No abstract

We evaluated the diagnostic accuracy of PET with L-methyl-11 Cmethionine ( 11 C-MET) for the differentiation of recurrent brain tumors from radiation necrosis. Methods: Seventy-seven patients who had been previously treated with radiotherapy after primary treatment for metastatic brain tumor (n 5 51) or glioma (n 5 26) were studied to clarify the diagnostic performance of 11 C-MET PET in differentiating between recurrent brain tumors and radiation necrosis. A total of 88 PET scans with 11 C-MET were obtained; sometimes more than one scan was obtained when there was an indication of recurrent brain tumor or radiation necrosis. A definitive diagnosis was made on the basis of pathologic examination for recurrent brain tumors and on the basis of pathologic examination or clinical course for radiation necrosis. Several indices characterizing the lesions were determined; these included mean and maximum standardized uptake values (SUV mean and SUV max , respectively) and the ratios of lesion uptake to contralateral normal frontal-lobe gray matter uptake corresponding to the SUV mean and the SUV max (L/N mean and L/N max , respectively). Receiver-operating-characteristic (ROC) curve analysis was used to determine the optimal index of 11 C-MET PET and cutoff values for the differential diagnosis of tumor recurrence and radiation necrosis. Results: The values of each index of 11 C-MET PET tended to be higher for tumor recurrence than for radiation necrosis. There were significant differences between tumor recurrence and radiation necrosis in all of the indices except for the L/N max for glioma. ROC analysis indicated that the L/N mean was the most informative index for differentiating between tumor recurrence and radiation necrosis. An L/N mean of greater than 1.41 provided the best sensitivity and specificity for metastatic brain tumor (79% and 75%, respectively), and an L/N mean of greater than 1.58 provided the best sensitivity and specificity for glioma (75% and 75%, respectively). Conclusion: 11 C-MET PET can provide quantitative values to aid in the differentiation of tumor recurrence from radiation necrosis, although these values do not appear to be absolute indicators. Quantitative analysis of 11 C-MET PET data may be helpful in managing irradiated brain tumors. Pri mary treatment of brain tumors usually consists of a combination of surgery, radiotherapy, and chemotherapy. Postradiation reactions in the central nervous system can occur after conventional radiotherapy and stereotactic radiosurgery (SRS) (1). Radiation necrosis after the aggressive use of irradiation for malignant brain tumors appears to be more common than previously estimated (2). Differentiating between recurrent brain tumors and radiation necrosis, however, is often difficult with conventional diagnostic imaging techniques, such as MRI (3). This is an unsolved issue in managing irradiated brain tumors.Recently, several imaging modalities, such as MR spectroscopy (4-6), SPECT with 201 Tl-chloride ( 201 Tl) (7), and PET with various radiotracers (...

The use of MET-PET scanning is a sensitive and accurate technique for differentiating between metastatic brain tumor recurrence and radiation necrosis following stereotactic radiosurgery. This study reveals important information for creating strategies to treat postradiation reactions.

A lthough malignant tumors metastasizing into the pituitary fossa are not infrequent events in autopsy series, 6,10,17,18 pituitary metastasis (PM) is rarely diagnosed ante mortem. 3,14,18 According to the Brain Tumor Registry of Japan, only 0.4% of intracranial metastatic tumors are located in the pituitary gland. 5 These tumors account for only 1% of surgically treated pituitary tumors. 8,16,31 Recently, as the number of patients diagnosed with cancer has increased and their survival time has been extended, PMs have been diagnosed more frequently than before. 16,20,24 Many authors have reported their own experiences or their institutional series on PMs. 3,11,13,14,20,26,31 There are also reviews involving large numbers of reported cas- results Between 1995 and 2010, 201 patients with PMs were treated by the participating physicians. The diagnosis of PM was histologically verified in 69 patients (34.3%). In the other 132 patients (65.7%), the PM was diagnosed by their physicians based on neuroimaging findings and clinical courses. The most frequent primary tumor was lung (36.8%), followed by breast (22.9%) and kidney (7.0%) cancer. The average interval between diagnosis of primary cancer and detection of PM was 2.8 ± 3.9 (SD) years. Major symptoms at diagnosis were visual disturbance in 30.3%, diabetes insipidus in 27.4%, fatigue in 25.4%, headache in 20.4%, and double vision in 17.4%. Major neuroimaging features were mass lesion in the pituitary stalk (63.3%), constriction of tumor at the diaphragmatic hiatus (44.7%), hypothalamic mass lesion (17.4%), and hyperintensity in the optic tract (11.4%). Surgical treatment was performed in 26.9% of patients, and 74.6% had radiation therapy; 80.0% of patients who underwent radiotherapy had stereotactic radiotherapy. The median survival time was 12.9 months in total. Contributing factors for good prognosis calculated by Cox proportional hazard analysis were younger age, late metastasis to the pituitary gland, smaller PM size, and radiation therapy. The Kaplan-Meier survival was significantly better in patients with breast cancer and renal cell cancer than in those with lung cancer. coNclusioNs At the time of this writing, approximately 60% (120/201) of PMs had been treated by stereotactic radiation therapy in Japan. The median survival time was much longer than that reported in past series. To confirm the changes of clinical features and medical practice, a prospective and population-based survey is mandatory.

There were no significant differences between recurrent malignant glioma and radiation necrosis following SRS in Met-PET. However, this study shows Met-PET has a sensitivity and accuracy for differentiating between recurrent glioma and necrosis, and presents important information for developing treatment strategies against post radiation reactions.