What is the carcinogenic risk of CT examination?

Among the essential medical inventions listed by the world’s top general practitioners, the most important inventions are MRI and CT scans. However, compared with MRI, which takes 20 to 30 minutes to complete, CT scans, which take only 10 seconds to complete, are obviously more advantageous and more widely used. CT scans are the first choice for acute head or abdominal injuries and lung examinations.

However, the ionizing radiation caused by X-rays also makes people turn pale. Acute exposure to X-rays cannot be sensed, but high enough doses can kill people within days or weeks. Therefore, people have reason to worry about unnecessary X-ray exposure.

The risks reported in different literatures vary greatly.

The American Journal of Respiratory and Intensive Medicine has published two articles on the carcinogenic risk assessment of CT scans in patients with cystic fibrosis.

One of them believed that the probability of cancer death caused by diagnostic CT examination was 13%, while the other believed that the risk of cancer caused by radiation examination was less than 0.5%. Since the death rate of cancer is about 50%, this article believed that the probability of cancer death caused by diagnostic CT examination is less than 0.25%. The difference in death risk between the two articles can reach 50 times.

According to the 2013 Position Statement of the International Organization of Clinicians, a prospective assessment of cancer caused by imaging examinations in similar medical treatment should include a statement stating that due to too much uncertainty, the assessment is largely based on speculation.

The over-magnified real carcinogenic risk

The risk of radiation is very low. Due to cognitive bias, the small probability event of radiation-induced cancer is magnified while the possibility of not causing cancer is underestimated.

The risk of cancer death in 10-year-old children received an average of 3 mGy of radiation per organ (similar to whole-body CT scans) is 1/3000 in girls and 1/4700 in boys.

How should we understand this kind of risk? The risk of cancer caused by radioactive examination is 1/4000, which means that it will not happen for 99. 75% of the time. The possibility of 1/4000 is equivalent to being able to toss a coin on the other side of the head 12 times in a row.

This probability is only twice the probability of dying from a car crash (1/100 million kilometers) every year in the United States. Even without additional radiation exposure, certain specific groups in the United States still have a 1/5 risk of dying from cancer.

The risk of radiation carcinogenesis is often unreasonably magnified and exaggerated, and spread among examiners. It is believed that all diagnostic imaging examinations in clinical application will bring this risk.

Comparison of Risks and Benefits

The risk of cancer caused by CT radiation can be understood as the risk of cancer occurring several years later. Epidemiological evidence shows that radiation-induced cancer often occurs late, which is similar to the onset age of naturally occurring tumors, mainly between 45 and 85 years old.

If the probability of death from radiation-induced cancer is 1/4000, then the average onset age of the tumor should be 65 years old, the average death age of the tumor should be 70 years old, and the expected life span is 85 years old, then the life span caused by radiation-induced cancer is reduced to 15 years. The average life span of the population is shortened to 15 years × 1/4000 = 1/267/year, or less than 2 days/year.

CT scans are often routine examinations for patients with life-threatening diseases. If disease-related mortality is also taken into account, the risk of radiation carcinogenesis and the shortened life span caused by radiation carcinogenesis will be less, because these patients may not be able to survive to the day when tumors appear.

A study on the risk assessment of CT examination in young people found that the risk of patients dying of potential diseases within 5 years after examination is 1-2 orders of magnitude higher than the theoretical risk of dying of cancer caused by CT examination.

It is not desirable to reduce the quality of diagnosis in order to reduce the amount of radiation.

In 2012, six pediatric imaging groups conducted a study aimed at improving the clinical diagnostic assistance level of abdominal CT. The study showed that 1/20 of pediatric abdominal CT images in some top US clinics have no diagnostic value after excessive reduction of radiation dose.

This meaningless radiation exposure is not only not conducive to clinical diagnosis and treatment, but also harmful, because inaccurate or wrong imaging images will cause misdiagnosis and mistreatment.

Radiation dose minimization and diagnostic optimization cannot be combined, Even the two are contradictory. For example, in the early stage of acute appendicitis, when clinical symptoms and ultrasound examination results are not specific, CT examination can avoid appendiceal rupture, prevent short-term complications such as peritonitis, sepsis, prolonged hospitalization and long-term complications such as adhesive intestinal obstruction.

Analysis shows that if the diagnostic value, radiation carcinogenic risk, appendicitis-related complications and death are taken into account, ultrasound alone has the lowest cost performance, while CT examination is the most cost-effective method for diagnosing pediatric appendicitis after ultrasound examination is negative or the results have no diagnostic value.

It is also not advisable for patients and their families to choose risk avoidance.

Recent studies have shown that only 70% of parents are still willing or very willing to perform head CT examinations deemed necessary by emergency doctors to evaluate craniocerebral injury after being informed of the risk of radiation carcinogenesis, compared with 90% before being informed.

Even if CT examination can benefit patients in this case, it is often a headache for patients and their families to choose risk avoidance. According to the bed diagnosis process, the detection rate of acute traumatic brain injury in pediatrics using CT scan is 1-8%, which is 100 times or more of the risk of radiation carcinogenesis in the future.

A recent study showed that the incidence of incidental lesions requiring emergency treatment was 0.14% or about 1/700 in children with blunt craniocerebral trauma examined by CT. The incidence of incidental lesions requiring emergency treatment is several times higher than the incidence of tumors caused by hypothetical pediatric head CT.

Selecting Imaging Examination Based on Radiological Risk

Since MRI does not use ion rays for examination, Therefore, brain MRI examination is often recommended as an alternative to CT. Due to the long imaging time, sedation is required for infants and young children. In comparative studies of CT and MRI, the risks of sedation and anesthesia are rarely taken into account. It is worth noting that narcotic drugs may cause permanent damage to infants’ brains.

A large preclinical study and retrospective clinical evidence show that exposure to common narcotic drugs will impair the development of children’s cognitive ability. Therefore, it is not only the possible carcinogenic risk of CT that needs to be considered when choosing between CT and MRI.

Statement of the Committee of Experts

In a statement issued by the American Medical Association in 2011, it was pointed out that the carcinogenic risk caused by multiple doses of less than 50mSv (15 times the above-mentioned assumed CT scan dose) or 100mSv in a short period of time during medical imaging examination was too low to be detected, or the risk did not exist at all.

Author: Dada Kayla