Late Genitourinary Toxicity Outcomes in 300 Prostate Cancer Patients Treated With Dose-escalated Image-guided Intensity-modulated Radiotherapy

Aims: To quantify and qualify late genitourinary toxicity in a cohort of patients with localised prostate cancer treated with image-guided intensity-modulated radiotherapy (IMRT) to doses ≥78 Gy.

Materials and methods: The cohort consisted of 300 patients treated with definitive dose-escalated IMRT between 2007 and 2013. Ninety-seven patients received 78-80 Gy in 38 fractions, and 203 received 82-84 Gy in 40 fractions. International Prostate Symptoms Score (IPSS) and supplemental quality of life data were recorded at baseline, weekly during treatment and at follow-up. Genitourinary toxicities were recorded using modified Radiation Therapy Oncology Group criteria during weekly treatment review and at each follow-up. Kaplan-Meier curves were used to assess the cumulative incidence of grade ≥ 2 genitourinary toxicity at 3 years. Baseline patient characteristics and symptoms were then used in univariate and multivariate analyses to identify predictors of late urinary toxicity.

Results: The median follow-up was 58 months (range 9-109 months). The actuarial cumulative 3 year rates of grade ≥ 2 and grade 3 genitourinary toxicity were 14.9% and 2.8%, respectively. There was no grade 4 toxicity. History of transurethral resection of the prostate (TURP), alpha blocker use before radiation, any hormone use, baseline IPSS ≥ 14 and pre-existing incontinence or nocturia were significantly associated with late ≥ 2 genitourinary toxicity on univariate analysis. On multivariate analysis, only previous TURP retained significance, with a hazard ratio of 2.54 (P=0.002).

Conclusion: Our study showed acceptable levels of late grade 2 genitourinary toxicity and low rates of late grade 3 genitourinary toxicity in a cohort of patients with prostate cancer treated with image-guided IMRT to doses between 78 and 84 Gy. Variables associated with increased late ≥ 2 genitourinary toxicity include previous TURP, alpha blocker use, hormone use and pre-existing urinary dysfunction.