| Objective Differential diagnosis between tumor recurrence and radiation necrosis is important in the clinical management of glioma after radiotherapy.In this study,we evaluate the value of 11C-methionine positron emission tomography/ X-ray computed tomography (MET PET/CT) in differentiation of tumor recurrence from radiation necrosis and the therapeutic results of recurrent glioma.Methods From June 2008 to September 2009, 30 patients who had previously been treated with radiotherapy were suspected to have recurrent glioma or radiation injury.MET PET was performed on these patients. According to the World Health Organization (WHO) classification, initial tumor histologies included 19 gradeⅡ, 9 gradeⅢand 2 gradeⅣ.30 patients had previously received operation and adjuvant radiotherapy,the dose of initial radiotherapy range from54 to60Gy(median dose 58Gy);only 17 received adjuvant chemotherapy after operation. The median time between initial radiotherapy and PET was 13.5 months,ranging from 5 to 90 months.There were 21 males and 9 females,the median patient age was 41 years ,ranging from 11 to 69 years. PET was carried out with Biograph HR16 scanner(Siemens,Germany),PET images were obtained as a static scan 10 minutes after injection of 740MBq MET.The PET images were reconstructed using measured attenuation reconstruction(3mm ).On PET scans,the portion of the tumor with the highest accumulation was selected as the region of interest(ROI),and several ROIs with the same diameter were located over the gray matter of the contralateral lobe.If no abnormality could be detected ,a circular ROI of the same size was located over the area corresponding to the MRI abnormality.The standardized uptake value(SUV) was caculated over the same tumor ROI as follows:SUV=[(pixel count/pixel volume)/(injected radioisotope activity/body weight)]×calibration factor. L/N(the lesion-to-normal tissue ratio )= SUVmean of the lesion/ SUVmean of the contrallateral gray matter. The survival time was calculated from the day of performing PET.The tumor recurrence was confirmed by correlating findings with subsequent histological analysis,the diagnosis of necrosis was based on histological analysis and the subsequent clinical follow-up(>6 months) and MRI/ CT in case without surgery or biopsy.Results The follow-up investigation continued to March 2010(the median time 11 months).19 recurrence and 11 radiation necroses were shown in PET images.There are 19 cases considered to have recurrent tumor were eveluated by histopathological findings,18 showed viable glioma and 1 showed necrosis .Within 18 recurrent cases,1 case whose initial tumor hisyology was WHO grade II was pathologically confirmed as having oligodendroglioma mixed with ependymoma;10 cases had the same hisyology after recurrence;7 cases whose initial tumor histology was WHO grade II was pathologically confirmed as having anaplastic astrocytoma. While 11 cases were considered to have radiation necrosis because they exhibited stable neurological sympotoms with no sign of massive enlargement of the lesion on follow-up MRI/CT after 6 months.According to a 2×2 factorial analysis,the sensitivity,specificity and accuracy of MET PET for detecting tumor recurrence were 100% and 91.7% and 96.7% respectively. The 1-year overall survival (OS) rates was 82%,and the median survival time 8.5 months (5-15 months) within the subset of patients with recurrent glioma.Only 3 patients died after biopsy(1 without further therapy,1 with SRS and 1 with chemotherapy). There was significant difference of survival time between craniectomy and biopsy in 18 recurrent cases(P=0.002).Conclusion PET is a powerful tool in differentiating brain tumor recurrence from radiation necrosis after radiotherapy and recurrent glioma may benefit more from craniectomy than biopsy. |
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