Need a CT scan? Here is why you should ask your doctor if it is absolutely necessary

In 2001, two researchers from Columbia University in the United States published a paper that suggested that roughly one in 1,000 children exposed to radiation from computed tomography or CT scans would go on to develop cancer due to the exposure. This is a rate of cancer that is on average four times higher than those not exposed to radiation.

The study triggered a debate about the safety and possible overuse of CT scans.

A CT scan is generated by passing radiation through a specific part of the body to general a three-dimensional image. CT scans are life saving in trauma cases, especially those that involve injuries to the head. Cancer patients and those with TB also need regular CT scans to monitor their treatment. The radiation used in a CT scan is 100 times more than that in an X-ray. So while a CT scan can reveal abnormalities that an X-ray cannot pick up, it also increases the risk of cancer due to radiation exposure significantly.

“Almost nothing in medicine is without risks,” said David Brenner, director of the Center for Radiological Research at Columbia University, who co-authored the paper, which was published in the American Journal of Roentgenology. “When a CT scan is medically justified then the risk-benefit balance changes dramatically in favor of conducting the scan.”

This research was followed by more studies in both the United Kingdom and Australia, that confirmed increased risk of cancer due to exposure to radiation from CT scans, more so among children. The US Food and Drug Administration has since then asked doctors to explain the radiation risk to patients beforehand and order a scan only when needed. Two decades on, India still lacks both guidelines and adequate data on the subject.

“Since 2011 the number of CT scans conducted annually, that was on a steep rise, has stabilised in the US as doctors grew more cautious,” Brenner said.

Unnecessary CT scans

Even as CT scans become more common in India’s public and private hospitals, there is no estimate of how many are essential and how many might be unnecessary.

A CT of the abdomen, that lasts less than a minute, delivers up to 10 millisieverts of radiation that one would otherwise get only over a three-year time period from the environment. The dose adds up when a scan is repeated. A head CT carries the least risk, delivering a comparatively low 2 millisieverts of radiation. Brenner and Hall’s study says a dose about 35 millisieverts or more is statistically significant and enough to increase lifetime risk of cancer.

As the US Food and Drug Administration points out, “If you combine the natural risk of a fatal cancer and the estimated risk from a 10 mSv CT scan, the total risk may increase from 400 chances in 2000 to 401 chances in 2000. Nevertheless, this small increase in radiation-associated cancer risk for an individual can become a public health concern if large numbers of people undergo increased numbers of CT screening procedures of uncertain benefit.”

Dr Norman Kleiman, radiation expert and researcher at the Mailman School of Public Health attached to Columbia University, said, “It is important to limit the number of CTs that are not essential. On a population level even a small rise in risk translates into huge numbers, making it a public health issue.”

In India, the use of CT scans is increasing as the government pushes for better access to healthcare. In 2016 the Delhi government announced free CT and magnetic resonance imaging or MRI scans for the poor. The Assam government followed suit with a state-level scheme in January 2018. The mechanism to check overuse of radiation diagnostics is absent.
While a general practitioner orders a CT scan, it is the radiologist in a diagnostic lab that conducts it. “By warning a patient a radiologist might feel that he/she is stepping on the general practitioner’s toes and so keeps mum,” said Ashank Bansal, a radiologist at the Lokmanya Tilak Medical General Hospital and Medical College in Mumbai. “Also, in the private set-up, if a patient is referred by the general practitioner, a radiologist in a lab doesn’t have the authority to say refuse a scan.”

Ask the doctor

“For a patient undergoing the scan once, the risk is too small but those in the post-operative stage need to undergo multiple scans as doctors have to monitor their recovery,” explained Dr Hemant Deshmukh, head of radiology at KEM hospital in Mumbai. “All patients are asked to sign a consent form before a CT scan but the radiation bit is not emphasised.”

According to Deshmukh, even though patients are given consent forms before CT procedures, doctors do not take the time to explain radiation risks to them.

India’s largest tertiary cancer care centre Tata Memorial Centre has developed a mechanism to check overuse of radiation diagnostics. “Our system informs us if the patient had been subjected to any imaging like CT scan in the past week to avoid repeated scans,” said Dr Subhash Desai, professor of radiodiagnosis at the hospital that receives close to 68,000 new patients every year.

But for private diagnostic centres, profit-making is an incentive to keep pushing up the number of scans.

“Physicians in some cases get 10% to 15% kickbacks from the diagnostic center for referring patients,” Bansal said.

In September last year, a group of senior doctors got together and ran a campaign against such referrals calling it “cut practice”, asking lawmakers to take notice. “Someone from the physician’s end might accompany the patient to the diagnostic centre or there could be an in-person discussion with the radiologist so that there no paper trail is left behind,” said Dr KK Agarwal, former president of the Indian Medical Association, who was one of those who spoke out against such referrals.

To patients, Brenner urges caution. “Hold the toes of your physician to the fire. Ask them questions about whether the scan is needed,” he said. “But when you need a CT scan, you should have one.”