Occupational Intakes of Radionuclides Part 1 - ICRP

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DRAFT REPORT FOR CONSULTATION
Table 1. ICRP radiation weighting factors
Radiation Type Radiation Weighting Factor, wR
Publication 103 Publication 60
Photons 1 1
Electrons and muons 1 1
Protons and charged pions 2 5*
Alpha particles, fission fragments, heavy
ions
20 20
Neutrons Revised continuous Step and continuous
function of neutron
energy
functions of neutron energy
*Pions were not considered
(25) The values of tissue weighting factors (wT) recommended in Publication 103
(ICRP, 2007) are shown in Table 2. Changes from values given in Publication 60
(ICRP, 1991) reflect improved knowledge of radiation risks. The main sources of data
on cancer risks were the follow-up studies of the Japanese atomic bomb survivors,
used to derive risk coefficients averaged over seven Western and Asian populations
with different background cancer rates (ICRP, 2007). The new wT values are based on
cancer incidence rather than fatality data, adjusted for lethality, loss of quality of life
and years of life lost. Weighting for hereditary effects is now based on estimates of
disease in the first two generations rather than at theoretical equilibrium. The main
changes in wT values in the 2007 Recommendations are an increase for breast (from
0.05 to 0.12), a decrease for gonads (from 0.2 to 0.08) and inclusion of more organs
and tissues in a larger ‘Remainder’ (from 0.05 to 0.12). The remainder dose is now
calculated as the arithmetic mean of the doses to the thirteen organs and tissues for
each sex (Table 2). Tissue weighting factors continue to represent averages across the
sexes and across all ages.
Tissue
Table 2. Publication 103 (ICRP, 2007) tissue weighting factors
wT ∑ wT
Bone-marrow, breast, colon, lung, stomach, remainder
tissues (13*)
0.12 0.72
Gonads 0.08 0.08
Urinary bladder, oesophagus, liver, thyroid 0.04 0.16
Bone surface, brain, salivary glands, skin 0.01 0.04
*Remainder Tissues: adrenals, extrathoracic (ET) regions of the respiratory tract, gall
bladder, heart, kidneys, lymphatic nodes, muscle, oral mucosa, pancreas, prostate (male),
small intestine, spleen, thymus, uterus/cervix (female).
(26) A further important change introduced in the 2007 Recommendations is that
doses from external and internal sources are calculated using reference computational
phantoms of the human body ICRP, 2009). In the past, the Commission did not
specify a particular phantom, and in fact various mathematical phantoms such as
hermaphrodite MIRD-type phantoms (Snyder et al, 1969), the sex-specific models of
Kramer et al (1982), or the age-specific phantoms of Cristy and Eckerman (1987)
have been used. Voxel models, constructed from medical imaging data of real people,
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