Radioprotectors

Abstract

SynonymsGamma ray-induced cancer; Ionizing radiationinduced cancer; Radiation-induced neoplastic transformation; X-ray-induced cancer DefinitionRadiation ▶ carcinogenesis is a biological phenomenon whereby living normal cells are damaged by ionizing radiations which starts a progressive process causing the surviving cells to change their phenotype such that normal controls of cell death and apoptosis are lost and uncontrolled cancerous growth is initiated. CharacteristicsRadiation Radiation is the deposition of energy into mass. Energy can appear as both corpuscles or electromagnetic quanta or photons. Some of the elementary forms are protons, neutrons, electrons, X-rays, and gamma rays. X-rays originate outside of the nucleus of an atom while gamma rays originate within the atomic nucleus. Both are identical electromagnetic radiation with varying energies. The equivalence of matter expressed as energy is given by Albert Einstein's relation: E = mc 2 where E is energy, m is mass, and c is the velocity of light (3 Â 10 8 m/s). People are exposed to radiation naturally from the surrounding environment, from space radiation arriving on Earth, and from man-made causes such as chest and dental X-rays and fallout from nuclear weapon testing. Due to the nature of radiations, that is, they cannot be seen or smelled, # Springer-Verlag Berlin Heidelberg 2017 M. Schwab (ed.), Encyclopedia of Cancer, DOI 10.1007/978-3-662-46875-3 governments and states have taken a conservative regulatory approach to containing and minimizing exposure of both those who may be exposed occupationally and for the general public. There are strict regulations that must be followed to keep exposures very low, and thus the risk from exposures is also very low. Interaction of Radiation with MatterMatter is composed of atoms, which in turn are composed of protons, neutrons, and electrons. High-energy X-rays and photons used in diagnostic radiology and radiation therapy and gamma rays from natural sources are electromagnetic radiation that can interact with the orbiting electrons which consequently cause the expulsion of secondary high-energy electrons. The energy of these secondary electrons is in millions of electron volts [meV]. The binding energy of electrons with molecules is only a few electron volts. Therefore, the energetic secondary electrons can collide with many atoms and molecules knocking out electrons as they give up energy until they no longer have enough energy to break any more chemical bonds. Each time an electron is dislodged from an atom or molecule, an ion is created that can combine with other atoms and molecules which therefore change the chemical composition of the molecules involved. It does not take very much ionizing radiation exposure to "hit" all the cells in the body. The number of times each cell will be hit will depend on the total dose, and the time between hits will depend on the total dose and the rate at which the dose is delivered. In general, calculations show that at total body dose of 1 cGy, each cell nucleus w...

Precision of Radiation Chemistry Networks: Playing Jenga with Kinetic Models for Liquid-Phase Electron Microscopy

“…Exposing aqueous systems to ionizing radiation triggers a physicochemical reaction cascade that causes the formation of so-called primary products (e h – denotes solvated electrons) . For low linear energy transfer (LET) irradiation, such as electrons, the following primary products are formed: normalH 2 normalO → irradiation normalH + , .25em OH , .25em normale normalh − , .25em normalH , .25em OH − , .25em normalH 2 normalO 2 , .25em normalH 2 , .25em HO 2 After about 1 μs, those are equilibrated so that this reaction cascade can be summarized by radiation-specific generation values (G-values, G i ) . Solution chemistry (and when relevant diffusion) must be considered to account for the subsequent reactions of the solvent molecules with primary species.…”

“…Exposing aqueous systems to ionizing radiation triggers a physicochemical reaction cascade that causes the formation of so-called primary products (e h – denotes solvated electrons) . For low linear energy transfer (LET) irradiation, such as electrons, the following primary products are formed: After about 1 μs, those are equilibrated so that this reaction cascade can be summarized by radiation-specific generation values (G-values, G i ) . Solution chemistry (and when relevant diffusion) must be considered to account for the subsequent reactions of the solvent molecules with primary species.…”