Incidence of radiation osteitis and its association with CT-derived bone density in patients undergoing neoadjuvant...

Radiation-induced reactions (RIR), including radiation osteitis (RO), insufficiency fractures (IF), and radionecrosis (RN), are potential complications after pelvic radiotherapy (RT) for rectal cancer (RCa). This study aimed to evaluate the incidence, anatomical distribution, and timing of RIR, and to explore the relationship between bone density and RIR development.

We retrospectively analyzed 133 patients with RCa who underwent pelvic MRI following neoadjuvant RT between 2015 and 2024. RIR were assessed by location (sacrum, iliac, pubic), laterality, and classified using the Radiation-Induced Sacral Changes (RISC) system. The presence of IF and RN was documented. The interval from RT to RIR detection was recorded. For patients with abdominal CT within three months before RT, bone density was measured in Hounsfield units (HU) at the L1 vertebra. Comparisons between patients with and without RIR were performed, and correlations with HU were assessed.

RIR were detected in 37 patients (27.8%). All 37 patients (100% of the RIR group) had radiation osteitis (RO), most commonly in the sacrum (54.1%). Among these, only one IF (2.7%) was identified, and no RN was observed. Median detection time was 93 days post-RT. Among patients with follow-up MRI, regression of RIR was observed in 75% of cases. Mean HU values did not differ significantly between the RIR group (145.3 ± 41.1) and controls (154.3 ± 40.7) (p = .325). No correlation was found between HU and RIR grade or stage.

RIR occurred in approximately one-quarter of patients with rectal cancer after neoadjuvant RT, with the sacrum most frequently affected. Only one IF and no RN were detected during the relatively early imaging interval; however, delayed complications could not be adequately assessed. No significant association was observed between L1 vertebral attenuation and RIR.