転移性脳腫瘍患者における全身FDG-PET/CTの有用性

The Usefulness of Whole Body FDG-PET/CT in Patients with Brain Metastasis

Ⅰ．はじめに

　転移性脳腫瘍は，癌患者の15～40％にみられ^4），日常診療で頻繁に遭遇する疾患である．転移性脳腫瘍の治療方針の決定や予後判定の因子として，脳転移巣の数や局在だけではなく，治療前の患者の状態（performance status），年齢，原発巣および他の全身転移の状態が挙げられるが，なかでもperformance statusと頭蓋外の全身転移の状態が最も患者の転帰を左右するといわれる^5,8）．したがって，転移性脳腫瘍の治療では，全身転移を考慮した総合的な判断が必要である．

　従来，転移性脳腫瘍の患者の全身検索は，CT，MRI，シンチグラムなど多種の検査を組み合わせて行われてきたが，多種検査による患者への負担が大きく，さらに結果的には不必要な検査に終わることもある．近年，癌患者の全身検索および治療効果の判定を目的として，¹⁸F-fluorodeoxyglucoseを用いて病巣の糖代謝を評価するFDG-PET（¹⁸F-fluorodeoxyglucose positron emission tomography）検査の有用性が報告されている^11,15）．さらに，FDG-PETの空間分解能の低さを補うべく，CT画像とFDG-PET画像を融合させるFDG-PET/CTが開発された^9）．われわれは，転移性脳腫瘍患者に対して，全身検索目的にFDG-PET/CTを施行し，その有用性について得られた結果を基に報告する．

　In patients presenting with brain metastases, the evaluation for extracranial metastases is important to determine the therapeutic strategies and predict the patients’outcome. We investigated the findings of whole-body FDG-PET/CT in 30 patients with metastatic brain tumors. The patients were divided into two groups consisting of 16 patients with precocious or synchronous metastases (PS group), or 14 patients with metachronous metastases (M group), according to the brain metastatic patterns. In all patients of the PS group, the primary site was the lung. In one patient of the PS group, the primary lesion was detected neither by FDG-PET/CT nor by contrast-enhanced CT or MRI in one patient of the PS group. The primary site of another patient in the PS group was confirmed only by FDG-PET/CT. The sensitivity of FDG-PET/CT in search of primary site was 93.3%, while that of conventional modalities was 87.5%. Maximum standardized uptake value (SUV) of the primary lesions did not show statistically significant difference between groups with single and multiple metastatic brain lesions. SUV also failed to show a statistically significant difference between groups with and without extracranial metastatic lesions. In patients comprising the M group, breast cancer was the most frequent primary site. 3 patients in the M group showed no definite hypermetabolic lesions including the primary sites. Two of them have been clinically independent for more than 20 months. 22 (73.3%) of all patients presented extracranial metastases when brain lesions were found. FDG-PET/CT is a useful modality in detecting the primary cancer and evaluating extracranial systemic metastases. It is important to establish a refined clinical staging system and predict the patient's prognosis based upon the findings of FDG-PET/CT in patients with brain metastasis.