Proton therapy is an advanced form of radiation that uses accelerated hydrogen protons instead of X-rays, exploiting the Bragg peak to concentrate radiation dose within the tumor while delivering almost no exit dose to surrounding healthy tissue. Pencil beam scanning enables intensity-modulated proton therapy (IMPT), painting dose layer by layer for highly conformal treatment. With a substantially lower integral radiation dose than photon therapy, protons may reduce integral dose and, in selected patients, may reduce long-term toxicity — making them especially valuable for pediatric patients and tumors adjacent to critical structures such as the brain, heart, and eyes.