How is the absorbed dose defined in the context of radiation therapy?

The absorbed dose in the context of radiation therapy is defined as the energy absorbed per unit mass of tissue. This measurement is critical because it helps determine how much radiation energy is transferred to the tissue, which directly relates to the potential effects of radiation on that tissue, including both the therapeutic effects of killing cancer cells and the potential damage to surrounding healthy tissue.

The unit of absorbed dose is the gray (Gy), where one gray represents one joule of radiation energy deposited in one kilogram of matter. Understanding this definition allows healthcare professionals to calculate and deliver the appropriate dose of radiation to maximize treatment efficacy while minimizing damage to healthy tissues.

Other options like the rate of energy deposited over time pertain more to dose rate or exposure time rather than the absolute measurement of absorbed dose. Total energy exposure is a broader term that does not specify the tissue mass, and enzyme activity has no direct relevance to the definition of radiation dose absorbed by tissues.