Comparing organ-at-risk doses for high-dose-rate vaginal brachytherapy between three different planning workflows

The aim of this study was to compare the organ-at-risk doses to the rectum and the bladder in postoperative endometrial cancer patients who receive high-dose-rate vaginal brachytherapy (HDR-VB), when using three different methods of treatment planning: (Workflow A) individualized treatment planning before every fraction, (Workflow B) individualized treatment planning for first fraction only), and (Workflow C) using a template plan based on applicator choice and prescription specifics without patient-specific imaging or planning (standardized template approach).

Alternative plans were retrospectively created using workflows B and C for 22 patients who previously received postoperative HDR-VB using a vaginal cylinder and planned using Workflow A for endometrial cancer. The rectum and bladder were contoured on the CTs used for each fraction for dose comparison between the three methods. D₅₀, D_2cc, D_1cc, D_0.1cc, and V₁₀₀ of the bladder and the rectum were compared using the two-sided Wilcoxon signed-rank test.

A total of 123 fractions were available for comparison. For Workflow A vs. Workflow B, there was no significant difference for any rectal or bladder dosimetric parameter. For Workflow A vs. Workflow C, Workflow A delivered a significantly higher median dose to the rectum than Workflow C for D₅₀, D_2cc, D_1cc, and V₁₀₀. Workflow C delivered a significantly higher dose to the bladder than Workflow A: D_2cc, D_1cc, D_0.1cc, and V₁₀₀. However, the magnitudes of the differences were small; the dose index difference was >75 cGy for only two fractions.

Plan standardization in HDR-VB may result in considerable time and cost savings with minimal organ-at-risk dose differences.