(kg) The base SI unit of mass of the metric system.
Definition: 1 kilogram is defined as the mass of the standard kilogram, a platinum-iridium bar in the custody of the International Bureau of Weights and Measures (BIPM) near Paris, France.
A traditional unit of mass or weight is also the pound (in general use, e.g. in the United States and Great Britain), with the symbol lb (derived from the Latin word libra).

1 kg = 2.204627 pound (lb. av., lbs.)
1 pound (lb. av., lbs.) = 0.453 kg.

Smaller units are, e.g.
1 000 gram (g) = 1 kg
1 000 milligram (mg) = 1 g
1 000 microgram (µg) = 1 mg

The absorbed dose is the average energy absorbed per unit mass.

The tissue absorbed energy in a small mass volume:
D = (dW/dm) [ Gy ]
D = absorbed dose in Gray (Gy); dW = in the tissue energy absorbed; DM = small volume of the mass.

The SI unit of absorbed dose is the joule per kilogram and its special name is the gray (Gy). In units often used by federal and state agencies, absorbed dose is given in rad; 1 rad = 0.01 Gy.

Absorbed dose is a feature that should increase dose awareness and help users in dose optimization. Absorbed dose in CT is quoted using the CTDI (computed tomography dose index)

CTDIvol (volume-averaged CT dose index) and the dose-length product (DLP) give an indication of the average absorbed dose and relative radiation risk to a standard patient. The user is being warned to scan parameter settings that may lead to high doses, and can adjust the protocol if appropriate. It should be noted that CTDIvol and DLP do not take patient size into account, and will give overestimates and underestimates for large and small patients, respectively.

The directional dose equivalent is the equivalent dose at a point in a radiation field that would be produced by the corresponding expanded field at depth on a radius in a specified direction. The unit of directional dose equivalent in the SI system of units is joule per kilogram (J/kg) and sievert (Sv).

(Gy) Gray is the SI unit of absorbed radiation dose. 1 Gray is equal to the energy absorption of 1 Joule per kilogram. The absorbed dose due to any type of radiation is measured in Gray. 1 Gray is equal to 100 rads in the older terminology.

Mass is the quantity of matter, the unit is kilogram (kg).