A medical test used to detect cancer may actually be contributing to the disease, research suggests.
California researchers found computerized tomography (CT) scans, which use X-rays to create detailed images of the body, could be emitting unsafe levels of radiation which fuel the formation of tumors.
In 2009, researchers estimated high doses of radiation from CT scans were responsible for two percent of all cancers (or roughly 30,000 per year).
However, the new research published this week estimated ‘CT-associated cancer could eventually account for five percent of all new cancer diagnoses annually.’
The researchers looked at CT scans performed in California from 2018 to 2020 and found 103,000 CT radiation-induced cancers were projected to result from the scans over the course of the lifetime of people exposed.
CT scans can be life-saving tests, catching disease or bleeding early enough to be treated. They also used to diagnose and monitor diseases like cancer and bone injuries, as well as to assist in surgeries and evaluate efficacy of certain treatments.
However, experts say they are sometimes overprescribed and performed unnecessarily, potentially because of the money-making opportunities for the hospitals, as the tests are very expensive, or out of doctors’ fears of missing a diagnosis and being sued.
There are about 93million CT scans performed annually – a number on the rise – but there is little to no regulation of the scanners and radiation levels emitted can vary widely machine to machine.
CT scans are used to diagnose and monitor cancers and bone injuries
The above graph shows the number of CT scans performed in millions (right axis and blue lines) and the incidence of cancer per 1,000 CT scans (left axis and black lines)
Dr Rebecca Smith-Bindman, a professor at the University of California-San Francisco medical school, is one of the authors of the 2009 study, as well as an author of the new research.
She had previously told NBC: ‘It’s unfathomable. We keep doing more and more CTs, and the doses keep going up.’
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Dr Smith-Bindman said between two machines, one could be exposing patients to 10 to 15 times higher radiation doses than the other.
She added: ‘There is very large variation and the doses vary by an order of magnitude — tenfold, not 10 percent different — for patients seen for the same clinical problem.”
Radiation exposure is measured in millisieverts (mSv), which measures the amount of radiation absorbed by the body.
People are exposed to small amounts of radiation every day from their background environment or through things like flying.
A roundtrip flight between New York and Tokyo exposes a person to 0.19 mSv. An x-ray of the stomach emits 0.6 mSv.
Cancers that have previously been linked to radiation include leukemia, breast, colon, bladder, stomach, ovarian, lung and liver cancers, according to the US Nuclear Regulatory Commission.
The above graph shows the projected number of CT-induced cancers by body region exposed to the scan in adults
The above graph shows the projected number of CT-induced cancers by body region exposed to the scan in kids
In Dr Smith-Bindman’s new research, the team found the three most common cancers observed in exposed patients were lung cancer – 22,400 cases – colon cancer – 8,700 cases- and leukemia – 7,900 cases.
Estimated radiation-induced cancer risks were higher in children, despite adults receiving more CTs.
Men and women experienced CT-related cancers at about the same rate across all ages and number of scans.
Cancer risk related to CT exposure was highest in people in the 60s and lowest for children under 10 years old.
In an attempt to tackle the problem, new Medicare regulations effective this year will require hospitals and imaging centers to collect and share information about the radiation emitted by their scanners.
The regulations also require a more careful inspection of the dosing, quality and necessity of CT scans.
The new rules, issued in the final weeks of the Biden administration, are being rolled out over three years in hospitals and outpatient clinics and providers could face fines if they do not comply, beginning in 2027.
The Trump administration has not commented on its plans to follow, revise or reverse the new policies.