Page 11 Complete Your CE Test Online - Click Here imaging underwent repeat imaging within three years. Overall, 0.2% of the nearly one million subjects followed for three years received doses above 50 milliSeivert (mSv) [89]. For comparison, the International Commission on Radiological Protection recommends a limit of 50mSv per year for people who work with artificial ionizing radiation, with a five-consecutive-year maximum of 100mSv [306]. For reference, 1mSv is 1/1000 of a Sievert, which is an International System of Units measure for equivalent dose – a measure of biological damage to living tissue from radiation exposure. The U.S. measures often use the ‘rem’ as the basic unit of equivalent dose: 100 rems equals one Sievert; a millirem (mrem) is 1/1000 of a rem; and 1mSv is 100mrems [236]. Table 3: Comparative exposure to ionizing radiation [220, 245, 282]. Exposure or procedure Estimated exposure for an adult* Bone densitometry. 0.001mSv Air travel per 1,000 miles flown. 0.01mSv Spine X-ray. 1.5mSv Head CT. 2mSv Background radiation, average yearly U.S. exposure.** 3.1mSv CT scan of abdomen and pelvis. 10mSv PET (Positron Emission Tomography)/CT scan. 25mSv Radiation therapy for cancer treatment. 20,000-60,000mSv *These are typical for average-sized adults but will vary based on size and practices. **This will be somewhat lower for people at sea level and higher at higher altitudes; it also varies by radon emission from the ground. This total adds the average cosmic radiation and radon gas exposures. One approach to estimate the potential contribution of exposure to ionizing radiation from medical imaging is to develop statistical models based on the estimated cancer risks associated with a range of dose levels. For example, one estimate that looked at CT scans performed in the U.S. in 2007 predicted that 29,000 (95% confidence interval: 15,000–45,000) cancers might result. One-third of the projected cancers were caused by CT scans done on individuals aged 35 to 54 years. This estimate was derived from risk models based on organ-specific radiation doses from national surveys, frequency of CT scans in 2007 by age and sex from survey and insurance claim data, and the National Research Council’s Biologic Effects of Ionizing Radiation VII report [50]. Data are now emerging from studies large enough to directly estimate the cancer risk associated with CT scans. For example, in a cohort of 10.9 million Australians, electronic medical records were used to document the diagnostic CT scans of youths who received the CT scans when they were aged 0-to-19 years. This cohort was then linked to the National Death Index and Australian Cancer Database [123]. Compared with those who did not have a CT scan, those who had at least one CT scan were statistically significantly more likely to be diagnosed with cancer as they were followed into young adulthood (RR, 1.24; 95% confidence interval, 1.20–1.29; average follow-up in those who had a CT was 9.5 years). A significant dose-response relationship was observed, with cancer risk increasing with each additional CT scan. Thus, the findings of cohort studies with directly measured CT scans now substantiate the statistical models and document the real-world cancer risks associated with exposure to ionizing radiation via medical imaging [148]. Evidence-based practice: Biphasic and repeat CT scanning can increase a person’s cancer risk over time. While CT may be an essential part of follow-up monitoring in many cancer patients, it should be kept to a minimum, especially in younger people. MRIs and lower-radiation scans might be acceptable substitutes in some cases [145]. Radiation therapy uses much higher doses than imaging studies to treat cancer, and it carries some future risk of cancer in patients treated with it. If radiation is used in children and teens, the risk of future cancer is higher than when it is used in adults, which in turn is higher than the risk for elderly patients. It is important to be sure that patients scheduled for radiation therapy, especially younger patients, understand the expected benefits and potential risks associated with radiation treatment [187]. Radon – ionizing radiation from the ground Radon is a radioactive gas given off by rocks and soil. Radon is formed when the radioactive element radium breaks down. Radium is formed when the radioactive elements uranium and thorium break down. People who are exposed to high levels of radon have an increased risk of lung cancer [187]. Staff alert: Nurses, radiology technicians, and others who work with diagnostic scanning, nuclear medicine, and radiation therapy should have procedures, structures, and other measures to shield them from exposure to ionizing radiation. People who work in these settings should be carefully protected and monitored at all times to ascertain exactly their exposure [306]. People who live in an area with high levels of radon in rocks and soil may wish to test their homes for this gas. Home radon tests are easy to use and inexpensive. Most hardware stores sell test kits, and some university or county extension services (in cooperation with the U.S. Department of Agriculture) offer lower-cost testing. If high levels of radon are found in the home, there are many ways to lower the amount of radon to a safer level [187]. Ultraviolet radiation The sun is a source of the full spectrum of ultraviolet (UV) radiation, which is a type of electromagnetic radiation above visible light, and a known cause of skin cancer. Sunlamps and tanning beds or booths all give off UV radiation, and the International Agency for Research on Cancer classifies tanning devices as “carcinogenic in humans.” The National Toxicology Program also states that exposure to sun lamps or tanning beds is known to be carcinogenic to humans. The US FDA requires that all tanning devices have warning labels indicating that the use of the device is contraindicated in people under age 18 or those with skin lesions or open wounds. The warning labels further say that they should not be used by people who have had skin cancer or who have a family history of skin cancer, and that people repeatedly exposed to UV radiation should be regularly evaluated for skin cancer [23]. Exposure to UV radiation causes early aging of the skin, and skin damage that can lead to skin cancer. People who tend to burn rather than tan are more susceptible to many types of skin cancer, but skin cancer is found in people with all skin colors. UV radiation is commonly subdivided into UV-A and UV-B [136]. UV-A light rays have long been known to cause skin aging and wrinkles. For many years UV-A rays were not thought to be carcinogenic, but it is now known that UV-A rays penetrate the human skin more deeply than UV-B rays. Newer information is emerging that UV-A damages keratinocytes in the basal epidermis. This layer is where most skin cancers arise: basal cells and squamous cells are both types of keratinocytes, and cancers from these cells are the most common types of skin cancer. UV-A promotes the growth of and may even initiate these types of cancers. Tanning beds put out large amounts of UV-A radiation [257]. UV-A can pass through most windows (depending on type of glass), and is not affected by altitude or weather [300]. UV-B rays are harmful, and are known to cause sunburn. Exposure to UV-B rays increases the risk of DNA damage and other cellular damage in all living organisms, not just humans. Fortunately, about 95% of