It has been believed that the first target of radiation carcinogenesis is DNA. However, this is not proved for radiation carcinogenesis yet. We discovered that frequency of aneuploid cell was closely related to that of radiation-induced cell transformation and natural cell transformation by high-density cultivation, but gene mutation was not. Cell with p53 gene becomes tetraploid, but does not get tumorigenicity. On the other hand, cells without p53 gene function become a triploid easily, and acquire tumorigenicity. Both radiation exposure and high-density cultivation elevated the level of intracellular oxidative radicals. These radicals induced centrosome destabilization and produced cells carrying extra centrosome, which promote merotelic attachment of chromosome by altering spindle geometry. Unresolved merotelic attachments can give rise to lagging chromosomes at anaphase. Aneuploidy was seen in high frequency in early process of cell transformation. These results strongly suggest that a main target of carcinogenesis by low dose radiation is not DNA, but is centrosome, which are the proteins to constitute chromosomal homeostasis maintenance mechanism. In addition, this route may be the same as that of natural carcinogenesis. These serial results support necessity of a review of a LNT hypothesis at a radioprotective point of view.
The ion exchange method is generally applied to the analysis of radioactive strontium, 89Sr and 90Sr, in environmental samples because it can be easily handled. However, there are two problems to be solved in this method. One is that it generates a large amount of waste of ion exchange resin and organic solvent. The other is that it uses the organic solvent such as methanol which has a high environmental load. The present study demonstrated that the amount of ion exchange resin can be reduced by choosing the optimal size of ion exchange column depending on calcium content in environmental samples. It also demonstrated that ethanol can be used as organic solvent instead of methanol. Therefore, the risks on the environmental load and working condition can be lowered.
The objective of this study was to evaluate radiation doses to infant, child and adult patients undergoing various types of plain radiography and to compare the doses among them. The doses were measured using newborn, 6-year-child and adult anthropomorphic phantoms, in which photodiode dosimeters were implanted at various tissue and organ positions. Measured doses were used to evaluate organ and effective doses. Organ doses obtained in various types of radiography were lower than 0.7mGy for adults, 0.3mGy for children and 0.2mGy for infants, excepting lens dose of approximately 1mGy in adult head radiography, where the doses for children and infants lowered to 1/2-1/3 of the doses for adults. Effective doses in various types of head radiography for adults, children and infants were in identical levels in a range of 5-30μSv. In chest, abdomen and hip-joint radiography, effective doses of 0.02-0.11mSv for children and 0.02-0.08mSv for infants were identical to or in a fraction of the doses for adults of 0.06-0.15mSv. In adult head and spinal radiography, effective doses by ICRP Publication 60 lowered respectively to 1/6-1/9 and 1/3-1/9 of the doses listed in UNSCEAR 2000.