Radiation Exposure Guide

People are exposed to different amounts of natural “background” ionizing radiation, depending on where they live. Radon gas in homes is a problem of growing concern. The sources and respective average annual dosages of background radiation from each source are as follows: [1] Terrestrial (radiation from soil and rocks): 0.5 mSv. [2] Cosmic (radiation from outer space): 0.5 mSv. [3] Radioactivity normally found within human body: 0.25 mSv. Depending geographic and other factors, the range of cumulative annual dose of background radiation is 0.75 to 5.0 mSv, with an average dose of 3 mSv.

In addition to exposure from normal background radiation, medical procedures may contribute to the ionizing radiation dose people receive. Average dosages received by the bone marrow of persons undergoing various procedures involving ionizing radiation are as follows (variations by a factor of 2 above or below the average dosages are not unusual): [1] Chest X-ray: 0. 1 mSv. [2] Standard dental X-ray: 0. 1 mSv. [3] X-rays of the rib cage: 1.4 mSv. [4] Cholecystogram: 1.7 mSv. [5] Barium enema large bowel examination: 5.0 mSv. [6] X-rays of the pelvis: 6.0 mSv.

The US Nuclear Regulatory Commission (NRC) regulations (10 CFR 20; Standards for Protection Against Radiation; §101) have set the limit on dose of ionizing radiation that can be received on the job (i.e. by a radiation worker) as 12.5 mSv per annual quarter, or 50 mSv per year. Working minors (age <18 years) are limited to one-tenth the dose permissible for adults, or 1.25 mSv per quarter and 5 mSv per year. Amendment to 10 CFR 20, §1208 (1994) has set the limit on dose of radiation to an embryo/fetus of a “declared pregnant” woman radiation worker as 0.5 rem during the entire pregnancy.

Regulations and guidelines of the US Nuclear Regulatory Commission (NRC) are based on the assumption that any amount of ionizing radiation, no matter how small, can have a harmful effect on an adult, child, or unborn child. This assumption is conservative, because there are no data showing ill effects from small dosages.

For small doses of radiation exposure, estimates of the significance of risks are quite inaccurate. For doses less than 10 mSv , the risk is too small to measure. For doses 10 to 50 mSv, the risk may be similar to other every day risks, such as driving a car. On the other hand, for radiation exposure exceeding 50 mSv, there is a measurable and significant increase in cancer risk; the magnitude of the risk varies widely, depending on the part of the body receiving the radiation. Thus, research involving radiation exposure of 50 or more mSv would be justifiable only if there is strong likelihood that the subject will benefit from the exposure directly, and if the expected benefits clearly outweigh the risks.

In studies involving ionizing radiation, the informed consent document should contain meaningful and understandable information on the quantity of exposure, the risks of the exposure directly attributable to the dose received within the framework of the study, and the risks in terms of cumulative life-time exposure to ionizing radiation. The amounts of exposure are to be given in Sieverts (Sv) or miliseverts (mSv), and interpreted in relation to three other types of radiation exposure: [1] background radiation, [2] other medical radiological procedures, and [3] permissible radiation exposure limits for radiation workers.

Suggested text for inclusion in the “Risks” section of the informed consent document can be found at https://ehs.umich.edu/research-clinical/radiation/rdrcshur-committees/

Numerous ‘Radiation Dose Calculators’ are publicly available to provide dosage estimates for daily-life activities and medical procedures, including

• American Nuclear Society (ANS) Radiation Dose Calculator
• RadiologyInfo.org Radiation Dose in X-Ray and CT Exams

Assistance for radiation dosimetric analysis is available through IRBMED ([email protected]) or at RDRC/SHUR Committees.