The effect of photon scatter and consequent electron build-up in air on the calculation of dose equivalent quantities in the ICRU sphere for photon energies from 0.662 to 10 MeV.
A Monte Carlo computer program, DEIPHOS has been modified and employed to calculate depth-dose distributions within the 30 cm diameter ICRU tissue-equivalent sphere for initially parallel beams of photons (0.662 to 10 MeV) when the sphere is in an air medium. Dose equivalent values are computed as the sum of two contributions, the dose equivalent when the sphere is in vacuo and the dose equivalent from scattered photons and the corresponding electrons and positrons produced in an air column in front of the sphere. The dimensions of the air cylinder required to attain full electronic equilibrium were derived for each photon energy. The calculation of absorbed dose to air in air is described. Dose equivalents at 300 and 1000 mg cm-2 depths, the restricted dose equivalent indices, the average dose equivalent in the sphere as well as depth-dose equivalent and angle-dose equivalent distributions are presented, normalised both to fluence and absorbed dose to air.
D000388:Air; D003201:Computers; D004583:Electrons; D008962:Models, Theoretical; D009010:Monte Carlo Method; D011829:Radiation Dosage; D011835:Radiation Protection / Q000592:standards*; D012542:Scattering, Radiation