Effective dose, E

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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

E=\Sigma_T (w_T*H_T)

where H_T is the equivalent dose in tissue or organ T and w_T is the tissue weighting factor. A summary of tissue weighting factors is given in the table below.

1991 (and 2007 in brackets) weighting factors for individual organs [ICRP]. Courtesy SRP

Recommended tissue weighting factors (ICRP 103 (2007)).
  Tissue wT ΣwT
  Bone marrow (red), Colon, Lung, Stomach, Breast, Remainder tissues* 0.12 0.72
  Gonads 0.08 0.08
  Bladder, Oesophagus, Liver, Thyroid 0.04 0.16
  Bone Surface, Brain, Salivary glands, Skin 0.01 0.04
Total 1.00
      * Remainder tissues: Adrenals, Extrathoracic (ET) region, Gall bladder, Heart, Kidneys, Lymphatic nodes, Muscle, Oral mucosa, Pancreas, Prostate(♂), Samll intestine, Spleen, Thymus, Uterus/cervix(♀).

See also Equivalent dose, Effective dose coefficient

Examples: Calculation of the effective dose

Further Information:

The ICRP weighting factors

Dosimetry & Shielding

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