Analysis of late toxicity associated with external beam radiation therapy for prostate cancer with uniform setting of classical 4-field 70 Gy in 35 fractions: a survey study by the Osaka Urological Tumor Radiotherapy Study Group

We aimed to analyse late toxicity associated with external beam radiation therapy (EBRT) for prostate cancer using uniform dose-fractionation and beam arrangement, with the focus on the effect of 3D (CT) simulation and portal field size. We collected data concerning patients with localized prostate adenocarcinoma who had been treated with EBRT at five institutions in Osaka, Japan, between 1998 and 2006. All had been treated with 70 Gy in 35 fractions, using the classical 4-field technique with gantry angles of 0°, 90°, 180° and 270°. Late toxicity was evaluated strictly in terms of the Common Terminology Criteria for Adverse Events Version 4.0. In total, 362 patients were analysed, with a median follow-up of 4.5 years (range 1.0-11.6). The 5-year overall and cause-specific survival rates were 93% and 96%, respectively. The mean ± SD portal field size in the right-left, superior-inferior, and anterior-posterior directions was, respectively, 10.8 ± 1.1, 10.2 ± 1.0 and 8.8 ± 0.9 cm for 2D simulation, and 8.4 ± 1.2, 8.2 ± 1.0 and 7.7 ± 1.0 cm for 3D simulation (P < 0.001). No Grade 4 or 5 late toxicity was observed. The actuarial 5-year Grade 2-3 genitourinary and gastrointestinal (GI) late toxicity rates were 6% and 14%, respectively, while the corresponding late rectal bleeding rate was 23% for 2D simulation and 7% for 3D simulation (P < 0.001). With a uniform setting of classical 4-field 70 Gy/35 fractions, the use of CT simulation and the resultant reduction in portal field size were significantly associated with reduced late GI toxicity, especially with less rectal bleeding.