Aperture-based IMRT for GYN malignancies - PowerPoint PPT Presentation

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Aperture-based IMRT for GYN malignancies

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  1. Aperture-based IMRT for GYN malignancies Myriam Bouchard S. Nadeau , I. Germain, P.-É. Raymond, F. Harel, F. Beaulieu, L. Beaulieu, R. Roy, L. Gingras Department of radiation oncology of L’Hotel-Dieu de Quebec, QC, Canada Results from the dosimetric study – 2005/2006

  2. Objectives • Contours definition • Target • Organs at risk • Aperture-based vs Beamlet-based IMRT • Gains vs Uncertainties in IMRT for GYN

  3. Purpose of tx Selected cases Endometrial / Uterus cervix cancer Post-operative EBRT = Local Control benefit PORTEC, Creutzberg et al. Lancet (2000) (endometrium) GOG-99 (endometrium) Sedlis Gyn Oncology (1999) (cervix) No survival benefit, attempt to reduce side effects from adjuvant treatments

  4. What do we treat? GYN postop EBRT

  5. CTV • External iliac nodes • Internal iliac nodes • Obturator nodes • Presacral region • 1/2 superior of vagina • Parameters

  6. Controversies CTV

  7. Controversies -- CTV • Endometrium CTV Þ Cervix CTV • Presacral region

  8. Presacral CTV / 4-field 95% Isodose CTV

  9. Controversies -- CTV • Endometrium CTV Þ Cervix CTV • Presacral region • Upper limit ? • L5-S1, L4-L5… (common iliac LN) • External iliac limit

  10. Ant limit / Ext. Iliac LN

  11. Controversies -- CTV • Endometrium CTV Þ Cervix CTV • Presacral region • Upper limit ? • L5-S1, L4-L5… (common iliac LN) • External iliac limit • Margin around vessels • How big?

  12. Pelvic LN mapping literature

  13. Taylor et al • 20 patients, GYN malignancies • MRI + iron oxyde particles • CTV = • margins 3-5-7-10-15 mm • PTV = CTV + 1 cm

  14. Taylor et al

  15. 99% coverage modified-7 mm Taylor et al

  16. 18 patients with prostate cancer N+ • Margin 2 cm around vessels (includes PTV) • 94,5 % N coverage

  17. Controversies -- CTV • Endometrium CTV Þ Cervix CTV • Presacral region • Upper limit ? • L5-S1, L4-L5… (common iliac LN) • External iliac limit • Margin around vessels • How big? • ITV… bladder filling • MDACC = fusion pre-postmictional CTsim

  18. ITV 1 cm

  19. + 5 mm around vessels ITV 1 cm CTV – ourinitial choices* • External iliac nodes • Internal iliac nodes • Obturator nodes • Presacral region • 1/2 superior of vagina • Parameters *Before RTOG 0418, Shih et al. and Taylor et al. publications

  20. 3D CTV

  21. PTV = CTV + 1 cm

  22. OARs • Bowel (colon + small bowel) • Region at risk to find bowel = RAR-B • Rectum • Bladder • Bone marrow

  23. Bowel / RAR-B

  24. Why IMRT for GYN ?

  25. PTV Conventional 4-fields 95% Isodose Inadequate coverage

  26. Inadequate coverage • Greer et al. (1990) • S2-3 post limit : 49% inadequate coverage • 87% com. il. bifurcation above L5-S1 • Bonin et al. / Pendelbury et al. (1993) • 45% / 62% inadequate coverage ext. il LN • Finlay et al. (2006) • 95,4% at least 1 inadequate margin with bony landmarks

  27. 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

  28. IMRT for GYN malignancies • Good clinical results with IMRT 1 • 36 patients, whole-pelvis IMRT • Median FU = 19,6 month • 13.9% less GI-GII toxicity • 3 year Pelvic LC 87,5% * (62 patients) • Cervix cancer • 71% intact uterus 1 Mundt et al. IJROBP, vol.56 #5 (2003) pp.1354-1360* Kochanski et al. ASTRO 2005 Abst #1114

  29. Disadvantages of IMRT • Target volume definition controversies • Impact of • Machine errors (MLC) • Patient positioning errors

  30. Disadvantages of IMRT • Large # of segments and MU • Scattered dose • Calculation uncertainties • Time consuming • Planning • Treatment • Quality assurance

  31. Can we improve treatment delivery issues? Ballista = Aperture-based IMRT A feasability study - dosimetric - clinic

  32. Let’s talk about IMRT Beamlet-based vs Aperture-based

  33. Forward planning(conventional) Manual (human) field definition Followed by calculation Inverse planning (IMRT) Dose objectives in specific areas (contours) Solution found by computer-assisted calculation Types of planning

  34. IMRT Intensity Modulated Radiation Therapy • Dose intensity varies inside the beam • Several sub-fields (segments) • Inverse planning

  35. Basic objectives Field geometry 1st Optimization of beam intensity profiles Segmentation Does the plan meet the clinical objectives? No Yes Final plan *** Calculation steps Beamlet-based IMRT 2nd

  36. Aperture-based IMRT

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

  38. Basic objectives Field geometry Aperture-based Segmentation Ballista

  39. Anatomy-based fields

  40. Basic objectives Field geometry Aperture-based Segmentation Only 1 Field weights optimization No Yes Does the plan meet the clinical objectives? Minor leaf corrections Final plan *** Calculation steps Ballista X

  41. Dosimetric study Ballista for GYN Pilot study -- Part I CHUQ -- Hotel-Dieu de Quebec Quebec city

  42. Dosimetric objectives • Evaluate Ballista as an alternative • Between 4-field and IMRT • For post-operative whole-pelvis radiotherapy in gynecologic malignancies

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

  44. Materials and methods • 10 patients • Endometrial or cervix malignancies • Post-operative external radiotherapy • 45 Gy / 25 fractions, whole-pelvis + brachy HDR boost

  45. 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

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

  47. 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

  48. Materials and methods Inverse planning IMRT Ballista

  49. 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

  50. Beam orientation for Ballista plans 9 beams 23 MV