A chest X-ray exposes you to 0.06 to 0.25 mSv of radiation, a unit that measures radiation exposure. (Representational Image/File)
A new study has sparked some concern as it says that computed tomography (CT) examinations in the US could result in 103,000 future cancers, which would account for 5% of all new cancer diagnoses. Study authors have projected that over 100,000 cancers would result from 93 million scans performed in 2023 alone. The study was published in JAMA Internal Medicine.
Should we be worried? “First, this is a theoretical association and has not been evidenced by human real case studies. Having said that, CT scans use ionising radiation, unlike other imaging techniques like X-rays, digital X-rays, magnetic resonance imaging (MRI) and ultrasound. Ionizing radiation can damage DNA, which raises the risk of cancer, if done frequently over one’s lifetime, for follow-ups of procedures etc. This is high in the US compared to India. However the amount of radiation in a single scan is very low,” says Dr Madhavi Nair, surgical oncologist, Manipal Hospital, Bengaluru.
How safe is a CT scan?
A chest X-ray exposes you to 0.06 to 0.25 mSv of radiation, a unit that measures radiation exposure. A mammogram exposes you to 0.21 mSv and a regular CT scan by comparison can expose you to 10 mSv. This radiation is more because a CT scan gathers more-detailed information. Still, this is very low and so far has not been shown to cause long-term harm in human subjects. Which is why this JAMA study data should now be validated by more studies on people who have had heavy CT scan use after 10 years.
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One CT scan is okay. But repeated scans could raise the lifetime risk of radiation-induced cancer. Doctors are aware of this and always do a cost-benefit analysis. They recommend a CT scan only when you need an imaging tool faster and in specific cases to study bones and tissue mass. Since it is also a costly procedure for many average Indians, though lower than MRI, we suggest it only when there is a need for detailed imaging in emergencies, before biopsies and staging.
In fact, as oncologists, we limit imaging to ultrasound and MRI on follow-ups of cancer patients.
Who should not use CT scans?
Pregnant women and foetuses are at risk from radiation. Those with chronic medical conditions requiring repeated imaging should minimise radiation exposure and go for other scans. If you are allergic to iodine contrast dye, used in CT scans, let your doctor know.
What are guardrails for CT scan abuse?
Doctors are very careful. But I had a patient who referred to ChatGPT based on his symptoms and since it recommended a CT scan, he went and got it himself. It was unnecessary. Always ask a doctor.
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Also while larger diagnostics insist upon a doctor’s referral, smaller centres do not and for the sake of business, they may do it at the patient’s request. There has to be gate-keeping.
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- Cancer
- CT scan
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