Peri-urethral calcifications as a potential biomarker for acute genitourinary toxicity following prostate stereotactic body radiotherapy

Peri-urethral calcifications (PUCs) are readily identifiable on planning computed tomography (CT) and may reflect chronic inflammation, fibrosis, and reduced peri-urethral tissue compliance. We evaluated whether baseline PUCs are associated with acute genitourinary (GU) toxicity following prostate stereotactic body radiotherapy (SBRT).

We retrospectively analyzed 60 consecutive patients with localized prostate adenocarcinoma treated with definitive SBRT between June 2023 and February 2026. PUCs were assessed on non-contrast planning CT using predefined criteria by blinded observers. The primary endpoint was acute grade ≥ 2 GU toxicity occurring during treatment or within 90 days, graded according to CTCAE v5. Associations with toxicity were evaluated using logistic regression, with Firth penalized regression used for multivariable analysis.

PUCs were identified in 17 patients (28.3%). Interobserver agreement was high (93.3%; Cohen's κ = 0.84). Overall, 21 patients (35%) developed acute grade ≥ 2 GU toxicity, including three (5%) with grade ≥ 3 toxicity. Acute grade ≥ 2 GU toxicity occurred significantly more frequently in patients with PUCs than in those without PUCs (64.7% vs 23.3%; OR 6.05, 95% CI 1.78-20.51; P = 0.006). After adjustment for baseline International Prostate Symptom Score (IPSS), PUCs remained independently associated with toxicity (adjusted OR 6.90, 95% CI 1.97-27.96; P = 0.002). Baseline IPSS was also independently associated with toxicity (adjusted OR 1.13 per point; P = 0.008).

PUCs on routine planning CT were independently associated with acute grade ≥ 2 GU toxicity after prostate SBRT. If externally validated, PUC assessment may provide a simple, cost-neutral imaging biomarker for pretreatment urinary toxicity risk stratification.