The downfall of CT scans

Medical imaging began with the discovery of x-rays in the late 1880s but one of the biggest advances arrived in the 1970s, with the introduction of CT scans.

Every year more CT scans are being ordered in Australia, providing valuable information to guide medical care, but it comes with its risks – a dose of radiation.

A plain x-ray takes just one picture, while during a CT scan many x-ray images can be taken of cross sections of our body allowing doctors to visualise organs, bones and blood vessels and diagnose health conditions such as cancer, trauma, injuries and abnormalities in the head and abdomen.

Both fast and painless, CT scans are growing in use in Australia every year, as in many other countries. The downfall is the scan can deliver radiation to our bodies, and at a much higher level than a traditional x-ray.

Experts say we are exposed to about 1.5 millisievert (mSv) of ‘background’ radiation every year from the radiation given off by the Earth itself. In comparison, a CT scan exposes us to a dose of radiation in the range of 1 mSv up to 15 mSv. A CT scan of the chest can be equivalent to having at least 100 chest X-rays, and translates to a very small increased risk of developing cancer over a person’s lifetime.

The age and sex of a person can also play a role in the increased risk of developing cancer due to radiation.  For instance, breast tissue in women and ‘young’ cells in children are more sensitive to radiation.

Younger patients are at a greater risk of developing cancer as a result of CT scan radiation than older people, simply because the effects of radiation exposure can possibly take decades to appear.

However, researchers have largely based their calculations on data from survivors of atomic bomb explosions, rather than people who have undergone CT scans and x-rays.

As a result there are divided opinions about the risk from very low levels of radiation exposure, with Dr Matthew Andrews, president of The Royal Australian and New Zealand College of Radiologists, explaining evidence at higher levels of radiation indicates an increased risk of cancer, but at lower doses the risk is more difficult to determine.

“Because there is a grey zone there, we take the attitude that it’s [more] responsible to minimise exposure than to take what may be an unnecessary risk,” Andrews says.

Clinical Professor Richard Mendelson, director of the West Australian Radiology Training Programme in Perth, says minimising radiation exposure is a very important part of training for all radiologists, and due to advances in technology and imaging techniques; the radiation dose used in medical imaging is constantly being reduced.

The Cancer Council offers these examples of situations where CT scans may be unnecessary:.

Routinely investigating common symptoms like back pain

Long-term follow-up in patients who have been successfully treated for cancer, who remain well and have no symptoms.

Although your doctor ultimately makes the referral for a scan, be aware that pressure from patients can sometimes lead to doctors ordering inappropriate tests.

However, experts say if a patient potentially has lung cancer that can be treated, then there is a clear benefit in having a CT scan to either confirm or rule out cancer.

“The risk of missing lung cancer is far greater than any slight risk from a radiation dose, even if it turns out there is no lung cancer,” experts suggest.