Welcome back to the RadOnc Smart Review Physics Series for our concluding episode! In P16b, we explored the crucial planning modalities of CT and MRI. Today, in Episode P16c: PET & Ultrasound Physics for RadOnc, we round out our imaging tour by looking at two other important technologies: Positron Emission Tomography (PET), which gives us insights into metabolic function, and Ultrasound (US), often used for real-time guidance and visualizing certain structures.