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QA for PROSTATE BRACHYTHERAPY

  1. 1. Quality Assurance (QA) for Prostate Brachytherapy Bashar Al-Qaisieh
  2. 2. Overview • TG 43 and TG43-U1 • Seed & Needle Check • Template Calibration • Ultrasound Machine Check • Commissioning Planning System • Treatment Plan Check • Post Implant QA
  3. 3. TG 43 and TG 43-U1 Report of American Association of Physicists in Medicine Radiation Therapy Committee Task Group 43 Medical Physics, 22(2), 209-235, Feb 1995 Update of AAPM Task Group No. 43 Report: A revised AAPM protocol for brachytherapy dose calculations Medical Physics, 31 (3), 633-674 Mar 2004
  4. 4. TG43-U1 • Clear definitions of physical quantities, and all the equations required for the calculation of dose. • Treatment planning systems. • Source calibration. • Planning systems commissioning. • Universal standards. • Theoretical and experimental recommendations. • And more……. .
  5. 5. TG-43 : General Dose Calculation Algorithm D(r,θ)=SkΛ[GL(r,θ)/GL(r0,θ0)]gL(r)F(r,θ) The dose rate, D(r,θ) is defined as
  6. 6. Cylindrically symmetrical source y z r0=1cm P(r,θ) β θ L P(r0,θ0) Reference point is chosen to lie on the transverse bisector of the source at a distance of 1cm from its centre i.e. r0=1cm and θ0=π/2
  7. 7. D(r,θ)=SkΛ[G(r,θ)/G(r0,θ0)]g(r)F(r,θ) Sk= air kerma strength of the source Λ= dose rate constant G(r,θ)=geometry factor g(r)=radial dose function F(r,θ)=anisotropy function
  8. 8. TG 43-U1, Why bother? HL241.44AL ALθ)(r,DD(r) . ××= ×=
  9. 9. TG43 TG43-U1
  10. 10. TG43-U1
  11. 11. Seed Calibration-Well chamber • Calibration every two years. Med. Phys. 18, 1991. • Consistency check. Cs-137, Co-60
  12. 12. Guidelines “The activity of all sources should be measured, and compared with the calibration certificate supplied by the supplier, before being administered to a patient”…..Medical and Dental Guidance Notes, IPEM
  13. 13. Seed Calibration •Sterile sources located in MICK magazine - a minimum of 10% of the total or two magazine cartridges of 15 seeds, whichever is greater. • Sterile stranded sources. - a minimum of 10% of the total or two strands of 10 seeds, whichever is greater. • Loose seeds - a minimum of 10% of the total or 20 seeds, whichever is greater.
  14. 14. Needles Check • Verification of loaded brachytherapy needles. • Place a film on top of the needles. The radiation from the loaded needles exposes an image in the film. • The film will verify correct loading of seeds and spacers within each needle, or indicate any discrepancies or missing seeds.
  15. 15. Needles Check
  16. 16. Template Calibration Ultrasound Template Planning TemplateGuidance Template Level of tolerance is ± 1mm
  17. 17. Template Calibration
  18. 18. Ultrasound Machine Check • Assurance of Mechanical and Electrical Safety • Distance Accuracy (vertical and horizontal) • Contrast and Brightness (Gray bar visualization) • Image Uniformity • Penetration • Lateral Resolution -IPEM report 71: Price R et al. 1995/2002 -TG –1: Goodsitt et al. Med Physics 25(8) 1998.
  19. 19. Clinical Commissioning of Planning System (VariSeed™ System & 6711 seed) – Test 1: Dose Point Calculation-TG 43-U1 – Test 2: Isodose Level-TG 43-U1 – Test 3: Volume and Dose Volume-TG 43-U1 – Test 4: Anisotropy Function/Line Source Calculation- TG43-U1 – Test 5: Data transfer and handling – Test 6: Stepper Depth and Angle Tracking and Accuracy Tests
  20. 20. Dose Point Calculation Test • This dose calculation verification test uses a dose point(s) to verify the calculations of the planning system. Discrepancy should be within 1%. 0.5cm P1 P2 1cm 2cm S2 S1 Dose rates (cGy h-1 U-1) as a function of distance
  21. 21. Isodose Level Test • This test is to verify the display of isodose levels • The distance discrepancy of contours and template should be within ± 2 mm
  22. 22. Isodose Level Test 0 click back 1 click back 2 clicks back 3 clicks back
  23. 23. Dose Volume Test • This test uses DVH values to verify the dose volume calculation of the planning system. • Discrepancy should not exceed 5%.
  24. 24. Dose Volume Test-Example 75.831 U 3.0cm 100Gy Isodose ccrV 1.113 3 4 3 == π
  25. 25. Dose Volume Test
  26. 26. Anisotropy Function/L-Source Calculation Test • This test is to verify the line source approximation calculation which uses anisotropy function data. • Discrepancy should not exceed 1%.
  27. 27. Anisotropy Function/L-Source Dose @ 0 degree Source Isodose
  28. 28. Anisotropy Function/L-Source Dose @ Arbitrary r and θ Example of Dose calculation for different point positions
  29. 29. Image transfer check (Ultrasound phantom) 1.4cm 1cm
  30. 30. Volume Test • Check volume captured from US is similar to the volume contoured on planning system. • Discrepancy should be within ± 1cc.
  31. 31. Stepper Depth and Angle Tracking Tests Longitudinal movement-Retraction Rotational movement- US Probe Angle
  32. 32. Stepper Depth and Angle Tracking Tests • Longitudinal Position Tracking. Accuracy should be within 0.5mm. • Rotational Tracking Test. Accuracy should be within 0.5 degrees.
  33. 33. Stepper Depth Tracking Test e.g: 3 clicks back = 1.5cm
  34. 34. Stepper Angle Tracking Test A B == )tan( A B arcθ θ
  35. 35. Treatment Plan Check • Physics check • template grid not calibrated correctly • planning grid not aligned with template grid correctly • wrong prescribed dose (beware boosts!) • wrong dosimetry data in computer • wrong activity seeds • incorrect manual transfer of information • Oncology check
  36. 36. Post implant CT-MR Image Fusion QA MRI CT + Fused Image
  37. 37. Image Fusion Protocol Phantom Study CT MRI Fused Image + = RMS Error < 1.0mm
  38. 38. QA for HDR Brachytherapy Besides the typical QA procedures established for common HDR Treatments, we need to implement additional ones
  39. 39. •Better visibility •Improved treatment planning •Reproducibility 3D ultrasound
  40. 40. Mechanical & US Image Geometry
  41. 41. Catheter Reconstruction      
  42. 42. Pre-Calculation Quality Assurance Checks • Objective: Test the integrity of the treatment planning system and check the current source data file and equipment setup. • Procedure US probe mark, verify stepper encoder, AKS, point dose calculation, isodose plot..etc
  43. 43. Isodose/DVH check This test uses DVH values to verify the dose volume calculation of the planning system. e.g. Oncentra Prostate valueParameter Value D90 5.9740 Gy V100 235.9343 cm3 V150 151.8108 cm3 V200 108.0353 cm3 Performed by:
  44. 44. Data transfer check e.g.
  45. 45. Data transfer check e.g.
  46. 46. Image transfer check (Ultrasound phantom) Correct value? (Tick)Parameter Ideal value Tolerance Vertical spacing 1.0 cm 0.1 cm Diagonal spacing 1.4 cm 0.1 cm Small volume 3.6 cm3 1.0 cm3 Medium volume 8.8 cm3 1.0 cm3 Large volume 20.4 cm3 1.0 cm3 Performed by: e.g.
  47. 47. 3D ultrasound 0 2 4 6 8 10 12 14 16 18 20 -6 -5 -4 -3 -2 -1 0 1 Slice position (cm) Slice area (cm2 ) 1st fraction 2nd fraction
  48. 48. External Catheter Length QA Measurements P.J. Hoskin et al. / Radiotherapy and Oncology 286 68 (2003) 285–288
  49. 49. Possible Sources of Catheter Movement P.J. Hoskin et al. / Radiotherapy and Oncology 286 68 (2003) 285–288
  50. 50. Possible Sources of Catheter Movement P.J. Hoskin et al. / Radiotherapy and Oncology 286 68 (2003) 285–288
  51. 51. Summary • Seed Calibration (Constancy check) • Template Calibration • Ultrasound Machine Check • Commissioning Planning System – Test 1: Dose Point Calculation Test – Test 2: Isodose Level Test – Test 3: Volume and Dose Volume Test – Test 4: Anisotropy Function/Line Source Calculation – Test 5: Data transfer – Test 6: Stepper Depth and Angle Tracking Tests • Treatment Plan Check – Check list • Post Implant QA

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