Radiotherapy treatment planning
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Radiotherapy Treatment Planning. Treatment planning is the task to make sure a prescription is put into practice in an optimized way. Prescription. Planning. Treatment. Objectives. Understand the general principles of radiotherapy treatment planning

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Radiotherapy Treatment Planning

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Radiotherapy treatment planning

Radiotherapy Treatment Planning


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

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

Prescription

Planning

Treatment

Anwar


Objectives

Objectives

  • Understand the general principles of radiotherapy treatment planning

  • Appreciate different dose calculation algorithms

  • Understand the need for testing the treatment plan against a set of measurements

  • Be able to apply the concepts of optimization of medical exposure throughout the treatment planning process

Anwar


Contents of the lecture

Contents of the lecture

A. Radiotherapy treatment planning concepts

B. Computerized treatment planning

Anwar


The need to understand treatment planning

The need to understand treatment planning

  • IAEA Safety Report Series 17 “Lessons learned from accidental exposures in radiotherapy “ (Vienna 2000):

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

  • May affect individual patient or cohort of patients

Anwar


A basic radiotherapy treatment planning concepts

A. Basic Radiotherapy Treatment Planning Concepts

i. Planning process overview

ii. Patient data required for planning

iii. Machine data required for planning

iv. Basic dose calculation

Anwar


I planning process overview

i. Planning process overview

  • Combine machine parameters and individual patient data to customize and optimize treatment

  • Requires machine data, input of patient data, calculation algorithm

  • Produces output of data in a form which can be used for treatment (the ‘treatment plan’)

Patient information

Treatment unit data

Planning

Treatment plan

Anwar


Ii patient information required

ii. Patient information required

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

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

Anwar


One needs to know

One needs to know

  • Target location

  • Target volume and shape

  • Secondary targets - potential tumor spread

  • Location of critical structures

  • Volume and shape of critical structures

  • Radiobiology of structures

Anwar


Radiotherapy treatment planning

Target delineation

ICRU 50 & 62

  • Gross Tumor Volume (GTV) = clinically demonstrated tumor

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

Anwar


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

Comparison of

three different

treatment techniques (red, blue and green)

in terms of dose to the target and a critical structure

Critical

organ

Target dose

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

Dose Volume Histograms are a way to summarize this information


The ideal dvh

Tumor:

High dose to all

Homogenous dose

Critical organ

Low dose to most of the structure

The ideal DVH

100%

100%

dose

dose

Anwar


Need to keep in mind

Need to keep in mind

  • Always a 3D problem

  • Different organs may respond differently to different dose patterns.

  • Question: Is a bit of dose to all the organ better than a high dose to a small part of the organ?

Anwar


In practice not always that clear cut

In practice not always that clear cut

  • ICRU report 62

  • Need to understand anatomy and physiology

  • A clinical decision

Anwar


Radiotherapy treatment planning

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

Boersma*et al., classified the following

(Dose,Volume) regions to be regions of high risk for developing rectal bleeding:

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

Anwar


In ebt practice

In EBT practice

  • Need to know

    • where to direct beam to, and

    • how large the beam must be and how it should be shaped

Anwar


Target design and reference images

Target design and reference images

  • In radiotherapy practice the target is localized using diagnostic tools:

    • Diagnostic procedures - palpation, X-ray, ultrasound

    • Diagnostic procedures - MRI, PET, SPECT

    • Diagnostic procedures - CT scan, simulator radiograph

Anwar


Selection of treatment approach

Selection of treatment approach

  • Requires training and experience

  • May differ from patient to patient

  • Requires good diagnostic tools

  • Requires accurate spatial information

  • May require information obtained from different modalities

Anwar


Minimum patient data required for external beam planning

Minimum patient data required for external beam planning

  • Target location

  • Patient outline

Anwar


Diagnostic tools which could be used for patient data acquisition

Diagnostic tools which could be used for patient data acquisition

  • CT scanner, MRI, PET scanner, US,…

  • Simulator including laser system, optical distance indicator (ODI)

  • Many functions of the simulator are also available on treatment units as an alternative - simulator needs the same QA!

Anwar


Note on the role of simulation

Note on the role of simulation

  • Simulator is often used twice in the radiotherapy process

    • Patient data acquisition - target localization, contours, outlines

    • Verification - can the plan be put into practice? Acquisition of reference images for verification.

  • Simulator may be replaced by other diagnostic equipment or virtual simulation

Anwar


Virtual simulation

Virtual simulation

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

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

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

Anwar


Virtual simulation1

Virtual Simulation

3D Model of the patient and the Treatment Devices

Anwar


Simulator

Simulator

Rotating

gantry

Diagnostic

X-ray tube

Radiation beam

defining system

Simulator couch

Image intensifier

and X-ray film

holder

Nucletron/Oldelft

Anwar


Radiotherapy simulator

Radiotherapy simulator

  • Obtain images and mark beam entry points on the patient

Anwar


Radiotherapy treatment planning

Isocenter Position

CT Simulation (Thanks to ADAC)

Marking the Patient already during CT

Moveable Lasers

CT images

Isocenter Projection

Anwar


Patient marking

Patient marking

Marks on shell

  • Create relation between patient coordinates and beam coordinates

Tattoos

Skin markers

Anwar


Beam placement and shaping

Beam placement and shaping

DRR with

conformal shielding

simulator film

with block

Anwar


Tools for optimization of the radiotherapy approach

Choice of radiation quality

Entry point

Number of beams

Field size

Blocks

Wedges

Compensators

Tools for optimization of the radiotherapy approach

Anwar


Optimization approaches

Optimization approaches

Choice of best

beam angle

beam

beam

target

patient

target

patient

wedge

target

Use of a beam

modifier

patient

Anwar


Beam number and weighting

Beam number and weighting

Beam 1

beam

50%

100%

50%

target

patient

Beam 2

patient

40%

30%

10%

20%

Anwar


A note on weighting of beams

A note on weighting of beams

Different approaches are

possible:

1. Weighting of beams as

to how much they contribute

to the dose at the target

2. Weighting of beams as

to how much dose is

incident on the patient

These are NOT the same

25%

40%

25%

25%

30%

10%

20%

25%

Anwar


Use of wedges

Use of wedges

  • Wedged pair

  • Three field techniques

Isodose lines

patient

patient

Typical isodose lines

Anwar


Beam placement and shaping1

Entry point

Field size

Blocks

Wedges

Compensators

a two-dimensional approach?

Beam placement and shaping

Anwar


Beam placement and shaping2

Entry point

Field size

Blocks

Wedges

Compensators

Multiple beams

Dynamic delivery

Non-coplanar

Dose compensation (IMRT) not just missing tissue

Biological planning

Beam placement and shaping

This is actually a 3D approach

Anwar


Target localization

Target Localization

  • Diagnostic procedures - palpation, X-ray, ultrasound

  • Diagnostic procedures - MRI, PET, SPECT

  • Diagnostic procedures - CT scan, simulator radiograph

Allows the creation of Reference Images for Treatment Verification:

Simulator Film, Digitally Reconstructed Radiograph

Anwar


Simulator image

Simulator image

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

  • A verification film is taken in ‘treatment’ geometry

Anwar


Simulator film

Simulator Film

  • Shows relevant anatomy

  • Indicates field placement and size

  • Indicates shielding

  • Can be used as reference image for treatment verification

Field defining wires

Anwar


Iii machine data requirements for treatment planning

iii. Machine data requirements for treatment planning

  • Beam description (quality, energy)

  • Beam geometry (isocentre, gantry, table)

  • Field definition (source collimator distance, applicators, collimators, blocks, MLC)

  • Physical beam modifiers (wedges, compensator)

  • Dynamic beam modifiers (dynamic wedge, arcs, MLC IMRT)

  • Normalization of dose

Anwar


Machine data required for planning

Machine data required for planning

  • Depends on

    • complexity of treatment approaches

    • resources available for data acquisition

  • May be from published data or can be acquired

  • MUST be verified...

Anwar


Quick question

Quick Question:

Who is responsible for the preparation of beam data for the planning process?


Acquisition of machine data

Acquisition of machine data

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

  • Done by physicist

  • Some dosimetric equipment must be available (water phantom, ion chambers, film, phantoms,…)

  • Documentation essential

Anwar


Machine data availability

Machine data availability

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

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

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

Anwar


Machine data availability1

Machine data availability

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

  • Treatment planning computer (as above or beam model)

  • Independent checking device (eg. mu checks)

The data must be dated, verified in regular intervals and the source (including the person responsible for it) must be documented

Anwar


Machine data summary

Machine data summary

  • Need to include all beams and options (internal consistencyالقوام، اللزوجة, conventions, collisionتصادم protection, physical limitations)

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

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

  • Only make available data which is verified

Anwar


Quick question what data is available for physical wedges in your center

Quick Question:What data is available for physical wedges in your center?

This should include at least:

Wedge angle - and how it is defined

Wedge output modification factor - and to which depth and field sizes it applies

The field sizes for which the wedge can be used

Beam hardening? Maybe a new beam must be defined by TMRs or percentage depth dose

Profiles in both directions (wedged and un-wedged - the latter is affected by divergence related profile changes)

Weight (eg for OHS restrictions on lifting)


From single to multiple beams

1

3

2

60 Gy

4

From single to multiple beams

  • Mainly an issue for megavoltage photons where we have significant contribution of dose to the target from many beams

Beam weighting must be factored in !!!

Anwar


Compensators

Compensators

  • Physical compensators

    • lead sheets

    • brass blocks

    • customized milling

  • Intensity modulation

    • multiple static fields

    • arcs

    • dynamic MLC

Anwar


Intensity modulation

Intensity modulation

  • Can be shown to allow optimization of the dose distribution

  • Make dose in the target homogenous

  • Minimize dose out of the target

  • Different techniques

    • physical compensators

    • intensity modulation using multi leaf collimators

Anwar


Intensity modulation1

Intensity Modulation

MLC pattern 1

  • Achieved using a Multi Leaf Collimator (MLC)

  • The field shape can be altered

    • either step-by-step or

    • dynamically while dose is delivered

MLC pattern 2

MLC pattern 3

Intensity

map

Anwar


Iv basic dose calculation

iv. Basic dose calculation

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

Anwar


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

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

Anwar


Dose calculation

Dose calculation

Anwar


Dose display options

Dose display options

Color wash

Isodose lines

Anwar


Isodose display can be complex and 3d

Isodose display - can be complex and 3D

Anwar


Radiotherapy treatment planning

مع أطيب الأمنيات بالتوفيق والنجاح

Anwar


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