The Museum of National Giant Dolls in Barcelona

Proton therapy uses charged particles instead of conventional X-rays. Because protons release most of their energy at a precise depth, doctors can target some tumours while reducing the dose to nearby healthy tissue — which can matter a great deal in children.

It is not the right tool for every case. Whether it helps depends on the tumour type, location and the child's situation. A specialist team decides if it is appropriate.