Dose-escalated adaptive image-guided radiotherapy versus high-dose-rate brachytherapy monotherapy for low-risk prostate cancer.

145 Background: Both IGRT and HDR are used for definitive treatment of low-risk prostate. No comparative study of these contemporary modalities exists. Methods: Charts for patients with low-risk prostate cancer by NCCN criteria treated 1999-2012 were reviewed. For IGRT, the clinical target volume (CTV) included the prostate and proximal seminal vesicles. A CT-based, off-line adaptive treatment plan was made with a patient-specific confidence-limited planning target volume (cl-PTV) based on the planning plus four additional daily CT scans. Overall survival (OS) was calculated by the Kaplan-Meier method (log-rank test), with Cox regression for uni- and multi-variate analysis. Cumulative incidence (Gray’s test), with competing risks analysis (Fine and Gray) were used for biochemical control (BC) and freedom from local recurrence (FFLR). Results: There were 598 IGRT and 399 HDR patients (see Table), with a median follow-up of 6.1 and 3.6 years, respectively (p<0.001). The median prescribed IGRT dose was 75.6 Gy (range 73.8-79.2). HDR doses were 24 Gy (n=126) or 27 Gy (n=151) in 2 fractions, or 36 Gy (n=3) or 38 Gy (n=335) in 4 fractions. Five- and 10-year BC was 99% and 94% for IGRT and 98% and 95% for HDR (p=0.77); FFLR was 100% and 99% for both (p=0.89); and OS was 95% and 75% for IGRT and 97% and 85% for HDR (p=0.04). On multivariate analysis, predictors (p<0.10) for OS were age (p<0.001) and PNI (p=0.04); for LR, PPC (p=0.01); and for BC, a trend for PSA (p=0.08). Treatment type was not a predictor of OS, BC or FFLR (p>0.5). Conclusions: Both dose- escalated IGRT and HDR monotherapy yield similarly excellent outcomes for low-risk prostate cancer. Our experience supports the continued use of brachytherapy as monotherapy in low-risk prostate cancer. [Table: see text]