Fig. 4-21 Exterior and cross-sectional view of mathematical human phantom. JAERI developed a mathematical human phantom based on ORNL's model, adding the esophagus and eye regions. The effective dose, representing a radiation risk for a whole body, can be evaluated by summing organ doses weighted by their relative risk coefficients.

Fig. 4-22 Effective dose per unit air kerma for external photons in anteroposterior (AP), posteroanterior (PA) and right-left lateral (LAT) incidences.

A precise estimation of organ doses for external radiations requires appropriate data on the location, shape, density, and elemental composition of the organs or tissues. Since the doses to internal organs cannot be measured directly, computer simulation techniques were developed to calculate the dose distribution in the human body for external photon and neutron irradiations. A mathematical human phantom is used in the dose calculation, which is modeled by combinations of geometrical elements, such as spheres, ellipsoids, and elliptical cylinders, and by three human tissues with different densities and elemental compositions. Figure 4-21 illustrates the exterior and a cross section of the mathematical phantom of an adult. Calculations of effective dose were performed on the basis of the ICRP 1990 Recommendations for six different age groups for photons and neutrons of various energies and incident directions. Figure 4-22 shows effective doses for an adult as a function of photon energy in anteroposterior (AP), posteroanterior (PA), and right-left lateral (LAT) incidences.

Reference Y. Yamaguchi, External Dose Calculation Using Computer Simulation, J. At. Energy Soc. Jpn. 36(7), p.624-630 (1994).

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