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Role of protein thiols in intrinsic radiation protection of DNA and cells.

Previous data have been consistent with the hypothesis that the thiol depleter dimethyl fumarate (DMF) increases radiation sensitivity of hypoxic mammalian cells by a combination of two actions: depletion of glutathione (GSH) which interferes with the chemical competition between damage fixation and repair and depletion of protein thiol (PSH) which causes inhibition of enzymatic repair processes. However, one cannot rule out the possibility that PSH also acts in the chemical competition to restitute damaged DNA. The studies presented here have addressed this question by studying the effects of ionizing radiation on isolated nuclei which contain very low levels of GSH, but substantial amounts of PSH, compared to intact cells. The results show that DNA damage, measured using the non-denaturing filter elution assay, is increased about 1.6-fold in isolated nuclei irradiated in air, compared to whole cells, and about 4.3-fold in nuclei irradiated in N2. Thus, the OER for DNA damage decreases from about 3 in whole cells to 1 in isolated nuclei. Also, although DMF increases radiation-induced DNA damage in whole cells irradiated in hypoxia about 2-fold, it does not increase DNA damage in isolated nuclei irradiated in hypoxia. These data do not support the idea that PSH can act in the chemical competition reaction to chemically repair radiation-induced DNA radicals. The data are discussed in relation to the effect that various procedures for nuclei isolation can have on radiation sensitivity of DNA and on the OER. We also address the question of whether radiation-induced DNA damage measured by non-denaturing elution correlates with cell killing.

Animals↗

Treating voxel geometries in radiation protection dosimetry with a patched version of the Monte Carlo codes MCNP and MCNPX.

The question of Monte Carlo simulation of radiation transport in voxel geometries is addressed. Patched versions of the MCNP and MCNPX codes are developed aimed at transporting radiation both in the standard geometry mode and in the voxel geometry treatment. The patched code reads an unformatted FORTRAN file derived from DICOM format data and uses special subroutines to handle voxel-to-voxel radiation transport. The various phases of the development of the methodology are discussed together with the new input options. Examples are given of employment of the code in internal and external dosimetry and comparisons with results from other groups are reported.

Body Burden↗

[Problems with radiation protection for adjuvant radiotherapy of thyroid cancer].

Ablative treatment of thyroid cancer with 131I is associated with the exposure to ionizing radiation of not only the target cells but also other cells and organs in the patient's body. Thermoluminescent dosimetry showed that the mean dose equivalent in ovaries equaled to several dozen mSv when the mean therapeutic dose was 2.8 GBq of 131I. In the treated young women the performed ovulation tests revealed no dysfunction of the ovaries. The highest dose equivalent in the clinic staff would not exceed 20 mSv per year. Accordingly, the dose equivalents to the public would not exceed the threshold limit of 1 mSv per year. In order to fulfill the requirements of regulations for disposal of radioactive waste and the necessity to store the waste for as long as 80 days it is obligatory to utilize setting tanks of very large capacity.

Environmental Exposure↗