18F-FDG-PET/CT in the quantification of photon radiation therapy-induced vasculitis.

Radiation therapy (RT) is an important component of care for head and neck cancers (HNC). Photon RT vasculitis is a complication of incidental dose delivery to nearby vascular structures. However, optimal methods for early diagnosis are not clearly established. The aim of this study was to evaluate 18F-FDG-PET/CT in detecting radiation-induced vasculitis of the left common carotid (LCC) and the arch of the aorta (AoA) in patients treated for HNC. 18F-FDG-PET/CT scans obtained before RT (Pre-RT) and 3 months after RT (Post-RT) were retrospectively reviewed in 30 HNC patients (25 males, 5 females; average age 57.9±8.1 years) treated with photon RT. All subjects underwent 18F-FDG-PET/CT imaging 60 minutes after 5.0 MBq/kg 18F-FDG injection. Average standard uptake values (Avg SUVmean) of the LCC and AoA were obtained by global assessment. A two-tailed paired t-test was used to assess the difference in Avg SUVmean between pre- and post-RT imaging. Subjects demonstrated significant increased Avg SUVmean within the LCC post-RT (pre = 1.42, post = 1.65, P<0.001), with a mean increase of 0.23 SUV. Similarly, subjects exhibited higher 18F-FDG uptake in the AoA post-RT (pre = 1.44, post = 1.69, P<0.01), with a mean increase of 0.23 SUV. 18F-FDG-PET/CT may be used to detect and quantify photon RT vasculitis in HNC patients. Further investigation is warranted to evaluate the clinical implications of this pathology and the role for alternative treatment strategies in minimizing tissue toxicity. AJNMMI