Risk Factors for Sacral Insufficiency Fracture After Pelvic Irradiation for Cervical Cancer

BACKGROUND/AIM: Sacral insufficiency fracture (SIF) is an important late adverse event after pelvic irradiation for cervical cancer and may impair long-term quality of life. This retrospective study aimed to identify clinical and dosimetric factors associated with SIF after pelvic radiotherapy for cervical cancer. PATIENTS AND METHODS: We analyzed 121 patients treated between 2014 and 2022, including 73 who received curative radiotherapy and 48 who underwent postoperative adjuvant radiotherapy. The sacrum was manually contoured on planning computed tomography (CT), and dose-volume histogram parameters, including mean sacral dose, V30, and V40, were evaluated. Sacral CT attenuation in Hounsfield units (HU) was also measured. RESULTS: SIF was diagnosed based on follow-up CT, and in patients with SIF, site-specific dose metrics were additionally assessed by fusing planning CT with follow-up CT. SIF occurred in 31 patients (25.6%). In univariate analyses, age ≥55 years, body mass index (BMI) ≤20.5, mean sacral dose ≥38 Gy, and sacral HU <142 were significantly associated with SIF. In multivariate analysis, low BMI and higher mean sacral dose remained independently associated with SIF. Receiver operating characteristic analysis identified 38 Gy as the optimal cut-off value for mean sacral dose in this cohort. Site-specific analysis suggested that fractures tended to occur in relatively high-dose regions within the sacrum. CONCLUSION: Low BMI and higher mean sacral dose were independently associated with SIF after pelvic irradiation for cervical cancer. The 38 Gy threshold and the site-specific dose findings should be considered exploratory and require further validation.