Once the physics delivers the dose, the biology of the cell takes over. The success of treatment is governed by five key biological principles known as the :
: Cells are most sensitive to radiation during certain phases of the cell cycle (like mitosis). Fractionating treatment (giving it in small daily doses) allows surviving cancer cells to move into these sensitive phases.
: These create dense "tracks" of ionization, causing complex, clustered DNA damage that is much harder for a cancer cell to survive. Further Reading Basic Radiotherapy Physics and Biology
Radiotherapy primarily uses high-energy , such as X-rays, gamma rays, protons, and electrons. Unlike visible light, this radiation carries enough energy to knock electrons out of atoms, a process called ionization .
: Different tissues have inherent differences in how they respond to radiation. For example, lymphocytes and bone marrow are highly sensitive, while muscle and nerve tissues are more resistant. 3. High-LET vs. Low-LET Radiation Once the physics delivers the dose, the biology
: The radiation hits water molecules in the cell, creating reactive oxygen species (free radicals) that then attack the DNA.
: These deposit energy sparsely. Most of their damage is indirect and easily repairable by healthy cells. : These create dense "tracks" of ionization, causing
: Oxygenated cells are about three times more sensitive to radiation than hypoxic (oxygen-poor) ones. As a tumor shrinks, previously hidden hypoxic areas get better blood flow and become easier to kill.