Impact of a dominant intraprostatic lesion (DIL) boost defined by sextant biopsy in permanent I-125 prostate implants on biochemical disease free survival (bDFS) and toxicity outcomes

Background and purpose: To compare bDFS and toxicity outcomes in a population of intermediate risk prostate cancer patients treated using I-125 LDR brachytherapy with or without DIL boost based on multiple core biopsy maps.

Materials and methods: Between January 2005 and December 2013, all our intermediate risk prostate cancer patients treated with LDR I-125 brachytherapy were reviewed. All patients were given 144 Gy to the prostate. A pathologic DIL distribution (defined by sextant biopsy) was contoured prospectively prior to planning, to be covered by the 150% isodose line. Of the 165 patients treated, 55 received a DIL boost. Patients completed prospectively the IPSS questionnaire, a sexual and bowel function questionnaire. Gastro-intestinal toxicities were graded according to CTCAE v4.03. A patient was considered to have erectile dysfunction if he was unable to achieve erection to perform intercourse. BDFS was determined according to the Phoenix consensus definitions.

Results: The median follow-up was 78 months. The estimated 7-year bDFS rate was 96% (95% CI, 74-99%) in the DIL group versus 89% (95% CI, 79-94%) in the control group (p = 0.188). There was no difference between groups in urinary, gastro-intestinal or sexual toxicities up to 5 years of follow-up. There was no difference in urinary obstruction with catheterization between DIL versus control groups (3,6 vs 2,8 %, p = 1.00). Only 1 patient in the DIL group had ≥grade 3 toxicity (TURP) and none in the control group.

Conclusions: Boost to DIL defined by sextant biopsy with permanent seed prostate implant shows a trend toward improvement of biochemical control in intermediate risk prostate cancer patient without increasing toxicity.