Impact of ¹⁸F-FET PET/MR on clinical management of brain tumor patients

Abstract

Multiparametric PET-MRI with the amino-acid analog ¹⁸F-FET enables the simultaneous assessment of molecular, morphologic, and functional brain tumor characteristics. Although it is considered the most accurate non-invasive approach in brain tumors, its relevance for patient management is still under debate. Here we report the diagnostic performance of ¹⁸F-FET PET/MR and its impact on clinical management in a retrospective patient cohort. Methods: We retrospectively analyzed brain tumor patients who underwent ¹⁸F-FET PET/MR between 2017 and 2018. ¹⁸F-FET PET/MR examinations were indicated clinically due to equivocal standard imaging or clinical course. Histological confirmation or clinical and standard imaging follow-up served as the reference standard. We evaluated ¹⁸F-FET PET/MR accuracy in identifying malignancy in untreated suspect lesions (category new diagnosis) and true progression during adjuvant treatment (category detection of progression) in a clinical setting. Using multiple regression, we also estimated the contribution of single modalities to produce an optimal PET/MRI outcome. We assessed the recommended and applied therapies before and after ¹⁸F-FET PET/MR and noted if the treatment changed based on the ¹⁸F-FET PET/MR outcome. Results: We included 189 cases in the study. ¹⁸F-FET PET/MR allowed the identification of malignancy at new diagnosis with an accuracy of 85% and identified true progression with an accuracy of 93%. Contrast enhancement, ¹⁸F-FET PET uptake, and tracer kinetics were the major contributors to an optimal PET/MR outcome. In the previously equivocal patients, ¹⁸F-FET PET/MR changed the clinical management in 33% of the untreated lesions and 53% of the tumor progressions. Conclusion: Our results suggest that ¹⁸F-FET PET/MR helps clarify equivocal conditions and profoundly supports brain tumor patients' clinical management. The optimal modality setting of ¹⁸F-FET PET/MR and the clinical value of a simultaneous examination need further exploration. At a new diagnosis, multiparametric ¹⁸F-FET PET/MR might help prevent unnecessary invasive procedures by ruling out malignancy; however, adding static ¹⁸F-FET PET to an already existing MR examination seems to be of equal value. At detection of progression, multiparametric ¹⁸F-FET PET/MR may increase therapy effectiveness by distinguishing between tumor progression and therapy-related imaging alterations.