Biophysik

An exposure system for examining in vitro effects of microwave irradiation on cellular and subcellar components has been developed. The system was used to test the effect of 2.45-GHz CW microwaves on the release of two lysosomal enzymes. At a specific absorption rate (SAR) of 10, 50 or 100 mW/g (90 min) no effects were noted at 37° C (pH of 7.3) on lysosomal fragility as determined by the release of the lysosomal enzymes cathepsin D andβ-glucuronidase. When the medium was adjusted to pH 5.0, microwave irradiation of the lysosomal suspension had no effect on the acid-induced enhancement of release of lysosomal enzymes. The data indicate that microwave irradiation had no labilizing effect on the lysosomal membrane, although other microwave-membrane interactions not associated with enzyme release may occur.

The example of thymine-(methyl-T) demonstrates that in the case of radiation damage to one type of molecule different dose-effect curves will occur depending on the state of the molecule. Radiation-induced tritium cleavage from an aerated aqueous solution of thymine-(methyl-T) shows a linear dose dependence without threshold, tritium cleavage from solid thymine-(methyl-T) follows a sigmoid dose-effect curve with threshold. TheG-values for the tritium cleavage from dissolved thymine-(methyl-T) depend on the concentration of the solution, while theG-values for the tritium cleavage from solid thymine-(methyl-T) depend on the dose. The extent of radiation damage in the solid state and in solution is subject to comparative analysis, and the difference in dose-effect relations is discussed.

Twoγ-ray hypersensitive cell lines, human ataxia telangiectasia (AT) and murine severe combined immune deficiency (SCID) cells, proved to be very competent in amplifying their dihydrofolate reductase (DHFR) gene under methotrexate selection stress. Over a period of months, methotrexate-resistant clones were obtained which were able to grow in progressively increasing methotrexate concentrations up to 1 mM. By then methotrexate-resistant AT and SCID cells had amplified their DHFR gene 6- and 30-fold, respectively, and showed very high DHFR mRNA expression. In contrast, related cells with normal radiosensitivity (human GM637 and mouse BALB/c fibroblasts) did not show DHFR gene amplification under comparable conditions. This correlation of the capacity of DHFR gene amplification andγ-ray hypersensitivity in AT and SCID cells suggests that gene amplification may have a mechanism(s) in common with those involved in repair ofγ-radiation-induced damage. No difference in cell killing could be observed following exposure to densely ionizing α particles: AT and SCID cells exhibited comparable survival rates to GM637 and BALB/c cells, respectively.

Exposure of the hindquarter of the rat to 1000 rad of gamma-radiation caused a significant increase in the release of glutamine and alanine into the perfusion fluid at 4 h post-irradiation. The extent of the release of glutamine exceeded that of alanine. Furthermore, the exposure to gamma-radiation brought about a significant lowering of the intra-/extracellular concentration gradient with respect to glutamine and alanine.

Thyroid cancer is one of the major health concerns after the accident in the Fukushima Dai-ichi nuclear power station (NPS). Currently, ultrasonography surveys are being performed for persons residing in the Fukushima Prefecture at the time of the accident with an age of up to 18 years. Here, the expected thyroid cancer prevalence in the Fukushima Prefecture is assessed based on an ultrasonography survey of Ukrainians, who were exposed at an age of up to 18 years to 131I released during the Chernobyl NPS accident, and on differences in equipment and study protocol in the two surveys. Radiation risk of thyroid cancer incidence among survivors of the atomic bombings of Hiroshima and Nagasaki and preliminary estimates of thyroid dose due to the Fukushima accident were used for the prediction of baseline and radiation-related thyroid cancer risks. We estimate a prevalence of thyroid cancer of 0.027 % (95 % CI 0.010 %; 0.050 %) for the first screening campaign in the Fukushima Prefecture. Compared with the incidence rate in Japan in 2007, the ultrasonography survey is predicted to increase baseline thyroid cancer incidence by a factor of 7.4 (95 % CI 0.95; 17.3). Under the condition of continued screening, thyroid cancer during the first fifty years after the accident is predicted to be detected for about 2 % of the screened population. The prediction of radiation-related thyroid cancer in the most exposed fraction (a few ten thousand persons) of the screened population of the Fukushima Prefecture has a large uncertainty with the best estimates of the average risk of 0.1–0.3 %, depending on average dose.

The application of a microchannel proton irradiation was compared to homogeneous irradiation in a three-dimensional human skin model. The goal is to minimize the risk of normal tissue damage by microchannel irradiation, while preserving local tumor control through a homogeneous irradiation of the tumor that is achieved because of beam widening with increasing track length. 20 MeV protons were administered to the skin models in 10- or 50-μm-wide irradiation channels on a quadratic raster with distances of 500 μm between each channel (center to center) applying an average dose of 2 Gy. For comparison, other samples were irradiated homogeneously at the same average dose. Normal tissue viability was significantly enhanced after microchannel proton irradiation compared to homogeneous irradiation. Levels of inflammatory parameters, such as Interleukin-6, TGF-Beta, and Pro-MMP1, were significantly lower in the supernatant of the human skin tissue after microchannel irradiation than after homogeneous irradiation. The genetic damage as determined by the measurement of micronuclei in keratinocytes also differed significantly. This difference was quantified via dose modification factors (DMF) describing the effect of each irradiation mode relative to homogeneous X-ray irradiation, so that the DMF of 1.21 ± 0.20 after homogeneous proton irradiation was reduced to 0.23 ± 0.11 and 0.40 ± 0.12 after microchannel irradiation using 10- and 50-μm-wide channels, respectively. Our data indicate that proton microchannel irradiation maintains cell viability while significantly reducing inflammatory responses and genetic damage compared to homogeneous irradiation, and thus might improve protection of normal tissue after irradiation.

We examined the production of dicentrics in human lymphocytes irradiated with 29 kV X-rays to a depth of 13.5 mm in a PMMA phantom. For these irradiation conditions, which are appropriate for the diagnostic application of mammography X-rays, a coefficient α of (5.88±0.66)×10−2 Gy−1 of the linear quadratic dose–response relationship was determined. This value does not differ significantly from the coefficient α of (6.55±0.97)×10−2 Gy−1 obtained earlier for a free-in-air set-up using blood of the same donor. The results are interpreted in terms of both the energy distributions of the photon fluence of mammography X-rays free-in-air and those in the PMMA phantom. Based on earlier results of experiments with monochromatic X-rays in the energy range 1.83–40 keV (completed here by an additional measurement at 25 keV), a fit function α(E) to the measured α coefficients as a function of the energy E of monochromatic X-rays was used to calculate weighted mean values % MathType!Translator!2!1!AMS LaTeX.tdl!TeX -- AMS-LaTeX! % MathType!MTEF!2!1!+- % feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGafqySdeMbae % baaaa!37A4! $$\bar \alpha$$ for both the mammography X-ray spectra free-in-air and in the phantom. As a result, weighted mean values of (4.9±1.0)×10−2 Gy−1 and (4.5±1.0)×10−2 Gy−1 were obtained, respectively. Although the measured α coefficients for mammography X-rays appear to be systematically higher than those calculated as weighted mean values % MathType!Translator!2!1!AMS LaTeX.tdl!TeX -- AMS-LaTeX! % MathType!MTEF!2!1!+- % feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGafqySdeMbae % baaaa!37A4! $$\bar \alpha$$ , it can be concluded that the modification of the mammography X-ray spectrum to a depth of 13.5 mm in a PMMA phantom compared with the free-in-air spectrum has no significant influence on the dicentric yields in human lymphocytes.