Dose effect of guidewire position in intravascular brachytherapy.

It has been reported that the dose effects of metallic guidewires are significant in intravascular brachytherapy (IVBT) using a beta source. The purpose of this work is to investigate the dependence of these dose effects on guidewire position. The EGS4 Monte Carlo codes were used to perform the dose calculations for the 90Sr (NOVOSTE), 32P (Guidant) and 192Ir (BEST Ind.) sources with and without a guidewire in place. Guidewires were placed at various distances from the central axes of the sources. Due to the attenuation by the guidewires, a dose reduction of up to 70% behind a guidewire was observed for the beta sources, while the dose perturbation was found to be negligible for the gamma source. The dose reduction for the beta sources was found to be dependent on the guidewire location. For example, the dose reduction was 10% higher for a stainless steel guidewire located at 0.5 mm than that for the guidewire at 2 mm from the central axis of the source, The portion of the target volume affected (shadowed) dosimetrically by the guidewire was reduced when the guidewire was positioned farther away from the source. The shadow volume (in which the dose reduction occurs) can be reduced by up to 45% as the guidewire is moved away from the source axis from 0.5 mm to 2 mm. The dosimetric perturbations due to the presence of a metallic guidewire as well as their dependence on guidewire location should be considered in designing a new IVBT delivery device, in analysing the treatment efficacy, and/or in dose prescription for a beta source.