Repeatability of Quantitative 18F-FET PET in Glioblastoma

Abstract

Purpose: O-(2-[ 18 F]fluoroethyl)-L-tyrosine (FET), a PET radiotracer of amino acid uptake, has shown potential for diagnosis and treatment planning in patients with glioblastoma (GBM). To improve quantitative assessment of FET PET imaging, we evaluated the repeatability of uptake of this tracer in patients with GBM. Methods: Test-retest FET PET imaging was performed on 8 patients with histologically confirmed GBM, who previously underwent surgical resection of the tumour. Data were acquired according to the protocol of a prospective clinical trial validating FET PET as a clinical tool in GBM. SUV mean , SUV max and SUV 98% metrics were extracted for both test and retest images and used to calculate 95% Bland-Altman limits of agreement (LoA) on lesion-level, as well as on volumes of varying sizes. Impact of healthy brain normalization on repeatability of lesion SUV metrics was evaluated. Results: Tumour LoA were [0.72, 1.46] for SUV mean and SUV total , [0.79,1.23] for SUV max , and [0.80,1.18] for SUV 98% . Healthy brain LoA were [0.80,1.25] for SUV mean , [0.80,1.25] for SUV max , and [0.81,1.23] for SUV 98% . Voxel-level SUV LoA were [0.76, 1.32] for tumour volumes and [0.80, 1.25] for healthy brain. When sampled over maximum volume, SUV LoA were [0.90,1.12] for tumour and [0.92,1.08] for healthy brain. Normalization of uptake using healthy brain volumes was found to improve repeatability, but not after normalization volume size of about 15 cm 3 . Conclusions Advances in Knowledge and Implications for Patient Care: Repeatability of FET PET is comparable to existing tracers such as FDG and FLT. Healthy brain uptake is slightly more repeatable than uptake of tumour volumes. Repeatability was found to increase with sampled volume. SUV normalization between scans using healthy brain uptake should be performed using volumes at least 15 cm 3 in size to ensure best imaging repeatability.

68Ga-Pentixafor PET/CT for In Vivo Imaging of CXCR4 Receptors in Glioma Demonstrating a Potential for Response Assessment to Radiochemotherapy: Preliminary Results

“…30 It has been reported that combining amino acid-based SPECT/PET and DSCE-MRI has complimentary role in differentiation of tumor recurrence from radiation-induced necrosis in glioma patients. 8,31,32 Therefore, 68 Ga-pentixafor PET/CT offering highcontrast images may also be used for treatment planning and response assessment to treatment in GBM. However, amino acidbased PET imaging cannot be expanded to a direct approach of matched 68 Ga/ 177 Lu theranostic pair, which has been used with remarkable impact on the treatment of neuroendocrine tumors and prostate cancer.…”

“…It has been reported that combining amino acid–based SPECT/PET and DSCE-MRI has complimentary role in differentiation of tumor recurrence from radiation-induced necrosis in glioma patients 8,31,32 . Therefore, 68 Ga-pentixafor PET/CT offering high-contrast images may also be used for treatment planning and response assessment to treatment in GBM.…”

“…5,6 Amino acid-based PET and SPECT and hybrid PET/MR techniques have yielded encouraging results for imaging brain tumors. [7][8][9] The currently available PET tracers using O-(2-18 Ffluoroethyl)-l-tyrosine ( 18 F-FET) and 10 C-methionine have improved diagnostic efficacy in GBM. 10,11 The 3-dimensional (3D) information provided by these PET tracers allows radiation dose modification selectively to subvolume/s of a heterogenous tumor showing higher tracer uptake, which has shown some clinical advantage in radioresistant tumors.…”

“…Advance MR techniques such as MR perfusion and diffusion spectroscopy have shown clinical advantages over the conventional MRI 5,6 . Amino acid–based PET and SPECT and hybrid PET/MR techniques have yielded encouraging results for imaging brain tumors 7–9 …”

The impact of fluorine-18-fluoroethyltyrosine positron emission tomography scan timing on radiotherapy planning in newly diagnosed patients with glioblastoma

“…Additionally, Fleischmann and colleagues demonstrated that when technology-specific GTV-CTV margins are used with combined ( 18 F-FET PET)-MRI, the glioblastoma CTV decreased in size, the dose to the healthy brain tissue was reduced, and patients experienced a similar pattern and frequency of recurrence [14] . However, there is still uncertainty around the impact of ( 18 F-FET PET) scan timing on the resultant CTV [17] .…”