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  • Part 10: Optimization in External Beam Radiotherapy Lesson 4: Treatment Planning Learning objectives: Upon completion of this lesson, the students will be able to: 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 Appreciate the need for quality assurance in radiotherapy treatment planning Activity: Lecture - 2 practical sessions: 1 Hand planning using isodose plots, 2 Monitor unit calculations Duration: 2 hours References: 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 . M Millar et al 1997 ACPSEM position paper. Australas. Phys. Eng. Sci. Med. 20 Supplement B Fraass et al 1998 AAPM Task Group 53: QA for clinical RT planning. Med. Phys. 25: 1773-1829
  • The last section of lecture 3 in part 10 is mainly concerned with computerized treatment planning, however, many points are also relevant for manual treatment planning.
  • This is a difference which often overlooked by administrators - it can result in vastly different time estimates.
  • The picture shows the set-up of a scanning water phantom
  • These are different aspects of the commissioning of computerised treatment planning - the lecture follows this outline...
  • The ruler illustrates the need for quantitative geometric information
  • This should all be familiar to the participants from the previous section of the lecture. The next slide is a reminder which is currently hidden. The lecturer should point out that the planning system (and any system which allows manual calculation of dose) must ‘know’ all this information
  • Hidden slide
  • The first test is equally applicable to computerized treatment planning systems and hand planning. Machine settings include what gantry angles and field sizes are allowed, what wedges fit where and what set-up requirements there may be.
  • All these tests can be performed in the water phantom shown...
  • Illustrated is a CIRS phantom In vivo dosimetry is discussed in more detail in the next lecture in part 10.
  • In a computerized world every step must be verified. For example, there are many conventions for patient orientation available - it must be ensured that a lesion on the left side of the brain is also represented on the left side in the data used for planning… (in general it is not easy to tell which side is which in a brain scan - are we looking at the patient from the head or the toes?)
  • This is just a summary - it would be beyond the scope of the course to provide more details on any of these.
  • This is an important slide - it summarizes the uncertainties which will affect the realization of a treatment plan in practice.
  • This is an important point: In regions where the dose is relatively homogenous (not much change of dose in the area of interest) on has to look primarily to the uncertainty in dose calculation. In regions of strong dose gradients this is not possible as the dose changes very rapidly and a small misplacement results in a large change in dose. Here it is more appropriate to characterize the dose calculation algorithm in terms of distance to agreement.
  • Important information for administrators - a new treatment planning system will not be available for clinical use a couple of days after installation.
  • Other aspects of QA are covered in part 12 of the course.
  • This slide is included in three lectures of the course - some repetition is useful and it helps participants to feel familiar within the course.
  • This slide preempts some of the discussions of part 12 of the course. However, it was felt that it would be beneficial for participants to discuss QA of treatment planning close to the introduction of the planning systems themselves.
  • The last point should be seen in the context of the material presented in the 4th lecture of part 10
  • This is a different aspect than the QA of planning systems - the QA here is directed towards the treatment plan of an individual patient.
  • This slide is too small to be read (see slides 37-39 for bigger text). The text could be handed out to participants. However, it may be better to just use this to emphasize that: this is a complex procedure it must be developed locally documentation is essential The next slide highlights just three points which should not be overlooked.
  • The key issues are: Communication and Documentation
  • The key issues are: Communication and Documentation
  • Again, the question can be omitted if deemed inappropriate, or if time is pressing. It is meant as a tool to get participants involved. The next slide provides some answers.
  • The next slide can be printed out for the students with its notes. The first process is already described. The participants shall discuss and label the additional processes. Important keywords are: 2: Electronic data transfer, digitisation of patient outlines, ensuring geometry, placement of beams 3: Patient outlines, immobilisation devices, external markers 4: Patient positioning, immobilisation 5: Data transfer (including beam modifiers, blocks, MLC), verification images (DRRs) 6: Simulator images
  • 1: It is essential to align the patient during any diagnostic procedure in a way which allows to reference the target anatomy to external landmarks. The latter may be bony landmarks or artificial marks like tattoos. In any case the procedure should allow the placement of external beams without repeating the diagnostic procedure. An important part of this is to perform the diagnostic procedure in the same patient position as the treatment. 2: 3: 4: 5:

rpop.iaea.org rpop.iaea.org Presentation Transcript

  • Radiation Protection in Radiotherapy Part 10 Good Practice including Radiation Protection in EBT Lecture 3 (cont.): Radiotherapy Treatment Planning IAEA Training Material on Radiation Protection in Radiotherapy
  • 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 .
  • 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
  • Some equipment required
    • Scanning beam data acquisition system
    • Calibrated ionization chamber
    • Slab phantom including inhomogeneities
    • Radiographic film
    • Anthropomorphic phantom
    • Ruler, spirit level
  • 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
  • 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”,…)
  • 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
  •  
  • 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
  • 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
  • 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
  • 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)
  • E. Data transfer
    • Pixel values, CT numbers
    • Missing lines
    • Patient/scan information
    • Orientation
    • Distortion, magnification
    All needs verification!!!
  • F. Special procedures
    • Junctions
    • Electron abutting
    • Stereotactic procedures
    • Small field procedures ( e.g. for eye treatment)
    • IMRT
    • TBI, TBSI
    • Intraoperative radiotherapy
  • Sources of uncertainty
    • Patient localization
    • Imaging (resolution, distortions,…)
    • Definition of anatomy (outlines,…)
    • Beam geometry
    • Dose calculation
    • Dose display and plan evaluation
    • Plan implementation
  • 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
  • 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)
  • 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
  • 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.
  • 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
  • Quick Question: What ‘commissioning’ needs to be done for a hand calculation method of treatment times for a superficial X Ray treatment unit?
  • 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)
  • 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
  • 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
  • Quality Assurance
  • Quality Assurance Check prescription Hand calculation of treatment time
  • 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
  • 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. )
  • 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
  • Quick Question: How much time should be spent on treatment planning QC?
  • 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
  • QA in treatment planning The planning system QA of the system Plan of a patient QA of the plan
  • 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)
  • 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
  • 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
  • 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.
  • 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 ?
  • 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 ?
  • 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.
  • Treatment plan QA summary
    • Essential part of departmental QA
    • Part of patient records
    • Multidisciplinary approach
  • Quick Question: What advantages has a multidisciplinary approach to QC of treatment plans?
  • 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
  • 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
  • Any questions?
  • Question: Please label and discuss the following processes in external beam radiotherapy treatment.
  • Question: Patient Treatment unit Diagnostic tools Treatment planning 1 3 5 4 2 6