It is not groundless to say that CT causes cancer. Radiological diagnostic examination is a double-edged sword. On the one hand, imaging can clearly distinguish the cause of disease and is an important means of diagnosis and treatment; On the other hand, more and more studies show that it is harmful to human body, and its abuse may induce cancer. But people don't seem to attach importance to it.
A new research report in the United States warns that doctors abuse CT scanning technology in the process of diagnosis and treatment, resulting in more than 20 million Americans, especially children, suffering from unnecessary "super X-ray" radiation, which puts them at higher risk of cancer.
The radiation carcinogenicity rate of CT scanning is 2%
This research report was jointly completed by Eric Hull and David Brenner, a medical physicist at Columbia University. Published in the New England Journal of Medicine on the 29th, the study was funded by the US government.
Hull estimates that as many as 2% of cancer cases in the United States in the past few decades may be caused by radiation from CT scans. He said that although the risk of cancer caused by a CT scan is very small, "we are very worried about the harm to public health caused by long-term accumulation."
Statistics show that since 1980, the average number of Americans receiving radioactive scans (most of which are CT scans) has doubled.
CT scanning technology is more widely used, mainly because it is fast, relatively cheap and won't make patients feel pain. The 3D images generated by it have high definition, which is very helpful for doctors to quickly diagnose trauma, abdominal pain, chronic headache, kidney calculi and other diseases. At present, half of the radiation suffered by Americans comes from medical radiation, but this proportion was only one-sixth before. The main radiation source at that time came from the natural environment.
However, CT scanning is extremely radioactive. Chest CT scan can reach 10 ~ 15 millisieverts, in contrast, conventional chest X-ray is 0.0 1 ~ 0. 15 millisieverts, mammography is 3 millisieverts, and dental X-ray is only 0.005 millisieverts.
The amount of radiation varies from machine to machine, and fat people need stronger radiation than thin people-and the harm caused by radiation can be accumulated continuously throughout one's life.
That adds up to atomic radiation?
Previous research by Hull's research team prompted the US Federal Food and Drug Administration to suggest that hospitals reduce the number of children undergoing CT scans by 200 1 year. But since then, CT scanning has been used more and more.
Some doctors said that some patients with chronic diseases such as kidney calculi may have too many CT scans, and even some patients as young as 30 received at least 18 CT scans.
It is reported that Japanese atomic bomb survivors have suffered 50~ 150 millisieverts of radiation, and the cumulative radiation of several CT scans has been equal to it. Some experts questioned this statement, but some experts expressed their support.
The appearance of computed tomography (CT) in 1970s was a great revolution in diagnostic radiology, and its clinical application became more and more extensive with the passage of time. It is reported that there are as many as 62 million CT scans every year in the United States alone, of which at least 4 million are aimed at children. However, the recent radiation reports from foreign media about CT scanning can not help but arouse people's deep thinking. According to a recent study published in the New England Journal of Medicine. In 2007,352 (22): 2277-2284.), researchers at Columbia University Medical Center in new york estimated that in the next 20 to 30 years, as many as 2% of cancer patients in the United States may be caused by radiation from CT scans.
Is radiation "reasonable" or "unreasonable"?
David Brenner, a professor of radiation oncology at Columbia University Medical Center in new york, pointed out in the New England Journal of Medicine that the radiation generated by CT scanning will undoubtedly increase the risk of cancer. Although CT scanning is unlikely to cause a person to get cancer, the harm to public health caused by long-term acceptance of such scanning cannot be ignored. Many radiologists support this view with reservations, because there is no strictly controlled epidemiological study so far, and how big the risk is still an unsolved mystery. Carl Schurz, a professor of clinical emergency medicine at the University of California, said: "This may be alarmist. Radiation is of course harmful to the human body, but the conclusion that CT scanning increases the risk of cancer needs definite evidence to support it. " . In addition, some experts question that this conclusion is only a theoretical prediction based on the data of Japanese atomic bomb victims, which may not be credible at all.
Coincidentally, a study published in the Journal of American Medical Association (JAMA. 2007,298: 317-323). It is also believed that the application of new fast CT scanning (64-slice CT) to examine the heart or its surrounding great vessels will increase the risk of cancer. This risk is more obvious for patients with breast cancer or lung cancer, especially young female patients. For example, the researchers said that a 20-year-old female patient underwent a 64-slice CT scan of the heart and aorta, and the cancer rate was1:14; If the patient is 80 years old, the ratio will drop to 1: 3000.
CT imaging can be widely used in the auxiliary diagnosis of diseases, such as cerebral hemorrhage, lung cancer and appendicitis. During the examination, the X-ray instrument takes a cross-sectional image of the human body by rotation, and after computer processing, a three-dimensional image can be obtained. Compared with traditional X-ray, the image quality of CT scanning is obviously improved, but the patient pays the price of increased radiation. For example, researchers say that abdominal CT scans are exposed to more than 50 times as much radiation as X-rays at the same site. The significance of this discovery is that the more effective the imaging instrument is, the stronger the radiation dose is exposed. Robert smith, director of the cancer screening department of the American Cancer Society, warned that in a word, abuse of testing will lead to excessive radiation, especially for children.
Children are more vulnerable to radiation?
The results of this study also reveal that children are at higher risk of cancer after radiation, and their sensitivity to radiation is 10 times that of adults. Thea McCullough, a radiation physicist at Mayo Medical Center, explained that children's tissues are more sensitive to radiation, and they are younger, so they are more prone to cancer than adults. But parents don't have to worry about this. After all, the probability of an individual getting cancer is very small. If you really need a CT scan, time can't be delayed. Mccullough said that 25% of Americans will get cancer in their lifetime, and the chances of children receiving CT scan will only increase by 0. 1%.
According to a report published in Pediatric Journal in 2007, the advantages of CT scanning for children outweigh the disadvantages. Ellen Brody, a researcher at Cincinnati Children's Hospital in Ohio, has come to the conclusion that the risk of cancer is almost negligible for children who need CT scanning. They found that CT examination was not directly related to subsequent cancer. There are many clinical examination methods, and ultrasound and magnetic resonance imaging (MRI) are relatively safer, because these two technologies will not cause radiation to people. In view of the particularity of children patients, Brody said that radiologists have the responsibility to consider further improving scanning technology. For pediatricians, it is necessary to consider whether CT scanning is necessary and communicate with parents to reach an agreement.
How big is the risk?
Although radiologists agree that CT scanning will slightly increase the risk of cancer, they are undecided about whether the risk is really high enough that patients should try to avoid CT scanning. The estimate of Columbia University researchers is based on a survey, which shows that the 25,000 survivors in Hiroshima and Nagasaki are at a very high risk of cancer death, while residents who are a few miles away from the atomic bomb are exposed to the same amount of radiation as patients undergoing CT scanning, both of which are 5~ 150mSv. In addition, a recent large-scale study involving 400,000 employees in the nuclear industry also supports the speculative conclusions of the survey. The average radiation dose received by these workers is 20mSv, which is close to the radiation dose received by specific organs in a single CT scan of adults. The results also show that when the radiation dose is between 5 ~150 msv, the radiation dose is highly correlated with the cancer risk. Nevertheless, some experts believe that the actual risk of CT scanning cannot be inferred only from this, because the radiation properties of the two are very different. Atomic bombs emit gamma rays, while CT scans use beta rays, which are low in energy and can be completely weakened by using protective devices. Schultz said, it's like comparing apples with oranges. There is no comparability between them.
In addition, radiologists and researchers have to admit that CT scanning technology is almost abused because of its convenience and rapidity. For example, the number of applications of CT scanning in the United States has soared from 3 million in 1980 to 68 million now. Devra Davis, director of the Center for Environmental Oncology at the University of Pittsburgh Cancer Institute, explained that this is mainly because clinicians rely too much on instrument examination and diagnosis and ignore the negative effects. On the other hand, the increasingly prominent medical disputes also force clinicians to conduct a comprehensive and detailed examination of patients.
Although CT scanning has made great contributions to clinical diagnosis, researchers say that as many as 65,438+0/3 CT scanning can be replaced by other methods or completely unnecessary. This means that in the United States alone, 20 million adults and 1 10,000 children are innocently exposed to radiation every year.
Davis said that CT scanning is a very important and valuable tool for truly urgent patients, but it is abusive to use other technologies in non-emergency situations. Schultz agrees: "Clinicians prefer CT scanning, mainly because it can replace detailed physical examination. In recent 20 years, the radiation dose of CT examination has been reduced a lot, but it is an arduous task to continue to reduce the radiation dose on the premise of ensuring the imaging quality. Therefore, both medical staff and the public must be cautious when applying potentially harmful diagnostic tools. "