Purpose: This study aims to clarify the time-course of gas accumulation in the rectum during treatment as guidance for the management of rectal volumes.
Materials and methods: We reviewed 2042 sets (35.2 sets per patient) of anteroposterior and right-left mega voltage (MV) images obtained for daily set-up from 58 patients who underwent radical external beam radiotherapy for localised prostate cancer. The patients were instructed to take magnesium oxide tablets during radiotherapy. They were also encouraged to avoid foods that might cause intestinal gas during radiotherapy. Gas accumulation in the rectum was graded into three classes by the same radiation oncologist. If no gas was seen in the rectum, it was classified as grade 0. A small amount of gas was classified as grade 1, whereas a marked amount of gas that required removal was classified as grade 2.
Results: Of the 2042 sets of MV images, grades 1 and 2 gas accumulation were seen in 332 (16%) and 156 (8%), respectively. By the trend test, gas accumulation significantly decreased towards the end of treatment (P = 0.02 for grade 1 or 2 and P = 0.02 for grade 2). On multivariate analysis, we did not identify any significant independent predictors for either baseline gas accumulation or gas reduction.
Conclusion: Gas accumulation tended to decrease until the end of treatment. This tendency should be reconfirmed by other institutions.
Keywords: gas; prostate cancer; radiotherapy; rectal volume.
© 2013 The Royal Australian and New Zealand College of Radiologists.