Preliminary impact of serial hybrid [18F]FET PET/MR perfusion on the management of patients with malignant brain tumors at a single United States institution.

Umber Shafique; Nathaniel Smith; Scott Snyder; Mark Green; Gary Hutchins; Michael Veronesi

Abstract

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Introduction: Conventional imaging is often inadequate for distinguishing tumor progression from treatment related change (TRC) in patients with malignant brain tumors. Although MR Perfusion imaging enhances management decisions for brain tumor patients, hybrid [¹⁸F]FET PET/MR Perfusion is considered even more accurate. However, data on the role of serial hybrid [¹⁸F]FET PET/MR Perfusion is lacking in assessment of malignant brain tumor patients who have undergone complex treatment decisions in the United States (U.S). The purpose of our study was to evaluate the impact of initial hybrid [¹⁸F]FET PET/ MR Perfusion imaging on patient management decisions as assessed with serial follow-up [¹⁸F]FET PET/MR perfusion imaging.

Methods: A retrospective analysis was performed on patients with malignant brain tumors who underwent serial [¹⁸F]FET PET/MR Perfusion imaging following standard of care at a U.S. institution from 2020-2021.

An initial hybrid [¹⁸F]FET PET/MR Perfusion exam was performed to evaluate patients with either high grade glioma or brain metastases with equivocal lesions on prior imaging. Clinical management decisions were then recorded, which included any change in surgical, radiation, or pharmaceutical therapy. Subsequent [¹⁸F]FET PET/MR Perfusion exams were also studied. Subsequent clinical management decisions and at least one subsequent brain MRI were included in the final analysis.

Conventional imaging parameters included changes in FLAIR signal or enhancement. Perfusion assessment included the Ktrans on Dynamic Contrast Enhancement (DCE) imaging and the rCBV ratio on Dynamic Susceptibility Contrast (DSC) imaging. [¹⁸F]FET PET parameters included the static Tumor to brain mean and maximum ratios as well as [¹⁸F]FET Late washout rate. The final decision of the [¹⁸F]FET PET/MR Perfusion exam was compared with each individual imaging parameter. The overall accuracy, positive predictive value (PPV), and negative predictive value (NPV) were then determined.

Results: 17 patients underwent at least two serial [¹⁸F]FET PET/MR Perfusion exams within a year over 37 total exams. Fourteen patients had 2 exams and three patients had 3 exams during their treatment.

Imaging features of progressive tumor were identified 21/37 times (57%) after an [¹⁸F]FET PET/MR Perfusion scan. There was resultant change in management 18 times (86%) following a diagnosis of progressive tumor. For 3/21 exams (15%) with a diagnosis of progressive disease, there was no initial change in management. However, concordant findings of tumor progression were again diagnosed on the second [¹⁸F]F-FET PET/MR Perfusion scan, which resulted in change in management.

Imaging features of TRC were identified on [¹⁸F]FET PET/MR Perfusion imaging in 16/37 total scans (43%). There was clinical and imaging concordance with TRC in 13/16 scans (81%) with no resultant change in management. The 3 remaining patients (19%) underwent a second [¹⁸F]F-FET PET/MR Perfusion scan which again received a diagnosis of TRC. Subsequent MR imaging showed eventual tumor progression which resulted in treatment delay (false negative). The false negative values of 2 scans were attributed to subthreshold uptake on [¹⁸F]FET PET due to small size of the lesion (1 cm or less) within a background of TRC. Overall, [¹⁸F]FET PET/MR Perfusion demonstrated a 92% accuracy with PPV of 100% and NPV of 81%.

Conclusions: Preliminary results on serial [¹⁸F]FET PET/MR Perfusion imaging appears to be a highly reliable tool for assessing difficult cases of progressive tumor vs TRC in patients with malignant brain tumors. [¹⁸F]FET PET/MR Perfusion has increased PPV compared to MRI alone which advocates for more timely change in management. The NPV was mainly limited by smaller lesion size against a background of TRC. These promising preliminary results will be studied in a larger patient population at our institution over longer periods of time.