NIMG-89. MULTI-THRESHOLD VOLUMETRIC MAPPING OF18F-FLUOROETHYLTYROSINE POSITRON EMISSION TOMOGRAPHY (18F-FET PET) IMPROVES TUMOR DETECTION IN PRIMARY MALIGNANT BRAIN TUMOR PATIENTS

Abstract PURPOSE The purpose of this study was to determine whether additional volumetric measurements yielded significant prognostic information than typically reported tumor-to-brain ratio thresholds (TBRmax) alone for accurately distinguishing progressive disease from treatment induced changes. METHODS Hybrid 18F-FET PET/MRI was obtained on pathology confirmed high-grade glioma in sixty patients from August 6th, 2022 to March 9th, 2023 at one US institution. We compared the diagnostic accuracy of various TBR thresholds and volumetric measurement combinations in identifying progressive disease. Specifically, we assessed TBR >1.6, 2.0, 2.5, 3.0, 3.5, 4, 4.5, and 5.0 alone and in combination with volumetric measurements greater than 1 mL. Survival data for all patients were analyzed using Kaplan-Meier curves. RESULTS Our analysis revealed that TBR > 2.5 and >1 mL yielded the highest diagnostic accuracy (100%) in distinguishing progressive disease from treatment induced changes. This was followed by the combination TBR >2.0 and >1 mL (98%), TBR > 2.5 alone (98%), TBR > 2.0 alone (86%), TBR >1.6 and >1 mL (84%), and TBR >1.6 alone (77%). TBR >3.0, 3.5, 4.0, 4.5, and 5.0 with and without volumetric measurements showed accuracies of 100%. Kaplan-Meier survival analysis showed significant results for all thresholds: TBR >1.6 alone (p = 0.047), TBR >1.6 and 1 mL (p = 0.003), TBR > 2.0 alone (p = 0.019), TBR >2.0 and >1 mL (p < 0.001), TBR >2.5 alone (p < 0.001), and TBR >2.5 and >1 mL (p = 0.002). CONCLUSION Our findings suggest that although TBRmax > 2.5 alone continues to be a reliable metric for distinguishing progressive disease from treatment induced changes, TBRmax >2.5 when volume is greater than 1 mL shows the greatest accuracy in detecting disease progression. Understanding the volumetric contribution to static FET TBRmax is important for tumor response assessment at TBRmax thresholds above 1.6 TBRmax.