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Anatomy-based MLC Field Optimization for the Treatment of Gynecologic Malignancies

Anatomy-based MLC Field Optimization for the Treatment of Gynecologic Malignancies. Myriam Bouchard M.D. Nadeau S, Germain I, Raymond P.E., Harel F, Beaulieu F, Beaulieu L, Roy R, Gingras L Dep. of radiation oncology of L’Hotel-Dieu de Quebec, QC, Canada

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Anatomy-based MLC Field Optimization for the Treatment of Gynecologic Malignancies

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  1. Anatomy-based MLC Field Optimization for the Treatment of Gynecologic Malignancies Myriam Bouchard M.D.Nadeau S, Germain I, Raymond P.E., Harel F, Beaulieu F, Beaulieu L, Roy R, Gingras L Dep. of radiation oncology of L’Hotel-Dieu de Quebec, QC, Canada Dep. of Physics, Physics Engineering and Optics, Laval University, Quebec, Canada

  2. IMRT for GYN malignancies • Mundt et al.(Chicago, 2000)Portelance et al.(St. Louis, 2001)Heron et al.(Pittsburgh, 2003)Lujan et al.(Chicago, 2003) D’Souza et al. (Houston, 2005) Adequate target coverage OARs sparing • Small bowel • Rectum • Bladder • Bone marrow Myriam Bouchard M.D.

  3. IMRT for GYN malignancies • Post-operative whole-pelvis radiotherapy • More bowel to spare, bowel replacing uterus • Less organ motion • Good clinical results with IMRT 1 • 36 patients, whole-pelvis IMRT • Median follow-up = 19,6 month • 13.9% less GI-GII toxicity 1 MUNDT et al. IJROBP, vol.56 #5 (2003) pp.1354-1360 Myriam Bouchard M.D.

  4. IMRT for GYN malignancies • Disadvantages of IMRT • Large number of segments and MU • Increased scattered dose • Dose calculation uncertainties • Higher potential impact of machine or patient positioning errors • Increased planning, treatment and quality assurance time • Higher impact of organ motion Myriam Bouchard M.D.

  5. BallistaA new inverse planning approach A dosimetric study Approved by the local institutional committee for medical ethics

  6. Objectives • Evaluate Ballista as an alternative • Between 4-field and IMRT • For post-operative whole-pelvis radiotherapy in gynecologic malignancies Myriam Bouchard M.D.

  7. Hypothesis • Same target coverage • Organs at risk (OARs) sparing • Better than 4-field • As good as IMRT ? • Treatment delivery advantages Myriam Bouchard M.D.

  8. Materials and methods • 10 patients • Endometrial or cervix malignancies • Post-operative external radiotherapy • 45 Gy / 25 fractions, whole-pelvis Myriam Bouchard M.D.

  9. Inverse planning Materials and methods For comparison purposes 4 plans created for each patient • Conventional 4-field • Enlarged 4-field • Results for OARs at same PTV coverage • IMRT • Ballista Myriam Bouchard M.D.

  10. Materials and methods Forward planning 4-field enlarged 4-field

  11. Materials and methods • Planning CTscan as usual • Conventional planning : • 4-field plans based on bony landmarks • Created before other plan conception • Enlarged 4-field • Aperture shaped to PTV Myriam Bouchard M.D.

  12. Materials and methods Inverse planning IMRT Ballista

  13. Vessels+ 5 mm ITV 1 cm CTV (ITV) • External iliac nodes • Internal iliac nodes • Obturator nodes • Presacral region • 1/2 superior vagina • Parameters Myriam Bouchard M.D.

  14. CTV / ITV Myriam Bouchard M.D.

  15. 3D CTV Myriam Bouchard M.D.

  16. PTV = CTV + 1 cm Myriam Bouchard M.D.

  17. OARs • Bowel (colon + small bowel) • Region at risk to find bowel = RAR-B • Rectum • Bladder • Bone marrow Myriam Bouchard M.D.

  18. Bowel / RAR-B Myriam Bouchard M.D.

  19. IMRT • Plans created with Pinnacle3 system • Step-and-shoot • 7 coplanar and equidistant 6 MV beams • 1 extraction • 10-12 intensity levels • Minimum field area = 4 cm2 Myriam Bouchard M.D.

  20. Ballista1 • Inverse planning system • Recently developed at L’Hotel-Dieu de Qc • Simultaneous optimization • Gantry, table and collimator angles • Wedge angle and beam weights • Intensity modulation • Anatomy-based MLC fields 1 BEAULIEU et al. Med.Phys.31, 1546-1557 (2004) Myriam Bouchard M.D.

  21. Anatomy-based fields Myriam Bouchard M.D.

  22. Number of fields • Gantry and table angle • optimization • Addition of sub- • anatomic structures Ballista Steps Result / conclusion Feasibility Selection of a fixed geometry (class solution) New treatment that is comparable to IMRT Myriam Bouchard M.D.

  23. Beam orientation for Ballista plans 9 beams 23 MV Myriam Bouchard M.D.

  24. Number of fields • Gantry and table angle • optimization • Addition of sub- • anatomic structures Ballista Steps Result / conclusion Feasibility Selection of a fixed geometry (class solution) New treatment that is comparable to IMRT Myriam Bouchard M.D.

  25. Sub-anatomic structures Myriam Bouchard M.D.

  26. Analysis For each plan (4) created for each patient (10) • DVH • PTV and OARs • Number of segments • Number of MU • Statistics : Student’s paired t-test Myriam Bouchard M.D.

  27. Results Target coverage

  28. 4-field Enlarged 4-field IMRT Ballista Myriam Bouchard M.D.

  29. 77% p =0.03 4-field Enlarged 4-field IMRT Ballista PTV coverage / homogeneity (Mean±SEM, n=10) Myriam Bouchard M.D.

  30. Results OARs sparing

  31. + 34.7 % 4-field Enlarged 4-field IMRT Ballista RAR-B 40 and 45 Gy (Mean±SEM, n=10) For the same PTV coverage Myriam Bouchard M.D.

  32. + 20.8 % 4-field Enlarged 4-field IMRT Ballista RAR-B (Mean±SEM, n=10) Ballista vs 4-field : V45 Gy, p < 0,001 Myriam Bouchard M.D.

  33. 4-field Enlarged 4-field IMRT Ballista (Mean±SEM, n=10) RAR-B (Mean±SEM, n=10) 45 Gy : p = 0.15 40 Gy : p < 0.001 (diff. = 61.4 cm3 or 9.9% ) Myriam Bouchard M.D.

  34. Rectum – mean V 45 Gy Myriam Bouchard M.D.

  35. Rectum – mean V 45 Gy Myriam Bouchard M.D.

  36. Bladder – mean V 45 Gy Myriam Bouchard M.D.

  37. Bladder – mean V 45 Gy Myriam Bouchard M.D.

  38. OARs V47.25 Gy Myriam Bouchard M.D.

  39. OARs V47.25 Gy Myriam Bouchard M.D.

  40. Enlarged 4-field 4-field IMRT Ballista (Mean±SEM, n=10) Bone marrow Enlarged 4-field vs Ballista : V40 Gy, p < 0,001 (forthe same PTV coverage) Myriam Bouchard M.D.

  41. 4-field Enlarged 4-f Volumeirradié Volume traité Irradiated volume Treated volume (Mean±SEM, n=10) V 50% and V 95% Myriam Bouchard M.D.

  42. Results Treatment delivery

  43. Number of segments (Mean±SEM, n=10) Myriam Bouchard M.D.

  44. 4-field Monitor Units (Mean±SEM, n=10) Number of MU Myriam Bouchard M.D.

  45. ± 1.4 Gy Calculated / delivered doses • Impact of leaf position errors Myriam Bouchard M.D.

  46. Discussion

  47. Dose constraint on OARs Priorities in our study • First priority on RAR-B • Bladder • Relative important weight given to it… • Organ motion +++ • Eventually replaced by small bowel • Bone marrow : when possible Myriam Bouchard M.D.

  48. OARs results • Bone marrow results • Worse compared to conventional planning • but PTV coverage not optimal • Similar gains IMRT vs Ballista Myriam Bouchard M.D.

  49. OARs results To enhance sparing… • Organ motion study necessary 2 • To limit as possible expansion for PTV • In our study, ITV/PTV limited sparing of rectum • Optimal patient immobilization • essential 2 AHAMAD et al. (MDACC). IJROBP 62 (4) p.1117-1124 (2005) Myriam Bouchard M.D.

  50. Advantages Ballistavs IMRT • Number of segments reduced by 75% • Number of MU reduced by 55% Result in  scattered radiation •  risk of second malignancies Myriam Bouchard M.D.

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