Effective dose, E
The equivalent dose is a measure of the harm from radiation to a particular tissue. A dose of 1 mSv, for example, to the liver will give rise to the same cancer risk regardless of the type of radiation concerned.
However, different tissues show different sensitivities to radiation. The thyroid is less sensitive than other tissues. In addition, following intake, some radionuclides will buildup in particular organs and irradiate them preferentially. Iodine isotopes, for example, concentrate in the thyroid whereas plutonium concentrates in the liver and bone. In order to take these effects into account, equivalent doses in different tissues must be weighted. The resulting effective dose is obtained using
where is the equivalent dose in tissue or organ T and is the tissue weighting factor. A summary of tissue weighting factors is given in the table below.
|Bone marrow (red), Colon, Lung, Stomach, Breast, Remainder tissues*||0.12||0.72|
|Bladder, Oesophagus, Liver, Thyroid||0.04||0.16|
|Bone Surface, Brain, Salivary glands, Skin||0.01||0.04|
|* Remainder tissues: Adrenals, Extrathoracic (ET) region, Gall bladder, Heart, Kidneys, Lymphatic nodes, Muscle, Oral mucosa, Pancreas, Prostate(♂), Samll intestine, Spleen, Thymus, Uterus/cervix(♀).|