Page 27 Complete Your CE Test Online - Click Here found in U.S. freshwater bodies, but more than 200 million people are infected worldwide [69]. The parasites that cause schistosomiasis live in certain freshwater snails during most of their lifecycle. The infectious form of the parasite, known as cercariae, emerges from the snail and contaminates the water. A person can become infected when skin comes in contact with contaminated water. Most human infections are caused by Schistosoma mansoni, S. haematobium, or S. japonicum, and can be treated with antiparasitic drugs. The parasites can cause chronic infections which can result in bladder cancer in untreated persons [69]. Opisthorchis viverrini parasitic flatworm This flatworm (fluke), which is found in Southeast Asia, can cause cholangiocarcinoma, or cancer of the bile ducts in the liver [172]. The flatworm is contracted when eating raw or undercooked fish, including salted, smoked, and pickled fish from parts of Thailand, Laos, and Cambodia. The infection usually is asymptomatic but can be detected by microscopic examination of the stool. It can be treated with antiparasitics [68]. Ionizing radiation What health care workers call “radiation” is only one of many types of electromagnetic radiation. Electromagnetic energy travels in waves and spans a broad spectrum, from very long radio waves to very short gamma rays. The human eye can detect only a small portion of this spectrum, called visible light. A radio detects a different portion of the spectrum, and infrared energy can be detected by the nerves in human skin or by a thermometer [135]. Unfortunately, differences between the medical and the scientific use of the word “radiation” can cause a great deal of confusion in people who now worry about microwaves and radio waves causing cancer. The electromagnetic energy produced by an X-ray machine or by a linear accelerator is called ionizing radiation, and the energy it produces can cause damage to human and animal DNA. Lower- energy, non-ionizing forms of radiation, such as visible light, wireless networks (Wi-Fi), the energy from cell phone towers, and magnetic fields produced by electricity (including MRI machines) do not damage DNA and have not been found to cause cancer, although a great deal of research and discussion surrounds the topic [187]. Medical radiation When nurses speak of radiation, he or she (s/he) is typically referring to very specific types of high-energy radiation rather than visible light, microwaves, or radio waves. Ionizing radiation includes radon, X-rays, gamma rays, and other forms of high-energy radiation. Ionizing radiation is defined as radiation with enough energy to remove tightly bound electrons from their orbits, causing atoms to become charged or ionized. Ions formed in the molecules of living cells can go on to react with and potentially damage other atoms in the cell. At low doses (e.g., those associated with background radiation and limited x-rays), the cells repair the damage rapidly. At moderate doses, the cells may be permanently mutated or die from their inability to repair the damage. Cells that are damaged and unrepaired but that do not die, may go on to produce abnormal cells when they divide. In some circumstances, these altered cells may become cancerous or lead to other abnormalities (e.g., birth defects). Defects in the ability to repair damage caused by ionizing radiation may influence the how much radiation exposure increases cancer risk [174]. There is extensive evidence linking exposure to ionizing radiation with the development of cancer. In particular, ionizing radiation is linked to cancer that involves the hematological system, breast, lungs, and thyroid [148]. The National Research Council of the National Academies ‘Committee to Assess the Health Risks from Exposure to Low Levels of Ionizing Radiation’ put out the Biologic Effects of Ionizing Radiation VII, which is the most widely cited source on the topic. In this report, three lines of evidence were cited documenting the links between ionizing radiation exposure and cancer [148]: ● ● The first line of evidence comes from studies of the development of cancer among Japanese atomic-bomb survivors. Even survivors who were exposed to lower doses of radiation were at a significantly increased risk of developing cancer. ● ● The second line of evidence comes from epidemiological studies of medically irradiated populations (in which people were medically irradiated for both malignant and benign diseases). Following high-dose radiation therapy for malignant disease, the risk of secondary malignancy is relatively high. The relatively common use of radiation for benign disease between 1940 and 1960 resulted in a substantial relative risk (RR) of developing cancer. ● ● The third line of evidence comes from an increased risk of cancer- specific mortality associated with exposure to medical ionizing radiation, for both the recipients of diagnostic X-rays and X-ray personnel. This is one reason that public health interests have worked to lessen the radiation levels for many diagnostic X-rays over the years (with some exceptions), and why radiology staff wear dosimeters to monitor actual exposure to radiation. The report concluded, after a comprehensive review of the medical literature, that no dose of radiation should be considered completely safe, and attempts should be made to keep radiation doses as low as possible. Of note, there are some experts who believe that there might be very low radiation exposure levels (thresholds) below which no harm might be done. It is difficult to measure long-term effects from very low radiation exposures, and it would be unethical to do clinical trials in which people are deliberately exposed to low levels that could possibly cause harm. However, scientific consensus has established the Linear No-Threshold (LNT) model as the most practical one to guide policy and safety measures regarding ionizing radiation exposures. The LNT model assumes that even very low levels of ionizing radiation might cause harm and that the dose-relationship is linear: simply stated, the higher the exposure, the higher the risk [220]. The major sources of population exposure to ionizing radiation are medical radiation (including computed tomography [CT], fluoroscopy, nuclear medicine, and regular x-rays) and naturally occurring radon gas in the basements of homes (see “Radon”). Limiting unnecessary CT scans and other radiation-based diagnostic studies as well as reducing radiation exposure doses for these studies are important prevention strategies [132,174,210]. Exposure to ionizing radiation has increased during the last two decades as a result of the dramatic increase in the use of CT scanning. The National Cancer Institute reports that exposure to ionizing radiation associated with CT is in the range where carcinogenesis has been demonstrated [50, 258]. Repeat exposure to radiation from medical imaging (mainly CT scans, but angiography and a few other techniques can use as much or more radiation) further increases cancer risk, assuming that risk is proportional to exposure [131]. One study found that half the subjects who were exposed to radiation from medical 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