Whole Versus Partial Gland Boost During Prostate SBRT

This is a phase 2 randomized clinical trial evaluating two dose escalation strategies during prostate stereotactic body radiotherapy (SBRT). A total of 160 patients with prostate adenocarcinoma will be enrolled and randomized in a 1:1 ratio to one of two treatment arms. 160 patients will be enrolled in this study over 3.2 years. Eligible participants will be stratified by risk group and tamsulosin use and randomized to one of two treatment arms. Both arms will receive 3625 cGy to the prostate plus planning margin delivered over 5 fractions. Arm A will receive an additional boost of 4000 cGy to the prostate alone. Arm B will receive an additional boost of 4500 cGy to the dominant intra-prostatic lesion (DIL). Acute and chronic GU and GI toxicities will be measured, as well as biochemical progression-free survival. Toxicities will be measured using CTCAE, Radiation Therapy Oncology Group, and Expanded Prostate Cancer Index Composite domains. Participants will be followed for up to 5 years after completion of treatment.