Radiation Dose and Safety

Utilizing the modalities of conventional radiography, computed tomography (CT), and fluoroscopy, diagnostic images are produced using ionizing radiation. It is well known that radiation can also have harmful effects if used in excess or certain situations. All healthcare providers should understand the risks associated with radiation exposure and limit exposure when possible.

Transmitted radiation is the radiation that passes through the patient and interacts with the detector to create the image. Unfortunately, only about 5% to 15% of the radiation produced by the source becomes transmitted radiation.

The majority of radiation produced by the source becomes either:

• Absorbed radiation, which is the radiation that interacts with the tissues of the patient depositing its energy in those tissues. It is the source of the patient’s radiation exposure.

• Scatter radiation, which is not transmitted or absorbed by the patient. As radiation passes through the patient, some of the radiation changes its original path with the scatter leaving the patient along a different course. Scatter radiation can degrade the quality of the image and can be an exposure source to personnel ( eFig. C.1 ).

  

The absorbed radiation is measured by the absorbed dose. The unit for absorbed dose is the Gray ( Gy ) , which is the energy absorbed per unit mass (kilogram).

The older unit for absorbed dose was the rad, where 1 Gy equals 100 rads. Absorbed dose does not take into account the biologic effect of the radiation.

Rather, the equivalent and effective doses attempt to correlate the absorbed dose with the potential biologic effects on different types of tissues. The unit for these doses is the Sievert ( Sv ) or rem , where 1 Sv equals 100 rem.