Stochastic and Nonstochastic Effects

As explained in the previous section, radiation imparts energy to the cell, which may trigger mechanisms that result in biological damage. This damage, which starts at the microscopic (cell) level, may, in some cases, manifest itself as a macroscopic observable biological effect. 

Examples of nonstochastic (or deterministic) effects are erythema, nausea, loss of hair, cataracts, sterility, etc. Stochastic (or probabilistic) effects are cancer and genetic defects (birth defects) (Table 16.7). Genetic effects are abnormalities that may appear in the offspring of persons exposed to radiation, one or many generations after the exposure. 

An important difference between stochastic and nonstochastic effects is that nonstochastic effects have a threshold stochastic effects do not. The threshold is a minimum radiation dose that has to be received in a relatively short time period for the effect to appear (Fig. 16.5). A dose below the threshold will not 

An example of stochastic versus nonstochastic effects can be made using alcohol. If a person drinks 20 glasses of wine in a short period of time, it is 

The incidence of stochastic effects can only be treated in a probabilistic manner. Consider cancer first. In the United States the normal incidence of cancer (not necessarily fatal) in the adult population is 25 percent. The estimate for radiation-induced cancer is (1.5-4.5) x 10 per manSv [(I.5-4.5) x lO per manrem]. To understand this estimate better, consider an example. In a group of 10,000 adult Americans, about 2500 cases of cancer will be detected (not necessarily fatal). If this group of 10,000 persons receives 0.01 Sv (1 rem) of radiation collectively, the estimated number of cancers due to this radiation dose is 1.5-4.5. Therefore, the total number of cancers expected to be detected will be between 2501.5 and 2504.5. The incidence of fatal cancer in the United States is 16.4 percent. The risk of deadly cancer from radiation is estimated to be (0.7-2.26) X 10 per manSv [(0.7-2.26) X lO per manrem]. 

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