Radiation radiosensitivity

Radiosensitivity—Relative susceptibility of cells, tissues, organs, organisms, or any living substance to the injurious action of radiation. Radiosensitivity and its antonym, radioresistance, are currently used in a comparative sense, rather than in an absolute one. 

In a re-evaluation of the Hanford cohort, which included approximately 28,000 male and female workers, Kneale et al. (1981) detected a significant increase in the cancers in radiosensitive tissues in workers exposed to external radiation. Radiosensitive tissues grouped together in their analyses included cancers of the stomach, large intestine, pancreas, pharynx, lung, breast, reticuloendothelial system (lymphoma, myeloma, myeloid leukemia and others), and thyroid. Approximately 50% of these cancers were in the lung however, smoking histories were not considered in the analysis. Of the male population, only 3% or 225 men had definite evidence of internal radiation. Due to this fact the authors stated that they could safely assume that the incidence of cancer from internal radiation was small compared with that associated with external radiation. 

TNE- a also protects mice against the lethal effects of radiation (164). TNE- a given before sublethal kradiation reduces the decline of neutrophils and total blood counts and accelerates the recovery of peripheral blood cells (190). TNE- a also alters the radiosensitivity of murine G1 progenitors (191). 

Radiation sterilization Radiochromic chemical Plastic devices impregnated with radiosensitive chemicals which undergo colour changes at relatively low radiation doses Only indicate exposure to radiation... 

Redpath, J.L. et al. (1975). Role of metal ions in the radiosensitivity of mctalloproteins. Model experiments with bovine carbonic anhydrase. Int. J. Radiat. Biol. 26, 243. 

Schoeters GER, Vander Plaetse F, Van Den Heuvel RL. 1992. High radiosensitivity of the mineralization capacity of adult murine bone marrow in vitro to continuous a-irradiation compared to acute X-irradiation. Int J Radiat Biol 61(5) 675-683. 

Some effects of irradiation on vitamins have been mentioned earlier. It appears that irradiation and heat treatment affect vitamins differendy. Apparendy, vitamins Br B6, B12 and folic acid decompose less under as high a radiation dose as 60 kGy than under autoclaving at 120°Cfor 20 minutes. On the other hand, vitamin C is much more sensitive to irradiation. Generally, the radiosensitive vitamins are also sensitive to light, heat, and oxygen. In fresh foods, the vitamins that are most susceptible to irradiation are A and E. There is also some decomposition of vitamins B, and C. Other vitamins are fairly stable under irradiation. However, for the most part, the vitamins are more susecptible to heat treatment than to irradiation. 

Acute biological effects of the Chernobyl accident on local natural resources were documented by Sokolov et al. (1990). They concluded that the most sensitive ecosystems affected at Chernobyl were the soil fauna and pine forest communities and that the bulk of the terrestrial vertebrate community was not adversely affected by released ionizing radiation. Pine forests seemed to be the most sensitive ecosystem. One stand of 400 ha of Pirns silvestris died and probably received a dose of 80 to 100 Gy other stands experienced heavy mortality of 10- to 12-year-old trees and up to 95% necrotization of young shoots. These pines received an estimated dose of 8 to 10 Gy. Abnormal top shoots developed in some Pirns, and these probably received 3 to 4 Gy. In contrast, leafed trees such as birch, oak, and aspen in the Chernobyl Atomic Power Station zone survived undamaged, probably because they are about 10 times more radioresistant than pines. There was no increase in the mutation rate of the spiderwort, (Arabidopsis thaliana) a radiosensitive plant, suggesting that the dose rate was less than 0.05 Gy/h in the Chernobyl locale. 

Witherspoon, J.P. 1969. Radiosensitivity of forest tree species to acute fast neutron radiation. Pages 120-126 in D.J. Nelson and F.C. Evans (eds.). Symposium on Radioecology. Proceedings of the Second National Symposium. Available as CONF-370503 from The Clearinghouse for Federal Scientific and Technical Information, Natl. Bur. Standards, Springfield, VA 22151. 

Effective dose equivalent The weighted sum, in sieverts (Sv), of the radiation dose equivalents in the most radiosensitive organs and tissues, including gonads, active bone marrow, bone surface cells, and the lung. 

Several genetic alterations can influence radiosensitivity of cancer cells and radioresponsive tumors are known to allow more easily radiation-induced apoptosis. Therefore, the proper functioning of the apoptotic machinery regulates radiosensitivity. As described above, a cracial role is played by p53, and its downstream genes p21 and bax, in activating the apoptotic process. Those cancers with mutations at these levels are expected to be radioresistant. 

Several compounds have been investigated as modulators of me biological response to ionizing radiation. Two approaches have been pursued increase of me tolerance to ionizing radiation for normal tissues (radioprotectors), inaeased biological activity of radiation toward cancer cells (radiosensitizers). 

For reviews see, e.g. Wardman P, Clarke ED (1985) In Breccia A, Fowler JF (eds) New chemo and radiosensitizing drugs, Edizione Scientifiche Radiation chemistry Principles and applications, Verlag Chemie, Weinheim, p 565... 

Hirst, D.G., Wood, P.J., Schwartz, H.C. The modification of hemoglobin affinity for oxygen and tumor radiosensitivity by antilipidemic dmgs. Radiat. Res. 1987, 112, 164-172. 

Biology Complicates the Delivery of Radiation Biology Also Complicates the Delivery of Chemotherapy Principles Guiding the Integration of Chemoradiation Ideal Radiosensitizer ... 

Redistribution There are results of classical experiments that show that cells respond differently to radiation depending on which part of the cell cycle they are in when radiation is delivered. For human cancer cells the G2M boundary appears to be the position in the cell cycle associated with the greatest sensitivity. It is likely that a drug that is able to block cell cycle progression in a radiosensitive phase will be associated with significant radiosensitization. The taxanes are an example of such a compound (40). 

Rao GS, Murray S, Ethier SP. Radiosensitization of human breast cancer cells by a novel ErbB family receptor tyrosine kinase inhibitor. Int J Radiat Oncol Biol Phys 2000 48(5) 1519-1528. 

Fluoropyrimidine-Radiation Interactions Mechanisms of Radiosensitization by Fluoropyrimidines Pharmacological and Scheduling Requirements for Obtaining Effective Radiosensitization with Fluoropyrimidines... 

Role of p53 in 5-FU-Induced Radiosensitization Role of 5-FU Radiosensitization in Gene Therapy Oral Forms of 5-FU Capecitabine (Xeloda) in Combination with Radiation Therapy Clinical Indications... 

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