Emulsion films characterize proton halo

Pencil beam scanning – moving a few millimetre sized beam to cover the target volume – represents the most advanced proton therapy delivery technique. The pencil beam, however, is unavoidably surrounded by a dose halo caused by scattering in the proton accelerator, the nozzle and the patient’s body. To assess the resulting peripheral dose, Swiss researchers have used nuclear emulsion films interleaved with tissue equivalent material to characterize the beam in the halo region.