Poster — Thurs Eve‐38: CT Imaging in high dose rate brachytherapy for treatment of cervical cancer: Estimation of dose to bowel

Treatment of cervical cancer often involves intracavitary high dose rate (HDR) brachytherapy. Dose delivered to the bladder and rectum are typically estimated using the ICRU reference points. Dose to the sigmoid and small bowel are not estimated, yet these organs typically exhibit significant complication rates. The objective of this study was to estimate dose to the small bowel and sigmoid using CT images. Bladder and rectum dose estimates obtained from the reference point method were also compared to those obtained from CT images. Eighteen CT scans taken before or after treatment of women treated with HDR using ring and tandem applicators were included in this study. The small bowel, sigmoid, bladder and rectum were contoured and the ICRU points were digitized. The minimum dose to 2cc (D_2cc ) of each organ was calculated and normalized to % prescribed to Point A. Average D_2cc bowel dose was 70%. D_2cc bowel dose was significantly higher than both D_2cc rectal (27%) and D_2cc sigmoid (31%) doses. The average D_2cc bladder and rectal doses were 68% (p=NS) and 27% (p<0.001) of prescribed Point A dose. D_2cc bowel dose, although significantly higher than rectum and sigmoid, is within an acceptable limit. D_2cc bladder and rectum values are either not significantly different from or are significantly lower than ICRU reference values. The results of this study suggest that CT imaging is not necessary for determination of dose to organs at risk. However, image guidance is of value for identifying perforations prior to commencing treatment.