Differentiation of Brain Tumor Recurrence from Post-Radiotherapy Necrosis with 11C-Methionine PET: Visual Assessment versus Quantitative Assessment.

The aim of this multi-center study was to assess the diagnostic capability of visual assessment in L-methyl-11C-methionine positron emission tomography (MET-PET) for differentiating a recurrent brain tumor from radiation-induced necrosis after radiotherapy, and to compare it to the accuracy of quantitative analysis.A total of 73 brain lesions (glioma: 31, brain metastasis: 42) in 70 patients who underwent MET-PET were included in this study. Visual analysis was performed by comparison of MET uptake in the brain lesion with MET uptake in one of four regions (around the lesion, contralateral frontal lobe, contralateral area, and contralateral cerebellar cortex). The concordance rate and logistic regression analysis were used to evaluate the diagnostic ability of visual assessment. Receiver-operating characteristic curve analysis was used to compare visual assessment with quantitative assessment based on the lesion-to-normal (L/N) ratio of MET uptake.Interobserver and intraobserver κ-values were highest at 0.657 and 0.714, respectively, when assessing MET uptake in the lesion compared to that in the contralateral cerebellar cortex. Logistic regression analysis showed that assessing MET uptake in the contralateral cerebellar cortex with brain metastasis was significantly related to the final result. The highest area under the receiver-operating characteristic curve (AUC) with visual assessment for brain metastasis was 0.85, showing no statistically significant difference with L/Nmax of the contralateral brain (AUC = 0.89) or with L/Nmean of the contralateral cerebellar cortex (AUC = 0.89), which were the areas that were the highest in the quantitative assessment. For evaluation of gliomas, no specific candidate was confirmed among the four areas used in visual assessment, and no significant difference was seen between visual assessment and quantitative assessment.The visual assessment showed no significant difference from quantitative assessment of MET-PET with a relevant cut-off value for the differentiation of recurrent brain tumors from radiation-induced necrosis

Results of quantitative analysis.

<p>AUC: area under the receiver-operating characteristic curve.</p><p>Results of quantitative analysis.</p

(A) 60-year-old male with recurrence of brain metastasis (lung carcinoma) at left temporal lobe (arrow head).

<p>MET uptake of the MRI-enhanced lesion showed higher than the region around the lesion, the contralateral brain, the contralateral frontal lobe and cerebellum. (B) 26-year-old male with recurrence of an anaplastic astrocytoma in the right temporal lobe. Contrast-enhanced MRI showed gadolinium-enhanced nodular lesion (arrow) in the right temporal lobe, which was the location of post-surgical resection of the primary brain tumor. MET uptake of the MRI-enhanced lesion (arrow head) showed higher than the region around the lesion, the contralateral brain, the contralateral frontal lobe and cerebellum. (C) 59-year-old female with radiation necrosis. Contrast-enhanced MRI showed gadolinium-enhanced lesion (arrow head) at the corpse callosum, which was suspected recurrent brain metastasis (lung carcinoma). MET uptake of the MRI-enhanced lesion showed slightly higher than the region around the lesion, the contralateral brain, and the contralateral frontal lobe, but similar to MET uptake at cerebellum.</p

Representative methionine PET (MET-PET) images from the three PET centers (A, B, and C) and reference contrast-enhanced MRIs from patients with recurrent gliomas.

<p>All lesions are indicated with arrow heads.</p