'Track your scans. Repeated CTs can increase your cancer risk'

Computed Tomography (CT) scans are widely used in modern medicine for accurate diagnosis of a host of diseases. But a recent study conducted in the US in 2023 and published in JAMA Internal Medicine says CT scans could cause over 1,00,000 extra cancer cases. Lata Mishra speaks to HN Reliance Foundation Hospital onco-surgeon Dr Ashutosh Kothari about why the growing use of CT scans in Indian healthcare is a cause for concern

The study suggests that CT-induced cancers could eventually account for 5% of all new cancer cases annually. Does this statistic surprise you, especially in the context of India’s increasing use of CT scans? Do you think we are likely to see a rise in radiation-induced cancers here?

Radiation exposure is known to increase cancer risks. And CT scans expose patients to a much higher level of ionising radiation than regular X-rays. A chest X-ray delivers around 0.1 mSv (millisievert) of radiation, while a CT scan can deliver around 10 mSv, which is 70 to 100 times more radiation in one scan. Exposure to ionising radiation can cause breaks in the DNA strands of cells, which one’s bodily mechanisms may not be able to repair perfectly, leading to mutations that can be passed on when the cells divide. Over time, these mutations can accumulate and cause cells to grow abnormally into a tumour, often leading to cancer. For a single CT scan, the risk is generally low, but cancer risk increases with repeated exposure.

Are Indians at risk owing to overuse?

The use of CT scans has increased globally, with an annual rise of about 3-4%. In 2023, 93 million scans were conducted in the US alone. The study is concerning given that the population of India is approximately four times larger than that of the US. This could mean that an indiscriminate and repeated use of CT and PET scans could potentially lead to an increase in new cancers such as lung, colon, leukaemia, thyroid and breast cancer. Organs with high cell turnover rates, like the colon and bone marrow, are more vulnerable to DNA damage from ionising radiation. Tissues with rapidly dividing cells, including the ovaries and breast tissue, are especially radiosensitive and mutations in these cells can trigger abnormal growth, increasing cancer risk over time.



CT scans are often critical to monitor disease progression or detect recurrence in cancer patients. But it must be used judiciously and not as a default approach. Overuse not only leads to unnecessary radiation exposure but also to increased healthcare costs.

How much radiation exposure is safe? Are younger patients at more risk?

Ideally, all radiation exposure should be minimised. According to the International Commission on Radiological Protection, for doctors and imaging technicians, the effective dose limit is 20 mSv per year, averaged over five years, with no single year exceeding 50 mSv. Also, organs like the eyes, skin, hands and feet have different thresholds. As for others, we are naturally exposed to about 3 mSv of background radiation annually, and any radiation from CT scans or other imaging adds to that. Children are especially vulnerable to radiation as their tissues are still developing, and they have a longer lifetime during which radiation-induced effects could manifest. That’s why the American Academy of Paediatrics follows the ALARA (As Low As Reasonably Achievable) principle for safe imaging practices in paediatric care.

Are there any protocols or regulatory bodies in India to monitor CT scan radiation exposure and limit unnecessary repeat scans, especially in private centres?

There are no formal governance structures in India that actively track the number of CT scans a patient undergoes, or the cumulative radiation dose over a period of time. Hospitals are expected to follow ALARA principles, but it largely depends on their discretion and awareness levels.



Can alternative imaging like MRI, ultrasound be used to cut radiation risk?

Yes, for certain conditions. MRI (Magnetic Resonance Imaging) uses magnetic fields and radio waves, and doesn’t involve ionising radiation. It’s often preferred for soft tissue imaging. Ultrasound, another radiation-free option, is commonly used for imaging organs like the liver, kidneys, and in obstetrics for foetal assessments. But CT scans remain a crucial tool for specific diagnoses. A risk-benefit analysis is essential before every scan. Patient safety and clinical necessity should be the utmost priority for physicians.

What steps can hospitals and doctors take for judicious use of CT scans?

Most hospitals now use dose-tracking software to track cumulative radiation exposure for every patient. Imaging centres can also get accredited by institutions such as the American College of Radiology to maintain radiation safety standards. Newer CT scanners have iterative reconstruction and dose modulation technologies that cut radiation doses by as much as 50% without sacrificing image quality. If patients are made aware of these, they will force hospitals to invest in such machines.

What should patients ask the doctor before agreeing to a CT scan?

They must ask if the scan is absolutely essential as lower-radiation alternatives might be equally effective. It’s a good idea to keep a personal record of previous X-rays, CT scans, or nuclear medicine tests, especially if they are seeing more than one doctor, to prevent unnecessary repeat scans.