Assessment of various strategies for 18F-FET PET-guided delineation of target volumes in high-grade glioma patients

Abstract

Purpose The purpose of the study is to assess the contribution of 18 F-fluoro-ethyl-tyrosine ( 18 F-FET) positron emission tomography (PET) in the delineation of gross tumor volume (GTV) in patients with high-grade gliomas compared with magnetic resonance imaging (MRI) alone. Materials and methods The study population consisted of 18 patients with high-grade gliomas. Seven image segmentation techniques were used to delineate 18 F-FET PET GTVs, and the results were compared to the manual MRIderived GTV (GTV MRI ). PET image segmentation techniques included manual delineation of contours (GTV man ), a 2.5 standardized uptake value (SUV) cutoff (GTV 2.5 ), a fixed threshold of 40% and 50% of the maximum signal intensity (GTV 40% and GTV 50% ), signal-to-background ratio (SBR)-based adaptive thresholding (GTV SBR ), gradient find (GTV GF ), and region growing (GTV RG ). Overlap analysis was also conducted to assess geographic mismatch between the GTVs delineated using the different techniques. Results Contours defined using GTV 2.5 failed to provide successful delineation technically in three patients (18% of cases) as SUV max <2.5 and clinically in 14 patients (78% of cases). Overall, the majority of GTVs defined on PET-based techniques were usually smaller than GTV MRI (67% of cases). Yet, PET detected frequently tumors that are not visible on MRI and added substantially tumor extension outside the GTV MRI in six patients (33% of cases). Conclusions The selection of the most appropriate 18 F-FET PET-based segmentation algorithm is crucial, since it impacts both the volume and shape of the resulting GTV. The 2.5 SUV isocontour and GF segmentation techniques performed poorly and should not be used for GTV delineation. With adequate setting, the SBR-based PET technique may add considerably to conventional MRIguided GTV delineation.

Textural Parameters of Tumor Heterogeneity in 18F-FDG PET/CT for Therapy Response Assessment and Prognosis in Patients with Locally Advanced Rectal Cancer

“…In our study, tumor volume was manually delineated on CT images. Tumor delineation on PET would be an alternative, but there is a controversial discussion on which method should be used to estimate tumor borders on PET images (23,24). Differences in tumor heterogeneity depending on the delineation method will also need to be investigated in further studies.…”

Multimodality Assessment of Brain Tumors and Tumor Recurrence

“…For this application, amino acid and nucleoid tracers are better suited (123)(124)(125)(126)(127). Several studies suggested that outcomes are better for patients in whom 11 C-MET or 18 F-FET PET coregistered to MRI are applied for treatment planning and follow-up than for patients diagnosed by MRI alone (123)(124)(125)(126)128). In the follow-up and for the management of patients with brain tumor, the differentiation between recurrent tumor as a sign of treatment failure and necrosis as an indicator of success is essential.…”

Adaptive threshold segmentation of pituitary adenomas from FDG PET images for radiosurgery

“…The challenge at hand was to segment the pituitary adenomas that are both small and also set against a high‐intensity background. Intuitively, since the images show a marked difference between the normal and abnormal glycolytic functions, thresholding was one of the easier methods to adopt and implement, 22 , 23 , 24 , 25 provided it is optimized for the specific scanner. Since we were delineating small tumors, fixed threshold was not an ideal option, given its own limitations (26) .…”