What is the purpose of tissue weighting factors in radiation dose calculations?

• A. They reflect differing biological sensitivities of tissues to radiation, enabling a single metric (effective dose) for risk comparison.
• B. They determine shielding thickness for each tissue.
• C. They define exposure limits for individuals.
• D. They measure energy absorbed per unit mass in tissues.

Answer: (A)

Tissue weighting factors quantify how biologically sensitive each tissue is to radiation, so we can combine the doses to different tissues into a single risk-related number. By weighting the equivalent dose received by each tissue with its w_T and summing, we get the effective dose. This means tissues that are more radiosensitive contribute more to the overall risk per unit dose, while less sensitive tissues contribute less. For example, organs such as gonads or bone marrow have higher weights than skin or muscle, so the same amount of energy deposited in a highly sensitive tissue raises the overall risk more. This single metric, effective dose, is used to compare potential risks across different exposure scenarios, rather than to determine shielding thickness, set regulatory exposure limits, or measure energy absorbed per mass (that last one is the absorbed dose, in Gy).