State Of The Art Crt Imrt

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

Issues

Radiation Planning: a Complex Art Plan Design and Implementation Best Possibility = computer assisted

optimization Hardware capability Quality assurance Radiobiology TCP/NTCP consideration

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.

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”

Advantages of IMRT

Superior dose distribution Better normal tissue sparing Better conformality Dose escalation possilities Objective based R/T planning More target-tailored plans

Superior Dose Distribution

IMRT plan for Prostate Cancer

Superior Dose DistributionDose (Gy)

50 24 43 62 81

Prostate IMRT plan

Superior Dose Distribution

Nasopharynx

50 70 Levels in % 100 110PTV Cord, Brainstem

IMRT of

Resultant Radiation Distributions

NPC Recurrent Disease

Dose Volume Histograms

IMRT for Brain Tumor

IMRT for Frontal Sinus Tumor

IMRT for Recurrent Endometrial Ca

IMRT for Lung Cancer

Lung, IMRT

Lung, Conventional

Issues



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

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.

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

Issues



Optimization and Delivery of IMRT

Optimization (Inverse Planning)

Delivery

Dose Calculation

Radiation Safety

Quality Assurance

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.)

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

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….



Issues

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

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

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

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

How’s IMRT Done?

Sliding Windows techniqueSliding Windows technique



Issues

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

??

Beam-letBeam-let

Graphics illustration of a Radiation Graphics illustration of a Radiation beam intensity being modulatedbeam intensity being modulated

Example (6-field head/neck RX):

gantry 0 gantry 30 gantry 60sup supsup

gantry 270 gantry 330 gantry 135sup supsup

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



Issues

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

Biological Target Volume?

PET ; F-miso Hypoxia

PTV

PTV MRI ; choline/citrate

Tumor burden

PET ; IUDRTumor growth

Biological Eye View BTV

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

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

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

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

Limited Experience at CSMDC Medical CenterDepartment of Radiation Oncology (Aug,2000~now)

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

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.

Thank You for Your Attention!

We’ll entertain question

State Of The Art Crt Imrt

Health & Medicine

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