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Intensity modulated radiotherapy for a prostate patient with a prosthetic hip

For a prostate carcinoma patient with a metallic prosthetic hip replacement, a 3D Conformal Radiotherapy (3DCRT) treatment plan is commonly created using only those fields that avoid the prostheses in beam's eye view (BEV). With a limited choice of fields, a resulting plan compromises in dose sparing of rectum and bladder. In this work, we investigate another option with Intensity Modulated Radiotherapy (IMRT). Three patients, previously treated with 3DCRT at the University of Chicago Medical Center for prostate carcinoma with single prostheses, were evaluated in this study. The clinical target volume (CTV-prostate+seminal vesicles), bladder, and rectum were identified on CT scans. The planning target volume (PTV) was generated by a 3D 1 cm expansion of CTV. For comparative studies, plans were generated with the PLUNC 3DCRT and the CORWS IMRT systems using the CT and contour data. The IMRT plans used 9 equally spaced 6 MV coplanar fields, with each field avoiding the prosthesis. The 3DCRT plans used 5 coplanar 18 MV fields, each field avoiding the prostheses, and a 1 cm block margin. The IMRT and 3DCRT plans were normalized so that 100% of a PTV were covered by at least 95% isodose line. Each IMRT plan spared bladder and rectum better than the corresponding 3DCRT plan. In the IMRT plans, a bladder volume getting 80% or greater dose decreased by 19-93 cc, and a rectal volume getting 80% or greater dose decreased by 29-54 cc. One negative feature of IMRT plans was the inhomogeneous PTV coverage, which ranged from [95-115]%.