Session Item

We previously published 5-year outcomes in two large multicenter trials of ultrahypofractionated stereotactic radiotherapy for organ-confined prostate cancer. Randomized trials have subsequently demonstrated that, with similar follow up, ultrahypofractionated radiotherapy is a suitable alternative to conventional fractionation.  Since data beyond five years are lacking, we now present combined 10-year survival and late toxicity outcomes from these two prospective trials.

39 centers enrolled 569 patients with prostate adenocarcinoma: 284 with low-risk and 285 with intermediate-risk disease. 101 patients had unfavorable intermediate-risk tumors (Gleason 4+3, two unfavorable risk factors, and/or ≥50% biopsy cores positive). All were treated with a non-coplanar robotic stereotactic platform using real-time tracking of implanted fiducials. Two dose regimens were used: 40Gy in 5 fractions of 8Gy, and 38Gy in 4 fractions of 9.5Gy. Adjuvant androgen deprivation therapy (ADT) was not allowed. Early (within 3 months of treatment) toxicity and 5-year survival outcomes have been previously described; we report outcomes in patients consenting to study participation beyond 5 years. Toxicities were assessed using Common Terminology Criteria for Adverse Events (CTCAE) version 3. All reported rates are actuarial, using Kaplan-Meier method. For relapse free survival (RFS), failure included initiating salvage or systemic therapy, local/regional/distant failure, or biochemical relapse using the “nadir + 2” definition.

Median follow up was 8.1 years, with 109 patients followed for 10 years. There were no grade 4-5 toxicities. Actuarial 10-year grade 2 and grade 3 late GU toxicity rates were 14.9% and 2.2%, respectively. The 10-year late grade 2 GI toxicity rate was 3.6%; there were no grade 3 GI toxicities. For the entire group, 10-year overall survival rate was 88.1%, local failure rate was 2.5%, and RFS rate was 92.0%. 10-year RFS for low- and intermediate-risk groups were 98.5% and 85.8%, respectively. 10-year RFS for favorable and unfavorable intermediate-risk patients were 91.5% and 75.3%. No statistically significant differences in rates of toxicity, survival, local failure, nor RFS were observed between the two dose regimens.

10 years following treatment of organ-confined prostate cancer with ultrahypofractionated robotic stereotactic radiotherapy, toxicity rates continue to be minimal, with few additional events observed beyond 5 years. Overall survival, local control, and RFS rates remain favorable at 10 years, confirming stereotactic radiotherapy as a suitable option for low- and intermediate-risk prostate cancer.