<unk>  <unk>  is a quantity used in assessing the radiation risk from diagnostic X-ray examinations and interventional procedures. It is defined as the absorbed dose multiplied by the<unk>  irradiated, expressed in gray-centimetres squared (Gy·cm2 – sometimes the prefixed units mGy·cm2 or cGy·cm2 are also used). Manufacturers of<unk>  meters usually calibrate them in terms of absorbed dose to air.<unk>  reflects not only the dose within the radiation field but also the<unk>  of tissue irradiated. Therefore, it may be a better indicator of the overall risk of inducing cancer than the dose within the field. It also has the advantages of being easily measured, with the permanent installation of a<unk>  meter on the X-ray set. Due to the divergence of a beam emitted from a "point source", the<unk>  irradiated (A) increases with the square of distance from the source (A ∝ d2), while radiation intensity (I) decreases according to the inverse square of distance (I ∝ 1/d2). Consequently, the<unk>  of intensity and<unk> , and therefore<unk> , is independent of distance from the source.
Dose area product
Equivalent dose
Effective dose 
Therapeutic index
Peak-to-trough ratio
Minimum alveolar concentration
Peak kilovoltage
Threshold dose