A new study published in the British Medical Journal highlights the importance of carefully choosing which children should receive diagnostic CT scans. As a diagnostic test, CT scans utilize ionizing radiation that can cause cellular DNA damage, increasing the risk of cancer. Children who received a CT scan were 25% more likely to develop a cancer in 10 years after radiation exposure, according to a study of 11 million children in Australia, 700,000 of whom received a CT scan.
The absolute number of children developing a cancer was low, equating to roughly one excess cancer per 4,000 head CT scans performed. Yet each one of the 608 “extra” cancers among these children is a deplorable, heart breaking outcome. For each additional CT scan received, the risk went up by an additional 16%.
This study also found that increased risk persisted through all 10 years studied, and so presumably the higher risk of cancer continues into future years. Current CT scanners use less radiation than older machines, so hopefully this 25% increased risk may be less in present times.
CT scanners are readily available, and provide a convenient and expeditious diagnostic tool. In this study the average dose of radiation from the CT scans received was 4.5 mSV. On average a person living in the UK is exposed to 2.7 mSV in an entire year, while in the US, thanks to heavy use of medical imaging, the average is above 6 mSV. A transatlantic flight from the UK to the US results in about a 0.07 mSV exposure.
So where does this lead us? The study’s authors make some excellent conclusions:
Practitioners will increasingly need to weigh the undoubted benefits of CT scans in clinical practice against the potential risks to justify each CT scan decision. Fortunately, many radiologists are now aware of the risks, and technological advances have already allowed CT scan doses to be reduced below those used in earlier decades. However, decision tools to objectively assess the need for CT are still not used routinely—for example, minor head trauma or suspected appendicitis are often managed using CT, rather than by observation, ultrasound, or magnetic resonance imaging. Imaging for head trauma still accounts for most CT scans in children. It is timely to alert the wider community, as well as the non-radiologist physicians who order most CT scans, to the potential risks. All parties, including patients and families, need to work together to ensure that CT scans are limited to situations where there is a definite clinical indication, and where every scan is optimised to provide a diagnostic CT image at the lowest possible radiation dose.
The amount of radiation received by Americans seems to be directly proportional to the rise of a lawsuit culture in which doctors are forced to practice defensive medicine.
It would be interesting to hear a patient state about their child who has just sustained a head injury: “Doctor, I am not going to sue you. But what I do want is for you to help make a decision about whether my child should have a CT of the head by using your best clinical judgement, as well as any relevant evidence-based guidelines.” I would imagine the first sentence would cut the number of CT scans ordered in the US by half. The second sentence is admittedly stilted, but you get the idea.
At the very least parents should have an open discussion about radiation when diagnostic tests are ordered for their children, and depending upon the situation, and ultrasound or MRI should be considered. Every cancer, especially in a child, is as bad as it gets in this already difficult life.