The Role of Radionuclide Diagnostic Methods in Neuro-Oncology

In recent years, positron emission tomography (PET) with amino acid radiopharmaceuticals has assumed increasing importance in the diagnosis of brain tumors and it has already become an additional method of examination along with magnetic resonance imaging (MRI) in many diagnostic centers. The markers of somatostatin receptors seem to be most promising for the PET diagnosis of meningiomas. PET provides important additional information in the diagnosis of brain changes of unknown origin and more accurate information about tumor boundaries, which is necessary for biopsy, neurosurgery, and radiation therapy. In addition, labeled amino acid PET aids in the assessment of disease prognosis, in the differentiation of continued tumor growth from nonspecific therapeutic pathomorphism of the brain, and in the evaluation of treatment efficiency at an earlier time than is possible with MRI

Photopenic defects on O-(2-18F-fluoroethyl)-L-tyrosine PET - clinical relevance in glioma patients.

V48Photopenic defects on O-(2-18F-fluoroethyl)-L-tyrosine PET - clinical relevance in glioma patientsN. Galldiks1, M. Unterrainer2, N. Judov3, G. Stoffels3, M. Rapp4, P. Lohmann3, F. Vettermann2, V. Dunkl1, B. Suchorska5, J. C. Tonn5, F. W. Kreth5, G. R. Fink1, P. Bartenstein2, K. J. Langen3, N. L. Albert21Uniklinik Köln, Klinik für Neurologie, Köln; 2Uniklinik München (LMU), Klinik für Nuklearmedizin, München; 3Forschungszentrum Jülich, Inst. für Neurowissenschaften und Medizin (INM-4), Jülich; 4Uniklinik Düsseldorf, Klinik für Neurochirurgie, Düsseldorf; 5Uniklinik München (LMU), Klinik für Neurochirurgie, MünchenZiel/Aim:In PET imaging, a fraction of approximately 5-10% of cerebral gliomas show no increased accumulation of O-(2-18F-fluoroethyl)-L-tyrosine (FET) compared to the normal brain. Some of these lesions present even as photopenic defects. The clinical relevance of this phenomenon remains to be elucidated.Methodik/Methods:Glioma patients with a negative FET PET scan prior to histological confirmation were retrospectively identified in three university centers. Gliomas were visually rated as having indifferent FET uptake or as photopenic when FET uptake was below background acitivity. For quantitative analysis, FET uptake in the area of signal hyperintensity on the T2-/FLAIR-weighted MRI was evaluated by mean standardized uptake values (SUV) and mean tumor-to-brain ratios (TBR). In patients without treatment (“watch and wait” strategy), the progression-free survival (PFS) of photopenic gliomas was compared with that of gliomas with indifferent FET uptake.Ergebnisse/Results:Of 104 FET-negative gliomas (2 WHO grade I, 75 WHO grade II, 23 WHO grade III, and 4 WHO grade IV), 36 cases with photopenic defects (35%) were identified (23 WHO grade II, 12 WHO grade III, and one glioblastoma). FET uptake in photopenic defects was significantly decreased compared to both the healthy-appearing brain tissue (SUV, 0.88±0.23 vs. 1.10±0.26; P0.05).Schlussfolgerungen/Conclusions:Around one-third of FET-negative gliomas exhibit photopenic defects. These photopenic gliomas should be managed more actively as they might have a higher risk for harboring a higher-grade glioma and an unfavorable outcome compared to gliomas with indifferent FET uptake

Dual-time-point O-(2-[18^{18}F]fluoroethyl)-L-tyrosine PET for grading of cerebral gliomas

ObjectiveWe aimed to evaluate the diagnostic potential of dual-time-point imaging with positron emission tomography (PET) using O-(2-[18F]fluoroethyl)-L-tyrosine (18F-FET) for non-invasive grading of cerebral gliomas compared with a dynamic approach.MethodsThirty-six patients with histologically confirmed cerebral gliomas (21 primary, 15 recurrent; 24 high-grade, 12 low-grade) underwent dynamic PET from 0 to 50 min post-injection (p.i.) of 18F-FET, and additionally from 70 to 90 min p.i. Mean tumour-to-brain ratios (TBRmean) of 18F-FET uptake were determined in early (20–40 min p.i.) and late (70–90 min p.i.) examinations. Time–activity curves (TAC) of the tumours from 0 to 50 min after injection were assigned to different patterns. The diagnostic accuracy of changes of 18F-FET uptake between early and late examinations for tumour grading was compared to that of curve pattern analysis from 0 to 50 min p.i. of 18F-FET.ResultsThe diagnostic accuracy of changes of the TBRmean of 18F-FET PET uptake between early and late examinations for the identification of HGG was 81 % (sensitivity 83 %; specificity 75 %; cutoff - 8 %; p < 0.001), and 83 % for curve pattern analysis (sensitivity 88 %; specificity 75 %; p < 0.001).ConclusionDual-time-point imaging of 18F-FET uptake in gliomas achieves diagnostic accuracy for tumour grading that is similar to the more time-consuming dynamic data acquisition protocol.Key Points• Dual-time-point imaging is equivalent to dynamic FET PET for grading of gliomas.• Dual-time-point imaging is less time consuming than dynamic FET PET.• Costs can be reduced due to higher patient throughput.• Reduced imaging time increases patient comfort and sedation might be avoided.• Quicker image interpretation is possible, as no curve evaluation is necessary

The usefulness of dynamic O-(2-18F-Fluoroethyl)-L-Tyrosine PET in the clinical evaluation of brain tumors in childrenand adolescents.

Experience regarding O-(2-18F-fluoroethyl)-l-tyrosine (18F-FET) PET in children and adolescents with brain tumors is limited. Methods: Sixty-nine 18F-FET PET scans of 48 children and adolescents (median age, 13 y; range, 1–18 y) were analyzed retrospectively. Twenty-six scans to assess newly diagnosed cerebral lesions, 24 scans for diagnosing tumor progression or recurrence, 8 scans for monitoring of chemotherapy effects, and 11 scans for the detection of residual tumor after resection were obtained. Maximum and mean tumor-to-brain ratios (TBRs) were determined at 20–40 min after injection, and time–activity curves of 18F-FET uptake were assigned to 3 different patterns: constant increase; peak at greater than 20–40 min after injection, followed by a plateau; and early peak (≤20 min), followed by a constant descent. The diagnostic accuracy of 18F-FET PET was assessed by receiver-operating-characteristic curve analyses using histology or clinical course as a reference. Results: In patients with newly diagnosed cerebral lesions, the highest accuracy (77%) to detect neoplastic tissue (19/26 patients) was obtained when the maximum TBR was 1.7 or greater (area under the curve, 0.80 ± 0.09; sensitivity, 79%; specificity, 71%; positive predictive value, 88%; P = 0.02). For diagnosing tumor progression or recurrence, the highest accuracy (82%) was obtained when curve patterns 2 or 3 were present (area under the curve, 0.80 ± 0.11; sensitivity, 75%; specificity, 90%; positive predictive value, 90%; P = 0.02). During chemotherapy, a decrease of TBRs was associated with a stable clinical course, and in 2 patients PET detected residual tumor after presumably complete tumor resection. Conclusion: Our findings suggest that 18F-FET PET can add valuable information for clinical decision making in pediatric brain tumor patients