Acute exposure to X-rays is not perceptible, but a high enough dose can kill a person in a matter of days or weeks. Therefore, there is reason to be concerned about non-essential X-ray exposure. Of the top 30 essential medical inventions listed by the world’s leading general practitioners, the most important are MRI and CT scanning, with CT scanning being more widely used.
Although MRI does not use ionizing radiation, CT scans, which take only 10 seconds to perform, are clearly superior to MRI, which takes 20-30 minutes to perform. CT scans are also preferred for acute head or abdominal injuries and lung examinations.
Alan S Brody et al. from the Department of Imaging at Cincinnati Children’s cite several risk assessments that are commonly made by healthcare professionals: from the benefits of imaging to the harm to patient health. The article was recently published in the journal Thorax.
Overestimating the risk of radiation cancer
The pathogenic risk of radiation is very low. Using the Biological Effects of Ionizing Radiation VII assessment, the risk of cancer death in 10-year-old children from an average exposure of 3 mGy per organ (similar to a whole-body CT scan) is 1 in 3,000 for girls and 1 in 4,700 for boys, and even without additional radiation exposure, there is still a 1 in 5 risk of dying from cancer in some specific populations in the United States.
How should we understand this risk? The risk of cancer from radiation screening is 1 in 4,000, which means that it does not occur 99.75% of the time. And a 1 in 4000 chance is equivalent to being able to flip a coin 12 times in a row on the heads side. This is twice the probability of dying in a crash in the United States each year (1 in 100,000,000 kilometers).
The small probability of radiation-induced cancer is magnified due to cognitive biases, while the probability of not causing cancer is downplayed.
When this risk is unknown or highly unlikely, the risk of radiation-induced cancer is often unreasonably magnified, overblown, and circulated among examiners as a risk associated with all diagnostic imaging tests used in clinical applications.
Risk Assessment of Patient Populations for Radiation Doses in Diagnostic Imaging
Statements issued by expert committees have not yet reached agreement on the level and accuracy of cancer risk assessment for radiological examinations and whether the amount of radiation used during an examination can pose a risk.
According to the 2011 APA statement, the cancer risk associated with medical imaging at radiation doses of less than 50 mSv per exam (15 times the assumed CT scan dose described above) or multiple doses of 100 mSv over a short period of time is either too low to be detected or does not exist at all.
Ignored Uncertainties and Inconsistencies in Published Risk Assessments
According to a 2013 Clinicians International position statement, prospective evaluations of cancer from imaging in medicine should include a statement that the evaluation is largely based on speculation because of the large number of uncertainties.
Taking into account uncertainties in the assessed dose, dose-response models, and individual patient variability, the error in individual assessment of cancer risk from CT examinations can be 500% or higher. The variation in risk reported in the current literature is even greater.
The American Journal of Respiratory and Critical Care Medicine has published two articles on the assessment of cancer risk on CT scans in patients with cystic fibrosis. One of these articles concluded that diagnostic CT exams have a 13% probability of causing cancer death.
The other article concluded that the risk of cancer from radiography was 0.5%. Since the mortality rate for cancer is about 50%, this article concluded that the probability of death from cancer from diagnostic CT is less than 0.25%. The difference in the risk of death between the two articles can be up to 50 times.
Radiation-induced DNA double-strand breaks (DSBs) can cause cancer if they are not self-repairing. It has been found that the repair of DNADSB differs dramatically between macrophages of the same individual before and after exposure to low doses of ionizing radiation.
This result suggests that an individual’s DNA repair capacity, rather than radiation dose, is a determinant of cancer risk in the dose range of diagnostic radiography. Diseases with both impaired DNADSB repair and high radiogenic cancer risk include capillary dilation syndrome and dissection syndrome.
Risk versus benefit
Future risk and current benefit cannot be compared. ct The risk of radiation carcinogenesis can be interpreted as the risk of developing cancer several years later. It is more meaningful to assess risk in terms of years of shortened life expectancy than in terms of mortality. Epidemiological evidence suggests that radiation-induced cancers often present with delayed onset, similar to the age of onset of naturally occurring tumors, mainly at 45-85 years.
If the probability of dying from radiation-induced cancer is 1 in 4000, then the average age of onset of tumor would be 65 years, the average age of death from tumor would be 70 years, and the expected life expectancy would be 85 years, resulting in a 15-year reduction in life expectancy due to radiation-induced cancer. The average life expectancy of the population is 15 years x 1/4000 = 1/267/year, or less than 2 days/year.
CT scans are often routine for patients with life-threatening diseases, and when disease-related mortality is taken into account, the risk of radiogenic cancer and the reduction in life expectancy due to radiogenic cancer will be even less because these patients may not survive to the day the tumor appears.
A study assessing the risk of CT screening in young people found that the risk of death from underlying disease within 5 years of screening was 1-2 orders of magnitude higher than the theoretical risk of death from cancer caused by CT screening.
Reducing Diagnostic Quality for Lower Radiation Volumes
In 2012, six pediatric imaging groups conducted a study with the goal of improving the clinical diagnostic assistance of abdominal CT. With 5% of the CT scans in the study considered to be of no diagnostic value based on existing operating guidelines for radiation doses below the 25th percentile, the study showed that after excessive dose reduction, 1 in 20 pediatric abdominal CT images in some of the top U.S. practices were not diagnostic.
This meaningless exposure is not only unhelpful, but even harmful, as inaccurate or erroneous imaging can lead to misdiagnosis and mistreatment.
Radiation dose minimization and diagnostic optimization cannot be achieved at the same time, or even the two are contradictory. For example, in the early stages of acute appendicitis, when clinical symptoms and ultrasound findings are not specific, the use of CT can avoid appendiceal rupture and prevent short-term complications such as peritonitis, sepsis, prolonged hospitalization, and long-term complications such as adhesive bowel obstruction.
An accuracy analysis study using the Markov model showed that ultrasound alone was the least cost-effective method of diagnosing pediatric appendicitis when diagnostic value, radiographic carcinogenic risk, appendicitis-related complications, and death were taken into account, while CT after negative ultrasound or no diagnostic value was the most cost-effective method of diagnosing pediatric appendicitis.
An unrealized logical error
Recommendations to reduce the risk of cancer from radiological examinations are often unsupported by evidence or are based on faulty logic. Multiple CT examinations in young patients have raised concerns.
However, this is often the case only in severely ill patients with cancer, bone marrow transplants, ventriculoperitoneal shunts, or cystic fibrosis who have a shortened life span and may even die before radiation-induced cancer develops.
Radiologists are reluctant to perform additional CT exams on these patients for fear of overexposure. Although previous radiation exposure cannot be undone, the risk of radiation-induced cancer from previous imaging-related exposures does not affect the risk-benefit analysis of subsequent imaging exams. It is unreasonable, and even damaging to the patient, to not perform a required CT exam simply because of excessive prior radiation exposure.
Unreasonable scaring of patients and families
Recent studies have shown that only 70 percent of parents are willing or very willing to have their child evaluated for cranial injury with a CT examination of the head deemed necessary by the emergency physician after being informed of the risk of radiation cancer, compared to 90 percent before being informed.
Even though CT can benefit the patient in this situation, the choice of risk avoidance by patients and families is often a headache. The detection rate for pediatric acute traumatic brain injury using CT scans is 1-8% based on bedside diagnostic procedures, which is 100 times or more the risk of later radiographic carcinogenesis.
Incidental lesions cause skewed risk: the balance of benefits
Compared to the detection rate of CT, the risk associated with CT screening is quite low, and the identification of incidental lesions is more likely to occur than the development of later tumors.
A recent study showed that the incidence of incidental lesions requiring urgent management in children with blunt cranial trauma who underwent CT was 0.14% or approximately 1/700. The incidence of incidental lesions requiring urgent management is several times higher than the assumed incidence of tumors from pediatric head CT.
Selection of imaging based on radiological risk
MRI of the brain is often recommended as an alternative to CT because MRI does not use ionizing radiation. Because of the long imaging time, sedation of infants and young children is required. The risks of sedation and anesthesia are rarely taken into account when comparing CT and MRI. It is important to note that anesthetic drugs may cause permanent damage to the infant brain.
In a study that included 30,037 sedated children, 1.5% had blood oxygen saturation below 90%, 0.2% had accidental asphyxia, and 0.04% had laryngeal spasm. The authors suggest that this rate may be higher in many institutions.
A study comparing 383 children who had inguinal hernia repair before age 3 with 5050 children with no history of inguinal hernia repair found that children with previous surgery were 1.3 to 4.1 times more likely to have delayed brain development or behavioral disturbances than children with no history of surgery.
A large preclinical study and retrospective clinical evidence suggest that exposure to general anesthetic drugs impairs cognitive development in young children. Therefore, the choice between CT and MRI requires consideration of more than the possible carcinogenic risk of CT.
In a 2010 study published in the New England Journal, it was found that medical errors causing patient deaths occurred in 6 of 1,000 facilities, and that 64% of these errors could have been avoided. Most importantly, the study found that avoidable medical harm did not decrease between 2002 and 2007. Avoidable medical errors were much more likely to cause patient death than CT, and these medical errors caused patient deaths very quickly, rather than decades later.