| Research Abstract |
(1) We subcutaneously transplanted cells of human ependymoblastoma, glioblastoma, and small cell lung cancer (SCLC) into nude mice, irradiated them with 10 Gy X-ray at 200 kV, excised the tumors 3, 4.5, or 6 hours after irradiation, produced sections, and examined the changes in the distribution of elements by cell death, apoptosis and necrosis, using an in-air micro-particle-induced X-ray emission (micro-PIXE). In the non-irradiated tumors, phosphorus (P), potassium (K), chlorine (C1), and sulfur (S) were observed in the nuclei and cytoplasm of viable tumor cells, and these elements were significantly decreased in small necrotic lesions. In ependymoblastoma, apoptosis was markedly induced after irradiation, but it was difficult to clearly detect the changes in the distribution of these elements by the micro-PIXE. In glioblastoma and SCLC, small necrotic lesions were observed, and P, K, Cl, and S were significantly decreased, agreeing well with morphological findings.
(2) Human brain tu
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mors (glioblastoma, ependymoblastoma, and primitive neuroectodermal tumor : PNET) were transplanted to nude mice subcutaneously, and the mice were irradiated with carbon ion beams (290MeV/u, 6cm SOBP) or 200kV X-rays. Tumors, brains, spleens, kidneys, duodenums, and testes were excised and weighed 6 or 48 hours after irradiation, and they were microscopically examined to evaluate apoptosis and other histological changes. Carbon ion beams were more effective than X-rays and the RBE values were more than 1.0, but the values varied according to the tumors and endpoints. The incidences of apoptosis 6 hours after 0.25-1 Gy irradiation were 5-49/high power field (HPF) by carbon ion and 3-9/HPF by X-ray in the ependymoblastoma. Those values were 1.2-4.0/HPF by carbon ion and 0.4-1.0/HPF by X-ray in the glioblastoma. RBE values were 3.0, 3.6, and 6.1 for the ependymoblastoma, the PNET, and the glioblastoma, respectively. In contrast, RBE values of radiosensitive normal tissues were 1.2-2.1. These results suggest that the heavy ion beams are more favorable for treating radioresistant tumors than X-rays. Less
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