RT Journal Article SR Electronic T1 Treatment Monitoring of Immunotherapy and Targeted Therapy Using 18F-FET PET in Patients with Melanoma and Lung Cancer Brain Metastases: Initial Experiences JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 464 OP 470 DO 10.2967/jnumed.120.248278 VO 62 IS 4 A1 Galldiks, Norbert A1 Abdulla, Diana S.Y. A1 Scheffler, Matthias A1 Wolpert, Fabian A1 Werner, Jan-Michael A1 Hüllner, Martin A1 Stoffels, Gabriele A1 Schweinsberg, Viola A1 Schlaak, Max A1 Kreuzberg, Nicole A1 Landsberg, Jennifer A1 Lohmann, Philipp A1 Ceccon, Garry A1 Baues, Christian A1 Trommer, Maike A1 Celik, Eren A1 Ruge, Maximilian I. A1 Kocher, Martin A1 Marnitz, Simone A1 Fink, Gereon R. A1 Tonn, Jörg-Christian A1 Weller, Michael A1 Langen, Karl-Josef A1 Wolf, Jürgen A1 Mauch, Cornelia YR 2021 UL http://jnm.snmjournals.org/content/62/4/464.abstract AB We investigated the value of O-(2-18F-fluoroethyl)-l-tyrosine (18F-FET) PET for treatment monitoring of immune checkpoint inhibition (ICI) or targeted therapy (TT) alone or in combination with radiotherapy in patients with brain metastasis (BM) since contrast-enhanced MRI often remains inconclusive. Methods: We retrospectively identified 40 patients with 107 BMs secondary to melanoma (n = 29 with 75 BMs) or non–small cell lung cancer (n = 11 with 32 BMs) treated with ICI or TT who had 18F-FET PET (n = 60 scans) for treatment monitoring from 2015 to 2019. Most patients (n = 37; 92.5%) had radiotherapy during the course of the disease. In 27 patients, 18F-FET PET was used to differentiate treatment-related changes from BM relapse after ICI or TT. In 13 patients, 18F-FET PET was performed for response assessment to ICI or TT using baseline and follow-up scans (median time between scans, 4.2 mo). In all lesions, static and dynamic 18F-FET PET parameters were obtained (i.e., mean tumor-to-brain ratios [TBR], time-to-peak values). Diagnostic accuracies of PET parameters were evaluated by receiver-operating-characteristic analyses using the clinical follow-up or neuropathologic findings as a reference. Results: A TBR threshold of 1.95 differentiated BM relapse from treatment-related changes with an accuracy of 85% (P = 0.003). Metabolic responders to ICI or TT on 18F-FET PET had a significantly longer stable follow-up (threshold of TBR reduction relative to baseline, ≥10%; accuracy, 82%; P = 0.004). Furthermore, at follow-up, time to peak in metabolic responders increased significantly (P = 0.019). Conclusion: 18F-FET PET may add valuable information for treatment monitoring in BM patients treated with ICI or TT.