MRI and ¹⁸F-FET PET for Multimodal Treatment Monitoring in Patients with Brain Metastases: A Cost-Effectiveness Analysis

Model 1 (upper panel): Decision tree for assessing effectiveness of additional ¹⁸F-FET PET for differentiating treatment-related changes (TRC) from brain metastasis (BM) relapse after multimodal therapy. Twenty-seven patients underwent ¹⁸F-FET PET. N1 divides patients into those diagnosed with brain metastasis relapse or treatment-related changes according to ¹⁸F-FET PET criteria (i.e., mean tumor-to-brain ratio of more or less than 1.95, respectively). N2 and N3 assign both groups to patients’ outcomes based on both clinical course during subsequent follow-up and either neuropathologic diagnosis or Response Assessment in Neuro-Oncology criteria for immunotherapy. Model 2 (lower panel): Decision tree model for assessing effectiveness of ¹⁸F-FET PET and MRI to identify nonresponder to multimodal therapy based on stable clinical course for <6 mo. Eleven patients underwent serial ¹⁸F-FET PET and MRI. N1 and N2 represent chance nodes to be responder or nonresponder according to ¹⁸F-FET PET and MRI criteria (i.e., relative reduction or increase in mean tumor-to-background ratio of 10% for ¹⁸F-FET PET, respectively; Response Assessment in Neuro-Oncology criteria for immunotherapy for MRI). N3–N6 divide each of 4 groups of ¹⁸F-FET PET and MRI responders (and nonresponders) into true and false responders (and nonresponders), respectively.

Tornado diagrams of cost-effectiveness ratio of additional ¹⁸F-FET PET scans for identification of treatment-related changes (upper panel) and ICER of ¹⁸F-FET PET for identification of nonresponder (lower panel) after multimodal therapy. Cost-effectiveness ratios and ICERs were calculated by applying upper and lower interval values, as shown in Table 1, onto N1–N3 and N1–N6, respectively.