Computed Tomography-Based High-Dose-Rate Intracavitary Brachytherapy for Uterine Cervical Cancer: Preliminary Demonstration of Correlation Between Dose-Volume Parameters and Rectal Mucosal Changes Observed by Flexible Sigmoidoscopy

Purpose: To compare the dose-volume histogram (DVH) parameters obtained by three-dimensional gynecologic brachytherapy planning with the rectosigmoid mucosal changes observed by flexible sigmoidoscopy. Methods and Materials: Between January 2004 and July 2005, 71 patients with International Federation of Gynecology and Obstetrics Stage IB-IIIB uterine cervical cancer underwent computed tomography-based high-dose-rate intracavitary brachytherapy. The total dose (external beam radiotherapy [RT] plus intracavitary brachytherapy) to the International Commission of Radiation Units and Measurements rectal point (ICRU_RP) and DVH parameters for rectosigmoid colon were calculated using the equivalent dose in 2-Gy fractions (α/β = 3 Gy). Sigmoidoscopy was performed every 6 months after RT, with the 6-scale scoring system used to determine mucosal changes. Results: The mean values of the DVH parameters and ICRU_RP were significantly greater in patients with a score of ≥2 than in those with a score <2 at 12 months after RT (ICRU_RP, 71 Gy_α/β3 vs. 66 Gy_α/β3, p = 0.02; D_0.1cc, 93 Gy_α/β3 vs. 85 Gy_α/β3, p = 0.04; D_1cc, 80 Gy_α/β3 vs. 73 Gy_α/β3, p = 0.02; D_2cc, 75 Gy_α/β3 vs. 69 Gy_α/β3, p = 0.02). The probability of a score of ≥2 showed a significant relationship with the DVH parameters and ICRU_RP (ICRU_RP, p = 0.03; D_0.1cc, p = 0.05; D_1cc, p = 0.02; D_2cc, p = 0.02). Conclusion: Our preliminary data have shown that DVH values of the rectosigmoid colon obtained by computed tomography-based three-dimensional brachytherapy planning are reliable and predictive of score ≥2 rectosigmoid mucosal changes.