Table 2: Radiation Quantities and Units of Measurement Quantity Measure
International Unit
Traditional Unit
Conversion
Exposure
Ionization of air
C/kg
R
1 C/kg = 3,876 R
Absorbed dose
Energy absorbed
Gy
rad
1 Gy = 100 rads
Equivalent dose
Biologic effects
Sv
rem
1 Sv = 100 rems
Effective dose
Estimated risk
Sv
None
None
Radioactivity
Decay rate
Bq
Ci
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.
Note . From Radiation Emergency Medical Management. (2016). Radiation units and conversions . Retrieved from https://www.remm.nlm.gov/ radmeasurement.htm 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 radiation 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 inhalation 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; United States 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 electromagnetic. (Particulate radiation is made up of particles; electromagnetic 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 (United States 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 (United States Environmental Protection Agency, 2021b). People who travel by airplane receive higher doses of cosmic radiation than those who do not. Passenger jets are not only closer to the sun; Artificial radiation Artificial radiation (also known as human-made radiation ) accounts for 50% of the radiation to which people in the United States are exposed annually (United States Nuclear Regulatory Commission, 2020; Health Physics Society, 2020). Artificial radiation is generated in medicine and dentistry, and it is found in consumer and industrial products. Medical diagnostic imaging is the largest contributor to artificial radiation (United States Environmental Protection Agency, 2021a). Radiation used in the practice of medicine includes interventional, nuclear medicine, medical and dental diagnostic imaging procedures, and radiation therapy. Exposures from medical procedures have significantly increased since the 1980s, primarily as a result of greater use of computed tomography (CT) and nuclear medicine procedures. The relative percentages of artificial sources of radiation are: ● Computed tomography (CT scan): 24%.
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, 2016). Terrestrial radiation is emitted from radioactive materials – such as potassium and the radioactive decay products of uranium and thorium – present in the earth and air. Terrestrial radiation has been measured in the air over a large segment of the United States. The dose of terrestrial radiation varies by location, with the highest doses in the mountains of the western states as granite and metamorphic rocks in the Rocky Mountains and the Sierra Nevada Mountains contain higher amounts of uranium compared to the sedimentary rocks of the East Coast (Alden, 2020). Terrestrial radiation makes up approximately 3.0% of all radiation exposure received by individuals in the U.S. (Health Physics Society, 2020). Persons living on the Atlantic or Gulf Coasts receive approximately 0.15 mSv annually, and persons living on the Colorado Plateau receive approximately 0.75 mSv in a given year (American Nuclear Society, 2016). Radon is the single largest contributor to the phenomenon of natural radiation. A gaseous element resulting from the disintegration of isotopes of radium (which is itself a product of the decay of uranium in the soil), radon can be found in the soil and rocks underneath houses, in well water, and in certain building materials (Environmental Protection Agency [EPA], 2016a). As radium disintegrates, large amounts of radon accumulate in areas where airflow is poor, such as in caves, mines, or in the basements of energy-efficient homes (EPA, 2016a). As people breathe, they inhale radon. The EPA estimates that radon and its decay products cause more than 21,000 cases of lung cancer annually, accounting for approximately 13% of all lung cancer deaths in the United States (EPA, 2016a).
● Nuclear medicine: 12%. ● Interventional fluoroscopy: 7%. ● Conventional radiography/fluorography: 5%. (Health Physics Society, 2020)
In the last category, dental imaging contributes 2.5% (The American Dental Association, 2019). This percentage does not include cone beam computed tomography (CBCT) examinations, which are on the rise in dentistry. The effective dose of radiation from a dentoalveolar CBCT with a small and medium field view ranges from 0.011-0.674 mSv while an effective dose of 0.030- 1.073 mSv accrues from a maxillofacial CBCT with a large field of view (American Dental Association, 2019). Table 3 lists some common diagnostic procedures, along with their effective doses of radiation.
EliteLearning.com/Dental
Book Code: DFL3024
Page 111
Powered by FlippingBook