Monte Carlo characterization of a P-32 source for intravascular brachytherapy

In this work, we have calculated the two-dimensional dose distribution in w ater for a P-32 intravascular brachytherapy source wire using the EGSnrc Mo nte Carlo code. The beta source, (Guidant Vascular Intervention) has a radi oactive core with a length of 27 mm and a diameter of 0.24 mm. The dose par ameters required by the AAPM TG-60 formalism are discussed and calculated. Dose rate evaluated at the reference point is 0.1311 +/-0.0001 Gy min(-1) m Ci(-1). For the beta source studied, the dose distribution is uniform along the axial direction z for a given radial position p for -10 mm less than o r equal toz less than or equal to 10 mm and rho less than or equal to7 mm. In such a dose-uniformity region, the dose field can be characterized by on e-dimensional dose distribution, D(rho), the dose distribution on the trans verse axis. Beyond this region a two-dimensional (2D) description is necess ary. However, for the long beta source wire the anisotropy function propose d by the TG-60 formalism becomes indefinable when the radial distance excee ds penetration depth of beta electrons. We have proposed that the anisotrop y function be expressed in the cylindrical coordinate system, instead of a polar system, to remedy this deficiency. For practical purposes, the entire 2D dose distribution and the dose parameters calculated in the work are ta bulated for ease of use. (C) 2001 American Association of Physicists in Med icine.