Source localization following permanent transperineal prostate interstitial brachytherapy using magnetic resonance imaging

Purpose: Dosimetric evaluation of completed brachytherapy implant procedures is crucial in developing proper technique and has prognostic implications. Accurate definition of the prostate gland and localization of the implanted radioactive sources are critical to attain meaningful dosimetric data. Methods using radiographs and CT accurately localize sources, but poorly delineate the prostate gland, MRI has been recognized 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 using MRI and compare to CT derived source localization, Methods and Materials: Multiple MRI scanning techniques were attempted until an acceptable sequence to visualize both the prostate gland and the implanted sources was found, The exams were performed using a pelvic coil only in approximately 15 min, The CT and MRI scans of 20 consecutive patients who had received TRUS-guided permanent transperineal interstitial prostate (125)Iodine or (103)Palladium brachytherapy were evaluated using an in-house dosimetry system, To eliminate anatomical dependence, the MRI-derived DVHs for the entire calculation volume were then compared to those derived from the CT scans, Results: The differences in isodose volumes, of the calculation volumes, for all implants at all dose levels were not statically significant at the 95% confidence level, Calculation volume isodose volumes derived from MR images were statistically similar to those derived from CT images at the prescription dose for both (125)Iodine (p < 0.01) and (103)Palladium (p < 0.026). Conclusion: 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 MRI, substantially more accurate dosimetric analysis of prostate implants is now possible, The cost of the optimized and abbreviated MR scanning sequence used in this study is comparable to a pelvic CT scan, Postimplant MRI allows more accurate volumetric and anatomically relevant evaluation of permanent prostate implants, which may provide useful clinical correlation. (C) 1997 Elsevier Science Inc.