Paul Reich
Royal Adelaide Hospital
Medical Physicist

Corey Bridger
Student
School of Physical Science, University of Adelaide, South Australia

Alexandre Santos
Medical Physicist
School of Physical Science, University of Adelaide, South Australia and Department of Medical Physics, Royal Adelaide Hospital, South Australia

Background and Purpose To commission a Leipzig-style applicator for superficial HDR brachytherapy at the Royal Adelaide Hospital (RAH). Methods The Varian Leipzig-style surface applicator is constructed of a high-density tungsten alloy and comes with four attachable inserts of 30, 35, 40 and 45 mm diameters. The surface applicator is available in a vertical or horizontal configuration of which the latter was purchased and commissioned. The applicator was initially examined for damage or defect, the insert dimensions were verified and the total length of the applicator and connected source guide tube was verified using Varian’s length gauge tool. The programmed dwell index corresponding to the centre of the applicator was determined from analysing the symmetry of dose profiles measured at depth in a solid water phantom for different source positions within the applicator. A GammaMedPlus™ iX HDR brachytherapy after loader was used to deliver the Ir-192 source within the applicator. The dosimetric accuracy of Acuros, a model-based dose-calculation algorithm in BrachyVision™ treatment planning system (V 13.7) was evaluated against measurements of beam profiles and depth doses using GafChromic® EBT3 film in a solid water phantom and Monte Carlo (MC) data provided by the vendor1. Results The applicator was found to be bulky and heavy. In addition, the inserts were large due to the additional shielding surrounding the open aperture. The insert dimensions were measured within ± 0.5 mm of the manufacturer. The combined length of applicator and source guide tube was within ± 1 mm of the nominal length of 1300 mm. The programmed dwell index corresponding to the source centre was 1294 mm. Dosimetric agreement between the treatment planning system (TPS) and measured beam profiles at depths of 2- 10 mm in water ranged from ± 3 – 6 % at the centre of the applicator. The TPS agreement with MC was ± 1 % at 3 mm depth (MC data only available for 3 mm depth). For depth doses, the TPS agreement with measured depth doses was ± 1 - 4 % for 2 – 10 mm depth in water. The TPS agreement with MC was similar with ± 1-2 % for the same depths. The estimated uncertainty (k =2) in the measured and MC data2 was ± 2.6 % and ± 7.2 %, respectively. Conclusions The bulkiness and weight of the applicator combined with the ring of shielding surrounding the inserts may be a limiting factor in the choice of anatomic site and lesion size that can be treated. However, a Universal Clamping Device purchased by the RAH may aid with set-up and mobilisation of the applicator at treatment. Measurements and published MC data were in good agreement with the TPS. References 1. Varian Medical Systems. Instructions for use: Dose characterization of the surface applicator set with Leipzig-style cone. Palo Alto, CA; 2015. 2. Fulkerson RK, Micka JA, DeWard, LA. Dosimetric characterization and output verification for conical brachytherapy surface applicators. Part II. High dose rate 192Ir sources. Med Phys. 2014;41(2):1-16


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