Dosimetric effects of source-offset in intravascular brachytherapy

In intravascular brachytherapy (IVBT), radioactive sources can he displaced (offset) laterally from the center of the lumen and/or longitudinally from the desired location due to the cardiac motion and/or the absence of a source-centerin g device. The purpose of this work is to study the dosimetric impact of such a source offset. Dose effects of both lateral and longitudinal source offsets with or without the presence of a calcified plaque or a metallic stent are calculated for the three most commonly used sources (P-32, Sr-90/Y-90, and Ir-192). The MCNP Monte Carlo code is used in the calculation. Static and random source offsets are considered. The major result,, include that W) dose can be changed significantly (by a factor of up to 4) due to a static lateral source offset: (b) this dose variation is reduced if the lateral source offset is considered as random moving within the vessel (the dose at the 2 mm reference radial distance is increased by 5-15% for the three sources ill the case of the 2D random offset studied) (c) the presence of a calcified plaque and/or a Metallic stent worsens the dosimetric effects: (d) the longitudinal random source offset results ill a reduction (15-18%) in the effective treatment length: (e) the dose effects of source offsets for the beta source are higher than those for the gamma source. The data presented in this paper may be used for IVBT treatment planning or for dosimetric analysis of treatment outcome. The dose change due to the source offset should be considered in dose prescription. The reduction of effective treatment length should be taken into account in selection of a proper Source length to ensure all adequate coverage of the treatment target. (C) 2002 American Association of Physicist. in Medicine.