Which statement correctly describes effective dose?

• A. It combines organ doses using tissue weighting factors to yield a single risk metric.
• B. It is the absorbed dose averaged over the whole body.
• C. It is the dose equivalent for a specific tissue only.
• D. It measures dose rate in air.

Answer: (C)

Effective dose is a single risk metric created by combining the dose to each tissue, weighted by how sensitive that tissue is to radiation. For each tissue, you multiply the absorbed dose by a radiation weighting factor to get the tissue’s equivalent dose, then weight that by the tissue’s weighting factor and sum across all tissues: E = sum_T w_T H_T. For photons, the radiation weighting factor is 1, so the tissue equivalent dose is essentially the absorbed dose, and the effective dose becomes a weighted sum of those absorbed doses. This approach explains why the correct description is that effective dose combines organ doses using tissue weighting factors to yield a single risk metric. It’s not the absorbed dose averaged over the whole body, not the dose equivalent for a single tissue, and not a measure of dose rate in air.