Ionizing radiation has been proven to be a risk factor for malignancy in the future. Evidence from studies conducted following the Chernobyl accident, nuclear tests, environmental radiation pollution, and accidental indoor contamination reveals consistently increased chromosome aberration and micronuclei frequency in those exposed to ionizing radiation. Ionizing radiation is of significant concern in the United States due to ubiquitous and often unnecessary imaging of patients with computerized tomography and x-rays. With the advent of multi-slice CTs[1], the indications for this imaging modality and its use is increasing. Although CT scans are often helpful for the clinician in making a diagnosis, they are not without risks. This risk of cancer later in life is most important for children. Ionizing radiation is cumulative. Once received, the effects remain in the body for life. As such, with increased levels of exposure to ionizing radiation to an individual, the greater the risk of malignancy later in life. Because children have more years of life remaining than adults, their cumulative risk of malignancy due to ionizing radiation is higher.[2]

Electromagnetic and particulate radiation are both capable of producing ion pairs by interaction with matter. Through ionizing radiation, high-quality images can be obtained by physicians to assist in helping to make a diagnosis. Ionizing radiation uses gamma, x, alpha particles, neutrons, beta rays, charged nuclei, and positron radiation. Ionizing radiation can be found in consumer products, radioactive substances, improper disposal of radioactive waste.[3] Radiation is also used in the treatment of certain types of cancers. Rural hospitals often are not aware of the public health risks of ionizing radiation and do not as frequently employ radiation reducing protocols in their radiology departments. Currently, 46% of ionizing radiation is from a medical source, as opposed to only 15% in the past. Natural sources of ionizing radiation include solar, cosmic, radioactive elements such as uranium, as well as gamma rays in lightning strikes. Radiation absorbed dose is measured in rad and gray units. Factors that impact exposure are the amount of time an individual is exposed to radiation, distance from the radioactive source, and the degree of radioactivity or rate of energy emission.

The lifetime cancer mortality risk from a pediatric CT scan has been determined to be higher than for adults, and the lifetime attributable risk to children of CT-induced cancer is estimated to be 1 in 1000.[3] Recent studies have demonstrated that pediatric CT scans have a direct association with an increased incidence of solid tumors, leukemia, lymphoma, and myelodysplasia. Another study,  extrapolating epidemiological data from survivors of an atomic bomb radiation exposure estimated that there may be a risk of 1 fatal cancer for every 1000 CT scans performed in young children.[4]

Over the past several decades, there has been mounting evidence regarding the carcinogenic risk of exposure to ionizing radiation. Several studies utilizing data from nuclear disasters have attempted to estimate cancer risk based on specific doses of ionizing radiation. Reducing radiation dose during imaging at a hospital is one means by which to limit excess exposure to ionizing radiation to patients. Children are at increased risk of receiving higher doses of ionizing radiation than adults due to their body habitus. Appropriateness of imaging must be evaluated by every physician ordering those images to minimize future harm to the patient[5].

The effect on the human body is cell damage. While the majority of the time the cell can repair itself, the damage to core DNA and repair mechanisms can render it unable to operate normally. Cells die and can slough off the mucosa. A high radiation dose over a short span spread across multiple doses is thought to be better for cell repair as compared to prolonged exposure at a low dose.

Teratogenic effects are associated with ionizing radiation. Direct radiation, especially to a fetus in early stages of development (first trimester) exhibits a high level of teratogenicity and may even result in fetal death.

Cellphones, AM/FM radio, microwaves, sunbathing, and lighting sources are all sources of nonionizing radiation. However, these are of extremely low doses of ionizing radiation with no detectable health effects. However, long-term exposure may lead to cancer and other adverse health effects. 

Ionizing radiation is being evaluated not only as a risk factor for malignancy but as one of the sources of excessive healthcare costs[6]. There is a push for physicians to utilize their clinical skills to diagnose patients rather than relying on computerized tomography and other imaging modalities in making a diagnosis. It is important to know that there is NO SAFE DOSE OF IONIZING RADIATION. There is a movement in health care known as ALARA  ("as low as reasonably achievable") where the exposure of ionizing radiation is limited while still achieving quality imaging. 

Radiation exposure to healthcare workers is higher than in the general population. The measurement of the effective dose of radiation on the human body is in roentgen equivalent man (or rem). The average dose of radiation per year in a healthcare worker is 5 rem/year compared to a member of the public which is  0.1 rem/year. It is important for healthcare workers to limit their radiation exposure time whenever possible. When not possible, these workers should use appropriate shielding and distance themselves during imaging procedures where ionizing radiation is in use. 

Note that radiation has beneficial uses in healthcare. Radiation therapy in cancer treatment is shown to decrease recurrence rates and minimizes the need for increased tissue resection, which would leave the patient with potentially increased levels of physical disfiguration (as with breast cancer).[7] It also improves survival rates in many malignancies including breast, prostate, gastric, esophageal, testicular,  and pancreatic cancers to name a few.