Rectal and bladder deformation and displacement during preoperative radiotherapy for rectal cancer: Are current margin guidelines adequate for conformal therapy?

With a limited number of CBCT scans, we found that the rectum tended to remain within 1.5 cm of the initial location on treatment planning CT. However, an anterior margin of 1.5 cm beyond the posterior bladder edge provides better coverage of the mesorectum than 1 cm for the initial CTV.