Monte Carlo dose simulation for intracoronary radiation therapy with a rhenium 188 solution-filled balloon with contrast medium

Background. The therapeutic efficacy of percutaneous transluminal coronary angioplasty is limited by the incidence of restenosis. Intracoronary irradiation has shown to be effective in restenosis control by inhibiting the neointimal proliferation. Methods and Results. Monte Carlo simulation has been performed to calculate the dose to the vessel wall for intracoronary irradiation with a rhenium 188 solution-filled balloon for restenosis inhibition. With a 3-mm-diameter and 30-mm-long balloon, the radiation dose at 1 mm from the balloon surface was 5.3% lower when the balloon structure was included in geometric modeling of the angioplasty catheter, as compared with that obtained by ignoring the structure. The additional dose reduction due to Hexabrix 320 contrast medium added in 30% of volume ratio was 4.7 %. With regard to axial dose distribution, the dose was uniform over the balloon length except near the balloon end, at which the dose was reduced by 35% at a 1-mm-deep layer in the vessel wall. With the Re-188 solution mixed with 30% of Hexabrix 320 in volume ratio, the Re-188 activity to be injected for delivery of 15 Gy to the 1-mm-deep layer by 1-minute irradiation was 27.3 GBq/mL. Conclusions. Dose estimates produced in this study should be helpful in determining the Re-188 activity to be injected or the irradiation time for a varying situation in terms of length and diameter of the irradiated arterial segment and depth of the target layer.