Abstract
Neuroimaging based on O-[2-(18F)fluoroethyl]-l-tyrosine (FET)-PET provides additional information on tumor grade and extent compared with MRI. Dynamic PET for biopsy target selection further improves results but is often clinically impractical. Static FET-PET performed at two time-points may be a good compromise, but data on this approach are limited. The aim of this study was to compare the histology of lesions obtained from two challenging glioma patients with targets selected based on hybrid dual time-point FET-PET/MRI. Five neuronavigated tumor biopsies were performed in two difficult cases of suspected glioma. Lesions with (T1-CE) and without contrast enhancement (T1 and T2-FLAIR) on MRI were selected. Dual time-point FET-PET imaging was performed 5–15 min (PET10) and 45–60 min (PET60) after radionuclide injection. The most informative FET-PET/MRI images were coregistered with MRI in time of biopsy planning. Five biopsy targets (three from high uptake and two from moderate uptake FET areas) thought to represent the most malignant sites and tumor extent were selected. Histopathological findings were compared with FET-PET and MRI images. Increased FET uptake in the area of non-CE locations on MRI correlated well with high-grade gliomas localized as far as 3 cm from T1-CE foci. Selecting a target in the motor cortex based on FET kinetics defined by dual time-point PET resulted in a grade IV diagnosis after previous negative biopsies based on MRI. An additional grade III diagnosis was obtained from an area of glioma infiltration with moderate FET uptake (between 1 and 1.25 SUV). These findings seem to show that dual time-point FET-PET-based biopsies can provide additional and clinically useful information for glioma diagnosis. Selection of targets based on dual time-point images may be useful for determining the most malignant tumor areas and may therefore be useful for resection and radiotherapy planning.
Highlights
Stereotactic biopsy (SB) of central nervous system (CNS) tumors aims to precisely collect tissue for histopathological examination
SB is often necessary for patients with inoperable gliomas, multifocal CNS tumors, lesions located in deep brain structures, large tumors that are ineligible for resection, suspected lymphomas, and lesions poorly defined on MRI [1]
The first focus was located at a considerable distance from the areas of contrast enhancement and T2-FLAIR, and the highest uptake was present in PET10 (Figure 2A) but lower in PET60
Summary
Stereotactic biopsy (SB) of central nervous system (CNS) tumors aims to precisely collect tissue for histopathological examination. We correlated the early and late images taken in dual time-point acquisition with the biopsy results from the center and periphery of the tumors to examine their true extent In this way, we could identify a tumor periphery (of grade III malignancy) not visible in T2-FLAIR but visible in early and late FET-PET images with moderate FET-PET uptake (above 1 SUV). Further studies should provide more insights into the threshold FET uptake values between the tumor periphery and normal brain tissue in dual time-point FET-PET. To our knowledge, this is the first biopsy-controlled study taking advantage of FET uptake kinetic to determine tumor diagnosis and tumor periphery characteristics. A retrospective study of dual time-point FET-PET for radiotherapy planning showed increased uptake in early but not late images that corresponded with sites of recurrence [26]
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