PubMed · 7956476
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S Z Liu. 1994. Low dose radiation effects.. https://pubmed.ncbi.nlm.nih.gov/7956476/
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PURPOSE: The aim of this study was to solve anisotropy in the dose distributions from rotational conformal radiotherapy (RCRT) by using a C-arm-mounted accelerator. MATERIALS AND METHODS: The linac head was designed to move along the C-arm with a maximum angle of 60 degrees (from a vertical position toward the gantry). Simultaneous rotation of the gantry creates a dynamic conical irradiation technique. Dynamic conical conformal radiation therapy (Dyconic CRT) was developed by combining the technique with continuous motion of a multileaf collimator. Dose distributions were measured in phantoms using film densitometry and compared with conventional RCRT. Dose distributions in actual radiation therapy patients are also presented. RESULTS: Dyconic CRT enabled the precise delivery of noncoplanar beams without rotating the table. The measurements showed that three-dimensionally isotropic dose falloff was achieved with Dyconic CRT. Dose inhomogeneity in the sagittal direction with Dyconic CRT was compensated for by use of wedge filters. CONCLUSIONS: The drawbacks of the dose distributions produced by RCRT were overcome with the use of Dyconic CRT.
The ongoing debate over the possible beneficial effects of ionising radiation on health, hormesis, is reviewed from different perspectives. Radiation hormesis has not been strictly defined in the scientific literature. It can be understood as a decrease in the risk of cancer due to low-dose irradiation, but other positive health effects may also be encompassed by the concept. The overwhelming majority of the currently available epidemiological data on populations exposed to ionising radiation support the assumption that there is a linear non-threshold dose-response relationship. However, epidemiological data fail to demonstrate detrimental effects of ionising radiation at absorbed doses smaller than 100-200 mSv. Risk estimates for these levels are therefore based on extrapolations from higher doses. Arguments for hormesis are derived only from a number of epidemiological studies, but also from studies in radiation biology. Radiobiological evidence for hormesis is based on radio-adaptive response; this has been convincingly demonstrated in vitro, but some questions remain as to how it affects humans. Furthermore, there is an ecologically based argument for hormesis in that, given the evolutionary prerequisite of best fitness, it follows that humans are best adapted to background levels of ionising radiation and other carcinogenic agents in our environment. A few animal studies have also addressed the hormesis theory, some of which have supported it while others have not. To complete the picture, the results of new radiobiological research indicate the need for a paradigm shift concerning the mechanisms of cancer induction. Such research is a step towards a better understanding of how ionising radiation affects the living cell and the organism, and thus towards a more reliable judgement on how to interpret the present radiobiological evidence for hormesis.
In the present work, the electron spin resonance (ESR) dosimetric properties of naproxen sodium (NS) was investigated in the dose range of (2.5-25 kGy). Irradiated NS exhibited a very simple ESR spectrum consisting of a broadened antisymmetric single resonance line not saturating up to 2 mW microwave power at room temperature. The sum of two exponential increasing functions associated with two different radicals of different spectroscopic features and relative weights were found best describing experimental dose-response curve. Radiation induced radicals were observed to be very stable at room temperature but the increase in storage temperature increased very appreciably the decay of the contributing radicals. The results of the simulation calculation based on a model of two radicals showed that two carbon dioxide ionic free radicals (*CO(2))(-) of different orientational and environmental features produced by preferential rupture of carboxyl group from the rest of NS molecules in the crystalline matrix, were, likely at the origin of the experimentally observed ESR spectrum. Features such as good time stability of the signal intensity and relatively high radiation yield (G=0.13) were considered providing NS with potential use as dosimetric material in measuring radiation dose in the range of 2.5-25 kGy by ESR technique.