Cancer The radiation used in<unk> s can damage body cells, including DNA molecules, which can lead to radiation-induced cancer. The radiation doses received from<unk> s is variable. Compared to the lowest dose x-ray techniques,<unk> s can have 100 to 1,000 times higher dose than conventional X-rays. However, a lumbar spine x-ray has a similar dose as a head CT. Articles in the media often exaggerate the relative dose of CT by comparing the lowest-dose x-ray techniques (chest x-ray) with the highest-dose CT techniques. In general, the radiation dose associated with a routine abdominal CT has a radiation dose similar to three years of average background radiation. Recent studies on 2.5 million patients and 3.2 million patients have drawn attention to high cumulative doses of more than 100 mSv to patients undergoing recurrent<unk> s within a short time span of 1 to 5 years. Some experts note that<unk> s are known to be "overused," and "there is distressingly little evidence of better health outcomes associated with the current high rate of<unk> s." On the other hand, a recent paper analyzing the data of patients who received high cumulative doses showed a high degree of appropriate use. This creates an important issue of cancer risk to these patients. Moreover, a highly significant finding that was previously unreported is that some patients received >100 mSv dose from<unk> s in a single day, which counteracts existing criticisms some investigators may have on the effects of protracted versus acute exposure. Early estimates of harm from CT are partly based on similar radiation exposures experienced by those present during the atomic bomb explosions in Japan after the Second World War and those of nuclear industry workers. Some experts project that in the future, between three and five percent of all cancers would result from medical imaging. An Australian study of 10.9 million people reported that the increased incidence of cancer after<unk>  exposure in this cohort was mostly due to irradiation. In this group, one in every 1,800<unk> s was followed by an excess cancer. If the lifetime risk of developing cancer is 40% then the absolute risk rises to 40.05% after a CT. Some studies have shown that publications indicating an increased risk of cancer from typical doses of body<unk> s are plagued with serious methodological limitations and several highly improbable results, concluding that no evidence indicates such low doses cause any long-term harm. One study estimated that as many as 0.4% of cancers in the United States resulted from<unk> s, and that this may have increased to as much as 1.5 to 2% based on the rate of CT use in 2007. Others dispute this estimate, as there is no consensus that the low levels of radiation used in<unk> s cause damage. Lower radiation doses are used in many cases, such as in the investigation of renal colic. A person's age plays a significant role in the subsequent risk of cancer. Estimated lifetime cancer mortality risks from an abdominal CT of a one-year-old is 0.1%, or 1:1000<unk> s. The risk for someone who is 40 years old is half that of someone who is 20 years old with substantially less risk in the elderly. The International Commission on Radiological Protection estimates that the risk to a fetus being exposed to 10 mGy (a unit of radiation exposure) increases the rate of cancer before 20 years of age from 0.03% to 0.04% (for reference a CT pulmonary angiogram exposes a fetus to 4 mGy). A 2012 review did not find an association between medical radiation and cancer risk in children noting however the existence of limitations in the evidences over which the review is based.<unk> s can be performed with different settings for lower exposure in children with most manufacturers of<unk> s as of 2007 having this function built in. Furthermore, certain conditions can require children to be exposed to multiple<unk> s. Current evidence suggests informing parents of the risks of pediatric<unk> ning. Contrast reactions In the United States half of<unk> s are contrast CTs using intravenously injected radiocontrast agents. The most common reactions from these agents are mild, including nausea, vomiting, and an itching rash. Severe life-threatening reactions may rarely occur. Overall reactions occur in 1 to 3% with nonionic contrast and 4 to 12% of people with ionic contrast. Skin rashes may appear within a week to 3% of people. The old radiocontrast agents caused anaphylaxis in 1% of cases while the newer, low-osmolar agents cause reactions in 0.01–0.04% of cases. Death occurs in about 2 to 30 people per 1,000,000 administrations, with newer agents being safer. There is a higher risk of mortality in those who are female, elderly or in poor health, usually secondary to either anaphylaxis or acute kidney injury. The contrast agent may induce contrast-induced nephropathy. This occurs in 2 to 7% of people who receive these agents, with greater risk in those who have preexisting kidney failure, preexisting diabetes, or reduced intravascular volume. People with mild kidney impairment are usually advised to ensure full hydration for several hours before and after the injection. For moderate kidney failure, the use of iodinated contrast should be avoided; this may mean using an alternative technique instead of CT. Those with severe kidney failure requiring dialysis require less strict precautions, as their kidneys have so little function remaining that any further damage would not be noticeable and the dialysis will remove the contrast agent; it is normally recommended, however, to arrange dialysis as soon as possible following contrast administration to minimize any adverse effects of the contrast. In addition to the use of intravenous contrast, orally administered contrast agents are frequently used when examining the abdomen. These are frequently the same as the intravenous contrast agents, merely diluted to approximately 10% of the concentration. However, oral alternatives to iodinated contrast exist, such as very dilute (0.5–1% w/v) barium sulfate suspensions. Dilute barium sulfate has the advantage that it does not cause allergic-type reactions or kidney failure, but cannot be used in patients with suspected bowel perforation or suspected bowel injury, as leakage of barium sulfate from damaged bowel can cause fatal peritonitis. Side effects from contrast agents, administered intravenously in some<unk> s, might impair kidney performance in patients with kidney disease, although this risk is now believed to be lower than previously thought.<unk>  dose Examination Typical effective dose (mSv) to the whole body Typical absorbed dose (mGy) to the organ in question Annual background radiation 2.4 2.4 Chest X-ray 0.02 0.01–0.15 Head CT 1–2 56 Screening mammography 0.4 3 Abdominal CT 8 14 Chest CT 5–7 13 CT colonography 6–11 Chest, abdomen and pelvis CT 9.9 12 Cardiac CT angiogram 9–12 40–100 Barium enema 15 15 Neonatal abdominal CT 20 20 The table reports average radiation exposures; however, there can be a wide variation in radiation doses between similar<unk>  types, where the highest dose could be as much as 22 times higher than the lowest dose. A typical plain film X-ray involves radiation dose of 0.01 to 0.15 mGy, while a typical<unk>  involve 10–20 mGy for specific organs, and can go up to 80 mGy for certain specialized<unk> s. For purposes of comparison, the world average dose rate from naturally occurring sources of background radiation is 2.4 mSv per year, equal for practical purposes in this application to 2.4 mGy per year. While there is some variation, most people (99%) received less than 7 mSv per year as background radiation. Medical imaging as of 2007 accounted for half of the radiation exposure of those in the United States with<unk> s making up two thirds of this amount. In the United Kingdom it accounts for 15% of radiation exposure. The average radiation dose from medical sources is ≈0.6 mSv per person globally as of 2007. Those in the nuclear industry in the United States are limited to doses of 50 mSv a year and 100 mSv every 5 years. Lead is the main material used by radiography personnel for shielding against scattered X-rays. Radiation dose units The radiation dose reported in the gray or mGy unit is proportional to the amount of energy that the irradiated body part is expected to absorb, and the physical effect (such as DNA double strand breaks) on the cells' chemical bonds by X-ray radiation is proportional to that energy. The sievert unit is used in the report of the effective dose. The sievert unit, in the context of<unk> s, does not correspond to the actual radiation dose that the<unk> ned body part absorbs but to another radiation dose of another scenario, the whole body absorbing the other radiation dose and the other radiation dose being of a magnitude, estimated to have the same probability to induce cancer as the<unk> . Thus, as is shown in the table above, the actual radiation that is absorbed by a<unk> ned body part is often much
CT scan
Fluoroscopy
Contrast CT
SAP scan
Imaging
Radiography
Exploratory surgery
Autoradiograph