To assess the incidence, predisposing factors, and clinical characteristics of insufficiency fractures (IF) in patients with prostate cancer, who received pelvic radiotherapy as part of their definitive treatment.

The charts of 134 prostate cancer patients, who were treated with pelvic radiotherapy between 1998 and 2007 were retrospectively reviewed. IF was diagnosed by bone scan and/or CT and/or MRI. The cumulative incidence of symptomatic IF was estimated by actuarial methods.

Eight patients were identified with symptomatic IF after a median follow-up period of 68 months (range, 12-116 months). The 5-year cumulative incidence of symptomatic IF was 6.8%. All patients presented with lower back pain. Insufficiency fracture developed at a median time of 20 months after the end of radiotherapy and was managed conservatively without any need for hospitalization. Three patients were thought to have metastatic disease because of increased uptake in their bone scans. However, subsequent CT and MR imaging revealed characteristic changes of IF, avoiding any further intervention. No predisposing factors for development of IF could be identified.

Pelvic IF is a rare complication of pelvic radiotherapy in prostate cancer. Knowledge of pelvic IF is essential to rule out metastatic disease and prevent unnecessary treatment, especially in a patient cohort with high-risk features for distant spread.