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Nuclear Medicine: Introduction to U.S. & International Regulations and Clinical Practice Resources: Radiation Exposure

Overview of Radiation Exposure

A special part of the practice of nuclear medicine is constant vigilance to minimize the radiation exposure for patients, staff, and the general public while still performing effective medical procedures.  Nuclear Medicine uses the ALARA principle.  Radiation exposure should always be As Low As Reasonably Achievable (ALARA).  To implement ALARA effectively, the physician and other staff must understand radiation, radiopharmaceuticals, radiation detection equipment, and radioisotope handling.

Jefferson Lab has a nice explanation of radiation fundamentals, and it even comes with a review quiz! 

For More Information

If you prefer to get information via videos, You Tube has a good selection of videos on understanding radioactivity, radiation exposure and radiation effects.

Radiation Exposure Limits

Per 10 C.F.R. § 20, those who are considered radiation workers, such as Nuclear Medicine Technologists and Physicians, have an annual radiation exposure limit of 5 rem to the whole body.  Because we want to protect the general public from needless exposure to radiation, the exposure limit for the general public is only 100 mrem (1 mSv).

To put this in perspective, the average American is exposed to about 300 mrem per year because there is always radiation from outer space, the earth itself, and other natural sources.  Therefore, the exposure limits are very conservative.  Exposures that are within these limits are considered very safe.

The International Atomic Energy Agency has ongoing efforts to reduce patient exposure to radiation. For resources, news, and audio/video clips, check out their Radiation Protection of Patients Web page.

Radiation Effects

The effect radiation has on humans varies by the type of radiation, how long the body is exposed to the radiation, and how much of the body is exposed.  A 100 rem exposure that is spread out over 50 years would not be harmful, but a very short pulse of 100 rem over the whole body might cause symptoms of radiation sickness.  A short pulse of 100 rem that is focused on one small area might cause burns to that part of the body.

The amount of radiation used for properly administered diagnostic nuclear medicine procedures is too low to cause any side effects.  Therapeutic nuclear medicine does use amounts and types of radiation for which effects are expected.  Therapeutic dosages are very carefully determined to minimize adverse effects while maximizing the beneficial effects of the treatment. 

For more information on the effects of radiation exposure, the Princeton Environmental Health and Safety Division has a nice module that explains the biological effects of radiation.

Radiation Terminology

Radiation has its own vocabulary to describe types of radiation, its measurement, and its effects.  A full discussion is beyond the scope of this library guide.  For those who wish to learn more, there are many resources available.

If you would like a non-technical explanation of radiation effects, the Nuclear Energy Institute has a nice online brochure. If you would prefer a review with more scientific, but still easy-to-understand, details, a nice online slide presentation is available. For a broader explanation of both ionizing and non-ionizing radiation, visit the EPA's Radiation Information page.

To help with a quick understanding of radiation and nuclear medicine, here are a few key terms:

Ionizing Radiation--particles or waves of energy that knock electrons from their atoms, causing the atoms to each have an electrical charge.  Radioactive materials and x-rays are types of ionizing radiation. Non-ionizing radiation does not have enough energy to ionize the atoms it hits.  Light, microwaves, and radiowaves are types of non-ionizing radiation.

Gamma Radiation--electromagnetic radiation, similar to x-ray radiation.  It is energy given off by an atom due to the interaction of atomic particles. Gamma radiation is emitted by the tracers (radioactive materials) used in nuclear medicine.  The devices used in diagnostic nuclear medicine that detect the gamma radiation and produce images are known as gamma cameras. Lead is used to protect you from gamma radiation.  A PET (Positron Emission Tomography) Scan uses a special type of gamma radiation known as positrons. 

Beta Radiation--high-energy electrons or positrons emitted from radioactive materials.  These are more powerful than gamma emissions, but  cannot travel as far.  In soft tissues, gamma radiation only travels a few millimeters.  Beta radiation is used in nuclear medicine therapies, such as when using Iodine-131 to treat thyroid cancer or hyperthyroidism.  Plastic is used to shield from beta radiation.

Alpha Radiation--a particle composed of two protons and two neutrons. This type of radiation is more powerful than beta radiation, but can only affect tissue immediately adjacent to the emitting source. Paper is enough to protect you from alpha radiation.  Some alpha emitters are used in radionuclide therapy.

Rem--a unit of measurement of radiation dose.  A millirem (mrem) is one-thousandth of a rem.  A Sievert (Sv) is the metric unit and 1 Sv = 100 rem.  Similarly, 100 mrem = 1 mSv (milliSievert).  In one year the average American is exposed to about 300 mrem of radiation (roughly, 1 mrem per day) just from cosmic radiation, earth radiation, and other radiation in the environment.  A Colorado resident receives about 1 rem (1,000 mrem; 10 mSv) per year.  A plane flight adds about 0.3 mrem per hour of flight time for shorter flights.  Long-haul flights, which are generally at higher altititude, may have about 0.6 mrem per hour exposure. A chest x-ray is about 10 mrem exposure. A TSA back-scatter x-ray at the airport security point produce about 0.01 mrem (10 microrem) exposure, about the same exposure as you already receive in 15 minutes each day.

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