S646 ESTRO 35 2016 _____________________________________________________________________________________________________ complemented by a boost to local recurrence to a total dose of 72 Gy. In case of no macroscopic tumor recurrence the total dose was 66.6 Gy. Results: MRI was performed in 233 patients and PET/CT was performed in 169 patients. A local recurrence in the prostate bed could be detected in 123 patients with a median volume of 0.5 ml (range, 0.03 -125.00 ml). The median follow-up

more »

... me after RT was 49.4 months (range, 7.3 -86.1 months). A total of 85 patients experienced a biochemical failure with a median time of 19.8 months (range, 1.9 -76.1 months) after sRT. Median PSA level at the time of recurrence was 0.91 ng/ml (range, 0.01 -2224.00 ng/ml). The median BRFS after radiation therapy was 73 months. The estimated 3-and 5year bRFS was 72% and 55%, respectively. On multivariate analysis, Gleason Score (hazard ratio, 6.946; p = 0.006) and pre-RT PSA level (hazard ratio, 2.265; p = 0.022) were statistically significant predictors for bRFS. bRFS was similar in patients with a macroscopic recurrence in either MRI or PET/CT compared to patients without a macroscopic recurrence. 5-year overall survival was 91% and 5-year cancer-specific survival was 96%. Grade 3 gastrointestinal toxicity was observed in 4 patients and 3 patients showed grade 3 genitourinary toxicities. No grade 4 gastrointestinal or genitourinary side effects were reported. Conclusion: Gleason score and pre-RT PSA were important predictors for bRFS. The dose in salvage radiotherapy should be increased to 72 Gy to prevent an early recurrence after sRT in patients with a macroscopic recurrence. A higher total dose of up to 72 Gy was well tolerated in this cohort of patients. EP-1383 PSA kinetics in prostate cancer patients after SBRT radiotherapy using CyberKnife.