To evaluate the prostate and seminal vesicle motion in patients during both simulation and radiotherapy by rectal gas removal.

A total of 34 patients were treated in a whole pelvic radiotherapy (WPRT) arm and 42 patients in a non-WPRT arm. Of the 76 patients, 42 (26 in the non-WPRT arm and 16 in the WPRT arm) were instructed to insert their index finger and wash their rectums to evacuate their rectal gas. In addition to the planning computed tomography scan, three subsequent computed tomography scans were obtained during RT. The organs were outlined on each computed tomography image. Changes in the position of the prostate and seminal vesicles were analyzed using the center of mass (COM) coordinate system. The time trend, overall variations, systematic variations, and random variations were analyzed.

The average cross-sectional area in the rectal gas removal group was significantly smaller than in all patients and in the WPRT arm. The vector of the prostate and seminal vesicle displacement for the rectal gas removal group was significantly smaller than in all patients. With rectal gas removal, the 95% confidence limit of the prostate displacement vector was reduced by 2.3 mm in the non-WPRT arm and 2.9 mm in the WPRT arm. The 95% confidence limit of the seminal vesicle displacement vector was reduced by 0.3 mm in the non-WPRT arm and 4.4 mm in the WPRT arm.

Using rectal gas removal, the cross-sectional area could be decreased, resulting in reduced motion and margins for the prostate and seminal vesicles. This is especially important for WPRT patients who require RT to the prostate, seminal vesicles, and pelvic lymph nodes.