The Role of PET Imaging in the Differential Diagnosis between Radiation Necrosis and Recurrent Disease in Irradiated Adult-Type Diffuse Gliomas: A Systematic Review

SIMPLE SUMMARY: Adult-type diffuse gliomas are the most common primary brain tumours. Radiotherapy is one of the therapeutic options offered upfront and/or after surgery both in naïve and recurrent patients. Magnetic resonance imaging (MRI) is the recommended technique for treatment response evaluation and follow-up. However, in patients previously treated with radiotherapy, MRI might be difficult to interpret since recurrent disease and treatment-related changes often appear similar. Therefore, other imaging modalities, including positron emission tomography (PET), have been explored in this clinical setting. The present work focused on PET imaging in adult-type diffuse gliomas aims to review available literature data and assess the capability of PET in discriminating between radiation necrosis and disease relapse in irradiated patients. ABSTRACT: Adult-type diffuse gliomas are treated with a multimodality treatment approach that includes radiotherapy both in the primary setting, and in the case of progressive or recurrent disease. Radiation necrosis represents a major complication of radiotherapy. Recurrent disease and treatment-related changes are often indistinguishable using conventional imaging methods. The present systematic review aims at assessing the diagnostic role of PET imaging using different radiopharmaceuticals in differentiating radiation necrosis and disease relapse in irradiated adult-type diffuse gliomas. We conducted a comprehensive literature search using the PubMed/MEDLINE and EMBASE databases for original research studies of interest. In total, 436 articles were assessed for eligibility. Ten original papers, published between 2014 and 2022, were selected. Four articles focused on [(18)F]FDG, seven on amino acid tracers ([(18)F]FET n = 3 and [(11)C]MET n = 4), one on [(11)C]CHO, and one on [(68)Ga]Ga-PSMA. Visual assessment, semi-quantitative methods, and radiomics were applied for image analysis. Furthermore, 2/10 papers were comparative studies investigating different radiopharmaceuticals. The present review, the first one on the topic in light of the new 2021 CNS WHO classification, highlighted the usefulness of PET imaging in distinguishing radiation necrosis and tumour recurrence, but revealed high heterogeneity among studies.