This prospective phase 2 study followed 113 patients post-radiation for cervical or endometrial cancer. All patients received IMRT and serial surveillance MRI. After a median follow-up of 26 months, radiographic pelvic insufficiency fractures occurred in 33 patients (29%), typically within 9 months of treatment. Just over half of these patients (n=19) were symptomatic with mechanical pelvic pain. Two-thirds of fractures were multifocal, most commonly involving the sacrum, ilium, and para-acetabular region. Postmenopausal status and elevated baseline bone turnover (i.e. serum t-PINP ≥55 ng/mL) independently identified women at highest risk for pelvic insufficiency fractures, whereas dosimetric parameters did not, suggesting that underlying bone health may drive susceptibility. Finally, serial MRI demonstrated that fracture burden often progressed for up to 2 years before gradually regressing, highlighting the dynamic natural history of these injuries. | Huang, Int J Radiat Oncol Biol Phys 2026
