Kumiko Fukutsu

Inactivation of Aerobic and Hypoxic Cells from Three Different Cell Lines by Accelerated 3He-, 12C- and 20Ne-Ion Beams

Abstract Furusawa, Y., Fukutsu, K., Aoki, M., Itsukaichi, H., Eguchi-Kasai, K., Ohara, H., Yatagai, F., Kanai, T. and Ando, K. Inactivation of Aerobic and Hypoxic Cells from Three Different Cell Lines by Accelerated 3He-, 12C- and 20Ne-Ion Beams. The LET-RBE spectra for cell killing for cultured mammalian cells exposed to accelerated heavy ions were investigated to design a spread-out Bragg peak beam for cancer therapy at HIMAC, National Institute of Radiological Sciences, Chiba, prior to clinical trials. Cells that originated from a human salivary gland tumor (HSG cells) as well as V79 and T1 cells were exposed to 3He-, 12C- and 20Ne-ion beams with an LET ranging from approximately 20–600 keV/μm under both aerobic and hypoxic conditions. Cell survival curves were fitted by equations from the linear-quadratic model and the target model to obtain survival parameters. RBE, OER, α and D0 were analyzed as a function of LET. The RBE increased with LET, reaching a maximum at around 200 keV/μm, then decreased with a further increase in LET. Clear splits of the LET-RBE or -OER spectra were found among ion species and/or cell lines. At a given LET, the RBE value for 3He ions was higher than that for the other ions. The position of the maximum RBE shifts to higher LET values for heavier ions. The OER value was 3 for X rays but started to decrease at an LET of around 50 keV/μm, passed below 2 at around 100 keV/μm, and then reached a minimum above 300 keV/μm, but the values remained greater than 1. The OER was significantly lower for 3He ions than the others.

Characterization and application of UV detector spore films: the sensitivity curve of a new detector system provides good similarity to the action spectrum for UV-induced erythema in human skin

The UV action spectra of two different biologically weighting UV photofilms (spore films), produced with Bacillus subtilis spores (wild-type and DNA repair-deficient strains), were determined at the Okasaki large spectrograph (OLS) within the level of wavelength range 254-400 nm. The action spectrum of the mutant strain film was modified with a cut-off filter, yielding a sensitivity curve similar to the action spectrum for erythemal induction in human skin. The detector system was tested in a field study and in a study using lamps with different UV spectral compositions. The system demonstrated its applicability over the spectral region lambda = 290 nm to the visible light. The system could be calibrated to give the minimal erythemal dose.

Radon–Thoron Discriminative Measurements in Gansu Province, China, and Their Implication for Dose Estimates

Indoor radon measurements were carried out in cave dwellings of the Chinese loess plateau in Gansu province, where previously the Laboratory of Industrial Hygiene (LIH), China, and the U.S. National Cancer Institute (NCI) had conducted an international collaborative epidemiological study. The LIH–NCI study showed an increased lung cancer risk due to high residential radon levels, and estimated the excess odds ratio at 100 Bq/m3 to be 0.19 (Wang et al., 2002). The present study used two types of newly developed passive monitors: One is a discriminative monitor for radon and thoron; the other is a selective monitor for thoron decay products. The arithmetic mean concentrations of indoor radon and thoron were 91 and 351 Bq/m3, respectively. As reported by our previous study in Shanxi and Shaanxi provinces (Tokonami et al., 2004), the presence of high thoron concentration was confirmed and thoron was predominant over radon in the cave dwellings. However, the mean equilibrium equivalent thoron concentration (EETC) was found to be much lower than expected when assuming the equilibrium factor of 0.1 provided by the UNSCEAR (2000) report. The effective dose by radon and thoron decay products was estimated to be 3.08 mSv/yr. It was significantly lower than the dose of 8.22 mSv/yr estimated from the measurements that did not take into consideration any discrimination between radon and thoron. Excess relative risk of lung cancer per sievert may be much higher than the risk estimated from the LIH–NCI study, considering that discriminative measurements were not used in their study.

Response of mouse intestine after single and fractionated irradiation with accelerated carbon ions with a spread-out Bragg peak

The responses of mouse intestine were examined after irradiation with accelerated carbon ions with a spread-out Bragg peak. The carbon-ion beam (135 MeV/nucleon), accelerated by the RIKEN ring cyclotron facility, was modulated to have a spread-out Bragg peak (SOBP) 3 cm wide. In the SOBP the biological dose (relative physical dose x RBE) was designed in earlier studies to be flat at the 10% survival level of Chinese hamster V79 cells. The numbers of surviving crypt clonogenic cells after single and fractionated irradiation with the carbon-ion beam were obtained by a microcolony assay method. The composite single-dose survival curves for the crypt clonogenic cells were calculated and fitted by a linear-quadratic (LQ) model. An analysis with the LQ model for crypt clonogenic cells showed that the alpha coefficient increased along with increasing LET, and that the beta coefficient was relatively constant, even for high-LET radiations. The biological dose distributions for the crypt clonogenic cells at the 10% survival level were flat in the SOBP. The isoeffective design of the SOBP for the 135 MeV/nucleon carbonion beam, based on biological data from a mammalian in vitro cell system, appears to be applicable to the response of murine intestinal tissue in vivo.

Transmission experiments of cilia-associated respiratory bacillus in mice, rabbits and guineapigs

Transmission experiments of cilia-associated respiratory (CAR) bacillus were performed in mice in order to clarify the principal route of the infection, and in rabbits and guineapigs in order to examine their susceptibility. Determination of the infection was evaluated serologically by the indirect immunofluorescence assay (IFA) technique and histologically by the presence of CAR bacillus in the airways. BALB/c mice were intranasally inoculated with the SMR strain of CAR bacillus. The IFA antibody to the bacteria in these mice rose to more than 1 : 160 at 4 weeks postinoculation (PI) and the mice were utilized as transmitters for the following experiments. One out of 15 uninfected mice kept in intracage contact with infected mice became infected from 4 weeks after contact. Incidence of contact infection increased thereafter. On the other hand, there was no evidence of infection in the uninfected mice housed in the separate cages from the cage in which infected mice were housed throughout the 12-week observation period. The primary method of CAR bacillus transmission seems to be direct contact with infected mice or fomites contaminated by infected mice; airborne transmission appears to be of little importance. Rabbits and guineapigs were also intranasally inoculated with the SMR strain of CAR bacillus. IFA antibodies were positively detected by 4 weeks PI, but no CAR bacillus nor histological changes relating to the infection were observed in the airways of either species. It is suggested that rat origin CAR bacillus can transmit to rabbits and guineapigs, and that the infection can spread to other species of rodents and rabbits.

The role of DNA repair on cell killing by charged particles

It can be noted that it is not simple double strand breaks (dsb) but the non-reparable breaks that are associated with high biological effectiveness in the cell killing effect for high LET radiation. Here, we have examined the effectiveness of fast neutrons and low (initial energy = 12 MeV/u) or high (135 MeV/u) energy charged particles on cell death in 19 mammalian cell lines including radiosensitive mutants. Some of the radiosensitive lines were deficient in DNA dsb repair such as LX830, M10, V3, and L5178Y-S cells and showed lower values of relative biological effectiveness (RBE) for fast neutrons if compared with their parent cell lines. The other lines of human ataxia-telangiectasia fibroblasts, irs 1, irs 2, irs 3 and irs1SF cells, which were also radiosensitive but known as proficient in dsb repair, showed moderated RBEs. Dsb repair deficient mutants showed low RBE values for heavy ions. These experimental findings suggest that the DNA repair system does not play a major role against the attack of high linear energy transfer (LET) radiations. Therefore, we hypothesize that a main cause of cell death induced by high LET radiations is due to non-reparable dsb, which are produced at a higher rate compared to low LET radiations.

Repair of DNA double-strand breaks and cell killing by charged particles.

It has been suggested that it is not simple double-strand breaks (dsb) but the non-reparable breaks which correlate well with the high biological effectiveness of high LET radiations for cell killing (Kelland et al., 1988; Radford, 1986). We have compared the effects of charged particles on cell death in 3 pairs of cell lines which are normal or defective in the repair of DNA dsbs. For the cell lines SL3-147, M10, and SX10 which are deficient in DNA dsb repair, RBE values were close to unity for cell killing induced by charged particles with linear energy transfer (LET) up to 200 keV/micrometer and were even smaller than unity for the LET region greater than 300 keV/micrometer. The inactivation cross section (ICS) increased with LET for all 3 pairs. The ICS of dsb repair deficient mutants was always larger than that of their parents for all the LET ranges, but with increasing LET the difference in ICS between the mutant and its parent became smaller. Since a small difference in ICS remained at LET of about 300 keV/micrometer, dsb repair may still take place at this high LET, even if its role is apparently small. These results suggest that the DNA repair system does not play a major role in protection against the attack of high LET radiations and that a main muse of cell death is non-reparable dsb which are produced at a higher yield compared with low LET radiations. No correlation was observed between DNA content or nuclear area and ICS.

Intake ratio of 131I to 137Cs derived from thyroid and whole-body doses to Fukushima residents

This study deals with the intake ratio of (131)I to (137)Cs that allows for the utilisation of late whole-body measurements to reconstruct the internal thyroid doses to Fukushima residents. The ratio was derived from the thyroid dose distribution of children and the effective dose distribution of adults based on the assumption that various age groups of persons inhaled the two nuclides at the same activity ratio and at around the same time, while taking into account age-dependent ventilation rates. The two dose distributions were obtained from residents of Iitate village and Kawamata town, located northwest of Fukushima Daiichi nuclear power plant (FDNPP). As a result, the intake ratios for the residents were 2-3, which was much smaller than the activity ratio observed in air sampling. A main reason for this discrepancy presumably lies in the relatively smaller thyroid uptake for iodine in the Japanese subjects than that in the reference persons on whom the biokinetic model promulgated by International Commission on Radiological Protection is based. The actual intake ratio of the two nuclides is believed to have been higher south of the FDNPP; however, this would depend on which of three significant plume events dominantly contributed to the intake for individuals. Further studies are needed to clarify this issue as a part of the reconstruction of early internal doses related to the FDNPP accident.

Radiosensitivity and Cell Cycle Redistribution of Cultured Human Tumour Cells during Fractionated Daily 2-Gy Irradiations

Exponentially growing SQ-5 human lung squamous cell carcinoma cells were irradiated in vitro at 2-Gy per fraction per day continuously for 14 days. The number of total cells continued to increase exponentially till day 5, and reached a plateau level thereafter. The cell cycle distribution changed marginally for the first 5 days, and showed a prominent G2/M accumulation at day 7. Plating efficiencies decreased exponentially with increasing fractionation while the total clonogenic cell number remained constant until day 4. Radiosensitivity at each fraction was stable until day 9, but significantly increased at day 11. A comparison of plating efficiencies between the immediate and 24-h delayed assays revealed that the capacity of cells to spare 2-Gy damage increased with the number of 2-Gy fractions. These results suggest that sublethal damage could accumulate during multifraction daily irradiations, while repair of potentially lethal damage and/or proliferation could rather increase.

Newly designed graded screen array for particle size measurements of unattached radon decay products

A new graded screen array was designed for measuring the particle size distribution of unattached radon decay products. Its validity was verified by experimental approaches using a radon/aerosol chamber. Use of fine wire mesh screens achieved both a high volumetric air flow rate and high alpha count rate. Consequently, this improvement produced both a high sensitivity and good precision in the particle size distribution measurement for unattached radon decay products with an activity median diameter around 1 nm. A special Mylar film cover was used to protect the contamination of detector surface. And shielding effects by wire of a screen were examined in our alpha counting system for precise measurements. As for the results, the particle size distribution of unattached radon decay products was observed at around 1 nm as a narrow peak with the geometrical standard deviation of 1.1. When carrier aerosols were injected into the chamber, typical bimodal distribution was clearly observed. This clear bimodal distribution was observed even in an atmosphere with a relatively low radon concentration of 150 Bq m−3. It indicates that this system is adequate for measurements of the particle size distribution of unattached radon decay products in the natural environment.