Radiotheray transition from 2D to 3D Conformal radiotherapy(3D-CRT)

• ‘’It must be emphasized that the development of
radiotherapy facilities should be regarded as a
stepwise process’’

Out lines of presentation
• Introduction
• Clinical Evidences for 3D-CRT
• Milestones for 3D CRT
• Approaches to 3D-CRT
• Resources required to establish 3D-CRT
• Clinical Implementation of 3-D CRT
• Education & training Requirement
• Quality assurance and Quality control in 3D CRT
• References

Introduction
• The term cancer (Greek "karkinos") was
proposed for the first time by Hippocrates, who
argued the roots of this disease resided in a
humoral imbalance.
• Radiation oncology is that discipline of human
medicine concerned with the generation,
conservation, and dissemination of knowledge
concerning the causes, prevention, and treatment
of cancer and other diseases involving special
expertise in the therapeutic applications of
ionizing radiation.

Introduction
• There are three key milestones in the history of
radiotherapy
I) Discovery of X-rays- by Wilhelm Rőntgen, in
1895
II) Discovery of natural radioactivity- by Marie
Curie in 1898
III) Production of artificial radioactive elements

Introduction
• In 1897, Leopold Freund & Eduard Schiff proposed
X-rays to treat some diseases.
• In 1899, Tage Sjögren became the first person to
successfully treat a person with cancer through X-
rays
• In1900, Thor Stenbeck cured a skin cancer patient
with small doses of radiation
• In the 1980s the quadratic linear model was
proposed to describe the effects of radiation on
irradiated tissues

Introduction
• Between 1950 & early 1980s, the field of
radiotherapy began to use cobalt therapy
machines that allow the treatment of deeper and
“difficult” cancers,
• while X-rays only allow the treatment of
superficial tumors
• Subsequently, the linear particle accelerators
have begun to replace the cobalt units

Introduction
• When a physician decided administering RT to a
pt, six fundamental questions that must be
answered are:
1. Indication for RT?
2. Goal of radiation therapy?
3. Treatment volume?
4. Treatment technique
5. Treatment dose and fractionation?
6. Radiation tolerance of surrounding normal
tissues?

Introduction
• In technical terms, there are three main types of
radiotherapy
 Radiation through external therapy (teletherapy)
 Radiation through internal therapy (brachytherapy) and
 Systemic therapy with radioisotopes
• There are seven main types of teletherapy
1. Conventional external radiation therapy or 2-D
2. Conformational radiation therapy or 3-D
3. Stereotactic (precision) radiation therapy
4. Radiation beam intensity modulation or IMRT
5. Image-guided radiation therapy or IGRT
6. Volumetric modulation arc therapy or VMAT
7. Particle therapy

Introduction
• The European Dynarad consortium has proposed
that the complexity of RT planning & treatment
methodologies can be captured in 04 levels
• Level 0 -represents basic RT where no attempt is
made to shape the treatment fields & as such
can’t be described as conformal
• Level 2 conformal RT requires a full 3-D data set,
usually of CT images, on which the tumor volume
is defined

Conventional (2D) radiation therapy
-Old techniques of radiotherapy
-Treatments planned with limited number of
beams
- Boundaries delineated on orthogonal x-rays of
the patient

3D conformal radiation therapy (3D-CRT
• Main distinction between treatment planning
of 3-D CRT and conventional radiation therapy
is
• it requires 3-D anatomic information &
treatment-planning system that allows
optimization of dose distribution which meets
the clinical objectives.

3D conformal radiation therapy (3D-CRT)
• 3-D CRT-term to describe the design &
delivery of RT treatment plans based on 3-D
image data.
• Organ at risk also delineated &reduce
treatment side effects.
• RT planning software is used to design
complicated beam arrangements & to assess
DVH.

• If the adverse effects of treatment can be
reduced in this way, the dose of the target
volume can be increased with the expectation
of improving survival
• Its principal benefit therefore is to patients who
are to be given potentially curative radiotherapy

• The incremental benefits in the transition from
conventional RT to 3-D CRT are substantially
greater than those achieved in the transition from
3-D CRT to IMRT.
• It is therefore recommended that the
implementation of 3-D CRT should be given
priority over the implementation of IMRT

3D conformal radiation therapy (3D-CRT)
• While 2-D RT can be applied with simple
equipment, infrastructure & training, transfer to
3-D CRT requires more resources in technology,
equipment, staff & training.
• A novel radiation treatment approach using
IMRT demands even more:
 Sophisticated equipment
More teamwork
Consequentially more resources, advanced
training & more time for treatment planning &
verification of dose delivery than 3-D CRT.

• The design & delivery of a 3-D CRT treatment
requires a chain of procedures all of which must
be in place if the treatment is to be safe &
accurate.
• A chain is as strong as its weakest link.
• If any of the links of a chain are weaker than the
others the chain will break at that point.
• It is therefore essential that all the links have been
established before starting pt therapy.

• The links in this chain are:
1. Precise immobilization of pts throughout the
whole process
2. Use of high quality 3-D medical imaging to
determine GTV, CTV, PTV &PRV
3. Use of 3-D planning systems to choose beam
orientations & to display BEVs
4. computation of 3-D dose to the PTV & PRV
5. Evaluation of the dose plan effect using
-dose volume histograms (DVH)
-tumor control probability (TCP)
-normal tissue complication probability (NTCP)

• The links in this chain are…
6. Transfer of these planning data to the delivery
machine
7. Verification of pt position, beam placement &
dosimetry
8. Measurement of outcome

Clinical Evidence for 3D
• When the appropriate technology to deliver 3-D CRT,
such as
 CT simulators,
Radiation treatment planning systems (RTPS) capable
of performing 3D dose calculations, producing DRRs
and DVHs,
Beam shaping devices like MLCs became available,
• This way of planning & delivering RT soon gained
popularity.
• 3D CRT now become standard practice in the
developed world to treat many types of tumors with
curative intent.

Clinical Evidence for 3D…
• The largest body of available evidence in support
of 3-D CRT is in the treatment of prostate & lung
cancers.
• By conforming the dose to the target volume, a
reduction in the treated volume of about 30% to
50% can be achieved using 3-D CRT.

Clinical Evidence for 3D…
• Local control can therefore be improved by ↑ the
dose to the tumor, without unacceptable toxicity.
• Evidence exists of a dose-response relationship in
many tumors
• This possibility of escalating doses, thus increasing
local control & potentially improving survival,
help to change the treatment from palliative to
curative

Milestones for 3D CRT
• A conformal radiotherapy program should be built
on a firm foundation of expertise in conventional
radiotherapy, and should not be started until
certain basic milestones have been met.

• Milestones that must be achieved before
resources are committed to the establishment of
3-D CRT
Facilities are in place for the provision of
conventional RT
Adequate Dxtic imaging facilities are in place for
Dx & staging
ƒAdequate imaging facilities are in place for
planning CT scans
 ƒThere is an intention to deliver curative RT

• Milestones in the process once the project has started:
 Appointment of sufficient staff that the existing program of
conventional therapy will not be compromised
 ƒAcademic training of staff (radiation oncologist & medical
physicist)
 ƒSpecification & purchase of necessary additional
equipment
 ƒPractical training of radiation oncologist & medical
physicist
 Practical training of other staff (treatment planners & RTTs)
 ƒExtension of QA program to cover 3-D CRT
 ƒEstablishment of clinical treatment protocols

APPROACHES TO CONFORMAL RADIOTHERAPY
• Starting a conformal radiotherapy program requires
considerable planning.
• To establish 3-D CRT in an institution the following steps
should be taken:
 define the scope of the program
 develop staffing needs for the program
 ƒidentify necessary space and equipment
 develop a program budget
 ƒprepare space and purchase equipment
 ƒhire new staff
 ƒtrain all personnel to be involved with the program
 ƒacceptance & commissioning test of the new equipment
 develop necessary policies and procedures
 develop & implement a comprehensive QA program

APPROACHES TO CONFORMAL RADIOTHERAPY
• It is important to allow sufficient time for physics
staff training prior to the arrival of the equipment
so that trained staff are in place to carry out
acceptance testing & commissioning.
• A complete understanding of all these steps is
necessary before one can successfully begin a
new program in 3-D CRT

Resources required to establish 3D-CRT
• Imaging equipment:
• All radiation therapy centers require Dxtic imaging
for optimum imaging of each tumor site.
• Ideally, each cancer centre will have a CT
simulator housed in the RT department.
• If this is not possible, RT departments must have
access to a CT scanner for planning conformal RT

Resources required to establish 3D-CRT
• Dedicated CT simulators are based on
Dxtic CT scanners, with a few
modifications:
I. Laser alignment system as a
reference for pt positioning,
II. 3-D imaging workstation for image
visualization & manipulation
III. Larger bore size to accommodate pt
immobilization devices
IV. Flat tabletop to replicate the
radiotherapy treatment unit couch
V. Modern CT simulators are also
capable of acquiring 4-D data

Resources required to establish 3D-CRT…
• Other imaging modalities that are useful (but not
essential) in the delineation of target volume are:
• MRI
• US
• various functional imaging modalities(PET, SPECT,
functional MRI, MR spectroscopic & molecular
imaging.

• MRI imaging

• The incorporation of information from multiple
imaging modalities has proven useful, but is not
an essential prerequisite.
• So it is useful to be able to co-register the data
from other imaging modalities with the planning
CT data

• Immobilization:
• Reproducible immobilization techniques are
essential to safely use this treatment technique.
• Examples include thermoplastic masks with bite
block fixation, alpha cradle etc.

• Treatment machine:
• A linear accelerator fitted with a MLC is ideal for
the delivery of planned conformal radiation
therapy.
• Ideally, the accelerator will also be fitted with
EPID that used for verification of pt setup &
geometric verification of beam portals.
• If an accelerator is not fitted with an EPID,
conventional port films can be used for the
verification of pt setup & beam portals.

• Record and verification system and networking:
• When a MLC is used, a record and verification
(R&V) system is needed to ensure planned
conformal radiation therapy is delivered as per
prescription.
• Care must be taken to ensure that errors do not
occur during transfer of data between simulator
,RTPS & treatment machine.

• Record and verification system and networking:
• An electronic network system for data transfer
from imaging facilities to the RTPS and then to the
delivery systems is desirable and this should
comply with DICOM (Digital Imaging and
Communications in Medicine) DICOM-RT
protocols.
• If networking capabilities are not available, an
alternative means of data transfer, like CD-ROM,
should be developed to ensure accurate transfer
of digital data from scanning facilities to RTPS &
from the RTPS to delivery systems

• Staffing and training:
• Dose planning in CRT is accomplished by
optimizing the weights of strategically placed
radiation portals that conform to the target
volume.
• Treatment of pts using 3-D CRT is a significant
departure from treating pts with conventional 2-D
RT.
• Therefore, there is a significant sub optimal
potential of pts if members of the treatment team
lack the necessary training in the 3-D CRT process.

• Staffing and training:
• Thus, it is essential that the treatment team,
consisting of :
Radiation oncologists
Medical physicists
Dosimetrists
RTT
• are well-trained in image guided treatment
planning & delivery with good understanding of
the uncertainties involved in these technique

Clinical Implementation of 3-D CRT
• There are many steps that are required to
implement 3D-CRT in the clinic.

CLINICAL IMPLEMENTATION OF 3-D CRT

Clinical Implementation of 3-D CRT…
• Patient assessment and decision to treat with
radiation:
• The first step in the process is patient assessment and
deciding how the pt should be treated.
• During assessment various Dxtic procedures are
undertaken to define the state of the disease.
• This involves :
imaging
biochemical testing
review of pathologic information to identify the type,
stage and grade of the cancer.
• The decision to treat the patient with radiation
should be made by a team of clinicians.

• Immobilization and patient positioning:
• An immobilization device is any device that helps
to establish & maintain the pt in a fixed, well-
defined position from treatment to treatment -
reproduce the treatment everyday
• It is often more practical and accurate to have
minimal immobilization aids accurately placed by
a skilled teams, than an over-complex system.

• Immobilization and patient positioning:
• Before starting to develop the treatment plan the
team needs to decide on the position required for
the pt treatment & immobilization needed.
• The use of 3-D CRT is usually associated with a ↓
in the margins around the CTV, but this is only
safe if random & systematic errors can be ↓.
• The key to satisfactory positioning of the pt is to
ensure that they are as comfortable and relaxed
as possible!!

• Image acquisition and target Localization :
• Every RT department should develop protocols for
image acquisition for various body sites.
• These protocols will define the requirements for
the most common treatment sites.
• Where a protocol is not available a discussion
should take place among :
Treating radiation oncologist
Medical physicist
Dosimetrist
CT technologist on the goal of therapy

• CT imaging
• For many tumor sites CT scanning provides the optimal
method of tumor localization.
• All CT planning must be carried out under conditions as
nearly identical as possible to those in the treatment room,
including the:
 pt support system (couch top),
 laser positioning lights
 any patient positioning aids.
• For conformal therapy a slice separation and thickness of
between 3 mm and 5 mm is recommended for CT scanning.
• For head & neck and CNS-between 2 -3 mm

• CT imaging
• To define anatomy adequately & generate DRRs of
high quality use closer CT slices than of the rest
of the volume, provided that the RTPS can cope
with different slice spacing.
• Using radio-opaque markers lateral and anterior
reference points should be established on the
patient or the immobilization device.

• MR and other imaging modalities
• In radiation therapy, the main application of MRI
involves mapping of anatomical data across to a
planning CT study (co-registration).
• This process retains the benefits of :
CT scan- study for dose calculation & treatment
verification
MRI- improved tumor visualization particularly in
the CNS & prostate

• MR and other imaging modalities
• direct use of MRI for radiotherapy planning
purposes suffers from the following
disadvantages:ƒ
Geometric distortion of the image;
Absence of tissue density information
ƒPoor definition of bone
 ƒDRRs cannot be created
 ƒDisease visualization is strongly dependent upon
the scan settings

• To ensure the state-of-the-art Dxtic imaging
information (CT, MRI, PET, SPECT) is used to
provide an accurate GTV on a CT-based TPS,
→these images need to be registered at a single
workstation

• Segmentation of structures:
• 3D-CRT treatment planning is dependent on an
image based simulation approach for accurately
delineating tumor & OAR volumes for an
individual pt.
• These volumes are drawn on a slice-by-slice basis
on a CT data set.
• Target volumes are contoured manually or
automatically

• Target volume delineation:
• Volume definition is a prerequisite for meaningful
3-D treatment planning & for accurate dose
reporting.
• ICRU Reports No. 50 and 62 define and describe
several target & critical structure volumes that aid
in the treatment planning process & provide a
basis for comparison of treatment outcomes

• GTV-
• Gross palpable/visible/demonstrable extent of
location of malignant growth.
• Usually based on information obtained from:
Physical examination
Results from imaging modalities (CT, MR, PET…)
Other diagnostic modalities (pathologic)

• CTV
• is the tissue volume that contains a demonstrable
GTV and/or sub-clinical microscopic malignant
disease, which has to be eliminated.
• This volume has to be treated adequately in
order to achieve the aim of therapy ( cure or
palliation)

• ITV
• is a new concept introduced in ICRU Report 62
• To compensate for variations in size, shape and
location of the CTV relative to the patient’s reference
frame (i.e. bony landmarks), ITV is added to CTV .
• ITV can be small (brain) or large (physiological
movements such as respiration, bladder and rectal
filling etc…)
• When defining the ITV it is important to account for
the asymmetric nature of the organ motion.

• PTV
• is a geometrical concept
• Used to select appropriate beam arrangement in
order to ensure the prescribed dose is actually
absorbed in the CTV.

• PTV
• In order to achieve the prescribed dose to the CTV
throughout the course of irradiation, margins
need to be added to the ITV to account for
uncertainties in patient positioning and alignment
of treatment beams throughout a fractionated
course of radiotherapy (set-up margin)

• Organ at risk volumes
• ICRU Report 62 recognizes that normal tissue
structures are subject to the same movement
uncertainties as the target volumes.
• So the concept of Planning Risk Volume (PRV)
was introduced which is the volume of an organ
at risk with an appropriate margin for the
uncertainty in its position

• The treatment planning process:
• Once the target volume, organs at risk, and the
required doses have been defined, the treatment
plan will be produced by a person trained in 3-D
planning.
• The aim of the treatment planning process is to
achieve the dose objectives to the target and
critical structures and to produce a dose
distribution that is “optimal’’.

• TPS provides tools for
– Image registration
– Image segmentation or contouring
– Dose calculations
– Plan Evaluation
– Data Storage and transmission to console
– Treatment verification

• Tools used in the evaluation of the planned dose
distribution:
 Isodose lines
 Color wash
 DVH
• The ICRU report 50 recommends a target dose uniformity
within +7 % and -5 %.
• 95% of the PTV should received 95% the prescribed dose

• Data transfer for treatment delivery:
• Once the treatment plan has been designed and
approved by the radiation oncologist the details
need to be transferred to the treatment unit.
• If possible, a R&V system should be used to
control the treatment unit and data transfer
carried out electronically.
• Treatment errors are reduced by electronic data
transfer.
• If custom blocks are being used it may be
acceptable to use manual systems

• Data transfer for treatment delivery:
• A printout of the field shape is a useful method to
allow comparison of the treatment planning with
the field shape on the treatment machine.
• Safeguards must be put in place to prevent data
corruption due to infection by computer viruses,
etc

• Position verification and treatment delivery:
• Conformal radiotherapy by its nature requires
good geometrical accuracy in order for it to be
successful.
• It is normally the intention of conformal therapy
to reduce the volume of normal tissue included
within the treated volume.

EDUCATION AND TRAINING REQUIREMENTS
• There are significant differences between
conventional 2-D RT and 3-D CRT.
• Making a transition from one to the other is a
substantial undertaking.
• Experience gained by carrying out conventional
2D RT is essential; however, additional skill sets
are necessary to make the transition to 3-D CRT
• Each member of the team involved in the
planning & delivery of 3-D CRT understands
his/her role well for safe & effective of 3D-CRT

Quality assurance and Quality control in 3D CRT
• For the safe practice of 3-D CRT it is essential that
there is a QA program covering the whole process
from CT scanning through to treatment delivery

Radiotheray transition from 2D to 3D Conformal radiotherapy(3D-CRT)

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