Effect of rectal enema on intrafraction prostate movement during image-guided radiotherapy

Introduction Rectal volume and movement are major factors that influence prostate location. The aim of this study was to assess the effect of a rectal enema on intrafraction prostate motion. Methods The data from 12 patients with localised prostate cancer were analysed. Each patient underwent image‐guided radiotherapy (RT), receiving a total dose of 70 Gy in 28 fractions. Rectal enemas were administered to all of the patients before each RT fraction. The location of the prostate was determined by implanting three fiducial markers under the guidance of transrectal ultrasound. Each patient underwent preparation for IGRT twice before an RT fraction and in the middle of the fraction. The intrafraction displacement of the prostate was calculated by comparing fiducial marker locations before and in the middle of an RT fraction. Results The rectal enemas were well tolerated by patients. The mean intrafraction prostate movement in 336 RT fractions was 1.11 ± 0.77 mm (range 0.08–7.20 mm). Intrafraction motions of 1, 2 and 3 mm were observed in 56.0%, 89.0% and 97.6% of all RT fractions, respectively. The intrafraction movements on supero‐inferior and anteroposterior axes were larger than on the right‐to‐left axes (P