The impact of prostate gland dimension in genitourinary toxicity after definitive prostate cancer treatment with moderate hypofractionation and volumetric modulated arc radiation therapy

PURPOSE: To analyze clinical-dosimetric predictors of genitourinary (GU) toxicity in a cohort of prostate cancer (PC) patients treated with moderate hypofractionation and simultaneous integrated boost (SIB) using volumetric modulated arc therapy (VMAT) technique. MATERIALS AND METHODS: 60 patients were selected. Patients were stratified into low (43 %), intermediate (30 %) and high-risk (27 %) groups. Low-risk patients received 73.5 Gy to PTV1; intermediate-risk received 73.5 Gy to PTV1 and 60 Gy to PTV2; high-risk received 73.5 Gy to PTV1, 60 Gy to PTV2, and 54 Gy to PTV3. All patients were treated in 30 fractions. Androgen deprivation therapy (ADT) was prescribed upfront in intermediate and high-risk categories. Toxicity was scored according to Common Terminology Criteria for Adverse Events v4.0 scoring system. RESULTS: Median follow-up was 30 months (range 16-36 months). GU acute toxicity was recorded as followS: G0 = 16/60 (27 %), G1 = 18/60 (30 %); G2 = 26/60 (43 %). GU late toxicity was recorded as follows: G0 = 20/60 (34 %); G1 = 29/60 (48 %); G2 = 11/56 (18 %). The risk of acute G2 GU toxicity was three times higher for prostate volume ≥80 cc. In 60 % of the patients with a prostate volume ≥80 cc, the first 3 weeks are at particular risk for toxicity onset. In the late setting, no statistical significance was found between GU toxicity and prostate gland dimension. CONCLUSION: Prostate volume ≥80 cc resulted a predictive factor of acute G2 GU toxicity, in moderate hypofractionation and volumetric modulated arc radiation therapy for definitive PC.