April 10, 2012

expert reaction to new study on older-style, higher-dose dental X-rays and meningioma

A study published in Cancer suggested that people who had received frequent dental x-rays in the past had an increased risk of meningioma, a type of brain tumour. As well as comments, the SMC sent out a before the headlines analysis.

Professor Dame Valerie Beral FRS, Cancer Epidemiology Unit at the University of Oxford, said:

“I am familiar with this type of research, where people with known brain (or other) cancer are asked, in retrospect, how many X-rays they had had in the past. The responses about X-ray history in people with cancer are then compared with those of healthy people.

“There is known to be poor agreement between people’s recall of past X-rays and records of X-rays actually done. Furthermore there is considerable scope for different recall of past X-rays by people with and without cancer. The authors of this paper did not check whether the X-rays reported agreed with X-rays actually done. Hence their findings could be simply due to different reporting of past X-rays by those with and without cancer, rather than any true difference in exposure to X-rays.

“Other studies like this one have been done before, but the findings from all such studies are difficult to interpret for the reasons given above. Reliable evidence can come only from studies that use recorded information on X-rays done (not reported exposures to X-rays long ago) in people with and without cancer.”

Prof Malcolm Sperrin, Director Of Medical Physics at Royal Berkshire Hospital, said:

“Ionising radiation from any source is known to have a potential health detriment although the very low radiation dose leads to an overall risk that is extremely small. That being said, this paper does provide sensible statistical evidence for a correlation between dental radiation exposure and the incidence of meningioma. Howard, caution is needed in interpreting the conclusions since there is no data that summarises the radiation exposure to the patients. The paper does state that the findings relate to older, higher exposures and the overall intention is to raise awareness of risk factors which is commendable.

“Current best practice suggests a fatal risk of 6% per Sievert of radiation. In the UK a ‘typical’ dental X-ray causes a radiation dose of typically 0.005mSv or a fatal risk of 1 in 40 million. Whilst data varies with source, the likely incidence of meningioma is around 1 in 10000 hence radiation-induced effects are unlikely (but not impossible). It is important to realise that under UK legislation a thorough risk assessment is conducted before anyone is exposed to a source of ionising radiation and there is no reason for a patient, or relative of a patient, to be concerned by the findings of this paper.”

Dr Paul Pharoah, Reader in Cancer Epidemiology at the University of Cambridge, said:

“Meningioma is a rare form of benign cancer that affects the lining of the inside of the skull. The tumours are usually slow growing but can sometimes cause problems if they start to press on the brain.

“The disease is rare. It affects two to three people in every 100,000 in the UK every year. The lifetime risk of the disease is about 1.5 in a thousand, and it is approximately twice as common in women as it is in men.

“Ionizing radiation in large doses is a well-established risk factor for the disease, but the effects of lower dose ionising radiation – the sort of dose that comes from an X-ray – was not known.

“The study reported in Cancer has compared a large number of people with meningioma with a similar number of matched healthy individuals. The study has been carefully designed and is well-conducted. The analysis is sound. Bias is always a potential problem in case-control studies, but this is unlikely to have been a major problem in this study. The authors report that dental X-rays are associated with a small relative increase in risk of disease of approximately 50 percent or 1.5-fold. This finding is statistically significant.

“However, as the disease is rare, the increase in absolute risk is tiny – the lifetime risk increasing from 15 in every ten thousand people to 22 in ten thousand.

“People who have had dental X-rays do not need to worry about the health risks of those X-rays. Nevertheless, dental X-rays should only be used when there is a clear clinical need in order to prevent unnecessary exposure to ionising radiation.”

‘Dental X-Rays and Risk of Meningioma’ by Elizabeth Claus et al., published in Cancer on Tuesday 10 April. Before The Headlines analysis: Dental X-Rays and Risk of Meningioma. Before The Headlines is a service provided to the SMC by volunteer statisticians: members of the Royal Statistical Society and Statisticians in the Pharmaceutical Industry. A list of contributors, including affiliations, is available here.