A reassessment of the composition data given by ICRP (1975) has been completed, augmented with results from appropriate recent studies. The water, lipid, protein, carbohydrate and ash contents, together with elemental compositions, mass and electron densities are given here for 56 body tissues. Seven tissues (adipose tissue, heart, kidney, liver, mammary gland, muscle--skeletal and skin) had sufficient measured data to enable the spread in the results to be evaluated. All the compositions presented apply to healthy, adult humans, except for some new material on the bones of children.

Radiation dose from mammographic techniques was determined as a function of surface exposure, beam quality, and depth. Relative exposure vs. depth was measured in tissue-substitute materials by thermoluminescent dosimetry. The f-factors were calculated from elemental compositions of mastectomy specimens. Dose at depth depends on beam quality as well as exposure and tissue composition. Analysis of data from the ACS/NCI Screening Centers shows current average midbreast doses to be 25 times lower (film/screen) and 3 times lower (Xerox) than the 2 rads previously estimated. Quantitative risk indicators other than midbreast dose are also discussed.

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Average tissue compositions have been derived for seven groups of soft tissues found in "Reference Man". The analyses took into account some 40 soft tissues comprising the adult human. Different groups of soft tissues were selected to provide average tissue compositions of practical value in radiation dosimetry. In addition, as more reliable skeletal tissue data are now available, an updated tabulation is given of average bone formulations. Elemental compositions and mass and electron densities are tabulated for all of the derived systems.