Acuros XB Algorithm vs. Anisotropic Analytical Algorithm: A Dosimetric Study Using Heterogeneous Phantom and Computed Tomography (CT) Data Sets of Esophageal Cancer Patients

Our purpose in this study was to assess the dosimetric impact of the Acuros XB algorithm (AXB), in comparison with Anisotropic Analytical Algorithm (AAA) calculations, for esophageal cancer treatment plans created with RapidArc technique. First, we performed a phantom study by comparing the percent depth dose (PDD) calculated by AXB and AAA against the measured PDD in a slab phantom containing a 2 cm air gap thickness. Second, we performed a clinical study using a computed tomography (CT) data set from 10 esophageal cancer patients. The treatment plans calculated by AXB and AAA were evaluated for planning target volume (PTV) coverage, doses to the PTV and organs at risk (OARs). Dose calculations by the AXB and AAA were done for identical beam parameters. The AXB showed better agreement (within ±0.5%) with measurements than did the AAA (−4.9% to −6.2%). In comparison to the AAA, the AXB predicted a higher maximum PTV dose (2.0%), but lower mean (1.1%) and minimum (2.5%) PTV doses as well as reduced PTV coverage (9.1%). The averaged mean doses to all OARs predicted by the AXB were lower (up to 3.6%), and the percentage of lungs volume receiving at least 20 and 5 Gy were lower by about 3.6% in the AXB plans compared to the AAA plans. The AXB is more accurate than the AAA for dose predictions when air medium is involved. The use of AXB is more likely to avoid dose overestimation or underestimation for the esophageal cancer treatment plans compared to AAA.