# 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

$E=\Sigma_T (w_T*H_T)$

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

  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(♀).

Further Information:

The ICRP weighting factors

Dosimetry & Shielding