A comparative analysis of Acuros XB and the analytical anisotropic algorithm for volumetric modulation arc therapy

Background: This study aimed to verify the dosimetric impact of Acuros XB (AXB) (AXB, Varian Medical Systems Palo Alto CA, USA), a two model-based algorithm, in comparison with Anisotropic Analytical Algorithm (AAA) calculations for prostate, head and neck and lung cancer treatment by volumetric modulated arc therapy (VMAT), without primary modification to AAA. At present, the well-known and validated AAA algorithm is clinically used in our department for VMAT treatments of different pathologies. AXB could replace it without extra measurements. The treatment result and accuracy of the dose delivered depend on the dose calculation algorithm. Materials and method: Ninety-five complex VMAT plans for different pathologies were generated using the Eclipse version 15.0.4 treatment planning system (TPS). The dose distributions were calculated using AAA and AXB (dose-to-water, AXB(w) and dose-to-medium, AXB(m)), with the same plan parameters for all VMAT plans. The dosimetric parameters were calculated for each planning target volume (PTV) and involved organs at risk (OA R). The patient specific quality assurance of all VMAT plans has been verified by Octavius (R)-4D phantom for different algorithms. Results: The relative differences among AAA, AXB(w) and AXB(m), with respect to prostate, head and neck were less than 1% for PTV D-95%. However, PTV D-95% calculated by AAA tended to be overestimated, with a relative dose difference of 3.23% in the case of lung treatment. The absolute mean values of the relative differences were 1.1 +/- 1.2% and 2.0 +/- 1.2%, when comparing between AXB(w) and AAA, AXB(m) and AAA, respectively. The gamma pass rate was observed to exceed 97.4% and 99.4% for the measured and calculated doses in most cases of the volumetric 3D analysis for AAA and AXB(m), respectively. Conclusion: This study suggests that the dose calculated to medium using AXB(m) algorithm is better than AAA and it could be used clinically. Switching the dose calculation algorithm from AAA to AXB does not require extra measurements