Analysis of outcomes after non-contour-based dose painting of dominant intra-epithelial lesion in intra-operative low-dose rate brachytherapy.

Purpose: To compare the outcomes of patients with intermediate risk prostate cancer (IR-PCa) treated with low-dose rate I-125 seed brachytherapy (LDR-BT) and targeted dose painting of a histologic dominant intra-epithelial lesion (DIL) to those without a DIL.

Methods: 455 patients with IR-PCa were treated at a single center with intra-operatively planned LDR-BT, each following the same in-house dose constraints. Patients with a DIL on pathology had hot spots localized to that region but no specific contouring during the procedure.

Results: 396 (87%) patients had a DIL. Baseline tumor characteristics and overall prostate dosimetry were similar between patients with and without DIL except the median number of biopsy cores taken: 10 (10-12) vs 12 (10-12) (p = 0.002).19 (5%) and 18 (5%) of patients with and 1 (2%) and 0 (0%) of those without DIL experienced CTCAE grade 2 and 3 toxicity respectively. Overall, toxicity grade did not significantly correlate with presence of DIL (p = 0.10).Estimated 7-year freedom from biochemical failure (FFBF) was 84% (95% confidence interval: 79-89) and 70% (54-89) in patients with and without a DIL (log-rank p = 0.315). In DIL patients, cox regression revealed location of DIL ("Base" vs "Apex" HR: 1.03; 1.00-1.06; p = 0.03) and older age (70 vs 60 HR: 1.62; 1.06-2.49; p = 0.03) was associated with poor FFBF.

Conclusions: Targeting DIL through dose painting during intraoperatively planned LDR-BT provided no statistically significant change in FFBF. Patients with DILs in the prostate base had slightly lower FFBF despite DIL boost.