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

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 use of O-(2-F-18-fluoroethyl)-L-tyrosine PET in the diagnosis of gliomas located in the brainstem and spinal cord

Despite an increasing number of O-(2-F-18-fluoroethyl)-L-tyrosine (F-18-FET) PET studies in supratentorial gliomas, studies regarding the usefulness of F-18-FET PET in brainstem and spinal cord gliomas to date remain scarce. Thirty-six F-18-FET PET scans were performed in 29 patients with brainstem (n = 29 scans) or spinal cord glioma (n = 7 scans). In 32 of 36 PET scans, a dynamic acquisition was performed. Fifteen scans in 15 patients were performed to assess newly diagnosed lesions, and 21 scans were obtained during follow-up: for diagnosing tumor progression (n = 15 scans in 14 patients) as well as for treatment monitoring (n = 6 scans in 3 patients). Four patients underwent additional serial scans (range, 1-2), and 3 of these 4 patients were examined for more than one indication. Maximum and mean tumor/brain ratios (TBRmax/mean) of F-18-FET uptake (20-40 min post injection) as well as kinetic F-18-FET uptake parameters were determined. Final diagnoses were confirmed histologically (54%) or by clinical follow-up (46%). In all newly diagnosed high-grade (n = 3 patients) and in 5 of 11 patients with low-grade gliomas, F-18-FET uptake was increased (TBRmax a parts per thousand 2.5 and/or TBRmean a parts per thousand 1.9). In 2 patients with newly diagnosed gliomas without MR contrast enhancement, F-18-FET PET nevertheless showed increased metabolism. At suspected progression, the combination of TBRs with kinetic F-18-FET parameters correctly identified presence or absence of progressive disease in 9 of 11 patients (82%). This preliminary study suggests that F-18-FET PET adds valuable diagnostic information in brainstem and spinal cord glioma, particularly when the diagnostic information derived from MRI is equivocal

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

Background. O-(2-[F-18]-fluoroethyl)-L-tyrosine (FET) PET has a sensitivity of more than 90% to detect gliomas. In the remaining small fraction of gliomas without increased tracer uptake, some tumors even show photopenic defects whose clinical significance is unclear. Methods. Glioma patients with a negative FET PET scan prior to neuropathological confirmation were identified retrospectively. Gliomas were rated visually as (i) having indifferent FET uptake or (ii) photopenic, if FET uptake was below background activity. FET uptake in the area of signal hyperintensity on the T2/fluid attenuated inversion recovery-weighted MRI was evaluated by mean standardized uptake value (SUV) and mean tumor-to-brain ratio (TBR). The progression-free survival (PFS) of photopenic gliomas was compared with that of gliomas with indifferent FET uptake. Results. Of 100 FET-negative gliomas, 40 cases with photopenic defects were identified. Fifteen of these 40 cases (38%) had World Health Organization (WHO) grades III and IV gliomas. FET uptake in photopenic gliomas was significantly decreased compared with both the healthy-appearing brain tissue (SUV, 0.89 +/- 0.26 vs 1.08 +/- 0.23; P < 0.001) and gliomas with indifferent FET uptake (TBR, 0.82 +/- 0.09 vs 0.96 +/- 0.13; P < 0.001). Irrespective of the applied treatment, isocitrate dehydrogenase (IDH)-mutated WHO grade II diffuse astrocytoma patients with indifferent FET uptake (n = 25) had a significantly longer PFS than patients with IDH-mutated diffuse astrocytomas (WHO grade II) with photopenic defects (n = 11) (51 vs 24 mo; P = 0.027). The multivariate survival analysis indicated that photopenic defects predict an unfavorable PFS (P = 0.009). Conclusion. Photopenic gliomas in negative FET PET scans should be managed more actively, as they seem to have a higher risk of harboring a higher-grade glioma and an unfavorable outcome

Dynamic O -(2-18^{18} F-fluoroethyl)-L-tyrosine positron emission tomography differentiates brain metastasis recurrence from radiation injury after radiotherapy

BackgroundThe aim of this study was to investigate the potential of dynamic O-(2-[18F]fluoroethyl)-L-tyrosine (18F-FET) PET for differentiating local recurrent brain metastasis from radiation injury after radiotherapy since contrast-enhanced MRI often remains inconclusive.MethodsSixty-two patients (mean age, 55 ± 11 y) with single or multiple contrast-enhancing brain lesions (n = 76) on MRI after radiotherapy of brain metastases (predominantly stereotactic radiosurgery) were investigated with dynamic 18F-FET PET. Maximum and mean tumor-to-brain ratios (TBRmax, TBRmean) of 18F-FET uptake were determined (20–40 min postinjection) as well as tracer uptake kinetics (ie, time-to-peak and slope of time-activity curves). Diagnoses were confirmed histologically (34%; 26 lesions in 25 patients) or by clinical follow-up (66%; 50 lesions in 37 patients). Diagnostic accuracies of PET parameters for the correct identification of recurrent brain metastasis were evaluated by receiver-operating-characteristic analyses or the chi-square test.ResultsTBRs were significantly higher in recurrent metastases (n = 36) than in radiation injuries (n = 40) (TBRmax 3.3 ± 1.0 vs 2.2 ± 0.4, P < .001; TBRmean 2.2 ± 0.4 vs 1.7 ± 0.3, P < .001). The highest accuracy (88%) for diagnosing local recurrent metastasis could be obtained with TBRs in combination with the slope of time-activity curves (P < .001).ConclusionsThe results of this study confirm previous preliminary observations that the combined evaluation of the TBRs of 18F-FET uptake and the slope of time-activity curves can differentiate local brain metastasis recurrence from radiation-induced changes with high accuracy. 18F-FET PET may thus contribute significantly to the management of patients with brain metastases