Tissue to Air Ratio

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Tissue-Air Ratio (TAR) is a term used in radiotherapy treatment planning to help calculate absorbed dose to water in conditions other than those directly measured.

[edit] Definition

The TAR at a point in a water phantom irradiated by a photon beam is taken to be the ratio of the total absorbed dose at that point to the absorbed dose at the same point in a minimal-scatter phantom with just-sufficient build-up.