Session Item

To present the 5-year results from a prospective multicenter phase II randomized trial of every-other-day (EOD) vs. once-a-week (QW) urethra-sparing stereotactic body radiotherapy (SBRT) for localized prostate cancer (PCa).

Between 2012 and 2015, 170 patients from nine European institutions with cT1c-3aN0M0 PCa were randomized to 36.25 Gy in 5 fractions (7.25 Gy/fraction to the CTV; 6.5 Gy/fraction to the urethra) delivered either EOD (arm A, n=84), or QW (arm B, n=85). 82 patients from arm A and 83 from arm B were retained for the analysis (5 out of 170 randomized patients were never treated). The median follow-up time for the 170 randomized patients was 78 months (range, 3-110) and 77 months (range, 0-110 months) for arms A and B, respectively.

All patients in the study tolerated the treatment fairly well with mostly mild or no acute GU and GI toxicity (CTCAE v4.0 scale) and no differences between arms (p=0.227 and p=0.441). Grade-3 acute GU toxicity was observed in only one patient (urinary retention) (arm B). Late  grade 2 GU toxicity was observed in 20.7% and 22.5% of patients in arms A and B, respectively; with only one case of grade-3 GU toxicity (obstructive symptoms) observed in arm A at month 18. Late GI toxicity remained mild and similar in both arms, with no grade-3 events, < 4% grade-2, and grade-0 in more than 70% of patients. The 5-year  grade 2 GU toxicity-free survival was 75.9% and 76.1% for arms A and B, respectively (p=0.945), while the 5-year  grade 2 GI toxicity-free survival was 89% and 91.9% for arms A and B, respectively (p=0.596). No changes in EORTC QLQ-PR25 scores were observed in both arms for GU, GI, and sexual domains at 5-year follow-up compared to baseline. Furthermore, mean IPSS scores were also similar at last follow-up compared to baseline (6.4 vs 7.8, for arm A and 7.1 vs 7.5, for arm B). Median PSA values decreased over time from a median value of 8.3 ng/ml and 7.0 ng/ml at baseline to 0.28 ng/ml and 0.37 ng/ml at last follow-up in arms A and B, respectively. At the last follow-up, biochemical failure was observed in 14 patients in the EOD arm and in 7 patients in the QW arm with a 5-year biochemical relapse-free survival rate of 92.2% and 93% for arms A and B, respectively (p=0.13). Four patients in each arm presented a local relapse, while a nodal relapse-only was observed in one patient treated EOD. At last follow-up, two patients in arm A and one in arm B developed distant metastases.

SBRT for PCa with a 10% dose reduction to urethra was associated with a minimal impact on urinary function and quality of life regardless of a EOD or QW fractionation schedule. Biochemical control so far, has been encouraging and much alike in both study arms, though longer follow-up is probably needed to assess the true value of overall treatment time on disease outcome.