Radiation acute effects

Pentoxifylline is stmcturaHy related to other methylxanthine derivatives such as caffeine [58-02-2] (1,3,7-trimethylxanthine), theobromine [83-67-0] (3,7-dimethylxanthine), and theophylline [58-55-9] (3,7-dihydro-1,3-dimethyl-1 H-piirine-2,6-dione or 1,3-dimethylxanthine), which also show radioprotective activity in some instances, suggesting that methylxanthines as a dmg class may radioprotect through a common mechanism (see Alkaloids). In a retrospective analysis of cervical and endometrial cancer patients receiving primary or adjuvant XRT, no association between caffeine consumption and incidence of acute radiation effects has been found. However, there was a decreased incidence of severe late radiation injury in cervical cancer patients who consumed higher levels of caffeine at the time of thek XRT (121). The observed lack of correlation between caffeine consumption and acute radiation effects is consistent with laboratory investigations using pentoxifylline. 

In general, the guidelines established for radiation exposure have had as their principle objectives (1) the prevention of acute radiation effects (e.g., erythema, sterility), and (2) the limiting of the risks of late, stochastic effects... 

Not only is TCDO a potent therapeutic agent in acute radiation syndrome, but treatment using TCDO from days 4—11 after TBI increases the survival rate in rats for up to one year, protects against the development of late GI ulcers, and also reduces the development of y-ray-induced leukemias and malignant epitheHal tumors, but not sarcomas (202). The anticarcinogenic effect of TCDO maybe related to the inhibition of PGs, which promote carcinogenesis, or to immunostimulation, which may result in a more effective elimination of malignant cells. 

Empey, L.R., Papp, J.D., Jewell, L.D. and Fedorak, R.N. (1992). Mucosal protective effects of vitamin E and misoprostol during acute radiation-induced enteritis. Dig. Dis. Sci. 37, 205-214. 

Acute Radiation Syndrome—The symptoms which taken together characterize a person suffering from the effects of intense radiation. The effects occur within hours or days. 

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. 

Health effects from exposure to radiation fall into two categories stochastic (based on probability) and acute. Stochastic effects typically take several years to materialize (e.g., cancer appearing 20 years after an exposure) while acute effects such as nausea or reddening of the skin may take only weeks, days, or even hours to materialize. Stochastic and acute effects are described in more detail in the following sections. First, however, a brief discussion describes how radiation damages human tissue and why exposure may produce one or a combination of the described health effects. 

The human body is equipped to deal with nominal levels of radiation doses. Background (natural) radiation from radon gas, cosmic sources, soil, and water produces an average dose of about 0.3 rem (0.003 Sv) per year.4 However, large doses of radiation generated after a terrorist attack can overwhelm the body s ability to repair damage, leading to stochastic or acute health effects. 

Stochastic radiation effects are typically associated with those that occur over many months or years (i.e., are typically chronic instead of acute). Chronic doses are typically on the order of background doses (0.3 rem [0.003 Sv] or less) and are not necessarily associated with larger doses that could result from a terrorist attack with radiological weapons. However, stochastic health effects are defined here as effects that occur many years after chronic or acute exposure to radiological contaminants. Stochastic effects are categorized as cancers and hereditary effects. Because no case of hereditary effects (e.g., mutation of future generations) has been documented, this discussion focuses on cancer risk. 

Specific health effects resulting from an acute dose appear only after the victim exceeds a dose threshold. That is, the health effect will not occur if doses are below the threshold. (Note that this is significantly different from the LNT model used to predict stochastic effects.) After reaching the acute dose threshold, a receptor can experience symptoms of radiation sickness, also called acute radiation syndrome. As shown in Table 3.2, the severity of the symptoms increases with dose, ranging from mild nausea starting around 25-35 rad (0.25-0.35 Gy) to death at doses that reach 300-400 rad (3-4 Gy). Table 3.2 shows that the range of health effects varies by both total dose and time after exposure. 

It is also unlikely that the doses associated with a dirty bomb will produce even the milder acute effects. Although the observation of acute radiation syndrome may be unlikely after a dirty bomb explosion, doses should be kept ALARA to limit the potential for acute and stochastic effects. The entire range of acute radiation syndrome effects will be observed after an attack with a nuclear weapon, as described in Chapter 5. 

Legeza VI, Galenko-Yaroshevskii VP, Zinov ev EV, Paramonov BA, Kreichman GS, Turkovskii II, Gumenyuk ES, Kamovich AG, Khripunov AK (2004) Bull Exp Biol Med 138 311 Effects of new wound dressings on healing of thermal burns of the skin in acute radiation disease... 

Acute radiation exposure, which can cause radiation sickness, radiation burns, and so forth, is caused by the energy deposited in the body, and so we are looking for effects that will occur within hours, days, or weeks of the exposure. As cancer takes many years or decades to develop, quantifying the long-term effects of DNA damage resulting from an acute exposure is not as important. In the case of acute radiation exposure, then, we measure only the amount of energy deposited in the body, so we use units of Gy or rad. 

Since acute radiation toxicity responses become apparent shortly after exposme, history is an important criterion in determining whether the radiation is related to the cause of a particular complication or adverse effect. As with any attempt to specify a dose-response relationship, the dose is an important component. In contrast, late radiation toxicity in organs such as the kidneys, fiver, or central nervous system (CNS) will not be seen until months or perhaps even years after radiation exposure (Center for Drug Evaluation, 2005). The integrated response is often to the radiation response and attempts to heal any radiation damage that has been caused. 

Exposure to radiation can cause detrimental health effects. At large doses, radiation effects such as nausea, reddening of the skin or, in severe cases, more acute syndromes are clinically expressed in exposed individuals within a short period of time after the exposure such effects are called deterministic because they are certain to occur if the dose exceeds a threshold level. Radiation exposure can also induce effects such as malignancies, which are expressed after a latency period and may be epidemiologically detectable in a population this induction is assumed to take place over the entire range of doses without a threshold level. Hereditary effects due to radiation exposure have been statistically detected in other mammalian populations and are presumed to occur in human populations also. These epidemiologically detectable effects—malignancies and hereditary effects—are termed stochastic effects because of their random nature. 

Clinically observed effects The number of people who suffered clinically observed health effects individually attributable to radiation exposure due to the Chernobyl accident was relatively modest, given the accident s dimensions. A total of 237 persons, all of them workers dealing with the accident, were suspected of suffering clinical syndromes of radiation exposure and were hospitalized, and 134 of them were diagnosed with acute radiation syndrome. Of these, 28 died of the consequences of radiation injuries (three other persons died at the time of the accident two due to non-radiation blast injuries and one due to a coronary thrombosis). Some years after the accident, 14 additional persons in this group died however, their deaths were found to be not necessarily attributable to radiation exposure. 

If a person is exposed to a large amount of radiation (i.e., large radiation dose) delivered to the entire body, cells in tissues can be destroyed in large numbers. Because tissues have important functions, the destruction of significant numbers of cells can lead to impairment in one or more of these functions. The biological effects that arise when large numbers of cells are destroyed by radiation are called acute somatic effects if they occur in a relatively short period of time (e.g., within a few weeks) after brief exposure. Acute somatic effects are a subset of what is now formally called early and continuing deterministic effects (once called nonstochastic effects). 

Deterministic effects are those that increase in severity as the radiation dose increases and for which a threshold is presumed to exist. Besides acute somatic effects, deterministic effects also include radiation effects (other than cancer and genetic effects) that continue to occur after an extended period (e.g., years) of chronic exposure. Such chronic exposures can arise from long-lived radionuclides (e.g., isotopes of plutonium and cesium) ingested via contaminated food or inhaled via contaminated air... 

---