Welcome back to the RadOnc Smart Review Physics Series! In 14a, we explored the world of electron beams. Now, in Episode 14b: Proton Therapy Physics & Planning, we turn to the heavyweights: protons. Protons offer a unique dose deposition pattern, the Bragg peak, which allows for potentially superior sparing of normal tissues distal to the target. We'll delve into the physics behind proton interactions, how clinical beams are created, the critical challenge of range uncertainty, and specific planning considerations.