Effective dose is calculated as absorbed dose (D) multiplied by Wr and Wt. Which expression is correct?

Effective dose is calculated as absorbed dose (D) multiplied by Wr and Wt. Which expression is correct?

• A. D x Wr
• B. D x Wt
• C. D x Wr x Wt
• D. D + Wr + Wt

Answer: (C)

The main idea here is that effective dose combines the physical energy deposited with factors that adjust for how harmful that energy is for different radiation types and different tissues. The absorbed dose D tells you how much energy per kilogram is deposited. The radiation weighting factor Wr converts that energy into a quantity that reflects the biological impact of the radiation type. The tissue weighting factor Wt then scales that impact by how sensitive the tissue is to radiation. Put together, the overall risk is proportional to D × Wr × Wt, and the units work out to sieverts (Gy × Wr × Wt = Sv). This multiplicative form captures how both radiation quality and tissue sensitivity amplify or dampen risk. For example, if D is 2 Gy, Wr is 1 (typical for X-rays), and Wt is 0.05 for a given tissue, the effective dose would be 2 × 1 × 0.05 = 0.1 Sv. Using just D × Wr or D × Wt would ignore one of the necessary adjustments, and adding the factors wouldn’t represent how the risk scales with radiation quality and tissue sensitivity.

The main idea here is that effective dose combines the physical energy deposited with factors that adjust for how harmful that energy is for different radiation types and different tissues. The absorbed dose D tells you how much energy per kilogram is deposited. The radiation weighting factor Wr converts that energy into a quantity that reflects the biological impact of the radiation type. The tissue weighting factor Wt then scales that impact by how sensitive the tissue is to radiation. Put together, the overall risk is proportional to D × Wr × Wt, and the units work out to sieverts (Gy × Wr × Wt = Sv). This multiplicative form captures how both radiation quality and tissue sensitivity amplify or dampen risk.

For example, if D is 2 Gy, Wr is 1 (typical for X-rays), and Wt is 0.05 for a given tissue, the effective dose would be 2 × 1 × 0.05 = 0.1 Sv. Using just D × Wr or D × Wt would ignore one of the necessary adjustments, and adding the factors wouldn’t represent how the risk scales with radiation quality and tissue sensitivity.