Room: Exhibit Hall | Forum 4
Purpose: Leipzig-style cones are commonly used for treatment of small skin lesions or keloid-formations with HDR brachytherapyâ€“providing less toxicity to adjacent normal-tissues compared to superficial x-rays or electron beam. Commonly used TG-43 formalism cannot account tissue heterogeneities and lack of sufficient-backscatter. The aim of this report was to present dosimetric validation and clinical implementation of the Varian Leipzig-style surface applicators using deterministic AcurosBV algorithm. AcurosBV accounts for heterogeneities within the treatment area such as air, bone or muscle and predicts dose similar to a Monte Carlo calculation.
Methods: For all solid applicator models (30, 35, 40, and 45mm, diameter, cone-size): dose-rate, dose-profile and PDD (normalized to 3mm depth) along the nominal single-central source dwell-position were computed in Eclipse with AcurosBV algorithm. All computed parameters were compared with Gafchromicâ„¢ EBT3 film measurements in solid-water and the data provided by Varian. In addition, visual inspections and physical measurements of surface applicators source positional accuracy, catheter length verification, and leakage tests were performed.
Results: Acuros-BV calculated and vendor provided dose-rate, lateral dose-profile and PDD, agreed within 1%, 2.0%, and 2.0%, respectively, for all cone sizes, including surface dose. Our dose-rate, profile and PDD measurements with film agreed within 3.5%, 4.5%, and 3.5%, respectively, of the AcurosBV calculation for all cone sizes. Geometric center of source positional accuracy, which was marked with a pin prick on film agreed within 1mm of the central-axis dose profile. Catheter length measurement agreed within 1mm of vendor specification. Measured leakage values were about 5% along the source channel direction and 20% along applicator holder direction, similar to those predicted by AcurosBV calculation.
Conclusion: All applicators were functional and within 1mm of specifications. Our preliminary film measurement results were reproducible and in agreement with Acuros-based dose calculation and Varianâ€™s published dataâ€“suggesting that Acuros-based dose distributions can be used clinically.