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

Background and purposeTo 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 methodsTreatment 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.ResultsThe 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.ConclusionsThe 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.