[P224] Analytical anisotropic algorithm vs Acuros algorithm comparison

Purpose The aim of this work is to compare Acuros and Analytical Anisotropic Algorithm (AAA), focussing on tissue interfaces. Methods 20 head and neck pathology treatment plans were calculated with both algorithms. Density heterogeneities and air tissue interfaces in the lungs and oral cavity have been analysed. Radiotherapy Treatment Planning System (TPS) Eclipse version 13.7 was used. The grid size set was 0.25 cm. Dose matrix were exported from the RTP and compared with gamma 3D evaluation method with different distance and dose parameters using the software VeriSoft version 5.1. For every treatment plan gamma 3D analysis was performed in two dose planes (head and lung) to check dose differences. Values under 20% of the maximum dose are excluded of the comparison. Γ(3/1) and Γ(1/3) were also performed to evaluate dependence on dose and distance. Results The Γ(2/2) in 80% of cases between both dose distribution was higher than 95%. Γ(3/3) was higher than 100% for all the cases tested in the case of the head. For the case of the lung, 90% of cases Γ(2/2) between both dose distribution was higher than 95%. Γ(3/3) was higher than 100% for all the cases tested. Γ(3/1) vs. Γ(1/3) averages were 91.3% vs. 77% for head and 91.8% vs. 56.4% for lung. Conclusions Dose difference is much more dependent on the distance of the points under the Γ criteria than on the dose. Main differences are obtained at the skin, dose calculated with the Acuros algorithm is higher than the values with AAA algorithm, nevertheless maximum dose values are higher when the AAA algorithm is used. No significant dose difference has been observed in lungs.