Which statement correctly describes dose rate and cumulative dose?

• A. Dose rate measures biological effect; cumulative dose is exposure to the environment.
• B. Dose rate is the dose per unit time; cumulative dose is the total dose over a period.
• C. Dose rate is the total dose; cumulative dose is dose rate.
• D. Dose rate is dose per unit area; cumulative dose is dose per unit time.

Answer: (B)

Dose rate tells you how fast radiation energy is being deposited in tissue, i.e., dose per unit time (for example, Gy per hour or Sv per hour). Cumulative dose is the total amount of that energy deposited over a defined period, found by adding up the dose rate over time (D_cum = dose rate × time for a constant rate, or the integral of dose rate over time if it changes). So the best description is that dose rate is the dose per unit time and cumulative dose is the total dose over a period. For instance, a constant dose rate of 2 Gy/hour for 3 hours results in a cumulative dose of 6 Gy. The other statements mix up these meanings: dose rate is not the biological effect per se, cumulative dose is not just environmental exposure, and dose rate is not the total dose, nor is it dose per unit time like per area.