Radiation Protection in Radiotherapy

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Radiation Protection inRadiotherapy
IAEA Training Material on Radiation Protection in
Radiotherapy

• Part 10
• Good Practice including Radiation Protection in
  EBT
• Lecture 3 (cont.) Radiotherapy Treatment Planning

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C. Commissioning

• Complex procedure depending very much on
  equipment
• Protocols exist and should be followed
• Useful literature
• J van Dyk et al. 1993 Commissioning and QA of
  treatment planning computers. Int. J. Radiat.
  Oncol. Biol. Phys. 26 261-273
• J van Dyk et al, 1999 Computerised radiation
  treatment planning systems. In Modern Technology
  of Radiation Oncology (Ed. J Van Dyk) Chapter 8.
  Medical Physics Publishing, Wisconsin, ISBN
  0-944838-38-3, pp. 231-286.

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Acceptance testing and commissioning

• Acceptance testing Check that the system
  conforms with specifications.
• Documentation of specifications either in the
  tender, in guidelines or manufacturers notes
  may test against standard data (e.g. Miller et
  al. 1995, AAPM report 55)
• Subset of commissioning procedure
• Takes typically two weeks
• Commissioning Getting the system ready for
  clinical use
• Takes typically several months for modern 3D
  system

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Some equipment required

• Scanning beam data acquisition system
• Calibrated ionization chamber
• Slab phantom including inhomogeneities
• Radiographic film
• Anthropomorphic phantom
• Ruler, spirit level

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Commissioning

• A. Non-dose related components
• B. Photon dose calculations
• C. Electron dose calculations
• (D. Brachytherapy - covered in part 11)
• E. Data transfer
• F. Special procedures

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A. Non-dose components

• Image input
• Geometry and scaling of
• Digitizer,
• Scans
• Output
• Text information
• Anatomical structure information
• CT numbers
• Structures (outlining tools, non-axial
  reconstruction, capping,)

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Electron and photon beams

• Description (machine, modality, energy)
• Geometry (Gantry, collimator, table, arcs)
• Field definition (Collimator, trays, MLC,
  applicators, )
• Beam modifiers (Wedges, dynamic wedges,
  compensators, bolus,)
• Normalization

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B. Photon calculation tests

• Point doses
• TAR, TPR, PDD, PSF
• Square, rectangular and irregular fields
• Inverse square law
• Attenuation factors (trays, wedges,)
• Output factors
• Machine settings

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Photon calculation tests (cont.)

• Dose distribution
• Homogenous
• Profiles (open and wedged)
• SSD/SAD
• Contour correction
• Blocks, MLC, asymmetric jaws
• Multiple beams
• Arcs
• Off axis (open and wedged)
• Collimator/couch rotation

PTW waterphantom
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Photon calculation tests (cont.)

• Dose distribution
• Inhomogeneous
• Slab geometry
• Other geometries
• Anthropomorphic phantom
• In vivo dosimetry at least for the first patients
• Following the incident in Panama, the IAEA
  recommends a largely extended in vivo dosimetry
  program to be implemented

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C. Electron calculation

• Similar to photons, however, additional
• Bremsstrahlung tail
• Small field sizes require special consideration
• Inhomogeneity has more impact
• It is possible to use reference data for
  comparison (Shui et al. 1992 Verification data
  for electron beam dose algorithms Med. Phys. 19
  623-636)

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E. Data transfer

• Pixel values, CT numbers
• Missing lines
• Patient/scan information
• Orientation
• Distortion, magnification

All needs verification!!!
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F. Special procedures

• Junctions
• Electron abutting
• Stereotactic procedures
• Small field procedures (e.g. for eye treatment)
• IMRT
• TBI, TBSI
• Intraoperative radiotherapy

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Sources of uncertainty

• Patient localization
• Imaging (resolution, distortions,)
• Definition of anatomy (outlines,)
• Beam geometry
• Dose calculation
• Dose display and plan evaluation
• Plan implementation

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Typical accuracy required (examples)

• Square field CAX 1
• MLC penumbra 3
• Wedge outer beam 5
• Buildup-region 30
• 3D inhomogeneity CAX 5

From AAPM TG53
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Typical accuracy required (examples)

• Square field CAX 1
• MLC penumbra 3
• Wedge outer beam 5
• Buildup-region 30
• 3D inhomogeneity CAX 5

Note Uncertainties have two components Dose
(given in ) Location (given in mm)
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Time and staff requirements for commissioning (J
Van Dyk 1999)

• Photon beam 4-7 days
• Electron beam 3-5 days
• Brachytherapy 1 day per source type
• Monitor unit calculation 0.3 days per beam

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Some tricky issues

• Dose Volume Histograms - watch sampling, grid,
  volume determination, normalization (1 volume
  represents still gt 10E7 cells!)
• Biological parameters - Tumour Control
  Probability (TCP) and Normal Tissue Complication
  Probability (NTCP) depend on the model used and
  the parameters which are available.

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Commissioning summary

• Probably the most complex task for RT physicists
  - takes considerable time and training
• Partial commissioning needed for system upgrades
  and modification
• Documentation and hardcopy data must be included
• Training is essential and courses are available
• Independent check highly recommended

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Quick Question

• What commissioning needs to be done for a hand
  calculation method of treatment times for a
  superficial X Ray treatment unit?

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Superficial beam

• HVL
• Percentage depth dose (may be look up table)
• Normalization point (typically the surface)
• Scatter (typically back scatter) factor
• Applicator and/or cone factor
• Timer accuracy
• On/off effect
• Other effects which may affect dose (e.g.
  electron contamination)

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Quality Assurance of a treatment planning system

• QA is typically a subset of commissioning tests
• Protocols
• As for commissioning and
• M Millar et al. 1997 ACPSEM position paper.
  Australas. Phys. Eng. Sci. Med. 20 Supplement
• B Fraas et al. 1998 AAPM Task Group 53 QA for
  clinical RT planning. Med. Phys. 25 1773-1829

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Aspects of QA (compare also part 12 of the course)

• Training - qualified staff
• Checks against a benchmark - reproducibility
• Treatment verification
• QA administration
• Communication
• Documentation
• Awareness of procedures required

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Quality Assurance
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Quality Assurance
Hand calculation of treatment time
Check prescription
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Frequency of tests for planning (and suggested
acceptance criteria)

• Commissioning and significant upgrades
• See above
• Annual
• MU calculation (2)
• Reference plan set (2 or 2mm)
• Scaling/geometry input/output devices (1mm)
• Monthly
• Check sum
• Some reference test sets

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Frequency of tests (cont.)

• Weekly
• Input/output devices
• Each time system is turned on
• Check sum (no change)
• Each plan
• CT transfer - orientation?
• Monitor units - independent check
• Verify input parameters (field size, energy, etc.)

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Treatment planning QA summary

• Training most essential
• Staying alert is part of QA
• Documentation and reporting necessary
• Treatment verification in vivo can play an
  important role

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Quick Question

• How much time should be spent on treatment
  planning QC?

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Staff and time requirements (source J. Van Dyk
et al. 1999)

• Reproducibility tests/QC 1 week per year
• In vivo dosimetry about 1 hour per patient - aim
  for about 10 of patients
• Manual check of plans and monitor units 20
  minutes per plan

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QA in treatment planning
The planning system
Plan of a patient
QA of the system
QA of the plan
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QC of treatment plans

• Treatment plan Documentation of
• treatment set-up,
• machine parameters,
• calculation details,
• dose distribution,
• patient information,
• record and verify data

• Consists typically of
• Treatment sheet
• Isodose plan
• Record and Verify entry
• Reference films (simulator, DRR)

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QC of treatment plans

• Check plan for each patient prior to commencement
  of treatment
• Plan must be
• Complete from prescription to set-up information
  and dose delivery advise
• Understandable by colleagues
• Document treatment for future use

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Who should do it?

• Treatment sheet checking should involve senior
  staff
• It is an advantage if different professions can
  be involved in the process
• Reports must go to clinicians and the relevant QA
  committee

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Example for physics treatment sheet checking
procedure

• Check prescription (energy/dose/fractionation is
  everything signed ?)
• Check prescription and calculation page for
  consistency Isocentric (SAD) or fixed distance
  (SSD) set-up ? Are all necessary factors used?
  Check both,dose/fraction and number of fractions.
• Check normalisation value (Plan or data sheets).
• Check outline, separation and prescription depth.
• Turn to treatment plan Does it look ok ? Outline
  ? Bolus ? Isocentre placement and normalisation
  point ? Any concerns regarding the use of
  algorithms near surfaces or inhomogeneities?
  Would you expect problems in planes not shown ?
  Prescription ?
• Check and compare with treatment sheet
  calculation page treatment unit and type, field
  names, weighting, wedges, blocks, field size
  (FS), focus surface distance (FSD), Tissue Air
  Ratio (TAR) (if isocentric treatment) - is this
  consistent with entries in treatment log page?
• Electrons only
• Photons only
• Check shadow tray factor, wedge factor. Are any
  other attenuation factors required (e.g. couch,
  headrest, table tray...) ?
• Check inverse square law factor (in electron
  treatments is the virtual FSD appropriate?)
• Calculate monitor units. Is time entry ok ?
• Check if critical organ (e.g. spinal cord, lens,
  scrotum) dose or hot spot dose is required. If
  so, is it calculated correctly ?
• Suggest in vivo dosimetry measurements if
  appropriate. Sign calculation sheet (if
  everything is ok).
• Compare results on calculation page with entries
  in treatment log.
• Check diagram and/or set up description is there
  anything else worth to consider ?
• Sign top of treatment sheet (specify what parts
  where checked if not all fields were checked).
• Contact planning staff if required. Sign off
  physics log book.

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Example for physics treatment sheet checking
procedure

1. Check prescription (energy/dose/fractionation is
   everything signed ?)
2. Check prescription and calculation page for
   consistency Isocentric (SAD) or fixed distance
   (SSD) set-up ? Are all necessary factors used?
   Check both,dose/fraction and number of fractions.
3. Check normalisation value (Plan or data sheets).
4. Check outline, separation and prescription depth.
5. Turn to treatment plan Does it look ok ? Outline
   ? Bolus ? Isocentre placement and normalisation
   point ? Any concerns regarding the use of
   algorithms near surfaces or inhomogeneities?
   Would you expect problems in planes not shown ?
   Prescription ?

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Example for physics treatment sheet checking
procedure (cont.)

• Check and compare with treatment sheet
  calculation page treatment unit and type, field
  names, weighting, wedges, blocks, field size
  (FS), focus surface distance (FSD), Tissue Air
  Ratio (TAR) (if isocentric treatment) - is this
  consistent with entries in treatment log page?
• Electrons only
• Photons only
• Check shadow tray factor, wedge factor. Are any
  other attenuation factors required (e.g. couch,
  headrest, table tray...) ?
• Check inverse square law factor (in electron
  treatments is the virtual FSD appropriate?)
• Calculate monitor units. Is time entry ok ?
• Check if critical organ (e.g. spinal cord, lens,
  scrotum) dose or hot spot dose is required. If
  so, is it calculated correctly ?

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Example for physics treatment sheet checking
procedure (cont.)

• Suggest in vivo dosimetry measurements if
  appropriate. Sign calculation sheet (if
  everything is ok).
• Compare results on calculation page with entries
  in treatment log.
• Check diagram and/or set up description is there
  anything else worth to consider ?
• Sign top of treatment sheet (specify what parts
  where checked if not all fields were checked).
• Contact planning staff if required. Sign off
  physics log book.

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Treatment plan QA summary

• Essential part of departmental QA
• Part of patient records
• Multidisciplinary approach

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Quick Question

• What advantages has a multidisciplinary approach
  to QC of treatment plans?

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Did we achieve the objectives?

• Understand the general principles of radiotherapy
  treatment planning
• Appreciate different dose calculation algorithms
• Be able to apply the concepts of optimization of
  medical exposure throughout the treatment
  planning process
• Appreciate the need for quality assurance in
  radiotherapy treatment planning

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Overall Summary

• Treatment planning is the most important step
  towards radiotherapy for individual patients - as
  such it is essential for patient protection as
  outlined in BSS
• Treatment planning is growing more complex and
  time consuming
• Understanding of the process is essential
• QA of all aspects is essential

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Any questions?
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Question

• Please label and discuss the following processes
  in external beam radiotherapy treatment.

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Question
Diagnostic tools
1
Patient
2
4
6
3
5
Treatment planning
Treatment unit