3504 - Sacral and Other Pelvic Bone Fractures Following Short-Course Radiation Therapy and Consolidation Chemotherapy for Rectal Cancer

02:30pm - 03:45pm PT

Hall F

Screen: 4

POSTER

Presenter(s)

Panos Papanikolaou, MD - Johns Hopkins Hospital, Baltimore, MD

P. A. Papanikolaou¹, I. C. Liu¹, E. Christenson², A. Narang¹, and J. J. Meyer¹; ¹Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University School of Medicine, Baltimore, MD, ²Department of Oncology, Johns Hopkins University School of Medicine, Baltimore, MD

Purpose/Objective(s): Sacral insufficiency fractures (SIFs) are a recognized late complication of pelvic radiation therapy (RT), yet there are limited data characterizing their incidence and associated risk factors following neoadjuvant short course radiation therapy (SCRT, 5 Gy X 5 fractions) for rectal cancer. In this large single-institution study we evaluated sacral and other pelvic bone fractures following neoadjuvant SCRT used as part of total neoadjuvant therapy (TNT)/near-total neoadjuvant therapy (nTNT) for rectal cancer.

Materials/Methods: We retrospectively reviewed patients who received SCRT as part of TNT/nTNT for newly diagnosed rectal adenocarcinoma at a single institution between 2017 and 2024. All patients were treated with upfront SCRT followed by consolidation treatment with either CAPOX or FOLFOX-based chemotherapy, with subsequent surgery or nonoperative management. Patients with no available follow-up imaging were excluded. Demographic, clinical, and treatment-related data were collected, including baseline BMI, documented history of osteoporosis, RT technique (3DCRT vs IMRT), and surgical management. Surveillance imaging studies (either CT or MRI) were reviewed for SIFs and other pelvic fractures as identified by the reading radiologist. Fractures were classified as symptomatic or asymptomatic. Univariate and multivariable analyses were performed to identify factors associated with SIF development.

Results: Of 171 eligible patients (median age 58, range 31–82), 13 (7.6%) developed SIFs at a median follow up time of 2.2 years. The two-year actuarial incidence of SIF development was 8.8%. Median time to SIF was 1.64 years (range 0.75–4.56) post-RT. Of the 13 patients with SIFs, 4 (30.8%) had additional pelvic fractures identified (iliac = 2, pubis = 2). MRI was the primary imaging modality for detection (69.2%). Eleven (84.6%) of the sacral fractures were asymptomatic, and the 2 patients with symptomatic fractures had concurrent pubic ramus fractures. Female sex (HR 6.01, 95% CI 1.62–22.3, p=0.0073) and documented history of osteoporosis (HR 7.37, 95% CI 2.20–24.7, p=0.0012) were significantly associated with increased SIF risk on both univariate and multivariable analysis.

Conclusion: In this large cohort of patients treated with upfront SCRT as part of TNT/nTNT treatment for rectal cancer, the two-year actuarial rate of sacral fracture development was 8.8%, and most fractures were asymptomatic. Female sex and documented history of osteoporosis were related to the development of sacral fractures, and other pelvic bone fractures were rare.