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Comparison of AAA and Acuros Dose Calculations in a Hetergenous Phantom

A Readshaw

A Readshaw1*, R Lalonde2, H Kim3, (1) D3 Radiation Planning, Pittsburgh, PA, (2) D3 Radiation Planning, Pittsburgh, PA, (3) University of Pittsburgh Medical Center, Pittsburgh, PA

SU-E-T-569 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To compare the Anisotropic Analytical Algorithm (AAA) and Acuros algorithms for dose calculations in a heterogeneous phantom.

Methods: Dose calculations were performed for the 6MV and 18MV beams of a Varian 21EX linac for open field sizes ranging from 8x8 cm2 to 15x15 cm2. All calculations were performed in the Varian Eclipse planning system on a solid water slab phantom with cavity simulated lung density cavity. Calculations were performed using a 1mm calculation grid for both AAA and Acuros. For the Acuros calculations, dose was reported to both water and medium. The calculated dose points were compared to ionization chamber measurements at points in solid water, in simulated lung, and in solid water at points beyond the simulated lung cavity.

Results: AAA and Acuros calculations agreed to within 0.8% and 0.3%, respectively, to measured doses above the lung cavity, and to within 1.0% and 1.4% of doses measured in the simulated lung cavity. However, as previously reported in the literature, AAA overestimates dose at points beyond air heterogeneities. In this investigation, AAA over reported dose at points beyond the air cavity by 3.2 - 4.0%, relative to ionization chamber measurements. For points beyond the air cavity calculated with Acuros, calculations agreed within 1.1% of measured dose.

Conclusion: Acuros has improved accuracy, relative to AAA, for dose calculations at points beyond an air cavity.

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