The Use of Positron Emission Tomography and Computed Tomography (PET-CT) with 11C-L-Methionine in the Diagnosis of Glial Tumors

Background. Primary brain tumor lesions include gliomas, which, according to epidemiological data, make up about 30% of all tumors of the central nervous system and are the most common. Overall and relapse-free survival rates depend on the degree of glioma malignancy and the histopathological nature of the detected lesion. For better treatment and prognosis, it is necessary to determine the exact location and histopathological nature of the tumor. Magnetic resonance imaging (MRI) remains the method of choice for structural brain assessment, but even with the use of contrast enhancement (CE), it does not always allow for reliable differentiation between tumor progression and post-therapeutic changes (radionecrosis, postoperative scars, cysts, inflammation) in patients after antitumor treatment. Radiopharmaceuticals, in particular 11 C-L-methionine, provide an assessment of tumor amino acid metabolism and complement structural data, increasing diagnostic accuracy. MRI, positron emission tomography and computed tomography (PET-CT) with 11 C-L-methionine in combination with morphological examination of the sample after stereotactic biopsy have shown high efficiency in the diagnosis of gliomas with varying degrees of malignancy. Objective: to study the possibilities of applying PET-CT with 11 C-L-methionine in the diagnosis of continued growth and recurrence of glial tumors, as well as to conduct differential diagnostics with postoperative non-neoplastic changes. Material and methods. A retrospective, descriptive, analytical study was conducted in the Department of Radionuclide Therapy and Diagnostics of the Saint Petersburg Clinical Scientific and Practical Center for Specialized Types of Medical Care (Oncological) named after N.P. Napalkov. It included 67 patients (34 men and 33 women aged 17 to 75 years, mean age was 43.5±15.6 years) for whom PET-CT was carried out in the period from 2007 to 2015 after neurosurgical treatment with suspected continued growth of glial tumors. All patients underwent CE-MRI and CE-CT. Correlation coefficient (r) was used to estimate the level of dependence between PET-CT data. Results. In 55% of the cases, continued growth of high-grade gliomas (Grades IV and III) was detected. In these patients, the radiopharmaceutical accumulation index ranged from 1.3 to 5.1, with mean value 2.9±0.85. In patients with continued growth of benign astrocytomas, the degree of 11 C-L-methionine accumulation varied with mean value 1.6±0.51. The sensitivity and specificity of PET-CT in detecting brain glioma progression were 92.3% and 73.3%, respectively. The combination of CE-MRI and PET-CT provided a sensitivity of 96.1% in diagnosing glioma tumor progression. The results show that MRI and PET-CT data are consistent in 45 of 48 cases (92.8%) of proven glioma progression. An accumulation index greater than 2 can predict continuous growth of malignant glioma with 95% accuracy, and the threshold for differentiating benign glioma from inflammatory lesions is 0.9. Conclusion. Although PET-CT has good sensitivity in differentiating postoperative lesions in patients with glioma, CE-MRI is necessary for localized and earlier diagnosis. The lack of visualization of avascular gliomas is one of the limitations of PET-CT, although CE-MRI does not exclude them.