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Magnetic Resonance Imaging in Treatment Planning
Published in W. P. M. Mayles, A. E. Nahum, J.-C. Rosenwald, Handbook of Radiotherapy Physics, 2021
In addition, certain metabolites such as amino acids using either 11C-methionine (MET) or 18F-fluoroethyl-L-tyrosine (FET) can be labelled and probed with different magnetic nuclei to determine the location of active disease that needs targeting or higher doses. In multimodality image fusion studies, these metabolites have been reported to locate metabolically active tumour regions that are different from the spatial location of disease defined by standard MRI sequences (Matsuo et al. 2012; Pafundi et al. 2013). This will aid RTP by optimising target volume delineation to permit dose boosting where appropriate and avoid geographical miss. One study reported that the MET-defined activity was located 8 mm to 30 mm distant from the T1-weighted contrast enhancement region in up to nearly 70% of cases (Tsien et al. 2012).
Anatomical and Biological Imaging of Pediatric Brain Tumor
Published in David A. Walker, Giorgio Perilongo, Roger E. Taylor, Ian F. Pollack, Brain and Spinal Tumors of Childhood, 2020
Rob A. Dineen, Shivaram Avula, Andrew C. Peet, Giovanni Morana, Monika Warmuth-Metz
Amino acid analogs such as 18F-fluoroethyl-l-tyrosine (FET), 11C-methionine (MET), or 18F-dihydroxyphenylalanine (DOPA) are currently considered the most useful tracers in neuro-oncology106,107 and their superiority over 18F-FDG has been emphasized by guidelines for the clinical use of PET imaging in gliomas by the Response Assessment in Neuro-Oncology working group and the European Association for Neuro-Oncology.106 Metabolic imaging of brain tumors with amino acid analogs has advantages over 18F-FDG because of the high uptake in tumor tissue and the low uptake in normal brain tissue; furthermore, as these tracers utilize active transport mechanisms for tissue uptake, brain tumor visualization and characterization do not depend on the status of the blood–brain barrier, allowing amino acid uptake to occur in both enhancing and non-enhancing tumors.106–108
Non-FDG radionuclide imaging and targeted therapies
Published in Anju Sahdev, Sarah J. Vinnicombe, Husband & Reznek's Imaging in Oncology, 2020
Luigi Aloj, Ferdia A Gallagher
The development of new PET probes has provided a rich opportunity for interrogating varying aspects of tumour biology and a range of isotopes have been used to label these probes: each labelling approach has relative strengths and weaknesses. The relatively long half-life of fluorine-18 (18F; 110 min) allows slow metabolic processes to be studied, and these tracers can be generated at a central site and distributed locally for imaging. The use of 18F is often ideal when developing a novel probe, but incorporation of fluorine into a biological molecule can be chemically challenging and the derivative is frequently handled very differently in vivo compared to its unlabelled counterpart. Examples include 18F-labelled sodium fluoride (NaF), 3-deoxy-3-[18F]fluorothymidine (FLT), O-(2-[18F]fluoroethyl)-l-tyrosine (FET), and [18F]-fluoromisonidazole (FMISO); see Table 44.1.
Prognostic value of O-(2-[18F]-fluoroethyl)-L-tyrosine PET in relapsing oligodendroglioma
Published in Acta Oncologica, 2020
Florian Schneider, Fabian Wolpert, Paul Stolzmann, Abdulrahman A. Albatly, David Kenkel, Jonathan Weller, Michael Weller, Spyros S. Kollias, Elisabeth J. Rushing, Patrick Veit-Haibach, Martin W. Huellner
Positron emission tomography (PET) using amino acid radiopharmaceuticals is well-established for assessing primary and recurrent or secondary progressive gliomas [1–7]. Amino acid PET provides complementary information to magnetic resonance imaging (MRI) and may be used for tumor grading, guiding biopsy and therapy planning [8–12]. Amino acid radiotracers, such as O-(2-[18F]-fluoroethyl)-L-tyrosine (18F-FET), allow for a more accurate assessment of lesions than [18F]-fluorodeoxyglucose (18F-FDG), which is commonly used for oncologic imaging outside the brain [13]. This is based on different tissue properties imaged with these radiotracers (amino acid vs. glucose ‘metabolism’), yielding lower 18F-FET uptake in normal brain tissue compared to 18F-FDG, which in turn leads to an improved contrast resolution [8,14]. 18F-FET is also more accessible than the formerly used radiotracer L-methyl-11C-methionine (11C-MET), which is limited to hospitals with on-site cyclotron [14,15]. 18F-FET uptake characteristics of brain tumors may be expressed with static parameters, e.g. maximum standardized uptake value (SUVmax), and target-to-background ratios (TBRmax/TBRmean). Dynamic PET acquisition may improve the diagnostic value and allow for more accurate glioma grading [2,16,17].
Tumefactive demyelination: updated perspectives on diagnosis and management
Published in Expert Review of Neurotherapeutics, 2021
Pedro Sánchez, Fiona Chan, Todd A. Hardy
On 18F‐fluorodeoxyglucose positron emission tomography (18F‐FDG PET), demyelinating lesions are generally hypometabolic but uptake can be also mildly increased in TD [39] . Generally, uptake is significantly higher for primary CNS lymphoma (PCNSL) and gliomas compared to TD [39]. A study showed that 18F-fluoroethyl-L-tyrosine-PET parameters lesion-to-background ratio (TBR)max (cutoff 2.2) and standardized uptake value (SUV)max (cutoff 2.5) can distinguish TD from true neoplastic lesions [40]. A high positive 11C-MET uptake has a relatively high sensitivity favoring gliomas against non-neoplastic lesions, although there are false positives in up to 30% of gadolinium enhancing demyelinating lesions [41–43].
Diagnostic impact of additional O-(2-[18F]fluoroethyl)-L-tyrosine (18F-FET) PET following immunotherapy with dendritic cell vaccination in glioblastoma patients
Published in British Journal of Neurosurgery, 2021
Ann Kristin Schmitz, Rüdiger V. Sorg, Gabriele Stoffels, Oliver M. Grauer, Norbert Galldiks, Hans-Jakob Steiger, Marcel A. Kamp, Karl-Josef Langen, Michael Sabel, Marion Rapp
The amino acid O-(2-18F-fluoroethyl)-L-tyrosine (18F-FET) was produced via nucleophilic 18F-fluorination as described previously with a specific radio-activity of more than 200 GBq/mmol.17 Acquisition of PET scans was performed after intravenous injection of 200 MBq of 18F-FET. Static and dynamic 18F-FET PET scans were performed. For all images, an ECAT EXACT HR1 scanner (Siemens Medical Systems) in 3-dimensional mode (32 rings; axial field of view, 15.5 cm) was used, and transmission was measured with three 68Ge/68Ga rotating line sources for attenuation correction. Following Fourier rebinning and correction for attenuation, scattered coincidences, random coincidences and decay, 63 image planes were reconstructed in an iterative process (ordered-subsets expectation maximization, 6 iterations, 16 subsets) using the ECAT 7.2 software. Summed PET data from 20 to 40 min after injection was used for further evaluation. 18F-FET PET and contrast-enhanced MRI scans were co-registered with MPI tool software (version 6.48; ATV). Region of interest (ROI) analyses were performed at the trans axial slice, which showed the highest 18F-FET accumulation in the tumour and at a slice showing the contralateral hemisphere in an area of normal-appearing grey and white matter to gain 18F-FET uptake in the unaffected brain tissue. A tumour-to-brain ratio (TBR) of at least 1.6, evaluated in earlier studies,18 was used to determine the 18F-FET uptake in the tumour by an auto contouring, 2-dimensional process. By dividing the mean and maximum standardized uptake volume (SUV) of the tumour ROI by the mean SUV of normal brain in the 18F-FET PET scan, mean and maximum TBR (TBRmean, TBRmax) were calculated. Furthermore, time-activity curves (TAC) of mean SUV of 18F-FET uptake in the tumour and in the brain were generated by application of a spherical Volume-of-Interest with a volume of 2 ml centred on maximal tumour uptake and of a reference ROI in the unaffected brain tissue (as described above) to the entire dynamic data set. 18F-FET PET imaging was performed as soon as possible after surgery within a time window of 6 weeks to be reasonable to compare with MRI imaging.