Radiation Units and Dose Limits

The quantities

Each radiation quantity answers a different question. Air kerma, in gray (Gya), describes radiation in air, such as at the tube output or the skin entrance point. Absorbed dose, in gray (Gy), is the energy deposited per kilogram of tissue. Equivalent dose, in sievert (Sv), multiplies absorbed dose by a radiation weighting factor that accounts for the type of radiation. Effective dose, also in sievert, adds tissue weighting factors so that a partial-body exposure can be compared by overall risk.