IMRT - Intensity modulated radiation therapy State of the art therapy

1. State of the Art CRT: IMRT
Intensity Modulated Radiotherapy

2. Issues
♦ Radiation Planning: a Complex Art
♦ Plan Design and Implementation
♦ Best Possibility = computer assisted
optimization
♦ Hardware capability
♦ Quality assurance
♦ Radiobiology
♦ TCP/NTCP consideration

3. What is IMRT?
♦ I - Intensity
♦ M - Modulated
♦ R - Radiation
♦ T - Therapy
♦ Modulation and manipulation of radiation
given to certain part of tumor and normal
tissue to maximized tumor kill and
minimized normal tissue damage.

4. ♦ Intensity-modulated radiotherapy (IMRT) is
a method and process of assigning optimal
weighted individual small beamlets to the
treatment portals for purpose of attaining
dose distribution patterns that are as close
as possible to the required pattern.
♦ 3-D dose corformality around the GTV,
with sharper dose fall off at the peripheral
region for better sparing of normal organ
functions.
Essence of “IMRT”

5. Advantages of IMRT
♦Superior dose distribution
♦Better normal tissue sparing
♦Better conformality
♦Dose escalation possilities
♦Objective based R/T planning
♦More target-tailored plans

6. Superior Dose Distribution
IMRT plan for Prostate Cancer

7. Superior Dose Distribution
Dose (Gy)
50 24 43 62 81
Prostate IMRT plan

8. Superior Dose Distribution

9. Superior Dose Distribution

10. Nasopharynx
50 70Levels in % 100 110
PTV Cord, Brainstem
IMRT of

11. Resultant Radiation Distributions

12. NPC Recurrent Disease

13. Dose Volume Histograms

14. IMRT for Brain Tumor

15. IMRT for Frontal Sinus Tumor

16. IMRT for Recurrent Endometrial Ca

17. IMRT for Lung Cancer

18. Lung, IMRT
Lung, Conventional

19. Issues
♦ Radiation Planning: a Complex Art
♦ Plan Design and Implementation
♦ Best Possibility = computer assisted
optimization
♦ Hardware capability
♦ Quality assurance
♦ Radiobiology
♦ TCP/NTCP consideration

20. Conventional Conformal Therapy
and IMRT
♦ Conventional Conformal Therapy
♦ IMRT
Field shape conforms to
the outline of the target,
uniform intensity across
the field
Non-uniform intensity
inside the field to achieve
optimum dose distribution
target

21. Why IMRT?
♦ Generally speaking, by taking
advantages of:
1) sharp dose gradient
2) high degree of conformity to
irregularly shaped PTV
♦ lesions nested amongst healthy and
critical organs are most suited for IMRT.

22. IMRT Plan Design Process
Localization and
Image Transfer
Contouring
Beam Definition
Dose Calculation
Plan Evaluation
Pre-Optimization
Calculations
Optimization-
Std. Constraint Temp.
Leaf Motion Files (DVA) Independent MU check

23. Issues
♦ Radiation Planning: a Complex Art
♦ Plan Design and Implementation
♦ Best Possibility = computer assisted
optimization
♦ Hardware capability
♦ Quality assurance
♦ Radiobiology
♦ TCP/NTCP consideration

24. Optimization and Delivery of IMRT
♦Optimization (Inverse Planning)
♦ Delivery
♦ Dose Calculation
♦ Radiation Safety
♦ Quality Assurance

25. Optimization (Inverse Planning)
♦ Purpose: To find the ‘optimum’ intensity distribution
for all beams involved in a plan that will best meet the
planner’s requirements.
♦ What are the requirements? Objective functions
– dose, dose/volume - based,
– biological indices - based: TCP, NTCP
♦ How to find the optimum solution? Search algorithms
– deterministic methods
– stochastic methods
(*Optimization is conceptually separated from delivery, so in this
step we don’t need to be concerned about how it’s to be delivered.)

26. IMRT Planning
IMRT planning requires well defined setIMRT planning requires well defined set
of treatment planning goalsof treatment planning goals
IMRT Dose DistributionsIMRT Dose Distributions
Geometry of target/normal tissuesGeometry of target/normal tissues
Beam ArrangementBeam Arrangement
Optimization ParametersOptimization Parameters
Optimal Constraints are Patient SpecificOptimal Constraints are Patient Specific

27. Constraint Selection
IMRT Dose Distributions are controlled by:
Constraints (Global)
Contours (Local)
You can’t always get what you want….
Sometimes, you get to weighs pros and
cons and arrived at a compromise….

28. ♦ Radiation Planning: a Complex Art
♦ Plan Design and Implementation
♦ Best Possibility = computer assisted
optimization
♦ Hardware capability
♦ Quality assurance
♦ Radiobiology
♦ TCP/NTCP consideration
Issues

29. Let’s takeLet’s take
a closera closer
look of alook of a
““Multi-leafMulti-leaf
collimatorcollimator
(MLC)”(MLC)”
State of the Art Computer Driven Linear
Accelerator, with MLC

30. Shaping ofShaping of
Radiation fieldsRadiation fields
with a MLC havewith a MLC have
been the primarybeen the primary
use of MLC foruse of MLC for
many years.many years.
Computer-controlled Multileaf Collimator

31. But, MLCs can beBut, MLCs can be
used to modulateused to modulate
radiation beamradiation beam
intensity in additionintensity in addition
to the classical use ofto the classical use of
MLCs as radiationMLCs as radiation
field shaping devices.field shaping devices.
Computer-controlled Multileaf Collimator

32. How’s IMRT Done?
♦ There are two basic methods of using MLC to
modulate radiation beam intensity:
– 1. Sliding Windows technique
• (move leaves while radiation is on)
– 2. Stop and Shoot technique
• (move leaves then radiate - no radiation when
leaves are moving)
– 3. Some combination of the above

33. How’s IMRT Done?
Sliding Windows techniqueSliding Windows technique

34. ♦ Radiation Planning: a Complex Art
♦ Plan Design and Implementation
♦ Best Possibility = computer assisted
optimization
♦ Hardware capability
♦ Quality assurance
♦ Radiobiology
♦ TCP/NTCP consideration
Issues

35. IMRT QA and Treatment
MLC
Controller
TPS
Leaf Motion
Treatment
Machine
Record and
Verify
Log File
Indep. MU Calc.
DMLC Port Film/
DRR Comparison
Film/Ion Chamber
Verification
??

36. Beam-letBeam-let
Graphics illustration of a RadiationGraphics illustration of a Radiation
beam intensity being modulatedbeam intensity being modulated

37. Example (6-field head/neck RX):
gantry 0 gantry 30 gantry 60
sup supsup
gantry 270 gantry 330 gantry 135
sup supsup

38. For example: RXFor example: RX
fields with IMRT in afields with IMRT in a
6-field ABD6-field ABD
treatment.treatment.
gantry 15gantry 15
gantry 320gantry 320gantry 270gantry 270gantry 220gantry 220gantry 180gantry 180
gantry 70gantry 70

39. ♦ Radiation Planning: a Complex Art
♦ Plan Design and Implementation
♦ Best Possibility = computer assisted
optimization
♦ Hardware capability
♦ Quality assurance
♦ Radiobiology
♦ TCP/NTCP consideration
Issues

40. Factors Affecting Decison
♦ Intrinsic dose-dependent tumor resistance
♦ Treatment Uncertainties
– Inadequacy of tumor delineation
– Organ motion
– Daily patient positioning
– Accuracy of treatment delivery
– Accuracy of planning system

41. Biological Target Volume?
PET ; F-miso
Hypoxia
PTV
PTV
MRI ;
choline/citrate
Tumor burden
PET ; IUDR
Tumor growth
Biological
Eye View BTV

42. Ways of Correcting Uncertainties
♦ Large safety margin
♦ Immobilization devices
♦ Targeting system
♦ On-line real time portal verification
♦ Gating system
♦ Redundancy in setup system
♦ Setup protocol
♦ Computer-driven shaping devices

43. ♦ Radiation oncologists must first select clinical
sites suitable for IMRT treatments.
♦ Following clinical sites have been investigated
– 1. Prostate cancer
– 2. Head and neck cancer
– 3. Breast cancer
– 4. Brain tumors
– 5. Lung tumors
– 6. Uterine Cervical Cancer
– 7. Others
Selection of Clinical Disease

44. Milestones in IMRT Development at CSMDC
Medical Center Depart. of Radiation Oncology
♦ April, 1999 Installation of 1st
unit state of art
LINAC Varian 21EX with MLC and IMRT
capabilities
♦ October, 1999 Installation of 2nd
Unit
LINAC Varian 21 EX with MLC
♦ March, 2000 Installation of βeta Unit of
Helios Inverse Planning System
♦ April, 2000 completion of varis/vision
intradepartmental network system

45. Milestones in IMRT Development at CSMDC
Medical Center Depart. of Radiation Oncology
♦ June, 2000 Installation of commercial
version of Helios Inverse Planning System
and start of dry run and verification of
system.
♦ August, 2000 Official commissioning of the
Helios Inverse Planning System and start of
IMRT planning, with first patient, a breast
cancer patient

46. Limited Experience at CSMDC Medical Center
Department of Radiation Oncology (Aug,2000~now)

47. Conclusion
♦ IMRT is the trend setting technique for
future external R/T
♦ Tumor dose esclation and critical organ
sparing would not be a problem
♦ Expects greater tumor control and normal
tissue sparring leading to better survival
♦ R/T is both an Art and a Science

48. Thank You for Your Attention!
♦ We’ll entertain question