Relationship between rectal bleeding and radiation delivery time in intensity-modulated radiotherapy for localized prostate cancer: a preliminary study.

The present study investigated the relationship between late grade ≥ 2 rectal bleeding and radiation delivery time in intensity-modulated radiotherapy (IMRT) for localized prostate cancer. We analyzed patients with localized prostate cancer treated with IMRT at our institution between July 2012 and February 2018, including only those treated with 74.8 Gy in 34 fractions (i.e. a fraction dose of 2.2 Gy). To evaluate the relationship between risk factors and late grade ≥ 2 rectal bleeding, we performed univariate analyses using the Gray test and the Fine-Gray model, and multivariate analysis using the Fine-Gray model. Additionally, propensity score matching was performed to adjust for confounding factors. A total of 142 cases were analyzed. The median follow-up period was 83 months. The 7-year cumulative incidence of late grade ≥ 2 rectal bleeding for the entire cohort was 5.7%. The group with shorter delivery time (≤150 s) had a significantly lower 7-year cumulative incidence of late grade ≥ 2 rectal bleeding compared to the group with longer delivery time (>150 s) (1.5% vs. 9.7%, P = 0.036). Multivariate analysis showed a trend toward an association between longer delivery time and increased late grade ≥ 2 rectal bleeding (hazard ratio 6.1, 95% confidence interval 0.78-48, P = 0.085). In the propensity score-matched cohort, the shorter delivery time group showed a significantly lower incidence of late grade ≥ 2 rectal bleeding (0% vs. 11.1%, P = 0.024). In IMRT for localized prostate cancer, shorter radiation delivery time may reduce the incidence of late grade ≥ 2 rectal bleeding.