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Commissioning Data for HDR Vertical Entry Surface Applicators

A Markovic

A Markovic*, J Baldwin , Banner Health, Greeley, CO


SU-I-GPD-T-18 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: This work presents dosimetric data and the methodology in commissioning a set of round Varian vertical entry HDR surface applicators for clinical use. The information available to implement these applicators clinically is insufficient, and the data provided by the vendor suffers from poor measurement techniques. This work overcomes the challenges of measuring sharp dose gradients produced by these applicators by employing unique measurement methods that facilitate accurate results.

Methods: This work provides a method of measuring surface applicator PDDs, output factors and dose profiles. The set of applicators consists of a small and large cone which accommodate round inserts of various diameters. The PDDs were measured with a plane parallel chamber in water. Solid water was used as the medium for measuring output factors with OSLDs and profiles with gafchromic film. Various unique measurement methods(Fig.1) are presented in this work, such a 3D printed jig to ensure alignment accuracy. A source offset of 15mm was used. Our measurements were compared to data calculated by the Varian Acuros BV treatment planning algorithm.

Results: The output factors, normalized to a 10 Ci source and a depth of 5 mm, ranged from 83 cGy/min to 91 cGy/min(Table1) and were within 5% of Acuros calculations. The 90% width of the profiles at 4 mm depth ranged from 12.3 to 32.0 mm, agreeing within 3mm of Acuros calculations(Fig.2).

Conclusion: This work presents a commissioning method for HDR surface applicators that produces data agreeing well with Acuros BV. Our data showed little difference in the PDDs (Fig.3) among the inserts of different sizes(mostly within 5%). The widths of the 90% dose profiles were unexpectedly found to depend primarily on the cone rather than the insert diameter. This effectively left only 3 available widths to treat with: 12.3, 18, 30 mm.

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