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Computer algorithms for electron binding correction to Compton scattering and for detailed simulation of K-edge characteristic x-ray production were incorporated into EGS4 unix version 2.0. Based on detailed modelling of the internal structures of sources, the modified version was used to calculate dose rate constants, radial dose functions, and anisotropy functions on the long axis for an 125I model 6711 source, 169Yb Type 5 and Type 8 sources, and a stainless steel clad (SS) 192Ir source. The geometry of these sources is cylindrically symmetric. Calculated results are generally in good agreement with corresponding values recommended by TG-43 and Monte Carlo results published by other authors. The influence of electron binding in Compton scattering on the calculated dose distribution for an 125I model 6711 source in water, and of different characteristic x-ray production models for 125I model 6711 and 192Ir SS sources, were also studied.

The purpose of the work is to calculate basic dosimetry data for a VariSource high dose rate 192Ir source in water. These basic dosimetry data, expressed in the dose calculation formalism endorsed by the Interstitial Collaborative Working Group and AAPM Task group 43, include the dose rate constant, the radial dose function, and the anisotropy function. A modified version of the EGS4 Monte Carlo code was used to calculate (1) the transverse-axis dose distribution at radial distances from 0.1 to 14 cm, (2) the two-dimensional dose distribution for axial and radial distances from 0.1 cm to 10 cm, and (3) the air-kerma strength, for the VariSource high dose rate 192Ir source. From these Monte Carlo results the basic dosimetry data were derived. The calculated dose rate constant for the high dose rate source is 1.044 +/- 0.2% cGy h-1 per unit air-kerma strength. The anisotropy function exhibits 40%-60% deviations from isotropy at positions on the long axis. The radial dose function for the source is nearly identical to that for a microSelectron high dose rate 192Ir source, except at radial distances smaller than 0.5 cm where values for VariSource are 1.7%-2.8% smaller. These basic dosimetry data were compared with corresponding results from other authors for high and low dose rate 192Ir sources, as well as with Meisberger's fitting formula.

The dose parameters for the beta-particle emitting 90Sr/90Y source for intravascular brachytherapy (IVBT) have been calculated by different investigators. At a distant distance from the source, noticeable differences are seen in these parameters calculated using different Monte Carlo codes. The purpose of this work is to quantify as well as to understand these differences. We have compared a series of calculations using an EGS4, an EGSnrc, and the MCNP Monte Carlo codes. Data calculated and compared include the depth dose curve for a broad parallel beam of electrons, and radial dose distributions for point electron sources (monoenergetic or polyenergetic) and for a real 90Sr/90Y source. For the 90Sr/90Y source, the doses at the reference position (2 mm radial distance) calculated by the three code agree within 2%. However, the differences between the dose calculated by the three codes can be over 20% in the radial distance range interested in IVBT. The difference increases with radial distance from source, and reaches 30% at the tail of dose curve. These differences may be partially attributed to the different multiple scattering theories and Monte Carlo models for electron transport adopted in these three codes. Doses calculated by the EGSnrc code are more accurate than those by the EGS4. The two calculations agree within 5% for radial distance <6 mm.

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