Geometrical aspects of scatter-to-primary ratio and primary dose.
Using an approximation of Bjarngard and Petti [Phys. Med. Biol. 33, 21-32 (1988)] that the scatter-to-primary ratio SPR(r,d) is a linear function of the geometrical parameter z = rd/(r + d) (where r is the radius of photon beam and d is depth in phantom), a method was developed to determine primary dose directly from depth-dose data, measured within the range of fields with lateral electronic equilibrium. This method was evaluated using tabulated TAR data for Co-60 gamma radiation in water. The results for primary dose agree within approximately 1% of those from other studies. It was shown that this method is applicable within the energy range of therapeutic x rays. Primary dose was determined in the case of 6- and 18-MV x rays using proposed method.
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Department of Radiation Therapy, Harvard Medical School, Boston, Massachusetts 02115.
D003037:Cobalt Radioisotopes; D005720:Gamma Rays; D006801:Humans; D008961:Models, Structural; D011874:Radiometry / Q000379:methods*; D012542:Scattering, Radiation; D014867:Water
D003037:Cobalt Radioisotopes; D014867:Water