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Commissioning a 2.5 MV Portal Imaging Beam in the Eclipse Treatment Planning System

W Ferris*, W Culberson , Z Labby , University of Wisconsin-Madison, Madison, WI


(Saturday, 3/30/2019)  

Room: Exhibit Hall

Purpose: To test the feasibility of a commercial treatment planning system to model the TrueBeam 2.5 MV imaging beam and verify the accuracy of Acuros XB and the Anisotropic Analytical Algorithm (AAA). This beam has not been modeled by any commercial TPS in the literature.

Methods: Standard beam commissioning data were measured for a 2.5 MV beam line. Both algorithms were commissioned in Eclipse using these data. A diode was used to acquire dose profiles at one depth for jaw-collimated fields and spot sizes were tuned to these profiles. Both beam models were validated using MPPG 5a recommendations. Three heterogeneity cork setups were used, with varying field sizes and cork thicknesses. The ratios of dose above the cork to dose below the cork was compared between measured and computed.

Results: The TPS was able to model the low energy imaging beam. The optimal algorithm spot sizes differed substantially from those in typical models of therapeutic beam energies. The mean energy along the CAX for the 2.5 MV beam was 0.49 MV. For MPPG 5a Tests 5.4-5.7, the gamma pass rate was greater than 95% for a 2%/2 mm criteria for 21 of 23 profiles and PDDs for Acuros and 18 of 23 for AAA. Both algorithms underestimate out-of-field dose. For MPPG Test 6.2, the percent difference of the ratio of dose above cork to dose below cork between measured and Acuros was less than 1.5% for all three setups. The percent difference between measured and AAA was greater than 3% for all three setups.

Conclusion: Both Acuros and AAA can be used to model a 2.5 MV imaging beam. In general, Acuros passes gamma analysis with slightly higher passing rates than AAA for basic photon tests. Acuros performs significantly better than AAA for heterogeneity calculations.


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