SOURCE LOCALIZATION FOLLOWING PERMANENT TRANSPERINEAL PROSTATE INTERSTITIAL BRACHYTHERAPY USING MAGNETIC-RESONANCE-IMAGING

Purpose: Dosimetric evaluation of completed brachytherapy implant proc edures is crucial in developing proper technique and has prognostic im plications. Accurate definition of the prostate gland and localization of the implanted radioactive sources are critical to attain meaningfu l dosimetric data. Methods using radiographs and CT accurately localiz e sources, but poorly delineate the prostate gland, MRI has been recog nized as a superior imaging modality in delineating the prostate gland , but poor in localizing sources due to lack of source visibility, The purpose of this study was to optimize the visualization of sources us ing MRI and compare to CT derived source localization, Methods and Mat erials: Multiple MRI scanning techniques were attempted until an accep table sequence to visualize both the prostate gland and the implanted sources was found, The exams were performed using a pelvic coil only i n approximately 15 min, The CT and MRI scans of 20 consecutive patient s who had received TRUS-guided permanent transperineal interstitial pr ostate (125)Iodine or (103)Palladium brachytherapy were evaluated usin g an in-house dosimetry system, To eliminate anatomical dependence, th e MRI-derived DVHs for the entire calculation volume were then compare d to those derived from the CT scans, Results: The differences in isod ose volumes, of the calculation volumes, for all implants at all dose levels were not statically significant at the 95% confidence level, Ca lculation volume isodose volumes derived from MR images were statistic ally similar to those derived from CT images at the prescription dose for both (125)Iodine (p < 0.01) and (103)Palladium (p < 0.026). Conclu sion: This study presents the first evidence that MRI may be reliably used to identify permanently implanted (125)Iodine and (103)Palladium sources. Given the advantage of target definition characteristics of M RI, substantially more accurate dosimetric analysis of prostate implan ts is now possible, The cost of the optimized and abbreviated MR scann ing sequence used in this study is comparable to a pelvic CT scan, Pos timplant MRI allows more accurate volumetric and anatomically relevant evaluation of permanent prostate implants, which may provide useful c linical correlation. (C) 1997 Elsevier Science Inc.