THE POINT SOURCE METHOD OF DOSE CALCULATION IN MEDIA OF VARYING DENSITY, WITH SPECIAL REFERENCE TO β-PARTICLES

摘要

The point source method is adapted to calculating the energy deposition in media of varying density and discussed, with special reference to the dose from β-particles in trabecular bone. The dose. reciprocity theorem is re-stated, in a form consistent with the density-dependent point source formula. By way of illustration the Loevinger point source formula for β-rays is used to solve two models, (a) alternating infinite slabs of different substances, (b) a hollow sphere filled with one substance, and surrounded by another. The numerical values used in these solutions correspond to the bone-seeking nuclides 90Sr, 90γand 32P, and to substances with the density and mean composition of trabecular bone. The solutions indicate that the mean dose in trabecular bone is not markedly different from that which would be calculated on the assumption that the bone and marrow were intimately mixed.