CT-based dose-volume parameters of the rectum and late rectal complications in patients with cervical cancer treated with high-dose-rate intracavitary brachytherapy

Purpose: To evaluate the efficacy of CT-based dose-volume parameters of the rectum as the predictive factors for late rectal complications (LRC) in patients with cervical cancer treated with radiotherapy alone. \nMethods and Materials: Eighty-four patients treated with radiotherapy alone between January 2000 and December 2004 were retrospectively analyzed. All patients received the combination of external beam radiotherapy (EBRT) and high-dose-rate intracavitary brachytherapy (HDR-ICBT). The median total dose of EBRT was 50 Gy, consisting of whole pelvic irradiation and central shielding pelvic irradiation. The median total dose to point A in HDR-ICBT was 24 Gy in 4 fractions. HDR-ICBT was prescribed using X-ray based two-dimensional dosimetry and planning. Patients underwent CT scans of the pelvis with the applicators in place to generate three-dimensional dose distributions. The external contours of the rectum were delineated on the CT images, and the minimum doses delivered to 0.1cc, 1cc, 2cc, and 5cc of the most irradiated rectal volumes were determined from the dose-volume histgrams. The ICRU rectal reference point dose was derived from the conventional method. The doses in EBRT and ICBT were transformed to the biologically equivalent doses in 2 Gy fractions (EQD2) using a/B ratio of 3 Gy, and the total rectal doses for dose-volume parameters (D0.1cc, D1cc, D2cc, D5cc, and DICRU) were calculated. The correlation between the dose-volume parameters and the actuarial rate of LRC was analyzed.Results: The median follow-up duration for all patients was 46 months (range, 12-79 months). Twenty patients developed LRC (Grade 1: 12, Grade 2: 8). The 5-year actuarial rate of LRC was 27.4%. There was a statistically significant difference in D0.1cc, D1cc, D2cc, and D5cc between patients with and without LRC (p 60 Gy showed significantly greater incidence of LRC (p