Fifty-eighth annual meeting of the american association of physicists in medicine
SU-F-T-33: Air-Kerma Strength and Dose Rate Constant by the Full Monte Carlo Simulations
In general, the air-kerma strength (Sk) has been determined by the energy weighting the photon energy fluence and the corresponding mass-energy absorption coefficient or mass-energy transfer coefficient. Kerma is an acronym for kinetic energy released per unit mass, defined as the sum of the initial kinetic energies of all the charged particles. Monte Carlo (MC) simulations can investigate the kinetic energy of the charged particles after photo interactions and sum the energy. The Sk of 192Ir source is obtained in the full MC simulation and finally the dose rate constant Λ is determine.
MC simulations were performed using EGS5 with the microSelectron HDR v2 type of 192Ir source. The air-kerma rate obtained to sum the electron kinetic energy after photoelectric absorption or Compton scattering for transverse-axis distance from 1 to 120 cm with a 10 m diameter air phantom. Absorbed dose in water is simulated with a 30 cm diameter water phantom. The transport cut-off energy is 10 keV and primary photons from the source need two hundred and forty billion in the air-kerma rate and thirty billion in absorbed dose in water.
Sk is multiplied by the square of the distance in air-kerma rate and determined by fitting a linear function. The result of Sk is (2.7039±0.0085)*10-−11 µGy m2 Bq−1 s−1. Absorbed dose rate in water at 1 cm transverse-axis distance D(r0, θ0) is (3.0114±0.0015)*10−11 cGy Bq−1 s−1.
From the results, dose rate constant Λ of the microSelectron HDR v2 type of 192Ir source is (1.1137±0.0035) cGy h−1 U−1 by the full MC simulations. The consensus value conΛ is (1.109±0.012) cGy h−1 U−1. The result value is consistent with the consensus data conΛ.