Postimplant Multiparametric MRI-Based Dosimetry After Permanent Iodine Seed Prostate Brachytherapy: The Impact of the Dose Delivered to the Dominant Intraprostatic Lesion on Prostate-Specific Antigen Bounce

Abstract

Purpose/Objective(s): To evaluate the effectiveness and tolerability of neo-adjuvant/concomitant/adjuvant androgen deprivation therapy (ADT) for patients treated with external beam radiation therapy (EBRT) combined with high-dose-rate (HDR) brachytherapy boost for localized prostate cancer. Our hypothesis was that ADT does not add to the efficacy of the combined treatments. Materials/Methods: This is a retrospective cohort study conducted in a Canadian academic oncology center. All patients treated at our institution with EBRT followed by 192Ir HDR brachytherapy boost for localized prostate cancer between 1998 and 2010 were included in the study. Data on patients’ age, disease severity at diagnosis, androgen deprivation and radiation treatments received and follow up were collected from the patients’ medical records. The primary outcome was biochemical recurrence-free survival (bRFS). The secondary outcomes were genitourinary and gastrointestinal toxicities. Biochemical recurrence was determined according to the Phoenix consensus definition. Survival curves were calculated with the Kaplan-Meier method and compared between the two groups (ADT versus no ADT) with a logrank test. Multivariate Cox regressions were also performed to take into account potentially confounding variables such as age, PSA at diagnosis, TNM stage, Gleason score, biologically effective dose and type and duration of ADT. Genitourinary toxicities were assessed with the IPSS tool and compared between groups with student t-tests. Gastrointestinal toxicities (diarrhea, tenesmus, rectal bleeding) were evaluated with a three points scale (0: never, 1: occasionally, 2: frequently) and compared between groups with chi-squared tests. Results: Six hundred thirty-eight patients were treated with EBRT and HDR brachytherapy boost. Of those, 186 received ADT and 452 received no ADT. Doses ranged from 40 to 45 Gy in 20 to 25 fractions for EBRT and from 15 to 20 Gy in 1 to 3 fractions for the boost. According to NCCN risk classification, 7.8% of patients were low risk, 81.8% were intermediate risk and 10.3% were high risk. Median follow-up was 53 months. There was no significant difference in bRFS between groups in univariate (HR: 0.83; 95% CI: 0.51-1.38; p Z 0.48) and in multivariate analyses (HR: 0.72; 95% CI: 0.42-1.26; p Z 0.20). bRFS at 7 years was 86% in the ADT group and 92% in the no-ADT group (p Z 0.48). We observed no significant difference between groups in mean global IPSS scores at 3 months (ADT: 11.17 vs. no-ADT: 10.4; pZ 0.49) and at 12 months (ADT: 9.64 vs. no-ADT: 10.75; p Z 0.28) post-radiation therapy as well as in gastrointestinal toxicities at 3 and 12 months. Conclusions: For patients with a localized prostate cancer treated with EBRT combined with HDR brachytherapy boost, the addition of ADT does not seem to yield to a significant increased in bRFS neither to be associated with increased genitourinary and gastrointestinal toxicities. Author Disclosure: S. Magnan: None. P. Despres: None. W. Foster: None. A. Martin: None. E. Vigneault: None.