Prostate brachytherapy as salvage for local failure after external beam radiation.

Abstract

125 Background: Local failure (LF) after external beam radiation (EBRT) for prostate cancer is a serious problem. Most patients receive non-curative androgen deprivation therapy (ADT), but there is a subset with LF who are still potentially curable. There is limited evidence to suggest that prostate brachytherapy (BT) is an effective, potentially curative salvage therapy with acceptable toxicity. We hypothesize that salvage BT following EBRT can achieve high rates of biochemical control with acceptable toxicity. Methods: We analyzed 39 consecutive patients treated from 1998-2013 with salvage BT at 2 centers. All patients had pathologically confirmed LF following previous EBRT without distant mets & a disease-free interval of ≥ 18-24 mo. Salvage BT to the whole prostate was delivered to 29 patients using low-dose rate I-125 or Pd-103 seed implants (median dose 100 Gy with Pd-103) while 10 received HDR BT (median 30 Gy in 6 fractions). Cases were planned as if de novo but to a lower dose. 33 (85%) received neoadjuvant and/or adjuvant ADT as part of their salvage therapy. Biochemical failure (BF) was defined using the Phoenix criteria. Risk factor analysis was conducted to identify characteristics that predict BF after salvage BT. Results: For the 39 patients, median PSA at diagnosis was 8.4, and 21 (54%) had high-risk disease. Median EBRT dose was 70 Gy with 11 patients (28%) receiving ADT. Median PSA nadir following EBRT was 0.8 (range 0 – 2.6). Median time to recurrence was 53 mo (range 18 – 150), and median pre-salvage PSA was 4.8. Median follow-up after salvage BT was 60.1 mo (range 7 – 150). Biochemical failure-free survival, DMFS and OS at 5 & 7 yrs were 76% & 67%; 91% & 85% and 92% & 84%, respectively. On univariate analysis, PSA nadir after EBRT & pre-salvage PSA were significant predictors of BF (p< 0.01 for both). On multivariate analysis, only pre-salvage PSA was a significant independent predictor of BF (p< 0.01). Freedom from late grade 3 GU toxicity at 3 yrs was 83%. There were no late Grade 3 GI toxicities. Conclusions: This is the largest series reporting on salvage prostate brachytherapy plus ADT for local-only failures after EBRT & suggests that salvage BT with ADT offers selected patients prolonged disease-free survival with acceptable toxicity.