Dental X-rays may increase thyroid cancer risk
by Guy Hiscott
A collaborative study by scientists from Brighton, Cambridge and Kuwait showed that the risk of thyroid cancer increased with increasing number of dental X-rays taken.
The research team was led by Dr Anjum Memon, senior lecturer and consultant in public health medicine at Brighton and Sussex Medical School.
Lead researcher, Dr Anjum Memon
The thyroid gland is known to be highly sensitive to ionising radiation, particularly in children, and dental radiography, a source of low-dose diagnostic radiation, is often overlooked as a potential hazard to the gland.
The researchers studied 313 thyroid cancer patients in Kuwait where dental treatment is free and where the incidence of thyroid cancer is relatively high. They said the results of their study, although the largest case-control study on the subject, should be treated with caution because the data were necessarily based on self-reporting by the participants. Comprehensive historical dental X-ray records were not available from the clinics.
They said the results provide good evidence to warrant more research in settings where historical dental X-ray records are available and where doses of radiation can be estimated.
Dr Memon said the findings were consistent with previous reports of increased risk of thyroid cancer in dentists, dental assistants and X-ray workers, which suggest that multiple low-dose exposures in adults may also be important. He said dental X-rays have also been associated with an increased risk of brain and salivary gland tumours.
Dr Memon said: “The public health and clinical implications of these findings are particularly relevant in the light of increases in the incidence of thyroid cancer in many countries over the past 30 years.
‘It is important that our study is repeated with information from dental records including frequency of X-rays, age and dose at exposure. If the results are confirmed then the use of X-rays as a necessary part of evaluation for new patients, and routine periodic dental radiography (at 6–12 months interval), particularly for children and adolescents, will need to be reconsidered, as will a greater use of lead collar protection.’
He added: ‘Our study highlights the concern that like chest (or other upper-body) X-rays, dental x-rays should be prescribed when the patient has a specific clinical need, and not as part of routine check-up or when registering with a dentist.’
He concluded: ‘The notion that low-dose radiation exposure through dental radiography is absolutely safe needs to be investigated further, as although the individual risk, particularly with modern equipment, is likely to be very low, the proportion of the population exposed is high.’
The research team, whose findings have been published in Acta Oncologica (2010; 49: 447-453), called for further studies using dental X-ray records.
