A Monte Carlo calculation of dosimetric parameters of Sr-90/Y-90 and Ir-192 SS sources for intravascular brachytherapy

The AAPM TG-60 report has proposed various dose calculation parameters for intravascular brachytherapy (IVBT). These parameters include the dose rate constant (or the dose rate at a reference position for a beta-particle emit ting source), the radial dose function, and the anisotropy function. In thi s work, we have used a modified EGS4 Monte Carlo system to calculate these parameters for the two most commonly used IVBT sources (the beta-particle e mitting Sr-90/Y-90 source and the photon emitting Ir-192 SS source). To ens ure the calculation accuracy, the present calculation was compared with sev eral measurements and calculations reported by other authors. Excellent agr eement was found for the results with the photon source. For beta-particle source calculation, the present results for a variety of point sources agre e very well with a previous work. The presently calculated radial dose func tions for the Sr-90/Y-90 source are consistent with those of a published wo rk for intermediate radial distances. The dose uniformity in the axial dire ction was also studied. The contributions of bremsstrahlung photons to tota l doses for the Sr-90/Y-90 beta source, and the influence of ignoring elect ron transport on calculated doses for the Ir-192 SS photon source are discu ssed. (C) 2000 American Association of Physicists in Medicine. [S0094-2405( 00)01211-6].