Late rectal toxicity determined by dose-volume parameters in computed tomography-based brachytherapy for locally advanced cervical cancer

The aim of this study was to observe the relationship between dose-volume histogram (DVH) parameters and rectal late side effects (LSE) in computed tomography (CT)-based brachytherapy (BT) for patients with locally advanced cervical cancer. In total, 144 cervical cancer patients received external beam radiotherapy and CT-based BT. The data from 111 survival cases with pelvic local control (LC) were used to analyze the relationship between DVH parameters and rectal LSE. The total doses, manifesting 2, 1, and 0.1cm(3) (D-2cc, D-1cc, and D-0.1cc) of the rectum, and D-90 for high-risk clinical target volume (HR CTV) were computed and normalized to 2Gy fractions (EQD2) using a linear-quadratic model. The rectal LSE were evaluated by the late effects in normal tissues-subjective, objective, management, and analytic (LENT-SOMA) scale. A dose-response relationship was evaluated by probit analyses. For all patients, the total rate of rectal LSE was 56%, and the rate of Grade 2 LSE was 27.4%. For the 111 survival cases with pelvic LC, the total mean for D-2cc was 71.23 +/- 5.54Gy for the rectum, and the D-2cc, D-1cc, and D-0.1cc values for Grades 2 and 3 were higher than those for Grades 0 and 1. In addition, the number of complications increased, and the complications became more severe as the dose increased, with a dose of 73.5Gy resulting in a 10% probability of Grade 3 LSE. In conclusion, DVH parameters could predict the incidence and grades of rectal LSE in CT-based BT. D-2cc showed an excellent predictive value, and 73.5Gy for D-2cc of the rectum might be considered as an alternative dose limit.