Non-uniformity of absorbed dose due to curvature of β-emitter array in intravascular irradiation

The uniformity of dose delivered to the lesion could be broken in the region of curved coronary vessel. The authors present the Monte Carlo dose calculations to account for the curvature of vessel and trained seeds. A catheter-based β-emitter system (⁹⁰Sr/Y) is modeled using the Monte Carlo code, MCNP4B2. Dose distributions are calculated for linear and curved (10° shift between neighboring seeds) cylindrical vessels and then compared along inward-curvature and outward-curvature directions. At the total activity of 70 mCi (2.59×10⁹ Bq), the dose in the linear vessel varies from 40.0 to 0.53 cGy/sec as the radial distance (r) from the central axis of seeds increases from 0.64 to 5.4 mm. In the curved vessel, it varies from 41.8 to 0.91 cGy/sec for inward-curvature direction and 39.6 to 0.50 cGy/sec for outward-curvature direction at the same radial distance. In particular, the dose rates at r=2 mm are: 8.1 cGy/sec in the linear vessel, 10.1 cGy/sec in the inward-curvature (25% overdose compared to that of the linear vessel), and 7.8 cGy/sec in the outward-curvature (4% underdose compared to that of the linear vessel). In the region of interest, r=2-4 mm, the average inward-overdose and outward-underdose are 28% and 10%, respectively, with respect to those of the linear vessel. The overdose inside the curved seeds is more significant than the underdose outside them. This non-uniformity of dose should be taken into account in both the treatment planning and the design of radioactive seed delivery systems