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Equivalent dose (symbol HT) is a dose quantity calculated for individual organs (index T – tissue). Equivalent dose is based on the absorbed dose to an organ, adjusted to account for the effectiveness of the type of radiation. Equivalent dose is given the symbol H T.
Equivalent dose is a dose quantity H representing the stochastic health effects of low levels of ionizing radiation on the human body which represents the probability of radiation-induced cancer and genetic damage.
Equivalent dose is calculated for individual organs. It is based on the absorbed dose to an organ, adjusted to account for the effectiveness of the type of radiation. Equivalent dose is expressed in millisieverts (mSv) to an organ. Effective dose is calculated for the whole body.
In dosimetry, two key quantities are essential for understanding and assessing the impact of ionising radiation on matter and living organisms: the absorbed dose (D) and the equivalent dose (H).
The equivalent dose is a measure of the biological effect of radiation due to several factors. The factors to take into account are as follows:
Equivalent dose (symbol HT) is a dose quantity calculated for individual organs (index T - tissue). Equivalent dose is based on the absorbed dose to an organ, adjusted to account for the effectiveness of the type of radiation.
The Radiation Biologically Effective Dose (BED) Calculator calculates BED and equivalent dose (EQD2) for cancer radiotherapy.
The equivalent dose in an organ or tissue is given by: [math] H_T = \sum_{R} w_RD_{R,T} [/math] where [math]D_{R,T}[/math] is the mean absorbed dose from radiation [math]R[/math] in a tissue or organ [math]T[/math], and [math]w_R[/math] is the radiation weighting factor.
For organs and tissues that are only partly present in the head, such as bone marrow and skin, equivalent doses are obtained by multiplying by the ratios of their areas exposed to radiation (bone marrow: 10%; skin: 15%).
The biologically effective dose and equivalent dose in 2Gy calculators are based on the Linear Quadratic Model. As with any model there are limitations including the lack of a time factor and its applicability for low doses per fraction (1.2Gy).