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Comparison of AAA and Acuros XB Dose Calculation Algorithms for SRS

F Yeh*, J Adamson, Z Wang, Duke University Medical Center, Durham, NC

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose:
Since the delivered dose to the target and to the surrounding tissue affect SRS outcomes, the accuracy of dose calculation is the key the treatment planning system (TPS), Varian Eclipse. The purpose of this project is to compare SIMT SRS dose distribution obtained by AXB and widely used AAA and to investigate the effects of size, distance to isocenter and heterogeneity.

Methods:
40 clinical cases were used to evaluate the dose distribution differences. All plans were generated by the Eclipse TPS (V13.6) and calculated by AAA. Each plan consisted of 2 to 14 targets and treated by VMAT. These plans were recalculated by AXB, using the same geometry, voxel resolution and monitor units. Parameters used for plan comparison included planning tumor volume (PTV) coverage to 99%, 95%, and 1%, PTV minimum dose, PTV mean dose, PTV maximum dose, and whole brain V3Gy, V6Gy and V12Gy. The dosimetric accuracy was evaluated based on gamma pass rate with threshold criteria 3%/1mm on SRS MapCHECK.

Results:
The two algorithm comparison results showed large dose discrepancies in the PTV minimum dose (-8.2% to 5.1%), occurring also in small field size range and in the small range of distance from PTV to skull. The average difference for D1%, D95% and D99% were 0.8%, 0,2% and 0.03%, respectively. However, the difference of D99% revealed up to -6.1%. Relative to AXB, V3Gy, V6Gy and V12Gy decrease by 1.3%, 0.2% and 2.3% with AAA. Gamma analysis demonstrated higher gamma pass rate for AAA compared to AXB (99.9%, 97.9%).

Conclusion:
Sizable dose difference were found in AAA and AXB, particularly in the PTV minimum dose. Heterogeneity and tumor size introduced uncertainty for dose calculation. However, the dose difference showed no dependence on the distance to isocenter. AAA showed better agreements between calculated and delivered dose than Acuros XB.

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