This is Episode 22, Part A: Chemo+RT - Principles & Drug Classes.For decades, radiation therapy has been a cornerstone of cancer treatment, offering potent local control. But as we know, cancer can be a systemic disease, and sometimes radiation alone isn't enough, or we want to make its local effects even more powerful. That’s where combining it with chemotherapy comes into play. Today, we're going to lay the foundational principles for understanding how these two powerful modalities work together. We'll explore the basic rationale for combining them, define the different ways their effects can interact – think synergy, additivity, and antagonism – and then we’ll take a tour through the major classes of chemotherapeutic agents, focusing on their mechanisms of action and key examples you’ll encounter in chemoradiation regimens.