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Verification

Planning. Clinical Aspects. Radiobiological Aspects. Delivery. Arthur Boyer Stanford University School of Medicine Stanford, California. Verification. Conventional planning. Time. IMRT planning. Complexity. Establish the Correspondence Between Output and Input. Output. Input.

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Verification

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  1. Planning • Clinical Aspects • Radiobiological Aspects Delivery Arthur Boyer Stanford University School of Medicine Stanford, California • Verification

  2. Conventional planning Time IMRT planning Complexity

  3. Establish the Correspondence Between Output and Input Output Input Specify quantities that describe a patient’s quality of life (e.g., Karnofsky status) Desired output Specify TCP and NTCP--biological model Specify a dose distribution--dose based model

  4. Procedures of Inverse Planning Computation Optimal Input Output Construct an objective function F = F (input parameters) = F (w1,w2,w3,….,wJ) Optimize F and find the optimal beam profiles Convert beam profiles into MLC leaf sequences

  5. Dosimetric: F = [Dc(1)-D0(1)]2 +[Dc(2)-D0(2)]2 + ... w1 Beam profile Dc(1) D0(1) Dc(2) D0(2)

  6. An objective function is a mathematical “measurement” of radiation treatment. • ~2000 pencil beam weights, non-linear system. • It should, ideally, include all of our knowledge of radiotherapy: dosimetry based and biological model based objective function.

  7. Optimization of a multi-dimensional • objective function • Matrix Inversion • Iterative methods • Computer simulated annealing • Genetic optimization • Filtered backprojection

  8. Direct Matrix Inversion n=4 F = S [Dc(n)-D0(n)]2 Calculated dose n=1 w3 w4 Prescribed dose 3 4 D3 D4 1.0 0.5 w2 1 2 D1 D2 w1 1.0 1.0

  9. w4 w3 n=4 F = S [Dc(n)-D0(n)]2 n=1 D3 D4 w2 D1 D2 w1 D1= w1 d11+ w2 d21 + w3 d31 + w4 d41 D2= w1 d12+ w2 d22 + w3 d32 + w4 d42 D3= w1 d13+ w2 d23 + w3 d33 + w4 d43 D4= w1 d14+ w2 d24 + w3 d34 + w4 d44 • Direct Matrix Inversion

  10. A Simple Iterative Algorithm Dose to point n: 1 dn = w1d1n + w2d2n + w3d3n target organ 2 3

  11. Algebraic Iterative Method: Initial beam profiles Calculate dose at a voxel n Compare Dc(n) with D0(n) n+1 Dc(n) > D0(n) ? Yes No Decrease wi Increase wi

  12. Algebraic Iterative Method: n=6 F = S [Dc(n)-D0(n)]2 Calculated dose n=1 0.5 0.5 Prescribed dose 1.0 1.0 1.0 1.0 0.5 1.0 0.5 1.0 1.0 0.5 1.0 1.0 1.0 1.0 0.5

  13. Algebraic Iterative Method: Iteration step = 5 Iteration step = 1 0.51 0.45 0.50 0.49 1.01 0.95 0.50 0.99 1.00 0.50 0.95 0.99 0.90 0.44 0.97 0.49 1.02 1.01 0.99 1.00 0.50 0.50

  14. Objective function Iteration step = 10 i=6 F = S [Dc(i)-D0(i)]2 0.30 0.51 0.42 i=1 0.25 0.20 0.15 0.10 0.51 1.02 0.92 0.05 0.91 0.41 0.82 0 20 40 80 60 1.02 0.92 100 0 0.51 Iteration step Algebraic Iterative Method:

  15. Planning Parameters • Number of beams • Beam/Coll orientation • Isocenter placement • Beamlet size • Intensity levels • Margins & Targets • Tuning structure

  16. Beam Orientation • Coplanar vs Non-coplanar • Ease of setup • Ease of planning • Speed of treatment • Equi-spaced vs Selected angles • Entrance through table/immobilization device

  17. Beam Orientation 9 equi-spaced beams

  18. Beam Orientation 9 selected beams

  19. Collimator Orientation

  20. Collimator Orientation 180o collimator angle

  21. Collimator Orientation Collimator angle

  22. Isocenter Placement • Issues • Can a better plan be achieved by isocenter placement ? • Dosimetry and/or QA • Patient setup

  23. Isocenter Placement Isocenter in geometric center of targets

  24. Isocenter Placement Isocenter in geometric center of GTV

  25. Beamlet Size Yi et al. 2000

  26. Intensity Levels Lehmann et al. 2000

  27. Margins & Targets

  28. Tuning Structure • A structure added to control the dose distribution in IMRT plans • Reduce normal tissue dose • Reduce/Increase target dose

  29. Tuning Structure

  30. Tuning Structure

  31. Summary of Planning Parameters • Number of beams • Beam/Coll orientation • Isocenter placement • Beamlet size • Intensity levels • Margins & Targets • Tuning structure

  32. Verification

  33. Planning System Commissioning a b c d e f specially designed intensity patterns

  34. Planning System Commissioning 90% 90% 50% 50% 40% 10% 20% 20% 40% 70% 70% 10% 80% 80% 90% 90% 30% 50% 30% 10% 10% 50% 90% 90% Calculated Measured specially designed intensity patterns

  35. Patient Specific Field Verification Quantitative Comparison of Two Fluence Maps • Maximum difference in • pixel values---local quantity. • Correlation coefficient— • global quantity.

  36. Film QUANTITATIVE FILM ANALYSIS Courtesy, Tim Solbert

  37. Quantitative Film Analysis White = measurement Red = calculation Courtesy, Tim Solberg

  38. Calculated  Measured Quantitative Film Analysis - Profiles Horizontal and vertical profiles of measured data, calculated data, and  index. Courtesy, Tim Solberg

  39. 40 cm 1.5 cm 4.5 cm 30 cm Measurement Tissue Equivalent Phantom

  40. 50% 70% 90% -1.8% 1mm -3.5% 2mm Cylindrical Phantom Dose Verification Measured in Plane of Isocenter

  41. BANG gel Dosimetry Courtesy, Tim Solberg

  42. Periodic IMRT QA

  43. Periodic IMRT QA Test Pattern with Leaf Error Test Pattern after leaf replacement and MLC calibration

  44. IMRT MU Checks QUALITY ASSURANCE OF IMRT TREATMENT PLAN DEPARTMENT OF RADIATION ONCOLOGY ,STANFORD UNIVERSITY SCHOOL OF MEDICINE PATIENT NAME: xxx, xxxxxxx PATIENT ID: xxx-xx-xx TPS PLAN #: 2512 Treatment Machine: LA7 Beam Energy: 15 MV Calibration Setup: SSD Delivery Mode: Step and Shoot Beamlet Size: 1.0 x 1.0 (cm x cm) Calibration Factor: 1.000 Isocenter Dose Verification Report Field MU x1 x2 y1 y2 SSD beam-dose F 180-000 170 7.80 6.80 4.20 16.20 88.79 50.2 F 180-080 118 4.80 6.80 4.20 17.20 82.03 40.6 F 180-145 108 8.00 1.00 5.00 18.00 90.87 24.0 F 180-145a 101 1.00 8.00 4.00 18.00 90.87 17.9 F 180-215 80 9.00 0.00 3.00 18.00 90.49 1.6 F 180-215a 107 2.00 7.00 5.00 18.00 90.49 48.7 F 180-280 115 6.80 5.80 4.20 17.20 81.68 41.2

  45. IMRT MU Checks Calculated Isocenter Dose: 224.2 cGy TPS Isocenter Dose: 221.3 cGy Percentage Difference: 1.3 (%). Leaf Sequence Verification Report Field ID Gantry Angle Correlation Coefficient Maximum Difference 1 0 1.0000 0.5112 (%) 2 80 1.0000 0.4017 (%) 3 145 1.0000 0.6799 (%) 4 215 1.0000 0.7275 (%) 5 280 1.0000 0.4034 (%) Physicist: _________________________ DATE: 7/20/2001

  46. Isocenter Setup Verification with DRRs Anterior Isocenter Verification

  47. Isocenter Setup Verification with DRRs Lateral Isocenter Verification

  48. Align DRR with EPID Image To Verify Patient Positioning DRR Image AmSi EPID Image

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