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How is the gray used to measure radiation absorbed by living tissue?

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detector output connected to a measuring circuit — radiation measurement Figure 1: (A) A simple equivalent circuit for the development of a voltage pulse at the output of a detector. R represents the resistance and C the capacitance of the circuit; V(t) is the time (t)-dependent voltage produced. (B) A representative current pulse due to the interaction of a single quantum in the detector. The total charge Q is obtained by integrating the area of the current, i(t), over the collection time, t_c. (C) The resulting voltage pulse that is developed across the circuit of (A) for the case of a long circuit time constant. The amplitude (V_max) of the pulse is equal to the charge Q divided by the capacitance C.

The gray (Gy) is a unit of absorbed dose of ionizing radiation defined as the absorption of one joule of energy per kilogram of matter, including living tissue.12

While the gray measures the physical energy deposited in tissue, it is important to note that it does not account for the varying biological damage caused by different types of radiation. Because particulate radiations can cause greater injury than X-rays or gamma rays for the same absorbed dose, scientists use the sievert (Sv) to assess biological impact. The dose equivalent in sieverts is calculated by multiplying the absorbed dose in grays by a quality factor based on the relative biological effectiveness (RBE) of the specific radiation type.23

In summary, the gray quantifies the physical energy absorbed by tissue, while the sievert is used to normalize that dose to reflect its actual biological effectiveness.23