Even low doses of radiotherapy that are regarded as safe may contribute to progressive cognitive decline in patients with low-grade glioma brain tumours, according to an article published in the September edition of The Lancet Neurology.

Low-grade glioma (LGG) brain tumours are the most common type of brain cancer. Early or delayed radiotherapy is the most common treatment, but many questions remain about the best treatment strategy. Radiotherapy can cause damage to the brain over time and because the average survival time for patients with LGG is 10 years, these patients are at considerable risk of acquiring late or delayed radiation injuries.

In a previous study, the authors found that at an average of 6 years after diagnosis high-level radiation treatment as well as the tumour itself were associated with cognitive impairment. However, the effects of local radiotherapy on cognitive function in long-term survivors of LGG are not known.

In this study, Linda Douw from VU University Medical Center, Amsterdam, Netherlands and colleagues report the long-term radiological and cognitive abnormalities in survivors of LGG from the original study.

65 patients who had stable disease since the first assessment (of whom around half had received radiotherapy) had a follow-up cognitive assessment at an average of 12 years after treatment. Attention, executive functioning, verbal memory, working memory, psychomotor functioning, and information processing speed were calculated to detect differences between patients who were given radiotherapy and those who were not.

In total, 27% of patients who did not have radiotherapy had cognitive disability compared with more than half (53%) of those who had been given radiotherapy.

Overall, patients given radiotherapy had lower ability at attentional functioning, executive functioning, and information processing speed than patients not given radiotherapy. Findings also showed that patients who did not have radiotherapy showed stable radiological and cognitive status.

The authors say that: “By contrast with the results of our earlier study, the current results indicate that radiotherapy is associated with long-term cognitive deterioration, regardless of fraction dose…[and indicate that] all surviving patients who had radiotherapy are at risk of developing attentional problems”, not just those who were given a high-level dose.

They conclude by saying that treating patients who have LGG with radiotherapy should be considered carefully and suggest that deferring treatment might be the treatment strategy that is most beneficial to cognitive status and quality of life.

In an accompanying Reflection and Reaction comment, Paul Brown and Jane Cerhan from the Mayo Clinic in Rochester, USA, point out that there have been substantial improvements in radiotherapeutic techniques since the 1970s when the treatment period in the study started, and caution that it is therefore not possible to make firm generalisations about the risks of modern radiotherapy from these results.

They go on to call for more trials to assess the effects of modern radiotherapy techniques on cognitive function in patients with LGG.