Radiotherapy used to treat brain tumours may lead to a decline in mental function many years down the line, say Dutch researchers.
A study of 65 patients, 12 years after they were treated, found those who had radiotherapy were more likely to have problems with memory and attention.
Writing in The Lancet Neurology, the researchers said doctors should hold off using radiotherapy where possible.
One UK expert said doctors were cautious about using radiotherapy.
The patients in the study all had a form of brain tumour called a low-grade glioma – one of the most common types of brain tumour.
In these cases radiotherapy is commonly given after initial surgery to remove the tumour, but there is some debate about whether this should be done immediately or used only if the cancer returns.
It is known that radiation treatment in the brain causes some damage to normal tissue and the study’s researchers suspected it could lead to decline in mental function.
A previous study in the same patients done six years after treatment found no difference in aspects like memory, attention and the speed at which people could process information, in those who had received radiotherapy.
But the latest research, carried out more than a decade after original treatment, did find significant variation in the results of several mental tests between those who had had radiotherapy and those who had not.
In all, 53% of patients who had radiotherapy showed decline in brain function compared with 27% of patients who only had surgery.
How do the radio waves used to treat cancer differ from those which come from the cell phones we hold next to our heads? What about WiFi?