Computed tomography (CT) scans could soon account for 5 percent of all new cancer cases diagnosed annually if current practices persist, a new study has concluded. That sounds scary; but how serious is this risk, and what does it mean for the use of CT scans going forward? We take a look at the study and hear from a number of experts who have weighed in on the findings.
What the study showed
The study aimed to project the impact of CT scans carried out in 2023, in terms of the lifetime cancer risk in the US population. From their dataset, the team – led by Dr Rebecca Smith-Bindman of the University of California, San Francisco – estimated that over 61.5 million patients underwent at least one CT scan in 2023. The vast majority, 95.8 percent, were adults.
The team’s model predicted that approximately 103,000 cancers per year – around 5 percent of the 2 million new cancer diagnoses each year in the US – would result from these scans. The risk was found to be higher in children and adolescents, but this was tempered by the fact that CT scans are used much more sparingly in this population.
The most common cancers overall were lung cancer, colon, cancer, leukemia, and bladder cancer. In female patients specifically, breast cancer was the second most common.
Another factor that emerged was where on the body the scan was targeted – scans of the abdomen and pelvis were projected to result in more cancers.
“If current practices persist,” the team concluded, “CT-associated cancer could eventually account for 5 percent of all new cancer diagnoses annually.”
“These estimates put CT scanning on par with other well-known risk factors for cancer, including alcohol and obesity,” write Ilana B. Richman and Mitchell H. Katz in an Editor’s Note accompanying the study.
How CT scans could increase the risk of cancer
CT scans are a vital diagnostic tool. The scans use X-rays; but instead of the fixed beam used to take a traditional X-ray image, the source of the beam is motorized, so it can quickly be rotated around the body.
This takes place inside the circular structure of the scanner. The patient lies on a bed that can slowly pass through the circular opening as the X-ray source rotates around it.
A typical CT scanner. The X-ray source rotates inside the circular part as the patient passes through.
Image credit: C-R-V/Shutterstock.com
The result is a far more detailed picture than can be achieved with conventional X-rays. Some of the potential medical uses include locating blood clots, imaging complex bone fractures or joint damage, or screening for tumors.
“CT has become essential to the diagnostic process for many serious conditions, from trauma to cancer,” Richman and Katz write.
But as with any medical intervention, there are some risks. X-rays are a form of ionizing radiation, which – as Marie Curie would no doubt attest – is famously harmful to the human body.
Getting a medical scan is clearly not comparable to, say, being in the vicinity of a nuclear power plant when it goes boom – but exposure to X-rays is still a real risk that clinicians have to balance against the benefits of having the scan. That’s why, for example, extra precautions are taken if a pregnant patient requires a scan, due to the increased risk to the developing fetus.
Even at low doses, prolonged or repeated exposure to ionizing radiation can cause DNA damage that may increase the risk of uncontrolled cell growth – and therefore, the development of a tumor – further down the line. Doctors grapple with this problem every day when dealing with patients with long-lasting or chronic conditions that need to be monitored with scans.
What experts are saying about the study
The main message from scientists who have commented on the findings seems to be that while additional data is helpful, there is already an awareness of the risks of ionizing radiation. Moreover, people who are invited for a CT scan should not be put off after reading this study.
“Accurate communication around the benefits and risks of CT is essential to protect the public from harm. Focussing on risk alone is not helpful and, in some cases, might prevent a person from attending a scan that could provide early diagnosis of cancer,” said Lynda Johnson, Professional Officer for Clinical Imaging and Radiation Protection at The Society and College of Radiographers, in a statement to Science Media Centre.
Dr Doreen Lau of Brunel University of London noted that these results, based on a US population, may not apply more widely as different countries use different criteria when ordering scans: “CT scan rates are much higher in the US than in the UK, where imaging is used more conservatively and with stricter clinical justification.”
“Doctors do not order CT examinations unless they are necessary, and it seems to me that the likely benefit in diagnosis and subsequent treatment of disease outweighs the very small increase in cancer risk,” said Professor Stephen Duffy, an Emeritus Professor of Cancer Screening at Queen Mary University of London.
In their Editor’s Note, Richman and Katz spoke about the increase in CT scans in the last few decades – they’re quick, inexpensive, and relatively comfortable for patients, so it’s understandable they’ve become invaluable in lots of medical specialties.
But they do suggest ways that some of the risk could be mitigated. For example, scans like ultrasounds and MRIs, which don’t use radiation, could be appropriate alternatives in some instances. There may also be ways of improving scanning so that a lower dose of radiation is needed. As a 2019 report shows, this is already happening, with medical radiation doses in the US declining by up to 20 percent between 2006 and 2016.
“Although the findings highlight the need for vigilance around long-term radiation exposure, this should not discourage the use of CT imaging when clinically justified,” summarized Naomi Gibson, President of the Australian Society of Medical Imaging and Radiation Therapy, in a statement to the Australian Science Media Centre.
“In appropriately selected cases, the diagnostic and therapeutic value of CT scans significantly outweighs the potential radiation-associated risks.”
The study is published in JAMA Internal Medicine.
Source Link: CT Scans Could Soon Be Behind 5 Percent Of New Cancer Cases – What Does This Mean?
