RADIATION PROTECTION IN RADIOTHERAPY

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RADIATION PROTECTION IN RADIOTHERAPY
IAEA Training Material on Radiation Protection in
Radiotherapy

• Part 5 External Beam Radiotherapy
• PRACTICAL EXERCISE

IAEA Post Graduate Educational Course Radiation
Protection and Safe Use of Radiation Sources
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Objectives

• To become familiar with different radiation types
  used for external beam radiotherapy
• To understand the function of different equipment
  used for EBT delivery
• To appreciate the implications of different
  treatment units and their design
• To be familiar with auxiliary equipment required
  and used for EBT
• To understand the measures used in this equipment
  to ensure radiation safety

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Part 5 External Beam Radiotherapy
IAEA Training Material on Radiation Protection in
Radiotherapy

• Practical 1 Isocentric Patient Set-up

IAEA Post Graduate Educational Course Radiation
Protection and Safe Use of Radiation Sources
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Isocentric treatment unit
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Contents Objective

• Learn about the the differences between
  isocentric and non-isocentric set-ups
• Discuss advantages and disadvantages

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Question

• Please discuss the advantages and disadvantages
  of isocentric patient set-up in the context of
  your radiotherapy practice

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What Minimum Equipment is Needed?

• White board
• Paper
• A model of a treatment unit would be useful

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Isocentric set-up

• Places the tumour in the centre - multiple
  radiation beams are easily set-up and deliver
  radiation from many directions to the target
  without moving the patient!

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Advantages

• No patient or couch movement between the delivery
  of different fields necessary
• faster treatment
• more stable set-up
• More efficient use of couch rotation - everything
  rotates around the target.
• Arc treatment are necessarily isocentric

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Potential problems

• Clearance between collimator and patient may be
  too small - collision danger
• Penetration may be less because shorter distance
  to the patients skin
• Dose calculation different

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PDD and TMR
source
Strong ISL dependence
beam

• Percentage depth dose (PDD) changes with distance
  of the patient to the source due to variations in
  the inverse square law (ISL), TAR, TMR and TPR do
  not.

Reference point
Weak ISL dependence
phantom
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Dose calculation in isocentric treatments

• Based on TMRs or TPRs rather than percentage
  depth dose (PDD) data
• Often less familiar to physicists who have
  performed beam data acquisition using PDD not TMR
  measurements
• May require new planning data

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Now it is over to you...

• Please discuss the advantages and disadvantages
  of isocentric patient set-up in the context of
  your radiotherapy practice
• This could be done in form a table
• And a bullet list of issues

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Examples

• Issues
• have only DD data
• isocentric could be faster for pelvic treatment
  if we commence treating with four fields
• 80cm FAD unit does not have enough clearance

• To do list
• check with oncologist about preference
• does our planning system support isocentric
  set-up?

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Considerations

• what set-ups are currently in place for which
  patients
• what is your case load like
• what data is available for planning
• what is your calibration set-up

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Questions?

• Lets get started...