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Impact of Dose Calculation Algorithms On Lung SBRT Treatments

J Rosenfield

J. Rosenfield*, X. Yang, X. Dong, E. Elder, K. Higgins, and A. Dhabaan, Emory University, Winship Cancer Institute, Atlanta, GA


SU-G-BRC-11 (Sunday, July 31, 2016) 4:00 PM - 6:00 PM Room: Ballroom C

Purpose: To investigate potential dosimetrical differences between the Acuros XB (AXB) and AAA dose calculation algorithms, with a specific focus on lung SBRT treatments involving inherently high degrees of anatomical heterogeneity, small field sizes, and varying tumor locations relative to critical structures.

Methods: A cohort of 20 SBRT patients treated in our clinic was selected to include varying lung tumor locations. For each patient, the Eclipse treatment planning system was employed to generate a lung SBRT plan using the AXB dose calculation algorithm, in addition to the AAA plan previously calculated for clinical use. The plans were then compared using common plan evaluation metrics. To assess the accuracies of the algorithms in a highly heterogeneous medium, identical AAA and AXB plans were delivered to a slab phantom consisting of solid water and a low-density insert representing lung. Field sizes of 3 x 3 cm through 12 x 12 cm were considered. The phantom dose was measured with OSLDs and radiochromic film and compared to the calculated dose distributions.

Results: The average difference in mean PTV dose between the AAA and AXB plans, expressed as a percentage of the prescription dose, was 2.24% ± 1.58%. The differences in doses to critical structures were negligible. The OSLD and film measurements showed that the AXB dose calculations are more accurate in heterogeneous media. The difference between the algorithms became more significant as field size decreased. Using the same dose normalization, the conformity indices for the AAA plans were slightly closer to unity than the AXB plans. This was expected due to the higher dose calculation accuracy of AXB in heterogeneous media.

Conclusions: Our results emphasize the importance of AXB for lung SBRT dose calculations due to its superiority in calculating dose for small lesions in heterogeneous tissue.

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