ABSTRACT
<p><b>OBJECTIVE</b>To investigate positron-emission tomography-computed tomography (PET/CT) findings of radiation encephalopathy (RE) following radiotherapy for nasopharyngeal carcinoma (NPC), observe the metabolic changes of the compromised brain tissues, and postulate the clinical classification of RE to provide reference for its diagnosis.</p><p><b>METHODS</b>This study included 53 pathologically confirmed NPC patients who received previous radical radiotherapy, and the diagnosis of RE was established according to the clinical manifestations and CT/PET findings. All the patients underwent PET/CT whole-body and head scans, and the image data were evaluated along with the clinical data of the patients.</p><p><b>RESULTS</b>RE most frequently involved the lateral or bilateral inferior temporal lobes. PET identified hypometabolic changes in the bilateral temporal lobes of 35 patients (70 lobes) and in the lateral temporal lobe of 18 patients (18 lobes). According to the PET/CT findings, the lesions were classified into 3 types, namely the oedema type (56 temporal lobes), liquefactive necrosis type (10 temporal lobes), and atrophic calcification type (22 temporal lobes). One patient with oedema type lesion received neurotrophic treatment and recovered completely with normal brain tissue density and metabolism, but the oedema type lesions in 2 patients progressed into to atrophic calcification type; the liquefactive necrotic lesions in another 2 patients also progressed into atrophic calcification type.</p><p><b>CONCLUSION</b>RE patients exhibit significant hypometabolic changes in the inferior temporal lobe on PET. According to the findings by PET/CT, RE can be classified into the oedema type, liquefactive necrosis type, and atrophic calcification type, and lesions of the former two types may progress into the third type.</p>