The optimization of dose delivery for intraoperative high-dose-rate radiation therapy using curved HAM applicators

Background and purpose: To determine the effect of the curvature of Harrison-Anderson-Mick applicators on the dose distribution in high-dose-rate intraoperative radiation therapy (HDR-IORT). Material and methods: Treatment planning was performed with flat applicators using ¹⁹²Ir as the radioactive source, and dwell times were optimized using dose-point optimization techniques. These optimized dwell times were then used for the curved applicators, and the dose distributions that would actually be delivered to patients were determined. Results: The dose directly below the central catheter was strongly dependent on the curvature of the applicator. Steep parabolic curves caused underdoses of as much as 19% at a point 1 cm from the convex side of the applicator. The rate of dose reduction with increasing distance from the applicator surface was also a function of the curvature of the applicator. Conclusions: The curvature of the applicator profoundly affects dosimetry and can be exploited to optimize coverage of the target during HDR-IORT procedures. To ensure accurate dose delivery, these dose perturbations must be accounted for in the planning process. We recommend maintaining a dosimetry atlas of various applicator sizes and curvatures in addition to one for flat applicators.