Postirradiation changes in the pelvis: assessment with MR imaging.

Magnetic resonance (MR) imaging features of pelvic radiation change were assessed in 51 patients and were correlated with tumor and critical tissue radiation dose, time after treatment, and clinical symptoms. The severity of MR tissue changes was graded. Radiation tissue toxicity increased significantly when the dose exceeded 4,500 cGy, with the incidence of marked bladder and rectal changes rising from 8% to 51% and from 24% to 48%, respectively. Similar dose-related changes were seen in other pelvic organs. All grades of tissue change were seen in the bladder and rectum regardless of the time from start of therapy. All patients who exhibited clinical grade 2 or 3 bladder and rectal changes showed moderate or severe changes on MR images. In asymptomatic patients, minimal MR changes were seen in the bladder (47%) and in the rectum (33%). The accuracy of MR imaging in differentiating between radiation damage and residual/recurrent tumor varied with the primary tumor site, being excellent for recurrent cervical cancer and less so for rectal carcinoma.