Body mass index can affect gastrointestinal and genitourinary toxicity in patients with prostate cancer treated with external beam radiation therapy.

The aim of the present study was to determine the impact of obesity on radiation-induced gastrointestinal (GI) and genitourinary (GU) toxicity. The cases of 54 patients with prostate cancer, treated with three-dimensional conformal radiation therapy (RT), were reviewed. For each patient, the body mass index (BMI), distance between the prostate and rectum (D) on a computerised tomography scan and the dosimetric parameters of the rectum and bladder in the planning data of RT, were analyzed. GI and GU toxicity was assessed during and following RT. The results of the patients with a BMI of <25 (lower BMI) were compared with those of the patients with a BMI of ≥25 (higher BMI). The higher BMI group exhibited significantly lower doses of V and V in the rectum than the lower BMI group. No significant differences were found in D and bladder doses between the two groups. The incidence of acute GI and GU toxicity and late GI and GU toxicity were 41.7, 19.4, 35.3 and 5.7% in the lower BMI group, respectively, and 27.8, 27.8, 5.9 and 35.3% in the higher BMI group, respectively. In addition, a significant difference was found in the incidence of late GU toxicity between the two groups. Among patients who underwent RT for prostate cancer, those with higher BMIs had a tendency to show lower incidences of GI toxicity and higher incidences of GU toxicity than patients with lower BMIs. To conclude, an increased effort must be made to reduce rectal doses in patients with lower BMIs. Conversely, increased care for GU toxicity must be provided for overweight patients.