Table 1

Radiation dose parameters

ModalityParameterDefinitionUnits
GeneralAbsorbed dose.Amount of energy deposited in a material per unit mass.Gray (Gy)
1 Gy=1 joules per kilogram.
Equivalent dose.Absorbed dose multiplied by weighting factor based on the type of radiation
(weighting factor of 1 for X-rays and gamma rays).
Sievert (Sv).
Effective dose.Whole body quantity based on absorbed organ doses weighted based on their radiation sensitivity and type of radiation; weighted sum of the organ equivalent dose.Sieverts (Sv).
FluoroscopyKerma (kinetic energy released per unit mass).Energy transferred per unit mass of irradiated material.Gray (Gy).
Air kerma.Energy transferred per unit mass of air measured with an ionisation chamber.Gray (Gy).
Dose area product.Product of the air kerma and X-ray beam area.Gy cm2.
Peak skin doseAccumulated absorbed dose to the most irradiated area of skin.Gray (Gy).
Fluoroscopy exposure timeCumulative time fluoroscopy is used.Seconds/minutes.
CTCT dose index (CTDI).Average absorbed dose from one axial CT scan measured with an ionisation chamberGray (Gy).
Weighted CTDI (CTDIw).CTDI weighted across the field of view with 1/3 for the centre and 2/3 for the edge.Gray (Gy).
Volume CTDI (CTDIVOL).CTDIw divided by pitch.*Gray (Gy).
Dose length product.CTDIVOL multiplied by total scan length.mGy cm.
RadioisotopesRadioactivity.Rate of nuclear decay events (decays per second).Becquerel (Bq).
  • *Pitch=table movement per rotation/slice thickness.