Ion beam large area irradiation is required in R&D for material science and bio-technology using a cyclotron. Easy measurement technique for two dimensional dose distribution was developed using combination of Gaf-chromic dosimeter film HD-810 (Surface protection layer:0.75μm, Sensitive layer:6.5μm) and an image scanner (Spatial resolution:5.3μm) for personal computer. A practical system giving a relative distribution by one arbitrary irradiation was realized on the basis of difference in dose response among RGB color components. All dose response curves measured by CCD and CIS (3LED) model scanners have a linear region from zero to some hundreds of Gy but with different slopes. Therefore any commercial scanner can be used for 2D relative dose distribution measurement system once after preparing dose response curve using irradiated Gaf-chromic film for calibration.

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Radioadaptive response is a biodefensive response observed in a variety of mammalian cells and animals where exposure to low dose radiation induces resistance against the subsequent high dose radiation. Elucidation of its mechanisms is important for risk estimation of low dose radiation because the radioadaptive response implies that low dose radiation affects cells/individuals in a different manner from high dose radiation. In the present study, we explored the molecular mechanisms of the radioadaptive response in human lymphoblastoid cells AHH-1 in terms of mutation at the HPRT gene locus. First we observed that preexposure to the priming dose in the range from 0.02Gy to 0.2Gy significantly reduced mutation frequency at HPRT gene locus after irradiation with 3Gy of X rays. As no significant adaptive response was observed with the priming dose of 0.005Gy, it was indicated that the lower limit of the priming dose to induce radioadaptive response may be between 0.005Gy and 0.02Gy. Second, we examined the effect of 3-aminobenzamide(3AB), an inhibitor of poly(ADP-ribose)polymerase1, which has been reported to inhibit the radioadaptive response in terms of chromosome aberration. However we could observe significant radioadaptive responses in terms of mutation even in the presence of 3AB. These findings suggested that molecular mechanisms of the radioadaptive response in terms of mutation may be different from that for radioadaptive responses in terms of chromosomal aberration, although we could not exclude a possibility that the differential effects of 3AB was due to cell type difference. Finally, by performing a comprehensive analysis of alterations in gene expression using HiCEP, we could identify 17 genes whose expressions were significantly altered 6h after irradiation with 0.02Gy. We also found 17 and 20 genes, the expressions of which were different with or without priming irradiation 3 and 18h, respectively, after challenge irradiation of 3Gy. By analyzing the gene function, it was found that expression of genes involved in intracellular signaling and redox-regulation is correlatively altered with, and therefore considered the molecular basis of, radioadaptive responses.

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To gain a better understanding on the β-ray radiography of lyophilized animal sections, the bone densities of the osteoporosis rats were measured using a ¹⁴⁷Pm planar radiation source. An imaging plate as a radiation sensor was overlaid on the animal section together with a density calibrator. After exposure, radioactivity recorded on the sensor was quantified using a bio-imaging analyzer. The density calibration curve showed linearity in the wide range with a good correlation coefficient(R²≥0.999). The inter- and intra-plate variability showed CV values less than 3.7%. On the measurement of bone density, bone density differences between the sham group and ovariectomized(OVX)group were statistically significant in the femoral cortical(p=0.001)and trabecular bone(p=0.07), and vertebral trabecular bone(p=0.043). Based on these results, we developed a new and valuable method, which made it possible to measure bone density of axial skeleton of a rat, as an alternative to commonly used methods.

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[in Japanese]

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