Comparative analysis of rectal dose parameters in image-guided high-dose-rate brachytherapy for cervical cancer with and without a rectal retractor

Abstract

The objective of this study was to determine if use of a rectal retractor (RR) in high-dose-rate intracavitary brachytherapy for cervical cancer reduces rectal dose parameters. We reviewed data obtained from patients treated with intracavitary brachytherapy for cervical cancer with and without an RR. Treatment plans for each brachytherapy fraction were separated into two groups; R group with use of an RR and P group with use of vaginal packing. Dose-volume parameters for high-risk clinical target volume (HR-CTV), rectum, sigmoid, small bowel, and vaginal surface were collected for each fraction. Rectal D2cc and International Commission on Radiation Units & Measurements (ICRU) rectal point doses were compared between groups using Student's t tests. Predictors of higher rectal D2cc were determined by univariate and multivariate regression analyses. Four hundred sixty-three brachytherapy fractions from 114 patients were used for analysis, 377 fractions with a RR (R group) and 86 with vaginal packing only (P group). Bothgroups were similar except for slightly higher mean HR-CTV and mean bladder volume in P group. Both mean ICRU rectal point dose (241.1 vs. 269.9cGy, p= 0.006) and rectal D2cc (240.6 vs. 283.6cGy, p < 0.001) were significantly higher in P group. Point A dose, HR-CTV, stage, and use of an RR were significant predictors of rectal D2cc on multivariate analysis. Our data show that use of an RR leads to lower rectal dose parameters compared with vaginal packing. Further study is needed to determine if this will lead to less long-term toxicity.