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MO‐D‐BRB‐09: IMRT Ad‐Hoc Adaption ‐ Initial Results for Prostate: A Retrospective Planning Study
Author(s) -
Gainey M,
Bratengeier K,
Polat B,
Meyer J,
Flentje M
Publication year - 2009
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3182219
Subject(s) - prostate , rectum , nuclear medicine , medicine , radiation treatment planning , plan (archaeology) , computer science , medical physics , radiology , radiation therapy , cancer , surgery , geology , paleontology
Purpose: A planning study was performed to investigate the geometry‐based adaption of a step and shoot IMRT‐plan. Method and Materials: Six cases with large rectum and prostate deformations were selected. A 9 field IMRT‐plan (A) was planned on a first CT(CT1). The plan fulfilled all requirements for prostate IMRT in our clinic and its quality was comparable to a conventional high‐quality step and shoot IMRT plan. For a second CT(CT2), three plans were considered: the original plan with optimized isocentre position (B), a newly optimised plan (C) and the original plan, adapted using optimization rules (D), based on a geometry‐based concept called “2‐Step IMRT”. Several DVH‐parameters were utilized for quantification of plan quality: CTV D99, central PTV D95, V95 for an outer PTV, V80 and V50 for rectum and bladder. Results: Unlike B, D achieved almost the same target coverage as plan C. For the OARs, the rectum V80 was slightly increased for the original plan. The volume with more than 95% of the target dose was 1.5 ± 1.5 cm 3 for C, compared to 2.2 ± 1.3 cm 3 for A in CT1 and 7.2 ± 4.8 cm 3 in CT2. D resulted in 4.3 ± 2.1 cm 3 , an intermediate dose load to the rectum. All other parameters were comparable for C and D in contrast to the results from B. Conclusion: The first results for adaptation using the 2‐Step IMRT algorithm are encouraging. The plans were superior to plans with optimised isocentre position B and only marginally worse than a newly optimized plan C. Computerisation is needed to accelerate the procedure, which is currently performed manually. Checks have to be developed to allow an ad‐hoc application of the adapted plan.