Monte Carlo characterization of a source for intravascular brachytherapy

Abstract

In this work, we have calculated the two-dimensional dose distribution in water for a 32P intravascular brachytherapy source wire using the EGSnrc Monte Carlo code. The beta source (Guidant Vascular Intervention) has a radioactive core with a length of 27 mm and a diameter of 0.24 mm. The dose parameters 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) mCi(-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< or =z< or =10 mm and p< or =7 mm. In such a dose-uniformity region, the dose field can be characterized by one-dimensional dose distribution, D(p), the dose distribution on the transverse axis. Beyond this region a two-dimensional (2D) description is necessary. However, for the long beta source wire the anisotropy function proposed by the TG-60 formalism becomes indefinable when the radial distance exceeds penetration depth of beta electrons. We have proposed that the anisotropy 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 tabulated for ease of use.

Dosimetry characterization of 32P intravascular brachytherapy source wires using Monte Carlo codesPENELOPEandGEANT4

“…The 32 P source mentioned above has been simulated with different MC codes (MCNPv4B2 [7]- [10], CYLTRAN/ITS3 [7,11], MCNPv4C [7], EGS4 [9,12,13] and EGSnrc [12]) and the calculated doses agree within < 10% with the experimental results.…”

“…These values must be compared with the results obtained with the other codes. The calculation with EGSnrc [12] [12]) are quoted to be below 1%. The CYLTRAN/ITS3 data have been obtained by scanning Fig.…”

“…Besides, these authors calculated the dose to water, away and along the source, using thin cylindrical shells with a thickness of 0.1 mm and a height of 0.1 mm as scoring voxels. Wang and Li [12] used scoring voxels equal to those we have considered here. Finally, Seltzer [11] quoted the results obtained for a simulation with CYLTRAN/ITS3, but did not give information about the scoring voxels.…”

“…In some of the calculations done for the 27 mm source, we have considered a helicoidal catheter (labeled catheter 1) reported in Refs. [7]- [12]. In the case of the 20 mm source, we have calculated using both this helicoidal catheter and a lobed catheter (labeled catheter 2) currently in use.…”

Monte Carlo dosimetric parameter study of a new32P brachytherapy source

“…The 32 P source is a pure beta emitter with a 14.3-day half-life, maximum beta energy of 1.71 MeV and average beta energy of 0.695 MeV. 5,6 According to the American Association of Physicists in Medicine (AAPM) TG60/TG149 report recommendations, 7,8 dosimetry at distances in the order of 1 mm from the beta-emitting sources are poorly understood, and a better understanding of dosimetry in the millimetre range will help these sources in the development of clinical practice. In addition, TG60 and TG149 are reports that provide the dose parameter formalism for a beta-emitting source, and the reference distance is defined to be 0.20 cm.…”