Highlights•18.4% patients of this cohort experienced Pelvic Insufficiency Fractures (PIFs), which indicate that this complication is not so rare affecting one in 5 patients.•Univariate analysis showed that older age (p < 0.01), postmenopausal status at baseline (p < 0.01), and lower sacral and spinal bone mineral density at baseline (respectively p < 0.001 and p < 0.01) were significantly associated to all sites of PIFs.•The novelty of this study was the calculation of BMD through computed tomography planning for radiotherapy.