Welcome back to the RadOnc Smart Review Physics Series! In P15a, we laid the groundwork for brachytherapy, focusing on the radioactive sources, how their strength is quantified using Air Kerma Strength (SK), and the details of the TG-43 dose calculation formalism. Now, in Episode P15b: Brachytherapy Applications, Systems & Planning Concepts, we'll explore how these sources are actually used clinically – looking at intracavitary vs interstitial techniques, historical planning systems, and specific dose points like ICRU 38's Points A and B.