Dose effects of guide wires for catheter-based intravascular brachytherapy

Purpose: Guide wires with high torquability and steerability are commonly u sed to navigate through a tortuous and/or branching arterial tree in a cath eter-based intravascular brachytherapy procedure. The dosimetric effects du e to the presence of metallic guide wires have not been addressed. This wor k investigates these dose effects for the three most commonly used beta and gamma sources (Sr-90, P-32, and Ir-192). Methods and Materials: The EGS4 Monte Carlo codes were used to calculate th e dose distributions for the Sr-90(NOVOSTE) P-32(Guidant), and Ir-192 (BEST Ind.) with and without a guide wire in place. Energy spectra for particles exiting the sources were calculated from the full phase-space data obtaine d from the Monte Carlo simulations of the source constructions. Guide wires of various thicknesses and compositions were studied. Results: The dose perturbations due to the presence of guide wires were fou nd to be far more significant for the Sr-90/Y-90 and P-32 beta sources than those for the Ir-192 gamma source. Because of the attenuation by the guide wires, a dose reduction of up to 60% behind a guide wire was observed for the beta sources, whereas the dose perturbation was found to be negligible for the gamma source. For a beta source, the dose perturbations depend on t he thickness and the material of the guide wire. When the region behind a g uide wire is part of an intravascular brachytherapy target, the presence of the guide wire results in a significant underdosing for beta sources. The underdosed region can extend a few rum behind the guide wire and up to I mm in other directions. Conclusion: Significant dose perturbations by the presence of a metallic gu ide wire have been found in catheter-based intravascular brachytherapy usin g beta sources. The dose effects should be considered in the dose prescript ion and/or in analyzing the treatment outcome for beta sources. Such precau tions are not necessary if using a gamma source. (C) 2001 Elsevier Science Inc.