Proton therapy is a form of external beam radiotherapy that has several advantages over conventional photon (x-ray) radiotherapy. Protons are useful in 2 scenarios that apply to a large proportion of cancer patients: lack of exit dose allows for delivery of a therapeutic radiation dose to tumors in challenging anatomic locations, and reduction in integral dose (low-dose bath) to normal tissues that may reduce the risk of late toxicities and secondary cancers. The emergence of smaller, more economically viable single-room proton units has led to the expansion in use of this technology across the world.