Protontherapie

Proton therapy, or protontherapy, is a form of external beam radiation therapy that uses protons rather than photons to treat cancer. Protons are accelerated to high energy in a particle accelerator such as a cyclotron or synchrotron and directed to the tumor. The physical property of protons, known as the Bragg peak, causes most of the radiation dose to be deposited at a finite depth with rapidly decreasing dose beyond the target, allowing a steep dose fall-off outside the tumor. This can reduce radiation exposure to surrounding healthy tissue and critical structures compared with conventional photon therapy, potentially lowering the risk of side effects, especially in children and in tumors near sensitive organs.

Delivery methods include passive scattering and pencil beam scanning, also called spot scanning. In pencil beam scanning, a focused beam of protons is steered across the tumor and delivered layer by layer to paint the target volume, which can further reduce integral dose and secondary neutron production compared with passive scattering.

Clinical indications and applications vary, but proton therapy is widely used for pediatric cancers, skull base and skull‑proximal tumors (for example chordoma and chondrosarcoma), certain ocular tumors, brain and spine tumors, and select head-and-neck and gastrointestinal cancers where sparing healthy tissue is advantageous. Evidence for superiority over photons depends on the indication and individual factors, and ongoing research aims to clarify benefits in different settings.

Limitations include high facility and equipment costs, complex treatment planning, and range uncertainties due to tissue heterogeneity and motion. Access remains limited compared with conventional radiotherapy, and cost-effectiveness is an active area of study.