Incidence of osteoradionecrosis presented in 18F-FDG PET-CT of head and neck cancer patients after radiotherapy

Objectives Osteoradionecrosis (ORN) is one of the most serious complications after radiotherapy due to damages to the normal bony tissues after high dose of radiation. ORN may occur years after radiotherapy and clinical manifestation may mimic disease recurrence. This study aimed to determine the incidence of ORN shown in 18F-FDG PET-CT of head and neck (H&N) cancer patients who received radiotherapy.

Methods A 6-year-period retrospective analysis of 386 PET-CT scans of post-radiotherapy H&N cancer patients was performed. Two main indications for the scans were; to monitor radiotherapeutic response, and to confirm/exclude suspected disease recurrence. The total dose of radiotherapy, time duration after radiotherapy and SUVmax were recorded. Final diagnosis was reached by biopsy, clinical and imaging follow-up.

Results Out of 386 scans 41 cases demonstrated abnormal increased bony/cartilaginous uptake. Of which 22 were confirmed as residual local osseous involvement of pre-existed bony disease, 8 due to disease recurrence at new sites of bone/cartilage, 7 due to benign causes such as dental infection, and 4 due to ORN with no previous local osseous involvement. The incidence of ORN is 1.0%(4/136) of total PET-CT scans and 9.8%(4/41) of increased osseous FDG-uptake. Average occurrence of ORN was 6 months after radiotherapy (range 2 months to 3 years), all received over 60 Gray of radiation dose. SUVmax of ORN was 6.6 (range 3.2-8.9), not significantly different from disease recurrence (SUVmax 8.2, range 4.4-16.9, P=0.23).

Conclusions ORN is a rare complication after high-dose radiotherapy seen in PET-CT (1.0%), but when abnormal increased osseous FDG-uptake is seen within the previously radiotherapy field then ORN should be considered as a differential diagnosis (9.8% of increased osseous uptake). ORN may occur years after treatment and symptoms mimic disease recurrence. There is no significant difference in SUVmax values between ORN and recurrence.