SU-E-T-122: Anisotropic Analytical Algorithm (AAA) Vs. Acuros XB (AXB) in Stereotactic Treatment Planning

Authors


Abstract

Purpose:

To evaluate dosimetric differences between superposition beam model (AAA) and determinant photon transport solver (AXB) in lung SBRT and Cranial SRS dose computations.

Methods:

Ten Cranial SRS and ten Lung SBRT plans using Varian, AAA _11.0 were re-planned using Acuros _XB_11.0 with fixed MU. 6MV photon Beam model with HD120_MLC used for dose calculations. Four non-coplanar conformal arcs used to deliver 21Gy or 18Gy to SRS targets (0.4 to 6.2cc). 54Gy (3Fractions) or 50Gy (5Fractions) was planned for SBRT targets (7.3 to 13.9cc) using two VAMT non-coplanar arcs. Plan comparison parameters were dose to 1% PTV volume (D1), dose to 99% PTV volume( D99), Target mean (Dmean), Conformity index (ratio of prescription isodose volume to PTV), Homogeneity Index [ (D2%-D98%)/Dmean] and R50 (ratio of 50% of prescription isodose volume to PTV). OAR parameters were Brain volume receiving 12Gy dose (V12Gy) and maximum dose (D0.03) to Brainstem for SRS. For lung SBRT, maximum dose to Heart and Cord, Mean lung dose (MLD) and volume of lung receiving 20Gy (V20Gy) were computed. PTV parameters compared by percentage difference between AXB and AAA parameters. OAR parameters and HI compared by absolute difference between two calculations. For analysis, paired t-test performed over the parameters.

Results:

Compared to AAA, AXB SRS plans have on average 3.2% lower D99, 6.5% lower CI and 3cc less Brain_V12. However, AXB SBRT plans have higher D1, R50 and Dmean by 3.15%, 1.63% and 2.5%. For SRS and SBRT, AXB plans have average HI 2 % and 4.4% higher than AAA plans. In both techniques, all other parameters vary within 1% or 1Gy. In both sets only two parameters have P>0.05.

Conclusion:

Even though t-test results signify difference between AXB and AAA plans, dose differences in dose estimations by both algorithms are clinically insignificant.

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