DCA05DR Dental Radiation Health, Safety, and Protection, 3rd Edition _______________________________
In 2007, the ICRP revised its estimates of tissue radiosensitiv- ity and its corresponding tissue-weighting factors. Several oral and maxillofacial structures—such as oral mucosa, salivary glands, and airways of the respiratory tract—were included for the first time (Martin et al., 2020). The SI unit of measure- ment for effective dose is the Sv. There is no traditional unit of measurement for effective dose. RADIOACTIVITY Radioactivity refers to the rate of decay or disintegration of a sample of radioactive material. The SI unit used to measure radioactivity is the becquerel (Bq), named for the French physicist who discovered radioactivity. One Bq is defined as the activity of a quantity of radioactive material in which one nucleus decays per second. The traditional unit for this measurement is the curie (Ci). Table 1 provides a summary of the units of radiation mea- surement. These units of measurement may be expressed in smaller quantities by using the prefixes milli (m, e.g., mrem) or micro (µ, e.g., µSv). SOURCES OF RADIATION EXPOSURE Radiation is emitted from either naturally occurring or human- made sources. Although many types of radiation are innocu- ous, ionizing radiation can cause injury in humans. The sources of radiation exposure that the U.S. population is exposed to include (1) background radiation; (2) medical procedures; (3) consumer products; (4) industrial, security, medical, educa- tional, and research exposure; and (5) occupational exposure (U.S. Nuclear Regulatory Commission [USNRC], 2020). For the purposes of this course, the broad categories of natural background radiation and artificial radiation sources will be discussed. Patients may ask about the potential sources and amounts of radiation to which they may be exposed during dental treat- ment. It might surprise them to learn that, for people living in the United States, 50% of radiation exposure comes from natural background radiation (USNRC, 2020). However, medical sources of radiation exposure have steadily increased over time and now account for levels of exposure equivalent
to natural radiation exposure (U.S. Environmental Protection Agency, 2021b; U.S. Nuclear Regulatory Commission, 2020). NATURAL RADIATION Natural radiation —also known as background , environmental , or ubiquitous radiation—is a form of ionizing radiation that occurs in our environment. Natural radiation includes cosmic radia- tion from the sun and stars, as well as terrestrial radiation from radioactive materials found in the earth and air. Small amounts of naturally occurring radioactive substances—all of which give off radiation—are present in soil, rocks, plants, animals, and our own bodies. Internal sources of natural radiation include radionuclides taken up from the environment through inhala- tion and ingestion. It is estimated that the average resident in the United States receives an approximate total of 6.2 mSv of radiation each year with about 50% (3.1 mSv) originating from background sources (United States Environmental Protection Agency, 2021b; U.S. Nuclear Regulatory Commission, 2020). The levels of natural radiation to which people are exposed are dependent upon many factors, such as geographic location, altitude, latitude, and soil constituents. The different types of natural radiation are discussed here separately. Cosmic , or space , radiation is a source of natural background radiation that originates in outer space and is composed of penetrating ionizing radiation, both particulate and electro- magnetic. (Particulate radiation is made up of particles; elec- tromagnetic radiation travels in waves; both types of radiation can cause tissue damage.) In the United States, most people receive a 0.33 mSv average annual dose of cosmic radiation (U.S. Environmental Protection Agency, 2021b). The amount depends on where a person lives. For example, a person living in a higher altitude location such as Denver, Colorado (5,280 feet above sea level) will receive more cosmic radiation exposure than a person living at sea level (0 feet above sea level) in a place such as Honolulu, Hawaii (U.S. Environmental Protec- tion Agency, 2021b). People who travel by airplane receive higher doses of cosmic radiation than those who do not. Pas- senger jets are not only closer to the sun; they usually reach altitudes above the protective layer of Earth’s atmosphere. The approximate dose of cosmic radiation received by a person as a result of flying from the west to east coast of the United States would be 0.035 mSv (Centers for Disease Control and Prevention, 2024).
RADIATION QUANTITIES AND UNITS OF MEASUREMENT
Quantity
Measure
International Unit
Traditional Unit
Conversion
Exposure
Ionization of air Energy absorbed Biologic effects Estimated risk
C/kg
R
1 C/kg = 3,876 R 1 Gy = 100 rads 1 Sv = 100 rems
Absorbed dose Equivalent dose Effective dose Radioactivity
Gy
rad rem
Sv Sv
None
None
Decay rate 1 Bq = 2.7 × 10 -11 Ci C/kg = coulomb/kilogram; R = roentgen; Gy = gray; rad = radiation absorbed dose; Sv= sievert; rem = roentgen equivalent man; Bq = becquerel; Ci = curie. Source: Radiation Emergency Medical Management. (2025). Radiation Units and Conversion Factors. https://remm.hhs.gov/radmeasurement.htm Table 1 Bq Ci
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