TECHNICAL INFORMATION
Radiation Exposure and Dose
The concepts of radiation exposure and dose are important, for the patient as well
as x-ray personnel.
Dose Definition
When an x-ray is taken, radiation in the form of x-ray beams, are released. Using
these beams, the x-ray technician can make images of whatever is being
examined. This radiation penetrates objects and human bodies, passes through
them, and is weakened in the process.
In simple terms, this weakening is equivalent to a reduction in the number of
individual radioactive particles. A measurement of the amount of radiation
measured at a site over a specific period of time, produces the concept of "dose".
Not all the radiation particles generated during the x-ray are used to produce the
resulting images, and because radiation can cause damage to the human body,
medical personnel try to get the best possible image with the smallest possible
dose of radiation. The concept of "dose" can mean different things according to
the where and how the measurement is made, particularly with respect to the site
where the dose is measured.
Incident Dose
The incident dose is the dose measured in the middle of the radiation field on the
surface of a body or phantom. However, it is only measured at this point if there is
no body in the path of the x-ray beam. There is no scatter radiation from the body
or phantom during this measurement. Whenever radiation strikes a substance,
there is always some scattering of radioactive particles.
Absorbed Dose
Different materials when subjected to the same x-ray exposure will absorb different
amounts of energy. Changes to physical properties and induced chemical
reactions are expected as the amount of radiation is absorbed in human tissue or
the human body. The energy absorbed from radiation is defined as the absorbed
dose. The traditional unit of absorbed dose has been the rad, defined as 100
ergs/gram. The metric or SI equivalent, the gray (Gy) is defined as 1
joule/kilogram. The two units are related by the following formula:
1 Gy = 100 rad
The absorbed dose is a reasonable measure of the chemical and physical effects
by a specific radiation exposure in an absorbing material. When the effects of
radiation on living organisms are evaluated, the absorption of equal amounts
energy per unit mass will not have the same effects. The biological effects of
radiation is traceable to the chemical alteration of the biological molecules that are
influenced by the ionization or excitation caused by the radiation. The severity and
permanence of these changes are directly related to the local rate of energy or
dose. There are many papers and texts that describe the relation of dose,
