Bone complications after pelvic radiation therapy: evaluation with MRI.

INTRODUCTION: The purpose of this study was to assess the incidence, distribution and MRI characteristics of pelvic bone complications after radiation therapy.

METHODS: The medical charts of 345 patients who received pelvic radiation therapy were retrospectively reviewed. A total of 122 patients, 99 women and 23 men, with a mean age of 57 (range 32-87 years) were included in this study. The MR images were retrospectively reviewed by two radiologists.

RESULTS: Fatty replacement of bone marrow was seen in all patients. Pelvic bone complications and focal red marrow changes were identified in a total of 38 patients (31.1%). Pelvic insufficiency fracture was diagnosed in 17 patients (13.9%, with a total of 64 lesions) and radiation osteitis was diagnosed in 5 patients (4.1%, with a total of 13 lesions). Avascular necrosis of the femoral head was detected in one patient (0.8%). Focal red bone marrow changes were seen in 15 patients (12.3%). The median time from the end of radiotherapy to the diagnosis of pelvic bone complications or changes was 25 months (range 2-45 months). The 1-, 2-, and 3-year cumulative incidences were 22%, 41% and 49%, respectively. The distribution of insufficiency fractures was as follows: sacral ala, sacral body, ilium, acetabulum, pubis and lumbar spinal vertebra. The distribution of radiation osteitis was as follows: sacral ala, ilium and pubis.

CONCLUSION: Radiation-induced pelvic bone complications are not uncommon, and knowledge of characteristic imaging patterns is essential in order to rule out bone metastases and to avoid inaccurate or excessive treatment.