DR Niki Meston is running in today's London Marathon wearing a vest bearing a photo of her brother Paul, who died five years ago, aged 37.
Paul died from sudden unexpected death in epilepsy, known as Sudep.
Dr Meston, of St Anne’s Road, Headington, had her 41st birthday today and has run 26 marathons since 1996.
She said: "I’m hoping to raise more than £2,000 for the National Society for Epilepsy.
"Paul was an amazing person and he’ll be with me today. I just hope it doesn’t get too hot."