Gadolinium neutron capture therapy for malignant brain tumors

概要

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Tumoricidal effect on malignant brain tumor of gadolinium neutron capture reactions has been preliminary studied. In-vitro C6 37% survival dose (D_<37>) were obtained at 3.55×10^<12>n/cm^2 in 500ppm ^nGd medium, 1.40×10^<12>n/cm^2 in 2,500ppm ^nGd containing medium, and 6.80×10^<12>n/cm^2 in Gd-free medium. The relative killing effect of GdNCT against control study was 1.92 fold for 500ppm ^nGd(+) and 4.86 fold for 2,500ppm Gd(+). The significant survival prolongation of 9L brain tumor rat was observed by intra-venous injection of GdDTPA. Mean survival via GdNCT was 33.5±3.0 days, and that of control rats was 16.4±0.6 days. The optimal Gd concentration was estimated less than 1,000ppm ^<157>Gd for various reasons, since neutron fluence rapidly decrease in the deeply seated tumor due to high absorption of neutron by Gd atoms. The maximum contribution of γ rays on tumor absorbed dose was less than 50%. In a spherical tumor model in diameter of 3cm, approximately 25% of absorbed dose was transferred by γ rays and more that 50% of that by internal conversion electrons. The peri-tumoral dose distribution does not decrease sharply like BNCT. The 10% decrease level was estimated to be 2-3cm from the tumor margin. This blunt dose distribution might be effective to destroy the invading tumor cells in the peri-tumoral lesion manifesting as high density area in T^2-weighted MRI.
藍野大学の論文