Multiparametric MRI and post implant CT-based dosimetry after prostate brachytherapy with iodine seeds: The higher the dose to the dominant index lesion, the lower the PSA bounce

{Purpose: To determine whether post-implant MRI-based dosimetry of the Dominant Intra-prostatic Lesion (DIL) could best predict the occurrence of PSA bounce after prostate brachytherapy. Methods and materials: We selected 66 patients with a low risk prostate cancer treated with I-125 prostate brachytherapy as monotherapy. Post-implant dosimetry based on day 30 CT-scan and multiparametric MRI co-registration was generated: planned D90, D95, V100, V150 values were calculated for each DIL. Bounce was defined as a PSA elevation >= 0.2 ng/mL from the previous baseline value followed by a decrease to or below the prior nadir with no additional treatment. Results: After a median follow-up of 35.5 months (range 13.2-72.5), a PSA bounce occurred in 24 (36.4%) patients. The mean planned D90 of the DIL was significantly lower in bouncers: 196 +/- 61 Gy vs. 234 +/- 62 Gy