Focused protons irradiate tiny targets

Treatment of small targets, such as brain metastases and those in functional radiosurgery, with proton therapy can require the use of extremely narrow beam widths. While protons can be effectively collimated into small beams, as the field size decreases below 1 cm, the peak-to-entrance dose ratio is degraded by beam broadening due to multiple Coulomb scattering. Now, researchers have developed an alternative option, using magnetic focusing of protons to counteract this effect.
MedicalPhysicsWeb