Which statement correctly defines absorbed dose D in gray (Gy)?

• A. Energy deposited per kilogram of tissue
• B. Energy emitted per kilogram of tissue
• C. Energy deposited per liter of tissue
• D. Energy emitted per liter of tissue

Answer: (A)

Absorbed dose is about how much energy from radiation ends up deposited in a unit mass of tissue. The gray, the unit for absorbed dose, is defined as one joule of energy deposited in one kilogram of matter. So the statement that matches this is energy deposited per kilogram of tissue. For example, depositing 5 joules into 2 kilograms gives a dose of 5 J / 2 kg = 2.5 Gy.

Why the other ideas don’t fit: energy emitted per kilogram would refer to energy leaving a source rather than what remains deposited in tissue. Energy deposited per liter uses volume instead of mass, and because tissue density varies, using mass keeps the dose measurement consistent across different tissues.