Objectives: The purpose of this retrospective study was to evaluate patterns and prevalence of post-radiation changes to decrease the false positive results in Positron emission tomography/ computerized tomography (PET/CT) scans. Methods: 140 fluorine-18 fluorodeoxyglucose (18F-FDG)-PET/CT scans of 30 patients with head and neck cancer without prior surgical intervention were retrospectively reviewed. Baseline and follow-up PET/CT scans were reviewed. The main period of follow-up was 18.3 months. According to abnormal FDG uptake or abnormal CT findings nine categories of post-radiations changes were selected: cervical spinal cord uptake, esophageal uptake, Lung changes, reactive lymph node, neck muscles uptake, vascular uptake (carotid or subclavian arteries), soft tissue uptake at the radiation field, uptake at the dental regions and miscellaneous (parotid uptake, shoulder drop as a result of radiation induced nerve injury). All these changes were proved to be benign process either by repeated PET/CT follow-up scans or by pathological examinations. We calculated the percentage and the time of appearance and disappearance of each category.
Results: Soft tissue uptake was present in 21 (70%) of patients. Muscles uptake was present in 20 (66.7%) of patients. 17 patients (56.7%) had uptake at the dental regions. 16 patients (53.3%) had esophageal uptake. 13 patients (43.3%) had cervical spinal cord uptake. of 11 patients (36.7%) had Lung changes. 10 patients (33.3%) had vascular uptake. 8 patients (26.7%) had reactive lymph node. Bilateral parotid uptake was in three patients (10%) and shoulder drop was in one patient (3.3%). All studied patients had at least two post radiation changes. Conclusions: We conclude that significant post-radiation changes were encountered. Muscle uptake, soft tissue uptake and uptake in dental region were the most common changes. It is important to be aware of these changes to avoid false interpretations of PET/CT scans.