genreal principal of 3D_crt_imrt,3dcrt,igrt

diffrent techniques used in radiation therapy

1. GENERAL PRINCIPLE OF 3-D CRT,
IMRT AND 4D RADIOTHERAPY USING
IGRT
Gunjan Sharma
Medical physicist, Radiation Oncology
GMC Amritsar

2. Conventional radiotherapy

3. Concept of 3D-CRT,IMRT& IGRT
Limitation of 2 dimensional conventional RT: -
-Further dose escalation not feasible .
-Large amount of normal tissue irradiated leading to high late
radiation morbidity
-Tumour control and survival static for many years.

4. 3D-CRT
•3Dimensional Conformal Radiotherapy is the use of 3 dimensional
anatomical information to plan and deliver treatment so that the
resultant dose distribution conforms as closely as possible to the target
volume in 3 dimensions with minimum dose to the surrounding normal
tissue.
AIM: -
1. To irradiate target volume defined with 3-D Imaging study
2.Optimization of dose distribution accomplished by shaping incidence beam
aperture
3. Radiation beams are of equal intensity and can be modified.

5. 3-D CONFORMAL RADIOTHERAPY

In conformal radiotherapy, the dose distribution in tissue is shaped in
such a way that the high-dose region is located in the target volume
and in the neighboring healthy tissue, the radiation dose has to be
kept under the limit for radiation damage.
Increase in tumor control and a simultaneous decrease in side effects
means a higher probability of patient cure.

6. 1. We know that depth dose of a homogeneous
photon field is described by an exponentially
decreasing function of depth. Dose deposition
is normally higher close to the surface than at
the depth of the tumor
2.To improve this situation normally more than
one beam is used. Within the overlapping
region of the beams a higher dose is
deposited.
3.Conformal radiotherapy conforms or shapes
the prescription dose volume to the PTV while
at the same time keeping the dose to specified
organs at risk below their tolerance dose

7. Chain of 3D treatment planning and delivery
process
1. Patient positioning and immobilization
2.Imaging and information processing
3.Tumor localization
4.Treatment planning
5.Patient positioning
6.Quality assurance and verification
7.Treatment

8. Patient Positioning And Immobilization
Immobilization devices such as molds and masks used to hold the treatment area
perfectly still during radiation treatment. They are custom made to fit the body
area exactly and are used during each radiotherapy visit.
Different types of materials available for immobilization.
-Thermoplastics sheets
-Polyurethane foam
-Vaccum forming mold
Choose positions
• Which are comfortable
• With minimum normal tissue in the way of beam
• With minimum accessories in the way of the beam

9. IMAGE REGISTRATION
The gross tumor volume can be reconstructed in three dimensions from
tomographic slices, and taken in the tumor region,
 Computed tomography is an ideal basis for 3D treatment planning, CT
numbers used to calculate electron density
MRI is very often superior to CT, especially for the task of differentiating
between healthy tissue and tumor tissue. MRI is basically for soft tissues.
MRS and PET imaging have the potential to include information on tumor
metabolism and heterogeneity.
Fused Images allows superior outlining of targets in selected areas.

10. Determination Of The Target Volume And Organs At Risk
The gross tumour volume (GTV) is the macroscopic (gross)
extent of the tumour.
The GTV, together with the surrounding microscopic tumour
infiltration, constitutes the primary clinical target volume CTV.
The ITV encompasses the GTV/CTV plus margins, caused by
possible physiological movements of organs and tumour, due to
respiration, pulsation, or variations of tumour size and shape.
The planning target volume (PTV) incorporates the GTV/CTV plus
margins due to uncertainties of patient setup and beam adjustment.
The treated volume is the volume of tumour and surrounding normal tissue included in an isodose surface
representing the irradiation dose proposed for the treatment. As a rule this corresponds to the 95% isodose.
The irradiated volume is a volume included in an isodose surface with a possible biological impact on the
normal tissue encompassed in this volume
ICRU 62 introduces the concept of planning organ-at-risk volume (PRV), in which a margin is added around
the organ to compensate for that organs geometric uncertainties .

11. Treatment planning
Planning can be performed by following steps
»Beams Eye view (BEV)
»Rooms eye View (REV)
»Beam Arrangement
»Field Shaping

12. Beams Eye view (BEV)
•It provides the treatment planner with a viewing
point from the perspective of the source of radiation
looking out along the axis of the radiation similar to
that obtained when viewing simulation
radiographs.

Useful in identifying best gantry, collimator and
couch angle’s at which to irradiate target and
avoid irradiating adjacent normal structures by
interactively patient and treatment beam.

13. Rooms eye View (REV)
•Simulate any arbitrary viewing location
in the treatment room
• Complement the BEV in the beam
design phase of treatment planning
•Visualizing all or selected beams to
appreciate better the treatment
technique geometry
•More valuable in the plan evaluation
phase of 3DRTP by providing near real
time capability for evaluating hot or
cold spots occur in the dose distribution

14. 3D-CRT : Beam Arrangement
Use the Room’s Eye View (REV) to get a
practical idea about the geometry of
beam placement.
optimal 3-D plans usually require more than 4 beams
Coplanar or Non-coplanar?

15. 3D-CRT : Field Shaping
MLC are used to shape the field around PTV
Use the beam’s Eye view (BEV) to Place MLC
take into account structure to be shielded
automatic margins around PTV

16. Multi-Leaf Collimators
Multi-leaf collimators permit the quick and flexible adjustment of the
irradiation fields to the tumor shape and the shape of the organs at risk

17. Dose Calculation
The quality of treatment planning depends naturally on
the accuracy of the dose calculation. An error in the
dose calculation corresponds to an incorrect
adjustment of the dose distribution to the target
volume and the organs at risk. The calculation of
dose distributions has therefore always been a
special challenge for the developers of treatment
planning systems.
Two techniques
SAD
SSD
Once the parameters are defined, the
Treatment Planning Software generates the
dose distribution

18. Evaluation
The 3D-treatment planning leads to 3D-dose distributions, which must be
evaluated in an appropriate way. In particular this concerns the
occurrence of hot and cold spots, as well as the homogeneity and
conformity, of the dose distribution. Numerous computer graphics and
mathematical tools have been developed to support the evaluation of
dose distribution

19. DVH
PTV
Rectum
Bladder
PTV
Evaluate the dose distribution characteristics
of one or more plans using Dose volume
histograms (DVH)
The Cumulative (integral) DVH
represents a cumulative
frequency distribution of the
dose integrated over the VOI.
(volume of interest)
The Differential DVH
represents the absolute or
relative volume which receives
the dose specified within a
dose bin.

20. Slice by slice
Overdosage : 117%
Underdosage: <90%
Always verify the anatomical dose distribution slice by slice, in order to identify
where under dosage or over dosage is occurring.

21. Patient Positioning
•The fifth link in the chain of radiotherapy is the link between treatment
planning and the irradiation, the so-called problem of patient positioning.
The problem is to accurately transfer the planned irradiation technique to
the patient.
The patient first of all has to be placed in exactly the same position as during 3D
imaging. This is performed with a suitable immobilization device which can be
used during imaging and treatment.
Secondly, the treatment couch with the patient has to be adjusted until the
isocentre position matches the pre-calculated coordinates.

22. Quality Management in Radiotherapy
All steps and links of the chain of
radiotherapy are subject to errors and
inaccuracies, which may lead to
treatment failure or injury of the
patient. A careful network of quality
assurance and verification has to be
established in a radiotherapy unit in
order to minimize these risks. A quality
management system has to cover all the
components involved and all aspects of
the chain, e.g., dosimetry, software and
hardware testing, standardization,
documentation, archiving, etc.

23. Treatment
•The next and most essential link in the chain of radiotherapy, is
treatment, itself characterized by radiation delivery.
•Most conformal radiotherapy treatments are performed by
External radiation with photons,
Charged particle therapy with proton or electron beams

24. Limitations :
•Situation where 3DCRT cannot produce a satisfactory treatment plan due
to complex target volume.
•Close proximity of a sensitive normal tissue.
Problems with 3DCRT: -
• The dose-spillage can be higher.
• Forward planning – trial and error method.
• Element of subjective approach still present

25. IMRT

•Intensity Modulated Radiotherapy is a special form of 3DCRT in which non
uniform fluence is delivered to the patient from any given position of the
treatment beam to optimize the composite dose distribution; which is
calculated by an inverse treatment planning process designed to meet
specified dosimetric objectives. 3D treatment planning and process are
same as 3D-CRT.
•The term Inverse planning used to describe an optimization process that
translates the mathematic formalism of clinical requirement into
deliverable intensity pattern. Essential tool for IMRT delivery

26. To overcome limitation of 3D-CRT by doing modulation of beam
intensity and beam shaping.

Advantages
It can achieve any desired dose distribution
Significant reduces volume of normal tissues
Optimization is done
Most conformal and most efficient if all targets volumes treated simultaneously
using different fraction sizes. Such a treatment strategy has been called the
simultaneous integrated boost (SIB)
Concave dose distribution cannot be achieved by 3DCRT
Extreme proximity to critical structures exist.
When the target wraps around organ at risk.
Re-irradiation of certain areas require maximal dose fall – off adjacent to irradiated
area.

27. MlC-based IMRT
•Most modern linear accelerators are equipped with MLCs, which were
originally designed to replace the use of lead blocks to shield normal
tissue during the treatment.
•Two main dose delivery methods are
1. The “step-and-shoot” dose delivery
2. The “dynamic” dose delivery
The Step-and-Shoot Technique
Leaf-Sequencing Algorithms

28. The Step-and-shoot Technique
The “step-and-shoot” approach superimposes the dose delivered by a
number of irregularly shaped and partially overlapping treatment fields,
called subfields or segments. For each segment a well defined number of
monitor units is delivered. Then, the beam is turned off while the leaves
of the MLC move to the positions required by the next IMRT segment.
After the verification and record system (V&R) has validated the new leaf
positions, the beam is turned on and the dose is delivered for this
segment. This process is repeated for all segments per incident beam
angle and all beam directions.

29. Leaf-Sequencing Algorithms
•The “close-in” technique. For this example the fluence map was divided
into three levels. The numbers of levels for clinical cases is in the range of
five to ten. In the first step the left leaf is moved towards the first positive
gradient of the fluence pattern while the right leaf is moving towards the
first negative fluence gradient. This is the first segment then, next, the
two leaves move to the next positive and negative gradients of the
respective fluence map to define the next subfield followed by its delivery.
This procedure is repeated until the whole fluence map is delivered.

30. •The “sweep” approach is more complicated than the “close-in” technique.
For the “sweep” technique the left leaf again probes all positive fluence
gradients from the left side while the right leaf first moves to the negative
fluence gradient located most to the left. Then both leaves move in the
same direction while again left and right leaf stop at the respective
positive and negative fluence gradients. With this technique the
treatment time is reduced compared with the “close-in” technique since
the leaves are always moving only in one direction

31. The “Dynamic” Dose Delivery
The “dynamic” delivery technique (DMLC)the intensity modulation is
achieved by an individual variation of the velocities of the moving leaves,
i.e., the treatment can be realized without interrupting the treatment
beam.

32. • Conceptually simpler
• No need to control individual leaf speeds
• interrupted treatments are easier to
resume
• Easier to verify intensity patterns in
each subfield
• Fewer MUs
• Regions with zero dose are more easily
delivered, lesser dose to OARs
•Increased treatment time
• Smoothly varying intensities
• Need to control leaf positions
& speed
• Better dose homogeneity
• Less time consuming
• In principle is the most
efficient method of delivering
IMRT
Static Mode (Step & Shoot) Dynamic mode (Sliding window)

33. TOMOTHERAPY BASED IMRT
•Basic principle
–intensity photon therapy delivered using a rotating slit beam.
–A temporally modulated slit multileaf collimator (MIMIC ) used
to rapidly move leaves in or out of the slit.
–Like a computer tomography unit the radiation sources and the
collimotor continously revolves around the patients.
•Types
–Serial tomotherapy : patients is translated between successive
rotation.
–Helical tomotherapy : patients translated during radiation.

34. •Principle : The linear accelerator
mounted on CT-like gantry and
rotates through full circles.
•Flat couch provided allows
automatic translations during
treatment.
•Pateints couch translated slowly
through the aperture, thus
creating a helical motion of the
beam with respect to the patient.
•Equipped with diagnostic CT
scanner for target localization and
treatment planning
•Able to perform both the
diagnostic CT and mega voltage CT.

35. LIMITATIONS OF IMRT
Very time consuming
Knowledge about what is clinically optimal and achievable and how best to
define clinical and dosimetric objectives of IMRT limited.
Uncertainties of various types (i.e. displacement and distortions of internal
anatomy , intrafrction motion, changes in physical and radiobiologic.
characterstics of tumors may limit the applicability and efficacy of IMRT.
Most important factor that limit immediate success of IMRT is inadequacy
of imaging.

36. IGRT
Image Guided Radiotherapy combines scanning and radiation
equipment, to provide images of the patient’s organs in the treatment
position, at time of treatment, optimizing the accuracy and precision of
the radiotherapy.
•IGRT measures & corrects positional errors for target and critical
structures immediately prior to or during treatment delivery & accounts
for organ motion.
•Essential for the outcome of the treatment
•Planning target margins can be significantly reduced

37. Basic principle :
–Uncertainities about tumors position in daily treatment resolved by
acquiring volumetric images on the treatment mahcine.
–Makes possible to take tumour motion into account during radiation
treamtent planning.
–Enhances tumors localization leading to accurate image registration.
Ultimately leads to
–Correction of positional errors for target and critical structures
immediately prior to during treamtent delivery
–Essential for the outcome of the treatment
–Planning target margins can be significantly reduced.

38. Methods for Target Localization
•Trans abdominal ultrasound;
•Implanted Markers with in-room MV or KV X-rays
•Optical surface tracking systems
•Implantable electro-magnetic markers
•IN-ROOM CT
KV or MV Cone-Beam CT
Tomotherapy

39. The reconstruction of 3D volumes from a series of 2D projection images,
performed on the patient on the treatment table
CONE BEAM CT

40. GATED RADIOTHERAPY
•Method where on-off status of treatment beam is controlled by signals
produced whenever breathing signal falls in the preset gating window
•Instead of enlarging PTV to encompass the range of motion, treatment
delivered only during part of the respiratory cycle.

41. 4D Radiotherapy
4D radiotherapy is a special form of image guided IMRT which has the explicit
inclusion of temporal changes in anatomy during the imaging, planning, delivery
and validation of radiotherapy
Options for 4-D treatment delivery
–Freeze the motion
•Patients breathes normally (Respiratory gating )
•Breathing is controlled
–Breath holding (FGBH)
–Jet ventilation
–Active breathing control
–Follow the motion (tracking)
Feed back guided breath hold
Principle components
–Fabricating the hardware so the respiratory trace can be displayed to the patient.
–Assembling a delay box to be used as breath hold detector.
–Performing quality control tests to ensure that FGBH can be delivered accurately and
safely.

42. 4DRT Process

43. 4DRT
•On line approach
–It involves acquisition of images and correlation of error before
treatment delivery on a daily basis
•Off line approach
–It refers to acquistion of images at set intervals with immediate
correction

44. Steps : -
Commercial respiratory tracking system that uses an external fiducial to
monitor abdominal wall motion generates and displays the breathing
trace

Hardware developed to present this display to the patient in the
treatment position

Using the respiratory trace as a visual aid, the patient performs a breath
hold

A delay box fabricated to differentiate between gating signals received
during free breathing and those received during breath hold, allowing
radiation delivery only when fiducial within the breath hold gating
window

45. Tracking Target motion
Also known as real – time position management respiratory
system (RPM) (i.e. a form of automatic respiratory gating)
System of RPM
Video camera based tracking
(External )
Radiological tracking
1. Implanted fiducials
2. Direct tracking of tumor mass.
I.e. based on image graber an
requires desktop computer

46. 3D CRT, IMRT & IGRT
Methods to manage breathing motion
•Deep inspiration breath holding by patient
•Active breathing control (ABC)
•Passive Gating or Real Time Position Management
Components:Components:
• • Reflective external Marker Reflective external Marker
placed on abdomen or chestplaced on abdomen or chest
• • Infrared illuminator/CCD Infrared illuminator/CCD
cameracamera
• • Workstation to process Workstation to process
signals & signals &
Generate trigger for Generate trigger for
CT/simulator/ LinacCT/simulator/ Linac

47. Limitation of 4DRT
•Computing source intensive
•No Commercial TPS allows 4D dose calculation.
•Unpredictable nature of respiratory motion.
• Tumor tracking is needed for delivery of treatment

48. Cyber Knife
Definition :
An integrated, image guided, frameless radiosurgery system
used for radiosurgical applications outside the brain and for
staged radiosurgery.
Floor mounted
Amorphous silicon
detectors
6 MV
LINAC
Roof mounted KV X-
ray
Frameless patient
immobilization
couch
Robotic arm
with 6 degrees
of freedon
Circular
Collimator
attached to
head

49. Synchory system :
•A continuous respiratory tracking system where the cyber knife system
used to deliver dynamic radiosurgery to irradiate a tumor or other target
while it is moving.
•An non-isocentric system with real time organ position and movement
correction facility
•Use complex system of cameras, motion tracking softwares fibreoptic
sensing technology and infrared emitters.
•Records breathing movement with sequential x-ray images of implanted
radio opaque markers 3-4 mm. long.

50. Thank you