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CT scan alarm: radiation could cause 5% of tumours

According to an investigation by the University of California, San Francisco, the widespread use of computer tomography scans could cause over 100,000 malignancies a year in the US alone

by Francesca Cerati

15 April 2025

2' min read

Key points

Infants and children most at risk
Imaging between risk factors
Too many unnecessary exams

2' min read

How high is the risk of developing cancer due to radiation emitted by CT scans? A new estimate by a team of researchers at the University of California San Francisco (Ucsf) suggests that the most common scans could be responsible for around 5% of all cancers diagnosed each year. The findings were published in the journal Jama Internal Medicine.

Infants and children most at risk

According to the study, the ionising radiation emitted during these examinations - although essential for the diagnosis of many diseases - can significantly increase the risk of developing future cancers, such as lung, breast, bladder or thyroid cancer. Infants are the most vulnerable, with an estimated risk ten times higher than adults.

"CT scans can save lives, but their potential side effects are often ignored," explains the study's first author, Rebecca Smith-Bindman, a radiologist and epidemiologist. "With the current level of use, if we do not change our approach, we could see a significant increase in cancers in the future.

Imaging among risk factors

The analysis included more than 93 million examinations of 61.5 million patients in 2023 and, according to the researchers' calculations, this could translate into more than 103,000 new cancer cases. A number three to four times higher than previous estimates (since 2007, the number of annual examinations has increased by 30% in the US). This puts computed tomography among the risk factors for cancer on a par with excessive alcohol consumption or obesity.

The incidence of scans increases with age, peaking between the ages of 60 and 69. Children accounted for 4.2% of the total CT scans. Examinations performed in the last year of a patient's life were excluded from the analysis, as they do not correlate with future tumour development. In the projections, adults aged 50 to 59 years had the highest number of tumours potentially caused by radiation (10,400 cases among women and 9,300 among men).

The most common cancers? Lung, colon, breast, bladder and leukaemia, while in children, the most expected neoplasms were thyroid, lung and breast. Among the most risky CT scans for adults are those of the abdomen and pelvis, while for children the greatest danger comes from head scans, especially if performed in the first year of life.

Too many unnecessary examinations

A critical point highlighted by the study is the excessive and, in some cases, unnecessary use of CT scans. They are often used in clinical conditions where the actual usefulness is low, such as for headaches without alarming signs or upper respiratory tract infections.

'Currently,' warns Smith-Bindman, 'there is unacceptable variability in the doses of radiation administered. Some patients receive far higher amounts than they need. There are two ways to reduce the risk of cancer: the first is to avoid scans, particularly unnecessary and so-called low-value scans; the second is to reduce the radiation dose per scan. I recommend that anyone undergoing a CT scan should ask for the lowest possible dose for the scan'.

Study coauthor Malini Mahendra adds: 'It is crucial that families are informed about the risks of paediatric scans. We hope that our results will help physicians discuss the pros and cons of CT scans in a clearer and more informed way".