Читать книгу A Comprehensive Guide to Radiographic Sciences and Technology - Euclid Seeram - Страница 25

Radiobiology is the study of effects of radiation on biologic systems which occur at the molecular, cellular levels and subsequently leading to whole‐body biological effects generally categorized as early and late effects.

The study of radiobiology is vital for technologists and radiologists working in radiology departments, and it involves an understanding of related physics and chemistry, types of biological effects, radiosensitivity, target theory, and direct and indirect effects. Furthermore, radiobiology involves discussing of deterministic effects (early effects) and stochastic effects (late effects). These topics and their associated subtopics (for example, subtopics for stochastic effects are radiation‐induced malignancy, and hereditary effects) will be outlined in Chapter 9.

Topics in physics that are significant to radiobiology include atomic structure, the nature and properties of x‐rays, ionization, excitation, linear energy transfer (LET), and relative biologic effectiveness (RBE). Additionally, the essential chemistry of the interactions of radiation and patient which occur with water (since the body contains 70–85% water) is the radiolysis of water. Such chemical interactions result in ionization of water, forming ion pairs and free radicals of which the latter can react further to form other molecules that are toxic to the cell.

Two significant and important topics in radiobiology are stochastic and deterministic effects. Stochastic effects are those for which the probability of the effect increases as the dose increases and for which there is no threshold dose. For stochastic effects, there is no risk‐free dose. These effects can occur at the local tissue level and can cause life‐span shortening, radiation‐induced malignancy, and hereditary effects (late effects that occur in the offspring of the irradiated individual). Stochastic effects are classified as late effects, since they occur years after the exposure of the individual. Deterministic effects on the other hand are those effects for which the severity of the effect depends on the dose. These effects have a threshold dose and increase with increasing dose. These effects are called early effects since they can occur within minutes, hours, days, weeks, and months after the exposure.