5 months (range 0.7-44.3) and 7 months
(range 0.7-45.7) respectively, Kaplan-Meier estimates of local failure were not statistically significant
between groups (p=0.303). Actuarial 6-month local failure rates were 7.2% and 12.6% (p=0.295), with
12-month local failure rates of 14.5% and 26.8% (p=0.185), respectively. There was no statistically
significant difference in symptomatic (p=0.391) or asymptomatic (p=0.149) radiation necrosis. Six-month
radiation necrosis was 0% and 1.6% (p=0.311) with 12-month rates of 20.2% and 3.8%, respectively
(p=0.059)7
.
Frameless cranial radiosurgery has become popular in the last decade which uses thermoplastic
mask for immobilization and as the indications of stereotaxy broadened into more than one fraction
stereotactic body radiotherapy (SBRT), frameless radiosurgery turned out to be a boon due to non-
invasive and relocatable nature of frameless stereotaxy.
Major concern regarding frameless stereotaxy is setup accuracy. The level of setup used in
conventional radiotherapy is not adequate for SBRT. Also the patient immobilization system should
account for intra- and interfraction motion compensation for the successful delivery of SBRT. Even with
highly sophisticated image-guided systems, immobilization is still critical. There are various commercially
available stereotactic body frames. With these devices, vacuum cushions are frequently used.
In addition to providing effective immobilization, Simulation must assess the target
motion.Commonly used techniques include slow CT, breath hold inspiration/expiration scans and 4D
reconstructed CTs.11

65. 4
In conclusion, radiosurgery has seen enormous evolution in the last century. The next few years
are going to be even more exciting in terms of newer indications and treatment sites. Radiosurgery is
probably going to emerge as one of the most powerful treatment modalities in medical science.
Understanding biology better, improvement in imaging /verification during treatment and its usage in
combination with other modalities are few of the key determinants of its future development.
References:
1. Andrews DW, Scott CB, Sperduto PW, et al. Whole brain radiation therapy with or without
stereotactic radiosurgery boost for patients with one to three brain metastases: Phase III results of
the RTOG 9508 randomised trial. Lancet. 2004;363(9422):1665-1672.
2. Aoyama H, Shirato H, Tago M, et al. Stereotactic radiosurgery plus whole-brain radiation therapy vs
stereotactic radiosurgery alone for treatment of brain metastases: A randomized controlled trial.
JAMA. 2006;295(21):2483-2491.
3. Horsley VA, Clarke RH. The structure and functions of the cerebellum examined by a new method.
Brain. 1908;31:45–124.
4. Spiegel EA, Wycis HT, Marks M, et al. Stereotactic apparatus for operations on the human brain.
Science. 1947;106:349–50.
5. Leksell L. The stereotaxic method and radiosurgery of the brain. Acta Chir Scand. 1951;102(4):316-
319.
6. Heck B, Jess-Hempen A, Kreiner HJ, et al. Accuracy and stability of positioning in radiosurgery: long-
term results of the gamma knife system. Med Phys. 2007;34(4):1487–95.

66. 5
7. Bennion NR, Malouff T, Verma V. A comparison of clinical and radiologic outcomes between frame-
based and framelessstereotactic radiosurgery for brain metastases. Pract Radiat Oncol. 2016 Nov -
Dec;6(6):e283-e290.
8. Kamath R, Ryken TC, Meeks SL, Pennington EC, Ritchie J, Buatti JM. Initial clinical experience with
frameless radiosurgery for patients with intracranial metastases. Int J Radiat Oncol Biol Phys.
2005;61(5):1467-1472.
9. Kataria T, Gupta D, Karrthick KP. Frame-based radiosurgery: Is it relevant in the era of IGRT?Neurol
India. 2013 May-Jun;61(3):277-81.
10. Talapatra K, Doss G, Sharma D et al. Comparison of Invasive and Noninvasive Frame for Set-up
Error Accuracy in Intracranial Radiation Therapy—An Indian Institute Experience. Int J Radiat Oncol
Biol Phys. 2016 Oct 1;96(2S):E132-E133.
11. Benedict SH, Yenice KM, Followill D, Galvin JM, Hinson W, Kavanagh B, Keall P, Lovelock M,
Meeks S, Papiez L, Purdie T, Sadagopan R, Schell MC, Salter B, Schlesinger DJ, Shiu AS, Song DY,
Stieber V, Timmerman R, Tome WA, Verellen D, Wang L, Yin F. Stereotactic body radiation therapy:
the report of AAPM Task Group 101. Med Phys. 2010;37(8):4078–101.

67. SRS SBRT PLAN EVALUATION
Maruthu pandyian
Treatment planning Aspects:
1. The treatment planning system must have the capability of accurately calculating the
predicted dose for the scope of SRS‐SBRT services to be offered.
2. Each treatment site should have a defined list of critical structures to evaluate and
stereotactic fractionation based tolerances should be defined based on clinical protocol
data or peer‐reviewed literature.The Medical Physicist should ensure that the radiation
oncologists are aware of the delivery system's tolerances relative to the planning target
volume and organs at‐risk avoidance margins. The planning target volume margins
should be clearly documented.
3. Image fusion requirements for target definition should be defined and target margins
should be clearly described. Target margins should be based on data from current
literature along with knowledge of the limitations of in‐house localization capabilities.
4. Planning strategies and techniques should be described for each treatment site, such as
conformal arcs, intensity‐modulated radiation therapy, and volumetric‐modulated arc
therapy. These technique definitions should include clinical limitations based on the
findings from commissioning. If non-coplanar techniques are included, potential collision
should be considered in determining overall beam configuration.
5. In cases of re‐irradiation, the cumulative dose should be evaluated by the treating
physician. A description of the method used and the outcome of the evaluation should be
documented.
6. The use of an isotropic calculation grid size of 2 mm or finer is recommended. The use of
a grid size >3 mm is discouraged.For very small targets, a 1 mm calculation grid size may
be necessary.
7. Target dose coverage, dose fall‐off beyond the target, dose conformity metrics, and
compliance with critical structure dose objectives should be clearly reported and signed
by the radiation oncologist to confirm that the chosen treatment technique is clinically
acceptable.
8. An independent dose calculation check must be performed prior to treatment.
Dose heterogeneity, gradient and fall-off, and beam geometry
1. Dose prescriptions in SRS/SBRT are often specified at low isodoses e.g., 80% isodose
and with small or no margins for beam penumbra at the target edge, as compared to
traditional radiation therapy.
2. The rationale is to improve dose fall-off outside of the targeted volume and help spare
nearby organs at risk. This practice increases dose heterogeneity within the target.
However, in contrast to conventionally fractionated radiotherapy, dose heterogeneities

68. within the target for SRS/SBRT are acceptable for targets not involving functional
normal tissue.
3. Hot spots within the target volumes are generally viewed to be clinically desirable, as
long as there is no spillage into normal tissue.
4. The use of multiple nonoverlapping beams is the primary means of achieving a sharp
dose fall-off in SRS/SBRT, similar to that in intracranial radiosurgery. This optimally
requires that radiation should converge on the target as concentrically as possible from
many directions.
5. Parameters that affect the dose fall-off are beam energy and the resolution of beam
shaping e.g., multileaf collimator MLC leaf width. For small beams such as those
commonly used in SBRT, the higher the beam energy, the larger the beam penumbra due
to lateral electron transport in medium. In a low-density medium, such as lung tissue, this
effect becomes more significant.
6. A 6 MV photon beam, available on most modern treatment machines, provides a
reasonable compromise between the beam penetration and penumbra characteristics for
SBRT lung applications. Additionally, most SBRT applications use MLC collimation.
While the finer MLC collimation resolution improves the conformity of target dose
distribution, this improvement is limited by characteristic blurring caused by the finite
source size and lateral range of secondary electrons.
7. The commonly available 5 mm MLC leaf width has been found to be adequate for most
applications, with negligible improvements using the 3 mm leaf width MLC for all but
the smallest lesions 3 cm in diameter.
Normal tissue dose tolerance
1. Normal tissue dose limits for SBRT are considerably different from conventional
radiotherapy due to extreme dosefractionation schemes and are still quite immature.
Thus, normal tissue dose limits for SBRT should not be directly extrapolated from
conventional radiotherapy data.
2. Particular attention should be paid to fraction size, total dose, time between fractions, and
overall treatment time, which are important radiobiological factors that need to be
maintained within clinically established parameters where available in the SBRT
literature.
3. New hypo fractionated schedules and trials for which there is no reliable mechanism to
estimate their radiobiological effects. Therefore, in a clinical trial situation, not only the
fraction size but also the frequency and overall treatment time should be maintained
throughout the entire trial for all patients to obtain reliable outcome data.
Treatment plan reporting

69. 1. SRS/SBRT treatment plans often use a large numbers of beams, unconventional dose
fractionations and delivery frequencies, and more comprehensive image guidance data
and information.
2. It is critical to accurately communicate the details of the treatment plan and its execution
to the treatment team. The quality of planned dose distributions for SBRT can be
evaluated from parameters characterizing target coverage, dose homogeneity, dose
outside of the target definition, and volumes of normal tissue exposed to lower doses.
3. Simple methods of articulating these parameters may rely on combinations of DVHs for
different organs and tables representing dose allocation in different subvolumes of these
organs.
4. Metrics to be evaluated include the following
 Prescription dose
 Prescription ICRU reference point or dose/volume e.g., isodose covering PTV to a
particular percentage,
 Number of treatment fractions,
 Total treatment delivery period,
 Target coverage,
 Plan conformity example: Ratio of prescription isodose volume to PTV or a
conformity index such as proposed by Hazard et al.,
 Dose falloff outside the target example: Ratio of the volume of the 50% of
prescription isodose curve to PTV,
 Heterogeneity index e.g., the ratio of highest dose received by 5% of PTV to lowest
dose received by 95% of PTV,
 Notable areas of high or low dose outside of the PTV, and
 Dose to organs at risk dose to 1% and 5% volumes and mean doses.
Conformity Index Evaluation
Conformity index (CI)= (
𝑃𝐼𝑉
𝑃𝑉𝑇𝑉
)/(
𝑃𝑉𝑇𝑉
𝑇𝑉
)
Isodose Surface (IDS) Selection
TV is the Target Volume
PIV is the Prescription Isodose Volume i.e.,total volume encompassed by the prescription IDS
PVTV is the TV encompassed by the IDS
Ref:

70. 1.Hazard LJ, Wang B, Skidmore TB, Chern SS, Salter BJ, Jensen RL, Shrieve DC: Conformity
of Linac-based stereotactic radiosurgery using dynamic conformal arcs and micro-multileaf
collimator. Int J RadiatOncolBiol Phys. 2009, 73:562-570.
2. The report of AAPM Task Group 101