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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. B. Computerized treatment planning Patient information Treatment unit data Planning Treatment plan Part 10, lecture 3: Radiotherapy treatment planning

  3. The treatment planning process Individual patient Radiotherapy treatment units Patient data: CT scan, outlines Beam data: radiation quality, PDD, profiles, ... Localization of tumor and critical structures Optimization of source or beam placement Simulation Dose calculation Preparation of treatment sheet and record and verify data Part 10, lecture 3: Radiotherapy treatment planning

  4. A note on inverse treatment planning Patient data: CT scan, outlines Beam data: radiation quality, PDD, profiles, ... Localization of tumor and critical structures Definition of dose levels and constraints Computerized optimization of source or beam placement Many iterations to find the optimum solution Virtual simulation Dose calculation Preparation of treatment sheet and record and verify data Part 10, lecture 3: Radiotherapy treatment planning

  5. Treatment planning computer Individual patient Radiotherapy treatment units Patient data: CT scan, outlines Beam data: radiation quality, PDD, profiles, ... Localisation of tumour and critical structures Optimization of source or beam placement Simulation Dose calculation Preparation of treatment sheet and record and verify data Part 10, lecture 3: Radiotherapy treatment planning

  6. Planning workstation …just a computer box, with highly specialized and complex software. ADAC Pinnacle Part 10, lecture 3: Radiotherapy treatment planning

  7. B. Computerized treatment planning i) Dose calculation algorithms ii) A quick tour through a planning system iii) Evaluation tools iv) Networking and output v) Purchase of a planning system Part 10, lecture 3: Radiotherapy treatment planning

  8. i) Elements of dose calculation • Dose calculation algorithm • Software coding and implementation • Beam data • Clinical set-up (data entry options, macros, evaluation sheet, hardcopy devices) Part 10, lecture 3: Radiotherapy treatment planning

  9. Elements of dose calculation • Dose calculation algorithm • Software coding and implementation • Typically, there is no user control for theses features - however it is essential that the user • is familiar with the physics algorithm • is aware of its implementation and possible software shortcuts • has tested the algorithm for most possible treatment scenarios Part 10, lecture 3: Radiotherapy treatment planning

  10. Elements of dose calculation • Dose calculation algorithm • Software coding and implementation Unfamiliarity with set-up of the treatment planning system has significantly contributed to the most recent radiotherapy accident in Panama (compare IAEA report) • Typically, there is no user control for theses features - however it is essential that the user • is familiar with the physics algorithm • is aware of its implementation and possible software shortcuts • has tested the algorithm for most possible treatment scenarios Part 10, lecture 3: Radiotherapy treatment planning

  11. Calculation methods • Photons • Kilovoltage (superficial/orthovoltage) • Megavoltage (60-Co, linear accelerators) • Electrons • Brachytherapy Part 10, lecture 3: Radiotherapy treatment planning

  12. Photons • Kilovoltage • Hand calculation from measured data or lookup tables (e.g. BJR Supplement 25, 1996) • Megavoltage • “correction” based methods • “model” based methods Part 10, lecture 3: Radiotherapy treatment planning

  13. “Correction” based methods Reconstitute water data Calculate contour corrections Calculate inhomogeneity corrections “Model” based methods Develop model of each beam (more than 1 model may be needed) Propagate model into patient data set Megavoltage photon dose calculation approaches Data measured in water and air Parameterized water data Part 10, lecture 3: Radiotherapy treatment planning

  14. “Correction” based methods Conventional approach Measured data used to create data which (hopefully) is adequate for patient treatment “Model” based methods Most recent planning systems use this Measured data only used to tune and verify a beam model Examples: Superposition/convolution; Monte Carlo Calculations Photon dose calculation approaches Data measured in water and air Parameterized water data Part 10, lecture 3: Radiotherapy treatment planning

  15. Some comments on model based algorithms • Calculation is from first principles • The corrections used (e.g. for inhomogeneities) typically have no equivalent in hand planning • Monitor units calculated without direct reference to measured data • Perform ‘better’ in complex patient than in water cube • Verification and QA more essential! Part 10, lecture 3: Radiotherapy treatment planning

  16. Electron dose calculation • Hand calculation • Pencil beam (2D  3D) • Phase space evolution • Monte Carlo Methods Part 10, lecture 3: Radiotherapy treatment planning

  17. Monte Carlo Calculations • The gold standard • Calculates the path of individual particles using ‘random’ decisions • Uncertainty depends on number of particles - need millions • Highly computer intensive Monte Carlo Calculation of ten tracks of 12MeV electrons Part 10, lecture 3: Radiotherapy treatment planning

  18. ii) A tour through a commercial planning system... • A series of screen shots from Theraplan Plus • An example, mainly to illustrate a planning session Many modules and options Part 10, lecture 3: Radiotherapy treatment planning

  19. All commences with creating a patient… Part 10, lecture 3: Radiotherapy treatment planning

  20. Anatomy of the patient must be defined • May be • outlines • CT scans • Can be • one slice • many slices • Here 21 slices in 1cm distance are created Part 10, lecture 3: Radiotherapy treatment planning

  21. Creation of external contours on all slices - this is not required if a CT scan is available Part 10, lecture 3: Radiotherapy treatment planning

  22. Creation of internal organs Part 10, lecture 3: Radiotherapy treatment planning

  23. A patient outline is filled with target structures (CTV) and other organs of interest Part 10, lecture 3: Radiotherapy treatment planning

  24. Points of interest are added (these could be dosimetric reference points and dose point relevant to effects in normal structures Part 10, lecture 3: Radiotherapy treatment planning

  25. Inhomogeneities are added • If appropriate • Here a low density is associated with lung • In case of a CT scan these are typically automatically created by the system Part 10, lecture 3: Radiotherapy treatment planning

  26. Full screen layout - can be customized Part 10, lecture 3: Radiotherapy treatment planning

  27. Making the CTV into a planning target volume (PTV) by including margins Part 10, lecture 3: Radiotherapy treatment planning

  28. CTV becomes PTV... Part 10, lecture 3: Radiotherapy treatment planning

  29. A radiation beam is added... Part 10, lecture 3: Radiotherapy treatment planning

  30. Physician’s eye view and Beam’s eye view (BEV) Part 10, lecture 3: Radiotherapy treatment planning

  31. Parameters for the beam are defined... Part 10, lecture 3: Radiotherapy treatment planning

  32. The dose calculation grid • Determines how detailed the dose distribution is calculated • Usually around 2 to 5mm • Depends on treatment situation • Increases calculation time dramatically Part 10, lecture 3: Radiotherapy treatment planning

  33. 3D display of beam placement may help to identify the structures in the field. Part 10, lecture 3: Radiotherapy treatment planning

  34. Dose calculation Part 10, lecture 3: Radiotherapy treatment planning

  35. Dose calculation Part 10, lecture 3: Radiotherapy treatment planning

  36. Dose calculation 4MV 10MV Part 10, lecture 3: Radiotherapy treatment planning

  37. Calculation with and without contour correction Part 10, lecture 3: Radiotherapy treatment planning

  38. Addition of a beam modifier - here a 45degree dynamic wedge Part 10, lecture 3: Radiotherapy treatment planning

  39. Inhomogeneity correction turned on Part 10, lecture 3: Radiotherapy treatment planning

  40. Beams eye view • A useful tool • Green - the beam • Blue and red - the target • Pink - a critical structure • Allows beam shaping and the creation of blocks Part 10, lecture 3: Radiotherapy treatment planning

  41. Creation of an opposing beam A parallel opposed pair (POP) Part 10, lecture 3: Radiotherapy treatment planning

  42. The resulting dose distribution Part 10, lecture 3: Radiotherapy treatment planning

  43. Dose display options Color wash Isodose lines Part 10, lecture 3: Radiotherapy treatment planning

  44. A third beam with multileaf collimator blocking Part 10, lecture 3: Radiotherapy treatment planning

  45. Information on the beams Part 10, lecture 3: Radiotherapy treatment planning

  46. Dose to the points of interest Part 10, lecture 3: Radiotherapy treatment planning

  47. Changing the beam weighting... Part 10, lecture 3: Radiotherapy treatment planning

  48. Changing the beam weighting and adding wedges creates a homogenous dose distribution in the target Part 10, lecture 3: Radiotherapy treatment planning

  49. Normalization - where do we connect a dose distribution with absolute dose... Part 10, lecture 3: Radiotherapy treatment planning

  50. A complex dose delivery in a 90deg arc... Part 10, lecture 3: Radiotherapy treatment planning