神経膠腫の悪性度別での201TlClの集積動態の差異—Dynamic SPECTを用いた検討

201TlCl Accumulation Dynamics in Glioma with Different Grades of Malignancy : an investigation using dynamic SPECT

I．はじめに

　²⁰¹Thallium chloride（²⁰¹TlCl）は，single-pho-ton emission computed tomography（SPECT）上，脳腫瘍への選択的な集積を示し，その集積程度は腫瘍代謝を反映するとされる^{1,3,5,8-12,14,15,18,19,21,22）}．神経膠腫においては，悪性度に伴って²⁰¹TlClが高集積を示す傾向にあり，鑑別診断上，有用と考えられている^{3,8,9,11,12,14,15,18）}．しかし，実際には，gliomaの悪性度を²⁰¹TlClの集積程度のみで明確に分けることができない症例が存在することも事実であり，未だ一般臨床において充分な情報を得られるまでに至っていないと考えられる．

　今回，われわれは，短時間データ収集によるdynamic SPECTを用いて，神経膠腫の各悪性度別での²⁰¹TlClの経時的な集積動態を比較し，その臨床的有用性を検討したので報告する．

Dynamic SPECT was performed using in a total of ²⁰¹TlCl in a total of 21 gliomas, 14 cases of glioblastoma multi-forme (GM) and 7 cases of anaplastic astrocytoma (AA), to investigate the relationship between test re-sults and malignancy. The accumulation of isotope (counts/pixel) in the tumor was measured every 3 mi-nutes with dynamic SPECT. The initial 3-minute value was reduced from subsequent accumulations(counts/minute) to obtain the time-activity curve (TAC. Thallium index (TL, index), the ratio of 15-mi-nute accumulation in the tumor to that in the same region of the contralateral normal brain, was also calcu-lated. Tl- index was significantly higher (p＜0.05, Mann-Whitney test) in GM (6.25±1.97) thanin AA(4.10 ± 1.66), although no clear differential value could be determined between the two. TAC in the GMgroup showed that compared with the initial 3-minute value, accumulation increased significantly(p＜0.05)at every measurement point after isotope injection : 6 minutes, 0.660±0.671 ; 9 minutes, 1.322±1.319 ; 12minutes, 1.315±1.632 and 15 minutes, 1.234±1.552. The increase in isotope accumulation in thetumor after6 minutes or later was noted in 11 of the 14 cases in the GM group. In the AA group, however, therewereno significant differences between the initial 3-minute value and value after 6 minutes (0.283±0.462), 9mintes -0.574±0.681), 12 minutes (-0.690±0.611) and 15 minutes (-0.707±0.636) afterisotope injec-tion. A decrease in isotope accumulation in the tumor after 6 minutes or later was noted in 6 of the7 casesin the AA group. Compared with static SPECT, dynamic SPECT, which can be performed easily andquickly, is more useful in clinical settings because of its high ability to differentiate the grade ofmalignan-cy of gliomas.