state of the art crt imrt
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State of the Art CRT: IMRTIntensity Modulated Radiotherapy
James C. Li M.D.Chung Shan Medical and Dental College Medical Center
Department of Radiation Oncology
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Issues
Radiation Planning: a Complex Art Plan Design and Implementation Best Possibility = computer assisted
optimization Hardware capability Quality assurance Radiobiology TCP/NTCP consideration
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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.
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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”
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Advantages of IMRT
Superior dose distribution Better normal tissue sparing Better conformality Dose escalation possilities Objective based R/T planning More target-tailored plans
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Superior Dose Distribution
IMRT plan for Prostate Cancer
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Superior Dose DistributionDose (Gy)
50 24 43 62 81
Prostate IMRT plan
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Superior Dose Distribution
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Superior Dose Distribution
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Nasopharynx
50 70 Levels in % 100 110PTV Cord, Brainstem
IMRT of
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Resultant Radiation Distributions
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NPC Recurrent Disease
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Dose Volume Histograms
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IMRT for Brain Tumor
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IMRT for Frontal Sinus Tumor
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IMRT for Recurrent Endometrial Ca
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IMRT for Lung Cancer
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Lung, IMRT
Lung, Conventional
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Issues
Radiation Planning: a Complex Art Plan Design and Implementation Best Possibility = computer assisted
optimization Hardware capability Quality assurance Radiobiology TCP/NTCP consideration
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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
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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.
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IMRT Plan Design Process
Localization and Image Transfer
Contouring
Beam Definition
Dose Calculation
Plan Evaluation
Pre-OptimizationCalculations
Optimization- Std. Constraint Temp.
Leaf Motion Files (DVA) Independent MU check
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Issues
Radiation Planning: a Complex Art Plan Design and Implementation Best Possibility = computer assisted
optimization Hardware capability Quality assurance Radiobiology TCP/NTCP consideration
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Optimization and Delivery of IMRT
Optimization (Inverse Planning)
Delivery
Dose Calculation
Radiation Safety
Quality Assurance
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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.)
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IMRT Planning
IMRT planning requires well defined set IMRT 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 Arrangement Beam Arrangement
Optimization ParametersOptimization Parameters
Optimal Constraints are Patient SpecificOptimal Constraints are Patient Specific
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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….
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Radiation Planning: a Complex Art Plan Design and Implementation Best Possibility = computer assisted
optimization Hardware capability Quality assurance Radiobiology TCP/NTCP consideration
Issues
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Let’s takeLet’s takea closera closerlook of alook of a““Multi-leafMulti-leafcollimatorcollimator(MLC)”(MLC)”
State of the Art Computer Driven Linear Accelerator, with MLC
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Shaping of Shaping of Radiation fields Radiation fields with a MLC have with a MLC have been the primary been the primary use of MLC for use of MLC for many years.many years.
Computer-controlled Multileaf Collimator
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But, MLCs can be But, MLCs can be used to modulate used to modulate radiation beam radiation beam intensity in addition intensity in addition to the classical use of to the classical use of MLCs as radiation MLCs as radiation field shaping devices.field shaping devices.
Computer-controlled Multileaf Collimator
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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
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How’s IMRT Done?
Sliding Windows techniqueSliding Windows technique
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Radiation Planning: a Complex Art Plan Design and Implementation Best Possibility = computer assisted
optimization Hardware capability Quality assurance Radiobiology TCP/NTCP consideration
Issues
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IMRT QA and Treatment
MLC Controller
TPS Leaf Motion
Treatment Machine
Record andVerify
Log File
Indep. MU Calc.
DMLC Port Film/DRR Comparison
Film/Ion Chamber Verification
??
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Beam-letBeam-let
Graphics illustration of a Radiation Graphics illustration of a Radiation beam intensity being modulatedbeam intensity being modulated
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Example (6-field head/neck RX):
gantry 0 gantry 30 gantry 60sup supsup
gantry 270 gantry 330 gantry 135sup supsup
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For example: RX For example: RX fields with IMRT in a fields with IMRT in a 6-field ABD 6-field ABD treatment. treatment.
gantry 15gantry 15
gantry 320gantry 320gantry 270gantry 270gantry 220gantry 220gantry 180gantry 180
gantry 70gantry 70
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Radiation Planning: a Complex Art Plan Design and Implementation Best Possibility = computer assisted
optimization Hardware capability Quality assurance Radiobiology TCP/NTCP consideration
Issues
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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
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Biological Target Volume?
PET ; F-miso Hypoxia
PTV
PTV MRI ; choline/citrate
Tumor burden
PET ; IUDRTumor growth
Biological Eye View BTV
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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
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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
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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 eta Unit of Helios Inverse Planning System
April, 2000 completion of varis/vision intradepartmental network system
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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
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Limited Experience at CSMDC Medical CenterDepartment of Radiation Oncology (Aug,2000~now)
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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
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Acknowledgement Credit is given to the physicians, physicists, radiation
therapists and supporting staffs of our department, for making the IMRT project very successful
Special mention for the time and effort spend on this special project is extended to:– Our capable physicist: Mr Kuo SC, Mr Chang SC and Mr
Hsu, CW Special thanks to Varian Medical System and
Cooperative Enterprises for technical and logistical support
Acknowledgement for Dr Chui and Dr Ting for use of some of their slides.
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Thank You for Your Attention!
We’ll entertain question