What you need to know
- A US study says that CT scans could account for 1 in 20 cancer cases diagnosed each year if current overuse doesn’t change.
- CT scans are an essential tool used to diagnose a range of medical conditions, but ionizing radiation exposure occurs as a result.
- Stringent use of CT scanning could help mitigate risk.
US researchers are warning of the potential risks from CT scans, a standard method used to create detailed images of the body for diagnosing diseases.
Computed tomography (CT or CAT) scans use X-rays to create a three-dimensional image of a patient.
The scanner looks like a large tube. A patient lying on a table is moved inside the scanner, and X-ray instruments inside the machine are used to take hundreds of pictures of their body.
The method is different than magnetic imaging resonance (MRI) scans, although the tube-like equipment used to scan the patient is similar. MRI scanners instead use powerful magnets to send radio waves through the body to create images.
Both enable highly detailed pictures of the human body to be produced.
However, exposure to X-rays comes with risks.
“CT can save lives, but its potential harms are often overlooked,” said Rebecca Smith-Bindman, a radiologist from University of California San Francisco, who was a lead researcher on the study.
Why X-rays harm
The electromagnetic spectrum is divided into radiation of different wavelengths.
At the center is the visible spectrum — the light that animals like us can perceive — including wavelengths that we see as red, orange, yellow, green, blue, indigo and violet.
But electromagnetic waves also exist on either side of the visible spectrum. On one side is low-frequency, long-wavelength radiation. This radiation includes radio waves, microwaves and infrared, and is less energetic than visible light. Radio waves are used by MRI.
On the other side is high-frequency, short-wavelength radiation that includes ultraviolet (UV), X-rays and gamma rays. These are more energetic than visible light.
It’s this high-frequency radiation — known as “ionizing” radiation — that poses a health hazard.
Ionizing radiation can strip atoms of their electrons. That means it has enough energy to damage tissue at the molecular level. In humans, this damage can lead to a range of issues, including cancer. UV is commonly known as a health risk due to sun exposure, for instance.
While X-rays are high-energy forms of radiation, they are also an essential tool for providing medical professionals with vital insights into patient conditions.
1 in 20 cancers could one day be traced to CT scan use
The new research modeled the likelihood of developing cancer in 61.5 million US patients who had received a CT scan.
The model estimated that about 103,000 cancer diagnoses could result from CT exposure over the lifetime of the patients studied. That equates to about 5% of the total number of new cases annually in the US, assuming no change to the rate of CT use and cancer findings.
CT scans are being used more and more frequently as a diagnostic tool — up about 30% since 2007. Scan frequency also increases with age, with those 60-69 having more than other groups.
The analysis also found CT scans of the abdomen and pelvis were more likely to result in cancers among adults, while head scans were the greatest risk for children.
Children who underwent CT scans before their first birthdays were at 10 times greater risk of developing cancer than any other age group.
“Our estimates put CT on par with other significant risk factors, such as alcohol consumption and excess body weight,” said Smith-Bindman. “Reducing the number of scans and reducing doses per scan would save lives.”
CT scans have some risk, but benefits are valuable.
The data obtained in the study applies to US patients and the American medical system.
Smith-Bindman pointed to the misuse of CT as a diagnostic tool, including unnecessary or excessive scanning, including those used for respiratory infections or headaches.
She also highlighted variations in radiation doses used to effectively perform the scan, saying some patients receive excessive amounts that are not clinically needed.
Other professionals in the field agree that misuse of CT scans can pose risks to patients.
“It is a well-established fact that high-energy radiation causes cancer,” said Pradip Deb, a radiation safety expert at RMIT University, Australia, who wasn’t involved in the study.
Deb said while it’s a known fact that ionizing radiation like X-rays can damage DNA, and that increased exposure could exacerbate the severity of that damage, it’s not clear how this would work for individuals.
“Not everyone who is exposed to radiation will get cancer,” Deb said.
While there are risks associated with radiation exposure, CT scans remain invaluable for diagnosing health problems that — when addressed — could improve quality of life.
“The estimated risk [of exposure] sometimes can cause panic among the patients who are benefiting from radiation,” Deb said. “Radiations are routinely used for diagnosis and treatment of cancer. This study has clearly established the importance of limiting the radiation dose where possible and of avoiding unnecessary CT scans if other low-radiation or no-radiation procedures can do the same job.”
Edited by: Derrick Williams
Source
Projected Lifetime Cancer Risks From Current Computed Tomography Imaging
