This document discusses image-guided radiation therapy (IGRT) and various IGRT techniques. It describes how IGRT aims to increase the accuracy and precision of radiotherapy delivery by applying image-based target relocalization. Common IGRT techniques mentioned include portal imaging, on-board cone-beam CT (CBCT), in-room CT, ultrasound and real-time tumor tracking. CBCT allows visualization of the tumor location using kilovoltage or megavoltage X-rays rotating around the patient. Real-time tumor tracking involves synchronizing radiation delivery with the respiratory cycle using implanted fiducial markers and fluoroscopy.

1. Dr swarnita sahu
Dnb resident
Radiation oncology
Batra hospital,new delhi.

2.  PROCEDURE THAT REFINES THE DELIVERY OF THERAPEUTIC
RADIATION BY APPLYING IMAGE BASED TARGET
RELOCALISATION TO ENSURE PROPER PATIENT
REPOSITIONING FOR THE PURPOSE OF ENSURING ACCURATE
TREATMENT AND MINIMIZING THE VOLUME OF NORMAL
TISSUE EXPOSED TO IONISING RADIATION.

3.  INCREASING THE ACCURACY AND PRECISION OF
RADIOTHERAPY DELIVERY.
INACCURACY:
SYSTEMIC ERRORS-
• IMPROPER TARGET DELINEATION.
• POORLY REPRESENTATIVE
SIMULATION.
• DISSOCIATION B/W SKIN MARK &
INTERNAL ANATOMY.
IMPRECISION:
STOCHASTIC (RANDOM) ERRORS-
PRODUCES VARIANCE IN THE SPATIAL
LOCATION OF THE TREATMENT AROUND
THE TRUE TARGET-
• INEVITABLE FLUCTUATIONS IN THE
DAILY SETUP.
• UNPREDICTABLE TARGET MOTIONS

4.  CONVENTIONAL: CT & MRI
 PET CT: UPCOMING

6.  PORTAL AND RADIOGRAPHIC IMAGES
 IN ROOM COMPUTED TOMOGRAPHY SCANNER
 KILOVOLTAGE CONE BEAM CT
 MEGAVOLTAGE CONE BEAM CT
 HELICAL TOMOTHERAPY
 ULTRASOUND

7.  PORTAL AND RADIOGRAPHIC IMAGES
 IN ROOM COMPUTED TOMOGRAPHY SCANNER
 KILOVOLTAGE CONE BEAM CT
 MEGAVOLTAGE CONE BEAM CT
 HELICAL TOMOTHERAPY
 ULTRASOUND

8. VARIAN TRUE BEAM ELEKTA’S VERSA HD
MODERN ACCELARATORS

9.  KV XRAY IMAGER
Conventional
Mounted on the gantry with an
opposing flat panel image detector.
BETTER CONTRAST
DETERMINING PLANNED
TARGET POSITION IN RELATION
TO BONY LANDMARKS OR RADIO-
OPAQUE MARKERS (FIDUCIALS)
IN THE TARGET TISSUES.
USED IN BOTH
RADIOGRAPHIC(check pt setup
before each treatment) /
FLOUROSCOPIC MODE (track
movement of fiducial markers due to
respiratory movement).
 MV ELECTRONIC PORTAL
IMAGING DEVICE
Has its own flat panel image detector.
PORTAL VERIFICATION BEFORE
EACH TREATMENT.
ONLINE MONITORING OF
TARGET POSITION DURING
TREATMENT DELIVERY.
Matrix of 256 x 256
solid state detectors of
amorphous silicon
photodiodes

10. KV
MV

11. • PORTAL AN RADIOGRAPHIC IMAGES
• IN ROOM COMPUTED TOMOGRAPHY SCANNER
• KILOVOLTAGE CONE BEAM CT
• MEGAVOLTAGE CONE BEAM CT
• HELICAL TOMOTHERAPY
• ULTRASOUND

12. CONVENTIONAL CT SCANNER HOUSED IN THE TREATMENT ROOM AND SHARES THE
COUCH WITH THE ACCELERATOR.
Images can be taken before each treatment.
Couch moved in axial direction to take CT images.
Couch is rotated back into alignment with the accelerator gantry for treatment.
NEITHER THE COUCH NOR THE PATIENT IS MOVED REALTIVE TO THE TREATMENT
ISOCENTER.
ADV:
High resolution 3-D volumetric data of patient anatomy in the treatment
coordinates-
1) Useful in target localization prior to treatment
2) Reconstructing dose distribution (ADAPTIVE RADIOTHERAPY)

13. • PORTAL AN RADIOGRAPHIC IMAGES
• IN ROOM COMPUTED TOMOGRAPHY SCANNER
• KILOVOLTAGE CONE BEAM CT
• MEGAVOLTAGE CONE BEAM CT
• HELICAL TOMOTHERAPY
• ULTRASOUND

14.  Technique integrates CT imaging with LINAC.
 Visualization of the exact tumor location.
 Acquiring multiple planar images produced by KV or MV cone beam rotating 360 degrees
around the patient.
 Filtered back projection algorithm is used to reconstruct the volumetric images of the target
volume.

15.  The Xray tube is mounted on a retractable arm at 90 deg with respect to
the central axis of the linear accelerator beam.
 Image is generated by the flat panel area detectors mounted opposite the
xray tube.
 3D volumetric images are reconstructed by the computer using a filtered
back projection algorithm.
 The on board KV imaging system is capable of radiography, fluoroscopy and
cone beam computed tomography.

16.  Made possible by the traditional EPID by a Si flat panel
detector.
 The Xray beam in this case is the therapy beam of the
accelerator.
 Planar projection images are acquired from multiple directions as
the xray source and the detector rotate about the patient.
 The soft tissue contrast is reduced in the MV-CBCT.

17.  Less susceptibility to imaging artifacts (d/t metallic objects eg-
hip implants, dental fillings and surgical clips).
 No need of extrapolating attenuation coeffiecients from KV
beams to therapeutic beams.
 The known dose distribution characteristics of the therapeutic
beam allow more accurate calculation of imaging dose in the
MVCBCT acquisition process.
 Implementation of MVCBCT does not require extensive
modification of linear accelerator that is already equipped with
EPID.

18. ADVANTAGES OF KV-CBCT OVER MV-CBCT
 Better contrast & spatial resolution.
 Better soft tissue visibility at much lower doses.
 Compatibility of KV-CBCT images with the reference treatment plan images
for patient setup verification and correction.
 Combination of Radiography, fluoroscopy, and CBCT capabilities from the
same source and detector which provides great flexibility in implementing
the goals of IGRT.

19. • PORTAL AN RADIOGRAPHIC IMAGES
• IN ROOM COMPUTED TOMOGRAPHY SCANNER
• KILOVOLTAGE CONE BEAM CT
• MEGAVOLTAGE CONE BEAM CT
• HELICAL TOMOTHERAPY
• ULTRASOUND

20. ULTRASOUND: NON INVASIVE, NON RADIOGRAPHIC
REAL TIME IMAGING TECHNIQUE
 MOST COMMON IGRT APPROACHES: particularly prostate.
 Rationale: emission of high frequency sound waves to produce
images of internal anatomy.
 (a transducer is encased in a probe applied to the skin
surface, reflecting sound waves back as echoes when a change in
impedance is encountered due to density differences between
tissues.)
 THE TIME AN ECHO TAKES TO RETURN IS USED TO
CALCULATE THE DEPTH OF TISSUE INTERFACE.
 3 operational modes: B (brightness) mode is the primary one.

21. NOMOS: B mode acquisition and targeting
system
2D
SonArray: 3D
LIMITATIONS:
POOR IMAGE QUALITY
EXPERIENCE
LARGE PLANNING MARGINS : d/t
inter and intrauser variability of
interpretation
ANATOMIC DISTORTION: d/t
transducer pressure.

22.  IMRT delivery technique – combines
features of linear accelerator + helical
CT scanner.
 The linear accelerator is mounted on a
CT like gantry and rotates through a
full circle.
 Treatment couch is translated slowly
through a doughnut like aperture.
 Creating a helical motion of the beam
with respect to the patient.
 Deliver IMRT & generate CT images
from the same MV beam as it uses for
the therapy.
 A unique device capable of delivering
both IMRT & IGRT in the same
treatment geometry.

23.  Detect systemic error.
 Position the patient, target or organ at risk.
 Modify the treatment plan or choose the appropriate plan.
 Detect changes in patient or target size.
 Helps in controlling the respiratory motion of the target, most
prominent in lung cancers.

24.  Tumor motion in lungs or other sites cannot be predicted with any
degree of accuracy.
 Real time tumor tracking or gating process is required to manage
target motion in radiotherapy.
 It can be done by -
1) 4D COMPUTED TOMOGRAPHY.
2) REAL TIME TUMOR TRACKING.

25.  Acquiring CT scans synchronously with the patient’s respiratory phases.
(4D – being time)
 Breathing cycle is divided into 10 respiratory phases and multiple CT volumes
are taken at each phase.
 May involve as many as 1500 slices.
 One commonly used method – use a reference signal from up and down motion
that could be correlated with the target motion.
eg-Varian Real Time Position Management and Gating System

26.  Computer controlled video based system : box with infrared reflectors is
placed on the patient’s surface and the motion of the box is tracked by IR
cameras.

27.  The RPM system can be interfaced with a CT or a PET-CT scanner for 4D CT
imaging.
 These images are used to design an individualized treatment plan in which
radiation is administered at optimum moments of breathing cycle.
 4D CT data acquisition:
2 modes - 1) Prospective gating.
2) Retrospective gating.
 Beam is synchronized with the respiratory cycle and switches the beam on
only at selected times of respiration.
 Gating threshold is set when the target is in the desired position of the
respiratory cycle .
 The gating system turns the beam on or off in accordance with the
programmed gating threshold.

28. prospective
 Images are collected only at
one phase of respiratory
cycle.
 Eg- end of expiration or end
of inspiration.
retrospective
 Scan data for each axial slice
are acquired at all phases of
respiration.
 Correlation or registration of
the CT images with the
respiratory phases is
conducted after the data is
acquired.

29.  To detect respiratory motion using radiation beam and to follow the
tumor’s changing position.
 Surrogate markers used.(identify tumor)
 External fiducials on the skin surface and internal fiducials
implanted directly into the tumor.
 In order to make this work- the time delay between detection of
motion and the corrective action should be short.(order of 100ms)
 2 ways-
1) Flouroscopy based tracking system.
2) Electromagnetic field tracking.

30.  Most available tracking system use fluoroscopy to detect metal fiducials
implanted into the tumor.
 It continuously images during treatment and the beam is turned on and off
depending on the detected image.
 Some are installed in the accelerator gantry while others are installed in the
room.
 Eg- 1) Room mounted
 2) Gantry mounted
 3) Robotic systems

31.  By University of Hokkaido.
 Dual Xray tube that rotate on a circular track embedded in the floor.
 Each tube has a Xray detector that rotates on the ceiling mounted track.
 During irradiation the 2 imaging systems continuously track fiducials in the
tumor.
 Two fluoroscopic images are combined to construct trajectories of tumor
motion in 3D.

33.  Provide IGRT for the delivery of stereotactic radiosurgery and stereotactic
radiotherapy.
 Optical + Flouroscopy based tracking are used together.
 Optical system consist of IR reflecting markers that are placed on marked
spots on the patients surface or on the immobilization device which is detected
by 2 IR cameras mounted in the ceiling .
 Internal target localization : done by stereoscopic Xray imaging device .
2 Xray device on the floor and 2 opposing a Si-detector mounted in the ceiling.
XRAY IMAGING SYSTEM IS FULLY INTEGRTED WITH IR TRACKING
SYSTEM .
TARGET ALIGNMENT IS BASED ON IMPLANTED FIDUCIALS OR
INTERNAL BONY LANMARKS.

35.  CYBERKNIFE: image guided frameless stereotactic radiosurgery system for
treating cranial & extracranial lesions.
 Two diagnostic xray tube mounted orthogonally in the ceiling and 2 opposing Si-
flat panel detectors.
 The robotic arm has 6 degrees of freedom and is capable of pointing the linac
beam almost anywhere in space.
 After sensing any target motion, robotic arm moves the beam to the newly
detected target position for alignment.
 Not restricted to isocenter geometry, can be directed independently without a
fixed isocenter.

37. EXCESSIVE RADIATION EXPOSURE
TO OVERCOME:
ELECTOMAGNETIC FIELD TRACKING
(without the use of ionization radiation)

38.  Based on real time localization of electromagnetic transponders(becons)
implanted into the tumor.
 Transponders: tiny oscillating circuits (1.8 x 8.6 mm2)
When excited by an electromagnetic field, emit a unique resonant frequency
signal – DETECTED BY MAGNETIC ARRAY POSITIONED CLOSE TO THE
PATIENT.
 MAGNETIC ARRAY:
source coils - generate signals to excite the transponders
Sensor coils-receive unique frequency signal returned by the responders.
 Fast enough to track tumor motion during the breathing cycle.

40.  Dynamic images are acquired to track patients.
 3-D anatomy while the treatment beam in on.
 ADV: superior soft tissue contrast
no ionizing radiation for imaging.
Suited for real time volumetric tracking of soft tissue targets.

41. Low field open MRI unit for real time
imaging
3 cobalt 60 sources, each equipped with
computer controlled MLCs.
Dynamic images are acquired to track
patient 3D anatomy while the treatment
beam is on.

42.  POTENTIAL OF EXCESSIVE DOSE TO THE PATIENT DUE TO VARIOUS
RADIOGRAPHIC IMAGING PROCEDURES.
 There’s a need to evaluate therapeutic & imaging dose in a much balanced manner.