Implementation of 3D image-guided brachytherapy for penile cancer: Impact of urethral dose on long-term morbidity

Purpose: Interstitial brachytherapy is a conservative treatment approach for localized penile glans cancer. We report our experience with pulse dose rate interstitial brachytherapy (PDR-BT) in the treatment of penile cancer and evaluated urethral dose-volume constraints for clinical practice. Methods and materials: Medical records of patients treated with PDR-BT for localized squamous cell carcinoma of the glans penis in our institution between July 2008 and February 2019 were reviewed. All patients underwent posthectomy followed by CT-guided PDR-BT. Urethral doses were calculated and predictors of urethral stenosis among various clinical and dosimetric characteristics were examined. Results: 65 patients were identified. Eight patients (12%) presented initially with inguinal lymph node metastasis. The median brachytherapy dose was 60 Gy (37–65 Gy). The median number of pulses was 150 pulses (87–175 pulses). With a median follow-up of 37 months (3–120 months), 12 patients (18.4%) had tumor local relapse. Three-year overall survival (OS) and disease-free survival (DFS) rates were 88.2% (95%CI: 79.7–97.7%) and 74.4% (95%CI: 63.9–86.6%) respectively. Twelve patients (20%) presented grade 2 painful ulceration resolving spontaneously and 13 patients (21.5%) experienced grade 2 meatal stenosis. No clinical or dosimetric factors correlated with painful ulceration were identified. The risk of meatal stenosis correlated with distal urethra D0.1cc (p = 0.0016) and D0.2cc (p = 0.0019) in multivariate analysis. The optimal cutoff for these constraints were 82 Gy (HR = 0.12, 95%CI: 0.04–0.38) and 79 Gy (HR = 0.19, 95%CI: 0.06–0.56) for D0.1 cc and D0.2 cc respectively. Conclusions: This institutional experience shows that 3D PDR-BT could be a valid option for penile preservation. Dosimetric constraints for late distal urethral toxicity were identified.