PET/MRI is useful for early detection of pelvic insufficiency fractures after radiotherapy for cervical cancer.

Radiotherapy (RT) is used to manage cervical cancer, and pelvic insufficiency fracture (PIF) is known as a late complication of RT. The present study identified risk factors for PIF after radiotherapy for cervical cancer, and investigated its incidence rate. It also considered the usefulness of positron emission tomography/magnetic resonance imaging (PET/MRI) in PIF diagnosis. A total of 149 patients with cervical cancer who received definitive or adjuvant RT with/without concurrent chemotherapy between January 2013 and December 2018 were investigated in the present study and followed up for more than one month after RT at Kobe University Hospital. The median follow-up period was 32 months (range, 1-87 months), and the median age of all patients was 66 years (age range, 34-90 years). Computed tomography (CT), MRI, PET/CT or PET/MRI were used for image examination. Among the 149 patients, 31 (20.8%) developed PIF. The median age of these patients was 69 years (age range, 44-87 years). Univariate analysis using the log-rank test demonstrated that age (≥60 years) was significantly associated with PIF. The median maximum standardized uptake value of PIF sites on PET/CT was 4.32 (range, 3.04-4.81), and that on PET/MRI was 3.97 (range, 1.21-5.96) (P=0.162). Notably, the detection time of PIF by PET/MRI was significantly earlier compared with PET/CT (P<0.05). The incidence of PIF after RT for cervical cancer was 20.8%, and age was significantly associated with risk factors for such fractures. Taken together, these results suggest that PET/MRI, which offers the advantage of decreased radiation exposure to the patient, is useful for diagnosing PIF and can detect it earlier than PET/CT imaging.