Monte Carlo dose calculations of beta-emitting sources for intravascular brachytherapy: A comparison between EGS4, EGSnrc, and MCNP

The dose parameters for the beta-particle emitting Sr-90/Y-90 source for in travascular brachytherapy (IVBT) have been calculated by different investig ators. At a distant distance from the source, noticeable differences are se en in these parameters calculated using different Monte Carlo codes. The pu rpose of this work is to quantify as well as to understand these difference s. 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 distribu tions for point electron sources (monoenergetic or polyenergetic) and for a real 90Sr/90Y source. For the Sr-90/Y-90 source, the doses at the referenc e position (2 mm radial distance) calculated by the three code agree within 2%. However, the differences between the dose calculated by the three code s can be over 20% in the radial distance range interested in IVBT. The diff erence increases with radial distance from source, and reaches 30% at the t ail of dose curve. These differences may be partially attributed to the dif ferent multiple scattering theories and Monte Carlo models for electron tra nsport adopted in these three codes. Doses calculated by the EGSnrc code ar e more accurate than those by the EGS4. The two calculations agree within 5 % for radial distance <6 mm. (C) 2001 American Association of Physicists in Medicine.