What are the radiation risks from CT?As in many aspects of medicine, there are both benefits and risks associated with the use of CT. The main risks are those associated with 1. abnormal test results, for a benign or incidental Contingent upon or pertaining to something that is more important; that which is necessary, appertaining to, or depending upon another known as the principal. Under Workers' Compensation statutes, a risk is deemed incidental to employment when it is related to whatever a finding, leading to unneeded, possibly invasive invasive /in·va·sive/ (-siv) 1. having the quality of invasiveness. 2. involving puncture of the skin or insertion of an instrument or foreign material into the body; said of diagnostic techniques. , follow-up tests that may present additional risks and 2. the increased possibility of cancer induction from x-ray radiation exposure. The probability for absorbed x rays to induce cancer is thought to be very small for radiation doses of the magnitude that are associated with CT procedures. Such estimates of the cancer risk from x-ray exposure have a broad range of statistical uncertainty and there is some scientific controversy regarding the effects from very low doses and dose rates as discussed below. Under some rare circumstances of prolonged pro·long tr.v. pro·longed, pro·long·ing, pro·longs 1. To lengthen in duration; protract. 2. To lengthen in extent. , high-dose exposure, x rays can cause other adverse health effects, such as skin erythema erythema (ĕr'əthē`mə), more or less diffuse redness of the skin due to concentration of an abnormally large amount of blood within the small vessels of the skin (hyperemia), as in burns. (reddening), skin tissue injury, genetic effects, and birth defects birth defects, abnormalities in physical or mental structure or function that are present at birth. They range from minor to seriously deforming or life-threatening. A major defect of some type occurs in approximately 3% of all births. . But at the exposure levels associated with most medical imaging procedures, including CT, these other adverse effects would not occur. Risk Estimates In the field of radiation protection, it is commonly assumed that the risk for adverse health effects from cancer is proportional to the amount of radiation dose absorbed and the amount of dose depends on the type of x-ray examination. A CT examination with an effective dose of 10 millisieverts (abbreviated mSv; 1 mSv = 1 mGy in the case of x rays.) may be associated with an increase in the possibility of fatal cancer of approximately 1 chance in 2000. This increase in the possibility of a fatal cancer from radiation can be compared to the natural incidence of fatal cancer in the U.S. population, about 1 chance in 5. In other words Adv. 1. in other words - otherwise stated; "in other words, we are broke" put differently , for any one person the risk of radiation-induced cancer radiation-induced cancer Radiogenic cancer Oncology CA induced by ionizing radiation–eg, ALL, thyroid cancer is much smaller than the natural risk of cancer. Nevertheless, this small increase in radiation-associated cancer risk for an individual can become a public health concern if large numbers of the population undergo increased numbers of CT screening procedures of uncertain benefit. It must be noted that there is uncertainty regarding the risk estimates for low levels of radiation exposure as commonly experienced in diagnostic radiology radiology, branch of medicine specializing in the use of X rays, gamma rays, radioactive isotopes, and other forms of radiation in the diagnosis and treatment of disease. procedures. There are some that question whether there is adequate evidence for a risk of cancer induction at low doses. However, this position has not been adopted by most authoritative bodies in the radiation protection and medical arenas. Radiation Dose The effective doses from diagnostic CT procedures are typically estimated to be in the range of 1 to 10 mSv. This range is not much less than the lowest doses of 5 to 20 mSv received by some of the Japanese survivors of the atomic bombs atomic bomb or A-bomb, weapon deriving its explosive force from the release of atomic energy through the fission (splitting) of heavy nuclei (see nuclear energy). The first atomic bomb was produced at the Los Alamos, N.Mex. . These survivors, who are estimated to have experienced doses only slightly larger than those encountered in CT, have demonstrated a small but increased radiation-related excess relative risk for cancer mortality. Radiation dose from CT procedures varies from patient to patient. A particular radiation dose will depend on the size of the body part examined, the type of procedure, and the type of CT equipment and its operation. Typical values cited for radiation dose should be considered as estimates that cannot be precisely associated with any individual patient, examination, or type of CT system. The actual dose from a procedure could be two or three times larger or smaller than the estimates. Facilities performing "screening" procedures may adjust the radiation dose used to levels less (by factors such as 1/2 to 1/5 for so called "low dose CT scans CT scan: see CAT scan. See CAT scan. ") than those typically used for diagnostic CT procedures. However, no comprehensive data is available to permit estimation estimation In mathematics, use of a function or formula to derive a solution or make a prediction. Unlike approximation, it has precise connotations. In statistics, for example, it connotes the careful selection and testing of a function called an estimator. of the extent of this practice and reducing the dose can have an adverse impact on the image quality produced. Such reduced image quality may be acceptable in certain imaging applications. The quantity most relevant for assessing the risk of cancer detriment Any loss or harm to a person or property; relinquishment of a legal right, benefit, or something of value. Detriment is most frequently applied to contract formation, since it is an essential element of consideration, which is a prerequisite of a legally enforceable contract. from a CT procedure is the "effective dose". Effective dose is evaluated in units of millisieverts (abbreviated mSv; 1 mSv = 1 mGy in the case of x rays.) Using the concept of effective dose allows comparison of the risk estimates associated with partial or whole-body radiation exposures. This quantity also incorporates the different radiation sensitivities of the various organs in the body. Estimates of the effective dose from a diagnostic CT procedure can vary by a factor of 10 or more depending on the type of CT procedure, patient size and the CT system and its operating technique. A list of representative diagnostic procedures and associated doses are given in Table 1 that is adapted from a report of the European Commission European Commission, branch of the governing body of the European Union (EU) invested with executive and some legislative powers. Located in Brussels, Belgium, it was founded in 1967 when the three treaty organizations comprising what was then the European Community .
Table I. - Radiation Dose Comparison
Time Period for
Diagnostic Typical Number of Chest Equivalent Effective
Procedure Effective X rays (PA film) Dose from Natural
Dose for Equivalent Background
(mSv) (1) Effective Radiation (3)
Dose (2)
Chest x ray (PA
film) 0.02 1 2.4 days
Skull x ray 0.07 4 8.5 days
Lumbar spine 1.3 65 158 days
I.V. urogram 2.5 125 304 days
Upper G.I. Exam 3.0 150 1.0 year
Barium enema 7.0 350 2.3 years
CT head 2.0 100 243 days
CT abdomen 10.0 500 3.3 years
(1.) Effective dose in millisieverts (mSv).
(2.) Based on the assumption of an average "effective dose" from chest
x ray (PA film) of 0.02 mSv.
(3.) Based on the assumption of an average "effective dose" from
natural background radiation of 3 mSv per year in the United States.
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