Welcome back to the RadOnc Smart Review Physics Series! In P16a, we covered the crucial principles of radiation protection and the regulations governing our field. Now, in Episode P16b: CT & MRI Physics for RadOnc, we dive into the physics behind the two imaging modalities most fundamental to treatment planning: Computed Tomography (CT) and Magnetic Resonance Imaging (MRI). How do they create the detailed anatomical images we rely on every day?