Is proton beam therapy the future of radiotherapy? Part I: clinical aspects

Proton beam therapy uses positively charged particles, protons, whose physical properties improve dose-distribution (Bragg peak characterized by a sharp distal and lateral penumbra) compared with conventional photon-based radiation therapy (X-ray). These ballistic advantages apply to the treatment of deep-sited tumours located close to critical structures and requiring high-dose levels. [60-250 MeV] proton-beam therapy is now widely accepted as the "gold standard" in specific indications in adults--ocular melanoma, chordoma and chondrosarcoma of the base of skull --and is regarded as a highly promising treatment modality in the treatment of paediatric malignancies (brain tumours, sarcomas…). This includes the relative sparing of surrounding normal organs from low and mid-doses that can cause deleterious side-effects such as radiation-induced secondary malignancies. Other clinical studies are currently testing proton beam in dose-escalation evaluations, in prostate, lung, hepatocellular cancers, etc. Clinical validation of these new indications appears necessary. To date, over 60,000 patients worldwide have received part or all of their radiation therapy program by proton beams, in approximately 30 treatment facilities.