Can X-rays and CT scans cause cancer? ----- from the suspected radiation accident at Wuhan Union Hospital

The reason may be that these doctors were radiated by medical X-rays in the orthopedic surgery room, and because the hospital did not do a good job of protection and isolation, it led to their collective cancer. At the same time, he also pointed out that in addition to ionizing radiation from X-rays, the hospital may also have suffered a nuclear leak. When the news came out, public opinion was in an uproar. Radiation, divided into ionizing radiation and non-ionizing radiation, the criterion for differentiation is whether the radiation energy is large enough to cause material ionization. Non-ionizing radiation, that is, we can see the light, as well as invisible ultraviolet light, infrared light, microwaves, radio waves and other electromagnetic waves, characterized by wavelength, low energy, will not cause material ionization. Ionizing radiation, including α-rays (α particles), β-rays (β particles), neutrons and other high-energy particle streams and γ-rays, X-rays and other high-energy electromagnetic waves. We often say that medical X-ray and CT, is the use of ionizing radiation in the high-energy electromagnetic waves X-rays can penetrate the human body, allowing the imaging doctor through the X-rays penetrate the human body after the formation of the image, indirectly observe the internal structure of the human body. X-rays used for X-rays and CTs do not have a residual problem; they disappear as soon as they are removed and do not continue to affect the human body. This is fundamentally different from "nuclear leakage" and "nuclear accidents". Nuclear leakage refers to the leakage of radioactive material, and even if the leakage stops, the residual radioactive material will continue to emit rays and cause damage, and the half-life is very long and the damage is long-lasting. For example, in the case of the Chernobyl nuclear power plant accident, the nuclear radiation at the site of the accident has continued until now, and will continue for a thousand years. The radioactive substances used in hospitals are different from nuclear power plants, there will not be high doses of radioactive substances with long half-life, the more commonly used cobalt 60, half-life is 5.27 years, and most of them are used for radiotherapy, and will not be used in X-ray and CT examination. Is it possible that the cancer of the gynecologist at the Union Hospital was caused by the leakage of radionuclides? The possibility is very small, because gynecologists do not come into direct contact with radioactive substances, and rarely use radioactive substances in the operating room (unless intraoperative radiotherapy), and if radioactive substances leakage, it is also the direct operation of the use of radioactive substances in ECT, radiotherapy doctors first cancer, but we have not seen such a situation. So, can X-ray and CT cause cancer? The key lies in the dose. Ionizing radiation, which is used in radiotherapy, may cause cancer due to its high dose, while X-ray and CT, which are used for examination and diagnostic imaging, are unlikely to induce cancer due to their low dose. Focus on the concept of dose of radiation. The commonly used unit of radiation dose is Gy, which represents the amount of energy per unit mass of material exposed to radiation and is equivalent to joules per kilogram, and this unit does not represent the dose of radiation that acts on the human body. In medicine, the dose of radiation that we are concerned with, especially the dose that produces biological effects, is related to two aspects, including the type of radiation and the type of tissue that is exposed to the radiation, and is expressed in units of Sv, with 1 Sv = 1,000 mSv. Sv and Gy are converted by multiplying the weighting factor (WR), which consists of the weights produced by the type of radiation and by the type of tissue, with 1 Sv = 1 Gy, which is equivalent to 1 Joule per kilogram. . For radiation types, the weights are 1 for gamma and X-rays and 20 for alpha rays.The tissue weighting factor varies from tissue to tissue because tissues have different sensitivities to radiation (see figure below). For the thyroid gland, the tissue weighting factor is 0.05, which means that the dose of X-rays to the thyroid gland is converted to 1 Sv = 1 Gy X 1 X 0.05. In order to compare the effects of X-rays and CT examinations on the human body in a more intuitive manner, we should introduce the term "background radiation", which refers to the small amount of ionizing radiation generated in the normal living environment, including It refers to the small amount of ionizing radiation produced in normal living environment, including the radiation produced by radon gas in nature and the cosmic radiation from outer space. Every human being is always in the midst of such background radiation throughout his or her life and cannot avoid it. According to a survey, an American receives an annual dose of 3 mSv of background radiation. People living in highland areas receive a higher dose of background radiation than those living in the coastal plains, for example, residents of New Mexico and Colorado are 1.5 mSv higher than those living by the sea, and an airplane traveling from the east coast of the U.S. to the west coast receives a dose of 0.03 mSv. We compare the usual radiological examinations with background radiation and come up with the following table: Marked in red is the X-ray examination of the extremities, which is often used in orthopedics, and which has an extremely low radiation dose of only 0.001 mSv, which is only equivalent to the 3 hours of background radiation we receive, and which has insignificant side effects on the human body, with an additional risk of fatal cancer of less than one in a million. Some studies have suggested that the thyroid gland is at increased risk of thyroid cancer if it receives a radiation dose of 0.06 Sv-0.1 Sv. After simple conversion, we can see that the radiation dose of medical diagnostic X-rays is so small (only 0.001mSv per time) that it would take 60,000 to 100,000 X-rays of the extremities to produce a possible carcinogenicity to the thyroid, not to mention that it is not in close proximity, but also across the ceiling. Therefore, even if the orthopedic surgery room is not properly protected from radiation, it is unlikely that the next floor of the gynecological surgery room doctor will be induced to develop thyroid cancer. In addition, each person receives a radiation dose of 3 mSv per year, which cannot be avoided. After 20-34 years, i.e., at the earliest age of 20 and at the latest age of 34, the cumulative dose of natural background radiation received by a person can reach 0.06-0.1 Sv, which is the level that may induce thyroid cancer, and the gynecologists who suffered from cancer in this case were over 40 years old, so is it possible to deduce that the background radiation caused them to suffer from cancer? The answer is no. With 3 mSv multiplied by the previously mentioned tissue weighting factor of 0.05, the annual dose of background radiation that actually produces a biological effect on the thyroid gland is in fact only 0.15 mSv, in which case a person would need to live for 400 years to accumulate a sufficient dose of background radiation. Therefore, to see whether the radiation will cause harm to the human body, mainly depends on its biological effect dose, medical diagnostic X-rays and CT, their carcinogenic effect is very weak, each of us has a lifetime of one-fifth of the possibility of dying from cancer, so the risk of death from cancer due to X-rays and CT examinations is basically negligible.