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Gamma-ray Dosimetry of Internal Emitters. Monte Carlo Calculations of Absorbed Dose from Point Sources

1964; Wiley; Volume: 37; Issue: 433 Linguagem: Inglês

10.1259/0007-1285-37-433-45

1748-880X

W.H. Ellett, Arthur B. Callahan, G.L. Brownell,

Nuclear Physics and Applications

Monte Carlo calculations of the absorbed dose delivered by point source γ emitters to tissue equivalent phantoms have been performed and the results tabulated in tables of A.F.; i.e. that fraction of the emitted energy absorbed by the phantom. The use of these tables makes it possible to calculate γ dose-rate in a manner analogous to that used for β-ray dosimetry. where Σγ is a constant for a particular isotope, C the average isotopic concentration and (A.F.) M,Eγ the A.F. for a particular phantom mass and γ energy. The effects of changing phantom mass, shape and source configuration have been considered and the results compared to analytical treatments of the same problem performed by others. Of some clinical interest are the following conclusions: (1) Tables of absorbed fraction afford an accurate and convenient method of estimating the total body γ dose; (2) The absorbed fraction is relatively independent of body height, shape, and the position of radioactivity within the patient; (3) A restricted distribution of activity in the trunk can be treated as a point source; (4) The use of spheres as patient models and the ICRP method of γ dose calculation should be discontinued. This project is being continued for extended sources of γ emitters; in particular, the A.F. for a uniform distribution of radioactivity in different phantoms is being calculated and the results compared to dosage estimates based on point source A.F. data and reciprocity theorems. We hope to extend these studies to include non-uniform distributions of γ emitters such as the hydrogen capture γ flux from neutron irradiation and the dose delivered to body organs containing a uniform distribution of activity.