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


Calculation of the Effective Dose:

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

Example 1

Suppose just the thyroid is irradiated by beta radiation and received an average absorbed dose of 400 mGy. What is the effective dose (E)?


Equivalent dose (HT) = 400 mGy x 1 = 400 mSv

Effective dose (E) = 400 mSv x 0.05 = 20 mSv


This dose would give rise to the same detriment as if all the organs in the body had been ex-posed to a total of 20 mGy.


Example 2

1991 Weighting factors for individual organs [ICRP]

In the course of a medical therapy, a patient receives an intake of I-131 to the thyroid. The thyroid receives a dose of HT = 80 mSv. What is the whole body effective dose?

The thyroid tissue weighting factor (from the table) is wT = 0.05. If there are no additional organs irradiated, the effective dose is given by


E = wT . HT = 0.05 x 80 mSv = 4 mSv.


Hence the risk of cancer arising in the thyroid due to the 80 mSv irradiation, is exactly the same total cancer risk following a homogeneous whole body irradiation of 4 mSv. By a homogeneous whole body irradiation, every organ receives a dose of 4 mSv. Since the sum of the tissue weighting factor is 1, the whole body dose or the effective dose is 4 mSv.


Example 3

A patient receives an intake of radiation which results in the lungs receiving a dose of 2 mSv and the thyroid a dose of 1mSv. What is the whole body effective dose?

The lungs tissue weighting factor (from the table) is wT = 0.12. The thyroid tissue weighting factor (from the table) is wT = 0.05. If there are no additional organs irradiated, the effective dose is given by


E = wT . HT = (0.12 x 2) + (0.05 x 1) mSv = 0.29 mSv.


Hence the risk of cancer arising from the lungs receiving 2 mSv and the thyroid receiving 1mSv, is exactly the same total cancer risk following a homogeneous whole body irradiation of 0.29 mSv. By a homogeneous whole body irradiation, every organ receives a dose of 0.29 mSv. Since the sum of the tissue weighting factor is 1, the whole body dose or the effective dose is 0.29 mSv.


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