Development and testing a model of energy absorption in biological objects from incorporated photon emitters

A new analytical method, previously developed for estimating beta absorbed fractions, was ex-tended for analytical estimating photon absorbed fractions in soft-tissue bodies from internal uni-formly distributed gamma emitters. The method involves a rescaling procedure with transfor-mation of real biological sizes to unitless effective ones combining information of both photon energy and object’s size. The rescaling was applied to large published datasets of photon ab-sorbed fractions in soft-tissue spheres. A new effect was demonstrated: the rescaled data were united into a single smooth “universal curve” with saturation. The universal curve for photon ab-sorbed fractions was described analytically as a function of a single argument – a rescaled effec-tive radius. Practical applicability of the approach for non-spherical convex bodies (ellipsoids) was demonstrated. Examples of analytical estimating the internal dose coefficients for repre-sentative terrestrial animals were calculated. The new method now available for electron and photon internal dosimetry, provides an effective analytical tool for calculating radiation absorbed fractions in organs and bodies of soft-tissue organisms.