Differential diagnosis of the treated brain malignancies by using 18F-BPA PET

Recently, new radiation therapies using high absorbed doses to tumor tissue have been developed for patients with malignant gliomas, mainly glioblastomas (GB). Clinically, the differential diagnosis of the tumor progression (TP) of GB and radiation necrosis (RN) has become important, as has the assessment of tumor activity after adjuvant therapy. We determined how to evaluate tumor activity before and/or after radiation therapy using positron emission tomography (PET) with boronophenylalanine (BPA) as a tracer. Fluoride-18 labeled BPA-PET (18F-BPA-PET) scans were performed on 38 cases of histologically verified GB. Nineteen cases had newly diagnosed glioblastomas (NDGB) and 19 had recurrent glioblastoma (Rec. GB), and the lesion/normal brain (L/N) ratios of NDGB ranged from 2.1 to 7.1 (4.3±1.3, mean±standard deviation (SD)), and those of Rec. GB ranged from 2.6 to 7.0 (3.9±1.4). There was no significant difference in the L/N ratio between NDGB and Rec. GB. Histologically verified RN cases were composed of eight complete RN, and five primarily RN with partial residual cells. There was a significant difference in the L/N ratio for complete RN and RN with tumor cells. Significant statistical differences of the L/N ratios were observed in both groups, all GB and RN with and without tumor cells. Of these, 10 cases showed enlargement of the original enhanced lesion or the occurrence of new lesions far from the original site (OS) after radiation therapy on follow-up MRI. From among these 10 cases, 12 lesions were re-analyzed with 18F-BPA-PET and, in 7 of those, a histological diagnosis was obtained after the second PET study. We compared the L/N ratios of BPA accumulation to differentiate RN and TP of GB. The L/N ratios of the 10 OS lesions were 3.6±1.0 in the first PET and 1.7±0.4 in the second (p<0.05). In the second PET, 2 lesions among the 10 cases still showed high L/N value, and were diagnosed as TP and the remaining 10 lesions were considered RN (histological confirmation: 7 cases, speculation from clinical course: 3 cases). There were significant differences between TP of GB and RN in the L/N ratio of 18F-BPA-PET. 18F-BPA-PET is an excellent modality for evaluating GB tumor activity before and/or after radiation treatment. (author)