Radiotherapy Treatment PlanningRadiotherapy Treatment Planning

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Treatment planning is the task to make Treatment planning is the task to make sure a prescription is put into practice sure a prescription is put into practice in an optimized wayin an optimized way

Prescription

Planning

Treatment

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ObjectivesObjectives Understand the general principles of Understand the general principles of

radiotherapy treatment planningradiotherapy treatment planning Appreciate different dose calculation Appreciate different dose calculation

algorithms algorithms Understand the need for testing the treatment Understand the need for testing the treatment

plan against a set of measurementsplan against a set of measurements Be able to apply the concepts of optimization Be able to apply the concepts of optimization

of medical exposure throughout the treatment of medical exposure throughout the treatment planning processplanning process

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Contents of the lectureContents of the lecture

A. Radiotherapy treatment planning A. Radiotherapy treatment planning conceptsconcepts

B. Computerized treatment planningB. Computerized treatment planning

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The need to understand The need to understand treatment planningtreatment planning IAEA Safety Report Series 17 “IAEA Safety Report Series 17 “Lessons Lessons

learned from accidental exposures in learned from accidental exposures in radiotherapyradiotherapy “ (Vienna 2000): “ (Vienna 2000):

About 1/3 of problems directly related to About 1/3 of problems directly related to treatment planning!treatment planning!

May affect individual patient or cohort of May affect individual patient or cohort of patientspatients

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A. Basic Radiotherapy Treatment A. Basic Radiotherapy Treatment Planning ConceptsPlanning Concepts

i. Planning process overviewi. Planning process overview

ii. Patient data required for planningii. Patient data required for planning

iii. Machine data required for planningiii. Machine data required for planning

iv. Basic dose calculationiv. Basic dose calculation

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i. Planning process overviewi. Planning process overview Combine machine parameters and individual patient Combine machine parameters and individual patient

data to customize and optimize treatmentdata to customize and optimize treatment Requires machine data, input of patient data, Requires machine data, input of patient data,

calculation algorithm calculation algorithm Produces output of data in a form which can be used Produces output of data in a form which can be used

for treatment (the ‘treatment plan’)for treatment (the ‘treatment plan’)

Patient information

Planning

Treatment unit data

Treatment plan

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ii. Patient information requiredii. Patient information required

Radiotherapy is a localized treatment of Radiotherapy is a localized treatment of cancer - one needs to know not only the dose cancer - one needs to know not only the dose but also the accurate volume where it has but also the accurate volume where it has been delivered to.been delivered to.

This applies to tumor as well as normal This applies to tumor as well as normal structures - the irradiation of the latter can structures - the irradiation of the latter can cause intolerable complications. Again, both cause intolerable complications. Again, both volume and dose are important.volume and dose are important.

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One needs to knowOne needs to know Target locationTarget location Target volume and shapeTarget volume and shape Secondary targets - potential tumor Secondary targets - potential tumor

spreadspread Location of critical structuresLocation of critical structures Volume and shape of critical structuresVolume and shape of critical structures Radiobiology of structuresRadiobiology of structures

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Target delineation Target delineation ICRU 50 & 62ICRU 50 & 62

Gross Tumor Volume (GTV) = clinically demonstrated tumor

Clinical Target Volume = GTV + area at risk (eg. potentially involved lymph nodes)

It all comes down to the correct It all comes down to the correct dose to the correct volumedose to the correct volume

Dose Volume Histograms are a way to Dose Volume Histograms are a way to summarize this information summarize this information

0

20

40

60

80

100

120

0 20 40 60 80

Dose (Gy)

Vo

lum

e (%

)

0

20

40

60

80

100

120

0 20 40 60 80

Dose (Gy)

Vo

lum

e (%

)Comparison of three differenttreatment techniques (red, blue and green)in terms of dose to the target and a critical structure

Target dose

Criticalorgan

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The ideal DVHThe ideal DVH

Tumor:Tumor: High dose to all High dose to all Homogenous doseHomogenous dose

Critical organCritical organ Low dose to most of Low dose to most of

the structurethe structure

100%

dose

100%

dose

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Need to keep in mindNeed to keep in mind

Always a 3D problemAlways a 3D problem Different organs may respond differently Different organs may respond differently

to different dose patterns. to different dose patterns. Question: Is a bit of dose to all the Question: Is a bit of dose to all the

organ better than a high dose to a small organ better than a high dose to a small part of the organ?part of the organ?

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In practice not In practice not always that clear cutalways that clear cut

ICRU report 62ICRU report 62 Need to understand Need to understand

anatomy and anatomy and physiologyphysiology

A clinical decisionA clinical decision

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*Int. J. Radiat. Oncol. Biol. Phys., 1998; 41:84-92.

In many organs, dose and volume In many organs, dose and volume effects are linked - eg.effects are linked - eg.

Dose(Gy)

Rectalvolume(%)

>65 40

>70 30

>75 5

Boersma* et al., classified the following (Dose,Volume) regions to be regions of high risk for developing rectal bleeding:

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In EBT practiceIn EBT practice Need to know Need to know

where to direct beam to, andwhere to direct beam to, and how large the beam must be and how it how large the beam must be and how it

should be shapedshould be shaped

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Target design and reference Target design and reference imagesimages In radiotherapy practice the target is In radiotherapy practice the target is

localized using diagnostic tools:localized using diagnostic tools: Diagnostic procedures - palpation, X-ray, Diagnostic procedures - palpation, X-ray,

ultrasoundultrasound Diagnostic procedures - MRI, PET, SPECTDiagnostic procedures - MRI, PET, SPECT Diagnostic procedures - CT scan, simulator Diagnostic procedures - CT scan, simulator

radiographradiograph

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Selection of treatment approachSelection of treatment approach

Requires training and experienceRequires training and experience May differ from patient to patientMay differ from patient to patient Requires good diagnostic toolsRequires good diagnostic tools Requires accurate spatial informationRequires accurate spatial information May require information obtained from May require information obtained from

different modalitiesdifferent modalities

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Minimum patient data required for Minimum patient data required for external beam planningexternal beam planning

Target locationTarget location Patient outlinePatient outline

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Diagnostic tools which could be Diagnostic tools which could be used for patient data acquisitionused for patient data acquisition CT scanner, MRI, PET scanner, US,…CT scanner, MRI, PET scanner, US,… Simulator including laser system, optical Simulator including laser system, optical

distance indicator (ODI)distance indicator (ODI) Many functions of the simulator are also Many functions of the simulator are also

available on treatment units as an alternative available on treatment units as an alternative - simulator needs the same QA! - simulator needs the same QA!

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Note on the role of simulationNote on the role of simulation Simulator is often used twice in the Simulator is often used twice in the

radiotherapy processradiotherapy process Patient data acquisition - target localization, Patient data acquisition - target localization,

contours, outlinescontours, outlines Verification - can the plan be put into Verification - can the plan be put into

practice? Acquisition of reference images practice? Acquisition of reference images for verification.for verification.

Simulator may be replaced by other Simulator may be replaced by other diagnostic equipment or virtual diagnostic equipment or virtual simulationsimulation

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Virtual simulationVirtual simulation

All aspects of simulator work are All aspects of simulator work are performed on a 3D data set of the performed on a 3D data set of the patientpatient

This requires high quality 3D CT data of This requires high quality 3D CT data of the patient in treatment positionthe patient in treatment position

Verification can be performed using Verification can be performed using digitally reconstructed radiographs digitally reconstructed radiographs (DRRs)(DRRs)

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Virtual SimulationVirtual Simulation

3D Model of the patient and the Treatment Devices

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SimulatorSimulatorDiagnosticX-ray tube

Simulator couch

Rotatinggantry

Image intensifierand X-ray film

holder

Radiation beamdefining system

Nucletron/Oldelft

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Radiotherapy simulatorRadiotherapy simulator

Obtain images and Obtain images and mark beam entry mark beam entry points on the patientpoints on the patient

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Moveable Lasers

Isocenter Projection

Isocen

ter P

ositio

n

CT images

CT Simulation (Thanks to ADAC)Marking the Patient already during CT

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Patient markingPatient marking

Create relation Create relation between patient between patient coordinates and coordinates and beam coordinatesbeam coordinates

Tattoos Skin markers

Marks on shell

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Beam placement and shapingBeam placement and shaping

simulator filmwith block

DRR withconformal shielding

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Tools for optimization of the Tools for optimization of the radiotherapy approachradiotherapy approach

Choice of radiation Choice of radiation qualityquality

Entry pointEntry point Number of beamsNumber of beams Field sizeField size BlocksBlocks WedgesWedges CompensatorsCompensators

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Optimization approachesOptimization approaches

patient

target

beam

patienttarget

beam

patient

target

wedge

Choice of bestbeam angle

Use of a beammodifier

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Beam number and weightingBeam number and weighting

patient

target

beam100%

patient

Beam 150%

Beam 2

50%

30%

40%

10%

20%

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A note on weighting of beamsA note on weighting of beams

30%

40%

10%

20%

Different approaches arepossible: 1. Weighting of beams asto how much they contributeto the dose at the target2. Weighting of beams asto how much dose isincident on the patient

These are NOT the same

25%

25%

25%

25%

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Use of wedgesUse of wedges

Wedged pairWedged pair Three field Three field

techniquestechniques

patient

Isodose lines

patient Typical isodose lines

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Beam placement and shapingBeam placement and shaping

Entry pointEntry point Field sizeField size BlocksBlocks WedgesWedges CompensatorsCompensators

a two-dimensional a two-dimensional approach?approach?

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Beam placement and shapingBeam placement and shaping

Entry pointEntry point Field sizeField size BlocksBlocks WedgesWedges CompensatorsCompensators

Multiple beamsMultiple beams Dynamic deliveryDynamic delivery Non-coplanarNon-coplanar Dose compensation Dose compensation

(IMRT) not just (IMRT) not just missing tissuemissing tissue

Biological planningBiological planning

This is actually a 3D approach

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Target LocalizationTarget Localization Diagnostic procedures - palpation, X-ray, Diagnostic procedures - palpation, X-ray,

ultrasoundultrasound Diagnostic procedures - MRI, PET, SPECTDiagnostic procedures - MRI, PET, SPECT Diagnostic procedures - CT scan, Diagnostic procedures - CT scan,

simulator radiographsimulator radiograph

Allows the creation of Reference Images for Treatment Verification:

Simulator Film, Digitally Reconstructed Radiograph

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Simulator imageSimulator image

During ‘verification During ‘verification session’ the treatment session’ the treatment is set-up on the is set-up on the simulator exactly like it simulator exactly like it would be on the would be on the treatment unit.treatment unit.

A verification film is A verification film is taken in ‘treatment’ taken in ‘treatment’ geometrygeometry

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Simulator FilmSimulator Film Shows relevant Shows relevant

anatomyanatomy Indicates field Indicates field

placement and sizeplacement and size Indicates shieldingIndicates shielding Can be used as Can be used as

reference image for reference image for treatment treatment verificationverification

Field defining wires

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iii. Machine data requirements for iii. Machine data requirements for treatment planningtreatment planning

Beam description (quality, energy)Beam description (quality, energy) Beam geometry (isocentre, gantry, table)Beam geometry (isocentre, gantry, table) Field definition (source collimator distance, Field definition (source collimator distance,

applicators, collimators, blocks, MLC)applicators, collimators, blocks, MLC) Physical beam modifiers (wedges, Physical beam modifiers (wedges,

compensator)compensator) Dynamic beam modifiers (dynamic wedge, Dynamic beam modifiers (dynamic wedge,

arcs, MLC IMRT)arcs, MLC IMRT) Normalization of doseNormalization of dose

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Machine data required for Machine data required for planningplanning Depends on Depends on

complexity of treatment complexity of treatment approachesapproaches

resources available for resources available for data acquisitiondata acquisition

May be from published May be from published data or can be acquireddata or can be acquired

MUST be verified...MUST be verified...

Quick Question:Quick Question:

Who is responsible for the Who is responsible for the preparation of beam data for preparation of beam data for

the planning process?the planning process?

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Acquisition of machine dataAcquisition of machine data

……from vendor or from vendor or publications (eg BJR 17 and publications (eg BJR 17 and 25) - this requires 25) - this requires verification!!!verification!!!

Done by physicistDone by physicist Some dosimetric equipment Some dosimetric equipment

must be available (water must be available (water phantom, ion chambers, film, phantom, ion chambers, film, phantoms,…)phantoms,…)

Documentation essentialDocumentation essential

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Machine data availabilityMachine data availability

Hardcopy (isodose charts, output factor Hardcopy (isodose charts, output factor tables, wedge factors,…) - for emergencies tables, wedge factors,…) - for emergencies and computer break downsand computer break downs

Treatment planning computer (as above or Treatment planning computer (as above or beam model) - as standard planning databeam model) - as standard planning data

Independent checking device (eg. mu Independent checking device (eg. mu checks) - should be a completely checks) - should be a completely independent set of dataindependent set of data

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Machine data availabilityMachine data availability

Hardcopy (isodose charts, output factor Hardcopy (isodose charts, output factor tables, wedge factors,…)tables, wedge factors,…)

Treatment planning computer (as above Treatment planning computer (as above or beam model)or beam model)

Independent checking device (eg. mu Independent checking device (eg. mu checks)checks)

The data must be dated, verified in

regular intervals and the source

(including the person responsible

for it) must be documented

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Machine data summaryMachine data summary

Need to include all beams and options Need to include all beams and options (internal consistency(internal consistency اللزوجة اللزوجة القوام، , ,القوام،conventions, collisionconventions, collisionتصادمتصادم protection, protection, physical limitations) physical limitations)

Data can be made available for planning in Data can be made available for planning in installments as requiredinstallments as required

Some data may be required for individual Some data may be required for individual patients only (eg. special treatments)patients only (eg. special treatments)

Only make available data which is verifiedOnly make available data which is verified

Quick Question:Quick Question:

What data is available for physical What data is available for physical wedges in your center?wedges in your center?

This should include at least:Wedge angle - and how it is definedWedge output modification factor - and to which depth and field sizes it appliesThe field sizes for which the wedge can be usedBeam hardening? Maybe a new beam must be defined by TMRs or percentage depth doseProfiles in both directions (wedged and un-wedged - the latter is affected by divergence related profile changes)Weight (eg for OHS restrictions on lifting)

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From single to multiple beamsFrom single to multiple beams Mainly an issue Mainly an issue

for megavoltage for megavoltage photons where we photons where we have significant have significant contribution of contribution of dose to the target dose to the target from many beamsfrom many beams

11

44

33 2260 Gy60 Gy

Beam weighting must be factored in !!!

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CompensatorsCompensators Physical compensatorsPhysical compensators

lead sheetslead sheets brass blocksbrass blocks customized millingcustomized milling

Intensity modulationIntensity modulation multiple static fieldsmultiple static fields arcsarcs dynamic MLCdynamic MLC

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Intensity modulationIntensity modulation Can be shown to allow optimization of Can be shown to allow optimization of

the dose distributionthe dose distribution Make dose in the target homogenousMake dose in the target homogenous Minimize dose out of the targetMinimize dose out of the target Different techniquesDifferent techniques

physical compensatorsphysical compensators intensity modulation using multi leaf intensity modulation using multi leaf

collimatorscollimators

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Intensity Intensity ModulationModulation

Achieved using a Achieved using a Multi Leaf Collimator (MLC)Multi Leaf Collimator (MLC)

The field shape can be The field shape can be altered altered either step-by-step oreither step-by-step or dynamically while dose is dynamically while dose is

delivereddelivered

MLC pattern 1

MLC pattern 3

MLC pattern 2

Intensitymap

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iv. Basic dose calculationiv. Basic dose calculation

Once one has the target volume, the Once one has the target volume, the beam orientation and shape one has to beam orientation and shape one has to calculate how long a beam must be on calculate how long a beam must be on (60-Co or kV X-ray units) or how many (60-Co or kV X-ray units) or how many monitor units must be given (linear monitor units must be given (linear accelerator) to deliver the desired dose accelerator) to deliver the desired dose at the target.at the target.

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3D display of 3D display of beam beam placement placement may help to may help to identify the identify the structures in structures in the field.the field.

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Dose calculationDose calculation

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Dose display optionsDose display options

Isodose lines Color wash

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Isodose display - can be Isodose display - can be complex and 3Dcomplex and 3D

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