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The aim of this study was to describe urinary toxicity after salvage stereotactic body radiation therapy (SBRT) for local prostate cancer recurrence after radiotherapy.

We retrospectively reviewed a total of 108 medical records of patients treated with salvage SBRT for prostate cancer recurrence, between July 2015 and February 2021 in our institution. Patients who had initial radical prostatectomy were excluded. The median time interval between the two radiation treatments was 9 years (range, 3-20 years).  Local recurrence was to be proven by biopsies, without distant lymph node or metastasis. The salvage treatment consisted in SBRT at a total dose of 36 Gy in six fractions delivered every other day, associated with androgen deprivation therapy in 44% of patients. Urinary toxicities after salvage SBRT were described according to the CTCAE v 4.03 classification. Clinical and dosimetric predictors of toxicities were searched by Cox analysis.

Median follow-up was 19.6 months (range, 2.3-67 months). The acute grade 2 and 3 overall GU toxicity rates were 22% and 2%, respectively. The 2 year grade ≥ 2 and ≥ 3 overall GU toxicity rates were 55% (95% CI: 44-66%) and 5% (95% CI: 0-10%), respectively. The acute and late GU toxicity rates by symptoms are provided in the Table. One patient experimented a grade 4 GU toxicity (bladder necrosis requiring a cystectomy) 8 months after SBRT. Predictors of grade ≥ 2 late overall GU toxicity in multivariate analysis were anticoagulant treatment (RR=2.2, p=0.01) and V37 in the bladder wall (in cc) (RR=1.8, p=0.01).

Urinary toxicity after prostate salvage stereotactic reirradiation is the main toxicity, with a 2 year grade ≥2 rate of 55%. It is mostly related to anticoagulant treatment and the V37 in the bladder wall.