Page 11 Complete Your CE Test Online - Click Here 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. 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. 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. 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. 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. Sun lamps 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 FDA requires that all tanning devices have warning labels indicating that the use of the device is contraindicated in people under age 18 and in 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. 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 of all skin colors. UV radiation is commonly subdivided into UV-A and UV-B. 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 do. 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. UV-A can pass through most windows (depending on type of glass) and is not affected by altitude or weather. 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 UV-B rays are absorbed by the ozone in the earth’s atmosphere. But the remaining percentage leaves plenty of cancer-causing UV rays to be absorbed by human skin. UV-B rays are most intense from midspring through midfall in the U.S. and during the daytime between 10 a.m. and 4 p.m.; however, UV-B rays can damage skin, or even burn it, year- round. This happens more in the southernmost parts of the U.S., at high altitudes, and on surfaces that reflect back sunlight: water, sand, snow, or ice. UV-B rays are also associated with cataracts but help the body make vitamin D, a necessary vitamin. UV-B rays do not significantly penetrate windows. Intermittent versus cumulative UV exposure Most evidence about UV radiation exposure and the prevention of skin cancer comes from observational and analytical studies. Such studies have consistently shown that increased cumulative sun exposure is a risk factor for nonmelanoma skin cancers, such as basal and squamous cell cancers. Exposure to solar UV radiation is the major cause of nonmelanoma skin cancers, which are by far the most common malignancies in humans. But the relationship between UV radiation exposure and cutaneous melanoma is less clear than that of nonmelanoma skin cancers. In the case of melanoma, it seems that intermittent acute sun exposure leading to serious sunburn is more important than cumulative sun exposure. Sunburn sustained during childhood or adolescence may be particularly important. And it is also important to know that acral lentiginous melanoma – a very aggressive form of melanoma that usually forms in areas not often exposed to sunlight such as mucous membranes, the palms, the soles, or under nails – is much more common among darker skinned people. Immunosuppression Medications that suppress the immune system are associated with an increased cancer risk. Many people who receive organ transplants take immunosuppressant drugs to ensure the body will not reject the organ. These medications make the immune system less able to detect and destroy cancer cells or fight off infections that cause cancer. Research has shown that transplant recipients are at increased risk of a large number of different cancers. Some of these cancers can be caused by infectious agents, whereas others are not. The four cancers that occur more commonly in transplant recipients than in the general population are non-Hodgkin’s lymphoma (NHL) and cancers of the lung, kidney, and liver. NHL can be caused by Epstein-Barr virus (EBV) infection, and liver cancer by chronic infection with the hepatitis B (HBV) and hepatitis C (HCV) viruses. Lung and kidney cancers are not generally thought to be associated with infection. Infection with HIV weakens the immune system and increases the risk of certain cancers, especially those that are caused by infections (see section “Infectious Agents”). HIV infection is also linked to increased risks of cancers that are not thought to be caused by infectious agents, such as lung cancer. Other Carcinogens Any substance that is known to cause cancer is classified as a carcinogen, but carcinogenesis is rarely simple. Many factors influence whether a person exposed to a carcinogen will develop cancer, including the amount, duration, and route of exposure as well as the person’s age and genetic background. Cancers caused by involuntary exposures to environmental carcinogens are most likely to be seen in subgroups of the population, such as workers in certain industries who may be exposed to carcinogens on the job. In fact, that is the way a lot of causal links have been found – workers who are exposed to a carcinogenic substance every workday for years are often the first ones found to have higher rates of a certain type of cancer, which often leads to a formal investigation of the substances to which they are exposed. The increased incidence in a small exposed group is much easier to detect and demonstrate than when scattered