Stereotactic body radiation therapy (SBRT), low dose rate brachytherapy (LDR-BT) and high dose rate brachytherapy (HDR-BT) are ablative-intent radiotherapy options for prostate cancer (PCa). These vary considerably in dose delivery, which may impact post-treatment prostate-specific antigen (PSA) patterns and biochemical control. We compared PSA kinetics between SBRT, HDR-BT, and LDR-BT, and assessed their relationships to biochemical recurrence-free survival (BCRFS).
Retrospective PSA data were analyzed for 3,502 men with low-risk (n=2223; 63.5%), favorable intermediate-risk (n=869; 24.8%), and unfavorable intermediate-risk (n=410; 11.7%) PCa treated with SBRT (n=1716; 49.0%), HDR-BT (n=512; 14.6%), or LDR-BT (n=1274; 36.4%) without upfront androgen deprivation therapy at 10 institutions from 1990-2017. We compared nadir PSA (nPSA), time to nPSA, achievement of nPSA <0.2 ng/mL and <0.5 ng/mL, rates of nPSA <0.4 ng/mL at 4 years, and BCRFS.
Median follow-up was 72 months. Median nPSA and nPSA <0.2 ng/mL were stratified by risk group (interaction p≤0.001). Median nPSA and time to nPSA were 0.2 ng/mL at 44 months after SBRT, 0.1-0.2 ng/mL at 37 months after HDR-BT, and 0.01-0.2 ng/mL at 51 months after LDR-BT (mean log nPSA p≤0.009 for LDR-BT vs. SBRT or HDR-BT for low/favorable intermediate-risk). There were no differences in nPSA <0.4 ng/mL at 4 years (p≥0.51). BCRFS was similar for all three modalities (p≥0.27). Continued PSA decay beyond 4 years was predictive of durable biochemical control.
LDR-BT led to lower nPSAs with longer continued decay compared to SBRT and HDR-BT, but no differences in BCRFS.

Copyright © 2020. Published by Elsevier B.V.