Sacral Fractures After Short-Course Radiation Therapy for Rectal Cancer

Purpose: Fractures of the sacrum are a recognized late complication of pelvic radiation therapy, yet their incidence and associated risk factors following short-course radiation therapy for rectal cancer are poorly characterized. Methods:We conducted a single-institution retrospective study of patients with rectal adenocarcinoma treated with neoadjuvant short-course radiation therapy and consolidation chemotherapy as part of total neoadjuvant/near-total neoadjuvant therapy to determine the incidence of sacral fractures.Demographic, clinical and treatment characteristics were collected.The incidence of sacral and other pelvic bone fractures was calculated.Univariate and multivariate Cox regression models were used to explore the association of sacral factures with patient-level characteristics.Results: Of the 171 eligible patients, the crude incidence of sacral fracture development was 7.6%, and the two-year cumulative incidence was 8.8% after a median follow-up of 2.2 years.Median time to sacral fracture development was 1.64 years.Four patients (30.8%) had multiple pelvic bone fractures.The majority of patients (84.6%) with sacral fracture development were asymptomatic.On multivariable analysis, female sex (aHR 6.01, 95% CI 1.62-22.3,p = 0.0073) and history of osteoporosis (aHR 7.37, 95% CI 2.20-24.7,p = 0.0012) were predictors of sacral fracture development. Conclusions:We present one of the largest series assessing the incidence of sacral fractures following short-course radiation therapy for rectal cancer.The overall fracture incidence was low.In most cases fractures were asymptomatic.The incidence of other pelvic bone fractures was very low.