Presentation Authors: Jared Winoker*, Rollin Say, Conner Brown, Richard Stock, Nelson Stone, New York, NY
Introduction: Owing to toxicity concerns with combination therapy, there has been a contemporary trend toward use of monotherapeutic brachytherapy (BT) for the treatment of localized prostate cancer (PC). Standard of care calls for a dose prescription sufficient to attain a D90 of â‰¥140 Gy with iodine, or a biological equivalent dose (BED) of 154 Gy2. For patients with insufficient dose delivered as determined on post-implant dosimetry, practitioners may initiate adjuvant external beam radiation (EBRT) or hormonal therapy (HT) to improve oncological outcomes, particularly in intermediate or high risk disease patients. We sought to quantify the marginal benefit gained by the addition of HT as a function of BED.
Methods: Among 2277 men who underwent BT Â± EBRT from 1990 to 2015, 688 (30%) men with intermediate risk disease were identified. We evaluated the influence of receiving HT at various maximum BED cut-points with respect to freedom from biochemical failure (FFbF), as defined by Phoenix criteria (nadir PSA + 2 ng/ml). Ten-year FFbF was estimated by Kaplan Meier method. A cut-point of BED < 150 with HT was set as the reference standard against which we tested other BED levels in the absence of HT. Chi-square test was used to evaluate difference in 10-year FFbF between the various BED levels.
Results: Median follow up was 8.3 years (range, 2.8-21.8). Median age was 67 years (range, 41-84) and median PSA was 8.4 ng/ml (range, 1-20). The 10-year FFbF for men receiving BED < 150 with HT was 81.6%. Compared to this reference group, FFbF was worse for men with BED < 150 (p=.002) and < 160 (p=.021) without HT. However, this statistical significance was lost at BED < 170 (p=.319) and for higher cut-points as there was no difference to the baseline group (BED < 150 with HT) in terms of FFbF.
Conclusions: In the case of a post-dosimetry BED < 150, intermediate risk patients gain an oncologic benefit from the addition of 6 months of HT, equivalent to receiving a BED of at least 170 Gy2 without HT. Alternatively, this marginal benefit of 20 BED from the addition of adjuvant HT also corresponds to receiving 2 weeks of EBRT at 1.8 Gy/fraction.