Modeling and dose calculations of a pure beta emitting 32P coated stent for intracoronary brachytherapy by Monte Carlo code

Background: Recently, different investigators have studied the possibility of radiation therapy in restenosis prevention and have shown promising results. In this study a unique radioactive source for intra vascular brachytherapy (IVBT) was investigated. The two-dimensional dose distribution in water for a 32P IVBT stent has been calculated. The pure beta emitter source 32P has been coated on Palmaz- Schatz stent. The dosimetric parameters required by the AAPM TG-60 formalism are discussed and calculated. Materials and Methods: The dose distribution of the activated stent was determined by Version 4C of the (MCNP) Monte Carlo radiation transport code in water and it was verified by TG-60 experimental results. Dosimetric parameters such as anisotropy function, F(r, θ), and the radial dose function, gL(r), around the Palmaz-Schatz stent at distances from 0.18 to 0.9 cm have been calculated. The Palmaz- Schatz stent with 3.5 mm external diameter and 14 mm length is coated with a thin layer of 32P. Results: The Monte Carlo calculated dose rate at the reference point is found to be 17.85 Gy. The results were compared with previously published paper for an actual same source. The difference between these two data sets is in acceptable range. There were almost little differences (less than 0.05%) in values among them. Conclusion: The dosimetry parameters such as, geometry function, G(r,θ), anisotropy function, F(r,θ) and radial dose function, g(r), were determined according to TG-60 protocols and listed in tabular format. High dose variants were visible near the 32P stent surface, but these values decreased with depth in vessel layers rapidly. There are an acceptable agreement between the calculated data in this study and other published data for the same source. However, the observed differences between the calculated and measured values could be explained by the measurement uncertainty and the geometry modeling during the simulations. Iran. J. Radiat. Res., 2012 9(4): 257-263