Primordial radionuclides with physical half-lives comparable to the age of the Earth (˜4.5 billion years) and their radioactive decay products are the largest sources of terrestrial radiation exposure. The radioactive materials that have been present on the Earth since its formation are called primordial radionuclides. Structures provide some protection from cosmic radiation the indoor effective dose rate is approximately 20% lower than outdoors. Cosmic radiation is also greater at the Earth’s magnetic poles than at the equator, as charged particles encountering the Earth’s magnetic field are forced to travel along the field lines to either the North or the South Pole. Exposures increase with altitude, approximately doubling every 1,500 m, as there is less atmosphere to attenuate the cosmic radiation. However, smaller populations receive much more than this amount ( e.g., Colorado Springs, CO, at 1,840 m, ˜0.82 mSv per year). The majority of the population of the United States is exposed to cosmic radiation near sea level where the outdoor effective dose rate is approximately 0.3 mSv per year. However, the range of individual exposures is considerable. The average per capita effective dose from cosmic radiation is approximately 0.33 mSv per year or approximately 11% of natural background radiation. g., electrons and muons) and electromagnetic radiation. Almost all primary cosmic radiation collides with our atmosphere before reaching the ground, producing showers of secondary particulate radiations ( e. Primary cosmic rays predominantly consist of extremely penetrating high-energy (mean energy ˜10 GeV) particulate radiation, approximately 80% of which is high-energy protons.
Cosmic radiation includes both the primary extraterrestrial radiation that strikes the Earth’s atmosphere and the secondary radiations produced by the interaction of Naturally occurring sources of radiation include (1) cosmic rays, (2) cosmogenic radionuclides, and (3) primordial radionuclides and their radioactive decay products. Doses to individuals from these sources vary considerably with a variety of factors discussed below. population from medical imaging procedures, likely due to advances in technology as well as campaigns to increase awareness of medical imaging doses and to optimize patient doses. 184, NCRP updated the information on the medical radiation exposure of patients in the United States, finding a 15% to 20% reduction, from 2006 to 2016, in the average dose to the U.S. Only about 2%, 0.14 mSv, was from other sources, such as consumer products and activities and occupational exposure. Approximately half of this, about 3.1 mSv, was from naturally occurring sources, whereas about 48%, 3.0 mSv, was from medical exposure of patients. These averages apply to the entire population of the United States. 160, the average annual per capita effective dose, exclusive of doses to patients from external beam radiation therapy, from exposure to ionizing radiation in the United States in 2006 was approximately 6.2 millisievert (mSv). Much of the data referenced below on sources of exposure to radiation is from National Council on Radiation Protection and Measurements (NCRP) reports 94, 160, and 184 ( NCRP, 1987, 2009, 2019) which have consolidated information on population exposure from both naturally occurring and artificially produced sources of exposure to radiation.
This chapter discusses the application of radiation protection principles (also known as health physics) in diagnostic x-ray and nuclear imaging, image-guided interventional procedures, and therapy with radioactive material. To a large degree, the success of radiation protection programs depends on the development of procedures for the safe use of radiation and radioactive material and the education of staff about radiation safety principles, the risks associated with radiation exposure and contamination, and the procedures for safe use. Radiation protection programs are designed and implemented to ensure compliance with these regulations. Federal and state governments and even some large municipalities have agencies that promulgate regulations regarding the safe use of radiation and radioactive material. It is incumbent upon all individuals who use radiation in medicine to strive for an optimal compromise between its clinical utility and the risk from radiation doses to patients, staff, and the public.
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