Radiation treatment for brain tumours can sometimes affect the parts of the brain that control hormones, called the hypothalamus and pituitary gland. When these areas are exposed to radiation, many children—up to 95%—develop hormone problems over time. These issues don’t usually appear straight away; instead, they tend to develop slowly over months or even years. The type of hormone problem and how quickly it shows up depends on the child’s tumour and the amount of radiation they received.

For children whose tumour did not directly involve the hypothalamus or pituitary gland, doctors usually begin checking their hormone levels about a year after treatment. More detailed hormone tests, such as those for growth hormone or stress hormone, are only carried out if routine blood tests show something unusual or if the child starts showing symptoms. These more detailed tests can take several weeks to organise. Even with this careful monitoring, around 1 in 10 children with medulloblastoma already have growth hormone problems within the first year after radiation.

Because of this, researchers want to better understand how quickly hormone and metabolism problems develop after radiation, and whether starting treatment earlier could be both helpful and safe.

Early results from the BRAINatomy research programme show that children with medulloblastoma who received higher doses of radiation to certain brain areas—like the frontal lobes and the hypothalamus—tend to have slower thinking speed later in life. Thinking speed is important for learning and school performance. Other studies, including work done at St. Jude Children’s Research Hospital, have found that children with craniopharyngioma who started growth hormone treatment within a year of diagnosis had better attention and intelligence scores than those who started treatment later. This suggests that early hormone treatment may help protect a child’s thinking and learning abilities.

Because radiation to the hypothalamus is linked to both hormone problems and changes in thinking skills, researchers now want to find out whether identifying and treating hormone deficiencies earlier could improve long‑term brain function—without increasing the risk of the tumour returning.

Before launching a large trial, the current study will first look at how common hormone problems are after radiation and whether testing children every four months is practical and acceptable for families and healthcare teams. Researchers believe that more frequent testing will help identify hormone problems earlier than is currently possible. If this is true, it could lead to better care and possibly better long‑term thinking and learning outcomes for children who have survived a brain tumour.