The aim of this study was to investigate the impact of heterogeneity on the dose calculation for two algorithms implemented in the TPS “Analytical Anisotropic Algorithm (AAA) and Acuros XB” and validated the use of Acuros XB algorithm in clinical routine. First, we compare the dose calculated by these algorithms and the dose measured at the given point P, which is found after heterogeneity insert. Second, we extend our work on clinical cases that present a complex heterogeneity. By evaluating the impact of the choice of the algorithm on the dose coverage of the tumor, and the dose received by the organs at risk for 20 patients affected by lung cancer.
The result of our phantom study showed a good agreement with several studies that showed the superiority of the Acuros XB over the AAA in predicting dose when it concerns heterogeneous media. The treatment plans for 20 lung cancers were calculated by two algorithms AAA and Acuros XB, the results show a statistical significant difference between algorithms for Homogeneity Index and the maximum dose of planning target volume (HI: 0.11±0.01 vs 0.05±0.01 p = 0.04; Dmax: 69.30±3.12 vs 68.51±2.64 p = 0.02). Instead, no statistically significant difference was observed for conformity index CI and mean dose (CI: 0.98±0.18 vs 0.99±0.14 p = 0.33; Dmean: 66.3±0.65 vs 66.10 ±0.61 p = 0.54). For organs at risk, the maximum dose for spinal cord, mean dose and D37 % of lung minus GTV (dose receiving 37% of lung volume) were found to be lower for AAA plans than Acuros XB and the differences were statistically significant (p<0.05). For the heart D33% and D67% were found to be higher for AAA plans than Acuros XB and the differences were statistically significant (p<0.05), but No difference was observed for D100% of the heart.
The use of the AXB algorithm is suitable in the case of presence of heterogeneity, because it allows to have a better accuracy close to the Monte Carlo calculation.