Calculation of cobalt-60 primary and scatter dose in layered heterogeneous phantoms using primary and scatter dose spread arrays.

IWASAKI Akira

doi:10.11182/jastro1989.5.107

A method of making ⁶⁰Co γ-ray primary and scatter dose spread arrays in water is described. The primary dose spread array is made using forward and backward primary dose spread equations (h₁ and h₂) where both equations contain a laterally spread primary dose equation (G), made from measured dose data in a cork phantom. The scatter dose spread array is made using dierential scatter-maximum ratio (dSMR) and differential backscatter factor (dBSF) equations (k₁ and k₂), where both equations are made to be continuous on the boundary. Primary and scatter dose calculations are performed along the beam axis in layered cork heterogeneous phantoms. It is found, even for ⁶⁰Co γ-rays, that when a small tumor in a lung is irradiated with a field that just surrounds the tumor, the beam entrance surface and lateral side of the tumor may obtain no therapeutic dose, because of loss of longitudinal and lateral electronic equilibrium, and when a large tumor in a lung is irradiated with a field just surrounding the tumor, the lateral side of the tumor may obtain no therapeutic dose due to loss of lateral electronic equilibrium.

Calculation of cobalt-60 primary and scatter dose in layered heterogeneous phantoms using primary and scatter dose spread arrays.

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