Reduction in rectal doses of pelvic radiotherapy with excessive rectal gas extraction: a single-institution case report.

During radiotherapy for pelvic tumors, there might be insufficient radiation doses delivered that result from concerns of immediately adjacent critical organs, most notebly the rectum. Several measures have been proposed to reduce the rectal doses, such as use of a radioprotective spacer to shift the rectum away from the lesion or an endorectal balloon to reduce the internal target volume (ITV). The removal of rectal gas is supposed to achieve the similar effect by reducing the rectal volume and ITV. This is because the distance of the rectum to lesions can be increased with decreasing rectal volumes, which also makes it easy for physicists to avoid the rectum during field design. Besides, a reduced ITV can be obtained due to stability in rectal volume, as with use of an endorectal balloon. The procedure is most suitable for patients receiving stereotactic body radiotherapy (SBRT) and high dose rate brachytherapy (HDR-BR) because of limited treatment sessions. In this study, we showed that the rectal dose decreased significantly with rectal gas extraction, as manifested by dose parameters of D2 cm3 and D0.1 cm3 (the doses delivered to the most exposed 2 cm, 3 and 0.1 cm3 of the rectum, respectively). This technique is especially benefitable for candidates with excessive rectal gas fillings.