• Ameya D Puranik, Venkatesh Rangarajan, Indraja D Dev, Yash Jain, Nilendu C Purandare, Arpita Sahu, Amitkumar Choudhary, Tejpal Gupta, Abhishek Chatterjee, Aliasgar Moiyadi, Prakash Shetty, Epari Sridhar, Ayushi Sahay, Vijay M Patil, Sneha Shah, and Archi Agrawal.
• Department of Nuclear Medicine and Molecular Imaging, Tata Memorial Hospital, Homi Bhabha National Institute, Mumbai, India.
• J Neuroimaging. 2021 Nov 1; 31 (6): 1211-1218.

Background And PurposeHighergrade glial neoplasms undergo standard treatment with surgery, radiotherapy, and alkylating agents. There is often a clinical/neuroimaging dilemma in the post-treatment setting to differentiate disease recurrence from treatment-related changes. FET (fluoro-ethyl-tyrosine) PET has emerged as a molecular imaging modality for cases where MR imaging is inconclusive. This study aims to develop a cutoff on FET PET for differentiating true recurrence from post-treatment changes.MethodsWe retrospectively analyzed72 patientswith post-treatment grade 3 or 4 brain gliomas. Five to six mCi of 18 F-FET was injected and static imaging of the brain was performed at 20 min. A tumor-to-white matter (T/Wm) ratio was used as semiquantitative parameter. A T/Wm cutoff of 2.5 was used for image interpretation. Imaging findings were confirmed by either histopathologic diagnosis in a multidisciplinary joint clinic or based on follow-up of clinical and neuroimaging findings.ResultsForty-one of 72 patients (57%) showed recurrent disease on FET PET. Thirty-five of them were confirmed to have tumor recurrence; six patients showed post-treatment changes. Thirty-one of 72 patients (43%) showed post-treatment changes on FET PET; 27 were confirmed as post-treatment change and four patients had tumor recurrence on subsequent MR imaging. An optimum T/Wm cutoff of 2.65 was derived based on receiver operating characteristic analysis with a sensitivity of 80% and specificity of 87.5%.ConclusionStatic FET PET can be used as problem-solving imaging modality with a T/Wm cutoff of 2.65 to differentiate late recurrence from post-treatment changes in grade 3 or 4 brain gliomas with equivocal MR features.© 2021 American Society of Neuroimaging.

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