Randomized trial of dose de-escalation in low-risk prostate cancer patients implanted with Pd-103

Palladium-103 (Pd-103) brachytherapy has been associated with excellent oncologic outcomes for favorable risk prostate cancer. Our purpose was to evaluate whether de-escalated dose Pd-103 was associated with a difference in biochemical failure (BF) compared with standard-dose Pd-103 for low-risk prostate cancer.

Patients with low-risk prostate cancer (cT1b-T2b, Gleason 6, and prostate-specific antigen (PSA) ≤ 10 ng/mL) were randomized 1:1 to standard dose (125 Gy) versus de-escalated dose (110 Gy) Pd-103 brachytherapy. The primary endpoint was biochemical failure (BF), defined as PSA ≥ 0.4 ng/mL. Fine-Gray regression analysis was used to identify baseline factors associated with BF, with death as a competing risk. Grade 3 genitourinary (GU) and gastrointestinal (GI) toxicities were reported.

This analysis included 316 patients, who were randomized between February 2006 and February 2014. At a median follow-up of 11.0 years, the 12-year cumulative incidences of BF for the standard and de-escalated dose arms were 1.3% and 2.7%, respectively (p = 0.40). On multivariate regression, body mass index (adjusted sub-distribution hazard ratio (sHR): 1.18; 95% confidence interval (CI) = 1.06-1.32; p = 0.003) and PSA (adjusted sHR: 1.76; 95% CI = 1.36-2.28; p < 0.001) were associated with BF. Cumulative incidences of Grade 3 GU toxicities at 12-years were 6.5% and 3.9% for standard and de-escalated arms, respectively (p = 0.34). There were no Grade 3 GI toxicities in either arm.

De-escalated dose Pd-103 (110 Gy) could be considered for patients with low-risk prostate cancer who opt for definitive treatment.