Room: Exhibit Hall | Forum 4
Purpose: HDR-IORT has been practiced at our hospital using standard planar applicators. Due to the applicator geometry and relative rigidity, it is not well suited for the treatment of irregular surfaces. We evaluate retrospectively the clinical implementation of custom HDR-IORT applicators.
Methods: Applicator manufacture: The anticipated surgical resection volume was delineated on pre-surgical CT and exported for 3D printing. As materials for this printer are not biocompatible, we had to recreate an applicator to be used intra-operatively. A mold (a negative imprint) of the 3D cavity model was made and used to cast a Silastic applicator matching the planned resection cavity. HDR catheters were placed manually in the applicator, and a CT of the applicator was acquired. To ensure the applicators were made correctly, the pre-operative CT and the scan of the applicator were registered. Treatment plans were generated based on anticipated high-risk margins and likely proximal OARs. Retrospective evaluation: In addition to evaluation of clinical placement, we sought to compare clinical plans to hypothetical planar IORT plans. For each case, a virtual HAM applicator was planned with pre-surgical imaging in the area identified, at the time of surgery, as high risk for recurrence.
Results: All three pediatric head and neck patients were successfully treated with 3D custom applicators. In all cases, the surgical team and radiation oncologist reported good fit of the applicator to the surgical bed. In locations such as base of skull and sinus cavity placement, dose delivery using standard planar applicators are inferior to custom applicators, despite the uncertainty in resection margins at the time of applicator design.
Conclusion: Custom applicator based IORT is a feasible and effective and highly conformal treatment method for irregular treatment geometries. Availability of 3D printing material usable in IORT settings would further streamline the applicator fabrication process.
Funding Support, Disclosures, and Conflict of Interest: This research was funded in part through the National Institute of Health/National Cancer Institute Cancer Center Support Grant P30 CA008748.