What are cell survival kinetics and what factors influence radiosensitivity?

Here's an explanation of the notes on cell survival kinetics:

Cell survival kinetics describes how cells respond to damaging agents, particularly radiation. It involves studying the proportion of cells that survive after exposure to varying doses of radiation. The notes mention that cells have a property of "stored mitochondria," which can be relevant for energy production needed for repair processes after damage. The goal is to determine if a tissue or cell is radiosensitive (easily damaged by radiation) or radioresistant (less easily damaged).

The cell surviving fraction is a quantitative measure used in cell survival kinetics.
Cell surviving fraction = (Number of cells that survive) / (Total number of cells exposed)

Different cell types and cell cycle stages exhibit varying degrees of radiosensitivity:

• Cell Type:
  • Neurons and muscle cells are generally radioresistant.
  • Stem cells are typically radiosensitive because they are actively dividing.
• Cell Cycle Stage:
  • G1 phase (cell growth) is generally considered relatively resistant.
  • S phase (DNA synthesis) is often radioresistant due to active DNA repair mechanisms.
  • G2 phase (preparation for mitosis) is typically radiosensitive.

The dose rate of radiation also affects cell survival:

• A high dose rate generally leads to more cell death because cells have less time to repair damage.
• A low dose rate allows for more repairs to occur, potentially leading to higher cell survival.