Transperineal Versus Transrectal Fiducial Marker Implantation for Prostate SBRT: A Prospective Comparison of Procedural Complications

To prospectively compare urinary tract infection (UTI) incidence associated with transperineal versus transrectal fiducial marker insertion in patients undergoing prostate stereotactic body radiotherapy (SBRT) and to evaluate the impact of prostate volume and age on infection risk. Eighty-five consecutive patients received fiducial markers via transrectal (n = 42) or transperineal (n = 43) routes at a tertiary cancer center. Age (≤70 vs. >70 years), prostate volume (<40 vs. >40 cc), and procedure type were analyzed using multivariable binary logistic regression. Model calibration was assessed with the Hosmer–Lemeshow goodness-of-fit test, and discriminative ability was evaluated using Nagelkerke R 2. Overall, UTI incidence was 11/85 (12.9%) within 30 days post-procedure. In multivariable analysis, prostate volume >40 cc was associated with significantly increased UTI odds (odds ratio [OR]: 14.73; 95% confidence interval [CI]: 1.69–128.60; p = 0.015), while transperineal insertion reduced UTI odds versus transrectal insertion (OR: 0.19; 95% CI: 0.04–0.83; p = 0.027). Age >70 years was not predictive of UTI (OR: 1.01; 95% CI: 0.25–4.09; p = 0.992). Model fit was adequate (Nagelkerke R 2 = 0.259; Hosmer–Lemeshow p = 0.182). Transperineal fiducial marker insertion significantly lowers UTI risk relative to transrectal insertion, with the strongest risk observed in patients with larger prostates (>40 cc). These data support preferential use of the transperineal approach during SBRT preparation to enhance patient safety and minimize treatment delays.