Radiation oncology has changed greatly in recent decades, driven mainly by technical advances in treatment planning and delivery. Proton radiation therapy is a further advance; however, it is more expensive than traditional photon therapy and its critics argue that its costs are not justifi ed. Proton therapy is distinct from traditional photon or x-ray-based therapy since the physical properties of charged particles such as protons enable radiation oncologists to control more precisely the radiation dose, and thus spare healthy tissues outside the target volume. A visual comparison of photon treatment and proton treatment plans will nearly always show that the spread of low-dose radiation is less with proton therapy. This is pertinent for medulloblastoma, the most common malignant paediatric brain tumour, for which the entire brain and spine must be irradiated to minimise the risk of recurrence, and for which late adverse eff ects can severely aff ect quality of life. Although visual comparisons of proton and photon radiotherapy are compelling, debate within the radiation oncology community continues as to the clinical benefi ts of this low-dose, tissue-sparing technique. Proton therapy has been in clinical use for decades; however, until recently, few centres have had access to it. This lack of availability is largely responsible for the paucity of clinical data supporting the routine use of protons for cancer treatment. In The Lancet Oncology, investigators from the Massachusetts General Hospital, one of the institutions that pioneered proton therapy, present outcomes from a prospective study of proton therapy for childhood medulloblastoma. 1 Given the rarity