More and more Americans are getting CT scans, which, while potentially lifesaving, raise some eyebrows among scientists. They’re worried that even the low doses of ionizing radiation involved might elevate cancer risk.
Now, it’s important to note that for the average person, the theoretical risk of cancer from a CT scan is considered quite low, maybe even negligible. If a doctor says you need one, it’s generally a good idea to just go ahead with it.
That said, usage has jumped over 30 percent in the United States since 2007. Researchers are pointing out that a number of these scans might not be necessary, which raises concerns about exposing people to radiation that isn’t warranted.
In a study from April, researchers from the US and the UK estimated that low-level ionizing radiation from CT scans could contribute to around 5 percent of new cancer cases annually. They predict that scans done this year alone could be linked to about 103,000 future cancer diagnoses.
Of course, this is based on various assumptions from historical data related to high radiation exposure. If these calculations hold true, it places CT scans alongside other notable cancer risk factors, sort of like how alcohol consumption is viewed.
“CT is often crucial, yet its possible risks frequently get overlooked. Even slight cancer risks can lead to a considerable number of future cases given how widely CT scans are used,” explains a team of analysts led by epidemiologist Rebecca Smith-Bindman from the University of California, San Francisco.
As it stands, these risks are mostly hypothetical, but they are still worth a thought or two. While it’s well established that high radiation levels are a definite cause of cancer, solid evidence linking lower doses to cancer risks is still lacking.
Most of the concerns come from long-term studies of atomic bomb survivors and those caught in nuclear plant accidents. For instance, 25,000 Hiroshima survivors who received radiation levels akin to multiple CT scans showed a faint but noticeable increase in cancer risk over their lifetimes.
Whether these findings apply to typical CT scans is still hotly contested. It’s a bit of a balancing act between weighing the theoretical risks against the benefits, considering CT scans can detect various hidden issues with relatively minor doses of radiation—about equivalent to what one might encounter in their environment over three years.
“Any risk from a CT scan is probably much lower than the risk posed by whatever illness is being investigated,” said Cynthia McCollough, a CT imaging expert and former president of the American Association of Physicists in Medicine.
For example, a national trial indicated a 20 percent reduction in lung cancer deaths among smokers who received low-dose CT scans compared to those who only had chest X-rays.
These recent cancer predictions also take into account a more detailed look at actual radiation exposure, something that can vary depending on the CT machine used, the duration of the scan, the patient’s size, and the specific body part being scanned.
The findings come from data collected at 143 hospitals across the US, covering statistics from 2016 to 2022. Researchers say around 93 million CT scans were anticipated in 2023, involving nearly 62 million patients.
Considering the radiation risks involved, the researchers suggest that these scans could be linked to approximately 103,000 future cancer cases.
“To accurately gauge lifetime risk would necessitate long-term studies of large cohorts,” the authors admit.
Interestingly, some people may be more susceptible to cancer from low-dose radiation, particularly children and adolescents, despite adults accounting for most CT scans.
For example, infants receiving CT scans appear to have a heightened lifetime risk for thyroid cancer, notably among female patients.
Much more research is needed to determine if low-dose ionizing radiation genuinely affects cancer risk, and if so, how.
Pradip Deb, a medical radiation specialist, noted that similar cancer risk estimates have been observed in Australian studies. She emphasized the importance of avoiding unnecessary CT scans when radiation-free alternatives could suffice.
Naomi Gibson, president of the Australian Society of Medical Imaging and Radiation Therapy, echoed this concern.
She acknowledged that while these findings underscore the necessity for caution regarding long-term radiation exposure, they shouldn’t deter clinicians from using CT imaging when it’s warranted. “When chosen wisely, the diagnostic and therapeutic benefits of CT scans generally far outweigh the potential risks associated with radiation,” Gibson said.
The study appeared in JAMA Internal Medicine.
