Dynamic ¹⁸F-FET PET in Newly Diagnosed Astrocytic Low-Grade Glioma Identifies High-Risk Patients

Abstract

Because the clinical course of low-grade gliomas in the individual adult patient varies considerably and is unpredictable, we investigated the prognostic value of dynamic 18 F-fluorethyltyrosine ( 18 F-FET) PET in the early diagnosis of astrocytic low-grade glioma (World Health Organization grade II). Methods: Fifty-nine patients with newly diagnosed low-grade glioma and dynamic 18 F-FET PET before histopathologic assessment were retrospectively investigated. 18 F-FET PET analysis comprised a qualitative visual classification of lesions; assessment of the semiquantitative parameters maximal, mean, and total standardized uptake value as ratio to background and biologic tumor volume; and dynamic analysis of intratumoral 18 F-FET uptake over time (increasing vs. decreasing time-activity curves). The correlation between PET parameters and progression-free survival, overall survival, and time to malignant transformation was investigated. Results: 18 F-FET uptake greater than the background level was found in 34 of 59 tumors. Dynamic 18 F-FET uptake analysis was available for 30 of these 34 patients. Increasing and decreasing timeactivity curves were found in 18 and 12 patients, respectively. Neither the qualitative factor presence or absence of 18 F-FET uptake nor any of the semiquantitative uptake parameters significantly influenced clinical outcome. In contrast, decreasing time-activity curves in the kinetic analysis were highly prognostic for shorter progression-free survival and time to malignant transformation (P , 0.001). Conclusion: Absence of 18 F-FET uptake in newly diagnosed astrocytic low-grade glioma does not generally indicate an indolent disease course. Among the 18 F-FET-positive gliomas, decreasing time-activity curves in dynamic 18 F-FET PET constitute an unfavorable prognostic factor in astrocytic low-grade glioma and, by identifying high-risk patients, may ease treatment decisions.

18F-FET PET Uptake Characteristics in Patients with Newly Diagnosed and Untreated Brain Metastasis

“…Nonetheless, we observed notable, partly even very high, 18 F-FET uptake in small lesions with a 0.6-to 1.0-cm diameter ce as well. Our results therefore suggest that 18 F-FETnegative findings may also occur in brain metastases (in our study in one third of metastases # 1.0 cm) but might mostly be related to partial-volume effects and limited scanner resolution, leading to underestimation of 18 F-FET uptake especially in tumors with low tracer uptake, rather than to a complete lack of 18 F-FET uptake as observed in 30% of low-grade gliomas (14,26). This might especially be the case because a missing expression of the L-amino-acid transporter, responsible for 18 F-FET uptake in brain metastases, was reported to be a rare condition itself (27).…”

“…Whether dynamic PET parameters before further therapies do have a prognostic value at initial diagnosis, such as shown in primary gliomas (14,15), has to be evaluated in prospective settings. Additionally, all metastatic lesions showed time-activity curves characteristic for brain neoplasms, whereas no time-activity curve with a shape specific for vascular structures was seen.…”

“…Furthermore, patterns of timeactivity-curves and minimal time-to-peak (TTP min ) values derived from dynamic 18 F-FET PET provide more detailed information on glioma characteristics. For example, it has been demonstrated that dynamic 18 F-FET PET parameters have a high prognostic value in newly diagnosed low-and high-grade glioma (14,15). In secondary cerebral neoplasms, a few PET studies on pretreated brain metastases are currently available and have assessed the value of amino acid PET for the differentiation of recurrent disease from radiation-induced changes after radiotherapy (13,(16)(17)(18)(19).…”

Dynamic 18F‐FET PET in suspected WHO grade II gliomas defines distinct biological subgroups with different clinical courses

“…Static 18 F-FET uptake parameters such as SUV max /BG did not gain relevance in prognostic models, which is supported by recently published data. 11,42,46 As SUV max /BG values were calculated in the summed images from 20 to 40 minutes this might have underestimated the SUV max /BG values of some of the tumors.…”

“…Thus, the place of invasive treatment modalities can be expected to become better defined by imagingderived biomarkers such as dynamic 18 F-FET PET. The elucidation of the prognostic impact of dynamic 18 F-FET PET independent of WHO grade is currently under investigation: Recently published retrospective data indicate that dynamic 18 F-FET PET might gain prognostic impact independent of the WHO grade 46 . TAC analyses were able to identify patients at risk in histologically verified low-grade gliomas.…”