Improving prostate brachytherapy quality assurance with MRI–CT fusion–based sector analysis in a phase II prospective trial of men with intermediate-risk prostate cancer

Abstract Purpose We combined sector analysis with MRI–CT fusion to comprehensively assess postimplant dosimetry after prostate brachytherapy. Methods and Materials Subjects were 50 men with intermediate-risk prostate cancer treated with 125 I brachytherapy in a prospective phase II clinical trial. On Day 30 after the implantation, dosimetry was evaluated in the prostate base, midgland, and apex regions on fused MRI–CT scans and CT scans. Volumes of each sector receiving 100% of the prescribed dose ( V 100 ) and doses to 90% of each sector ( D 90 ) were also calculated on the ultrasonogram used for treatment planning and compared with values derived from CT and fused MRI–CT scans. Results Fused MRI–CT scans revealed lower-than-expected doses for the whole prostate ( V 100  = 91.3%, D 90  = 152.9 Gy) compared with CT scans (98.5% and 183.6 Gy, p V 100  = 79%, D 90  = 130 Gy) vs. CT (96% and 170 Gy, p Conclusions MRI–CT fusion–based sector analysis was feasible and revealed significantly lower doses to the prostate base than doses estimated from CT alone, although this did not affect biochemical outcomes. MRI–CT fusion–based sector analysis may be useful for developing MRI-based dosimetric markers to predict disease outcomes and treatment-related morbidity.