Purpose: To assess the dose to the organs at risk (OARs) and utility of repeated OAR dose-volume histogram calculations in multifraction high-dose-rate vaginal cylinder brachytherapy using 3-dimensional imaging. Methods and Materials: Thirty-eight patients (125 fractions) received high-dose-rate brachytherapy to the vaginal vault between January 2005 and October 2005. All patients emptied their bladders before insertion. After each insertion, a CT scan with 2.5-mm slices and contours of the bladder, rectum, and sigmoid was performed. Dose-volume histograms were generated for the D 0.1cc and D 2cc for the OAR using a software program created at our institution. Variance component models estimated the within-patient variance of the dose to the OAR between fractions. Predictors of dose to the OAR were identified using linear mixed models. Results: The within-patient coefficients of variation of total D 0.1cc dose were bladder 14.0%, rectum 7.9%, and sigmoid 27.6%; for D 2cc, these were 8.1%, 5.9%, and 20.3%, respectively. Intraclass correlations ranged from 0.27 to 0.79. Larger OAR predicted greater total D 0.1cc and D 2cc. Other predictors of total D 0.1cc and D 2cc dose included the size of the cylinder and the length of the treatment field for rectum. Conclusions: CT simulation provides a noninvasive assessment of the dose to the bladder, rectum, and sigmoid. The small within-patient variation in doses to the bladder and rectum do not support reporting doses to the OARs beyond the initial fraction.
- HDR brachytherapy
- Vaginal vault
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging