is equal to the equivalent dose for the entire body. Use of tissue weighting factor The ICRP tissue weighting factors are given in the accompanying table, and the equations used to calculate from either absorbed dose or equivalent dose are also given. Some tissues like bone marrow are particularly sensitive to radiation, so they are given a weighting factor that is disproportionately large relative to the fraction of body mass they represent. Other tissues like the hard bone surface are particularly insensitive to radiation and are assigned a disproportionally low weighting factor. Calculating from the equivalent dose: . Calculating from the absorbed dose: Where is the effective dose to the entire organism is the equivalent dose absorbed by tissue is the tissue weighting factor defined by regulation is the radiation weighting factor defined by regulation is the mass-averaged absorbed dose in tissue by radiation type is the absorbed dose from radiation type as a function of location is the density as a function of location is volume is the tissue or organ of interest The ICRP tissue weighting factors are chosen to represent the fraction of health risk, or biological effect, which is attributable to the specific tissue named. These weighting factors have been revised twice, as shown in the chart above. The United States Nuclear Regulatory Commission still uses the ICRP's 1977 tissue weighting factors in their regulations, despite the ICRP's later revised recommendations. By medical imaging type Health effects Ionizing radiation is generally harmful and potentially lethal to living things but can have health benefits in radiation therapy for the treatment of cancer and thyrotoxicosis. Its most common impact is the induction of cancer with a latent period of years or decades after exposure. High doses can cause visually dramatic radiation burns, and/or rapid fatality through acute radiation syndrome. Controlled doses are used for medical imaging and radiotherapy. Regulatory nomenclature UK regulations The UK Ionising Radiations Regulations 1999 defines its usage of the term effective dose; "Any reference to an effective dose means the sum of the effective dose to the whole body from external radiation and the committed effective dose from internal radiation." US effective dose equivalent The US Nuclear Regulatory Commission has retained in the US regulation system the older term effective dose equivalent to refer to a similar quantity to the ICRP effective dose. The NRC's total effective dose equivalent (TEDE) is the sum of