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Response assessment in the context of immunomodulatory treatments represents a major challenge for the medical imaging community and requires a multidisciplinary approach with involvement of oncologists, radiologists, and nuclear medicine specialists. There is evolving evidence that [18F]FDG PET/CT is a useful diagnostic modality for this purpose. The clinical indications for, and the principal aspects of its standardization in this context have been detailed in the recently published “Joint EANM/SNMMI/ANZSNM practice guidelines/procedure standards on recommended use of [18F]FDG PET/CT imaging during immunomodulatory treatments in patients with solid tumors version 1.0”. These recommendations arose from a fruitful collaboration between international nuclear medicine societies and experts in cancer treatment. In this perspective, the key elements of the initiative are reported, summarizing the core aspects of the guidelines for radiologists and nuclear medicine physicians. Beyond the previous guidelines, this perspective adds further commentary on how this technology can advance development of novel therapeutic approaches and guide management of individual patients.

Central nervous system (CNS) malignant tumors are usually treated with different combinations of surgery, radiotherapy and chemotherapy to achieve a radical treatment. After therapy, conventional imaging procedures (CT and MR) are useful to detect disease relapse but a correct differential diagnosis in presence post-surgical fibrosis, radionecrosis or oedema (benign conditions) may sometime be difficult. CNS shows physiologically an intense uptake of FDG and consequently, small and/or hypo/isometabolic malignant lesions are very difficult to detect, as they may be masked by the hypermetabolic surrounding tissue. 11C-Methionine is a radiolabeled aminoacid that physiologically do not accumulate into the brain, nor in case of benign conditions such as fibrosis, necrosis or oedema. On the other side, malignant lesions (although low grade) present an increased 11C-Methionine uptake due to an increased proteic metabolism and vascular permeability. Therefore 11CMethionine has optimal tumor-to-background ratio, making this radiotracer very useful to study CNS malignant tumors. The most appropriate indication for 11C-Methionine PET is the presence of non conclusive conventional imaging procedures, not allowing to discriminate between benign conditions and disease relapse. Other applications of 11C-Methionine PET are the definition of the radiotherapy field, the localization of the most metabolic area inside a mass to guide the biopsy and the early evaluation of radiotherapy effect, but all these applications are marginal and not yet validated.

Carbon-11 methionine (11C-Methionine) is a radio-labeled amino acid currently utilized in Positron Emission Tomography (PET) for imaging primary and metastatic brain tumors. Its clinical use relies mostly on oncologic applications, but the tracer has the potential to investigate other non-malignant conditions. So far, very limited evidence concerns the use of 11C-Methionine in patients suffering from seizure; however, the tracer can find a proper utilization in this setting especially as a diagnostic complement to 18F-Fluorodeoxyglucose (18F-FDG).