MILLIONS of people with thyroid disease are being given excessive doses of radiation that could increase their risk of contracting cancer. That’s the conclusion of the Swedish Radiation Protection Authority (SSI), which says many hospitals around the world are ignoring international recommendations to minimise patients’ exposure to radiation.
Up to 5 per cent of women and a much smaller proportion of men contract Graves disease, an immune system defect causing the thyroid gland to produce too much hormone. For 50 years the disease has been treated by destroying all or part of the gland with radioactive iodine-131.
But Helene Jönsson, an SSI inspector, says doctors fail to optimise the radiation dose for individuals, as they do with X-rays and CT scans. “With iodine therapy, they don’t care,” she told 91av. “It is a concern.”
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Patients are commonly given a fixed amount of iodine-131, often 370 megabecquerels, without taking into account the size of the thyroid gland, the amount of iodine it takes up and the amount it loses, Jönsson says. All of these can vary widely, and Jönsson is particularly worried about young people being treated in this way because their chances of developing cancer as a result in later life are higher. She says some children in the US have been given large fixed doses of iodine-131, which she describes as “horrible”.
To test how much difference it makes to calculate the dose individually, Jönsson analysed 187 cases of Graves disease at Malmö University Hospital between 1984 and 1988 in which doses of iodine-131 were individually optimised. She worked out that if the patients had instead been exposed to a fixed 370 megabecquerels they would have received an average of two-and-a-half times as much radiation as they needed (Radiation Protection Dosimetry, vol 108, p 107).
That, Jönsson argues, would breach the recommendation by the International Commission on Radiological Protection to keep radiation exposure “as low as reasonably achievable”. For countries in the European Union, it would also be a breach of a 1997 directive protecting people against the dangers of medical radiation.
Keith Baverstock, an expert on radiation and health at the University of Kuopio in Finland, agrees there is cause for concern. “Iodine-131 is highly toxic to young children, increasing the risk of thyroid cancer even at low doses,” he says.
Dan Ash, president of the Royal College of Radiologists in the UK, agrees it is important to keep radiation doses as low as possible. “It is likely that some patients will get more than they need,” he says. “But that is better than failing to treat the disease, especially when there is no proof that the treatment causes long-term damage to health.”