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Radiation Protection in Radiotherapy

Radiation Protection in Radiotherapy

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Radiation Protection in Radiotherapy

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  1. 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

  2. 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. Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  3. 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 Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  4. Some equipment required • Scanning beam data acquisition system • Calibrated ionization chamber • Slab phantom including inhomogeneities • Radiographic film • Anthropomorphic phantom • Ruler, spirit level Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  5. 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 Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  6. 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”,…) Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  7. 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 Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  8. 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 Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  9. 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 Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  10. 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 Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  11. 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) Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  12. E. Data transfer • Pixel values, CT numbers • Missing lines • Patient/scan information • Orientation • Distortion, magnification All needs verification!!! Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  13. F. Special procedures • Junctions • Electron abutting • Stereotactic procedures • Small field procedures (e.g. for eye treatment) • IMRT • TBI, TBSI • Intraoperative radiotherapy Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  14. Sources of uncertainty • Patient localization • Imaging (resolution, distortions,…) • Definition of anatomy (outlines,…) • Beam geometry • Dose calculation • Dose display and plan evaluation • Plan implementation Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  15. 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 Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  16. 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) Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  17. 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 Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  18. Some ‘tricky’ issues • Dose Volume Histograms - watch sampling, grid, volume determination, normalization (1% volume represents still > 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. Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  19. 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 Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  20. Quick Question: What ‘commissioning’ needs to be done for a hand calculation method of treatment times for a superficial X Ray treatment unit?

  21. 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) Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  22. 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 Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  23. 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 Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  24. Quality Assurance Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  25. Quality Assurance Hand calculation of treatment time Check prescription Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  26. 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 Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  27. 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.) Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  28. 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 Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  29. Quick Question: How much time should be spent on treatment planning QC?

  30. 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 Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  31. QA in treatment planning The planning system Plan of a patient QA of the system QA of the plan Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  32. 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) QC of treatment plans Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  33. 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 Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  34. 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 Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  35. 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. Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  36. 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 ? Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  37. 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 ? Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  38. 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. Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  39. Treatment plan QA summary • Essential part of departmental QA • Part of patient records • Multidisciplinary approach Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  40. Quick Question: What advantages has a multidisciplinary approach to QC of treatment plans?

  41. 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 Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  42. 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 Part 10, lecture 3 (cont.): Radiotherapy treatment planning

  43. Any questions?

  44. Question: Please label and discuss the following processes in external beam radiotherapy treatment.

  45. Question: Diagnostic tools 1 Patient 2 4 6 3 5 Treatment planning Treatment unit Part 10, lecture 3 (cont.): Radiotherapy treatment planning