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Dosimetric Validation and Clinical Implementation of Varian HDR Surface Applicator Set with Leipzig-Style Cones

B Burgdorf

B Burgdorf*, J Scholey , B Teo , D Mihailidis , S Anamalayil , University of Pennsylvania, Department of Radiation Oncology, Philadelphia, PA


SU-J-CAMPUS-TT-1 (Sunday, July 30, 2017) 4:00 PM - 5:00 PM Room: Therapy ePoster Theater

Purpose: High dose-rate (HDR) surface applicators are a suitable alternative to external beam therapy for use in treatment of small skin tumors and superficial disease. Our institutional experience in commissioning a Varian surface applicator set with Leipzig-style cones and comparing to computer-simulated dose characterization data will be presented. Currently, there is no literature defining the best practice for dosimetric validation. This study outlines a technique for dosimetric validation and clinical implementation of the Varian Leipzig-style surface applicators using radiochromic film.

Methods: Varian provides the following data for each applicator size: dose-rate, percent depth dose (PDD), and lateral profile, all defined at 3mm depth, along with a nominal central source dwell position. We performed data validation measurements using Gafchromic™ EBT3 film and FilmQA™ Pro software. Relative dose analysis was performed for validation of the source position, profiles, and PDD curves. For dose-rate validation, a linear accelerator was first used to perform absolute dose calibration. A TPS-modeled HDR catheter was used to cross-check the calibration, confirming no film energy dependence existed. A dwell time calculation formula incorporating our results was created to convert prescription dose and isodose line into source dwell time. Finally, due to the sharp gradient fall-off of the lateral profile, we designed an alignment technique to ensure proper correlation between the target and delivered dose.

Results: The measured central source position was within 1mm of the nominal vendor-provided value. Our profile, PDD, and dose-rate measurements agreed within 3%, 5%, and 3.5%, respectively, of the vendor-provided data for all cone sizes. The physical geometric center of the cone, which we marked with a crosshair, agreed within 1mm of the dose profile central axis.

Conclusion: Dosimetric validation for clinical implementation of the Varian HDR Leipzig-style surface applicator set can be based on Gafchromic™ film dosimetry with great accuracy and reproducibility.

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