PURPOSE/OBJECTIVE(S) The Varian Eclipse implementation of the Linear Boltzmann Transport Equation, Acuros XB dose calculation algorithm has the same accuracy as Monte Carlo but is much faster and has already been implemented in many clinics. Like Monte Carlo, Acuros allows the user to report dose to water or dose to medium. The main aim of this study is to compare both Acuros XB dose-to-medium Dm,m and dose-to-water Dw,m algorithms with the widely used Collapsed Cone Convolution (CCC) algorithm and provide some implications on NRG clinical trials. MATERIALS/METHODS Six lung patients who previously received VMAT-based treatments at our institution were analyzed by recalculating their plans for each one with CCC algorithm (reviewed and approved by our Radiation Oncologists) and with both reporting modes of Acuros XB algorithm. All plans used the same monitor units (MU). For each patient, V100 of planning target volume (PTV) and D98 of gross tumor volume (GTV) in each plan were compared and dose distributions calculated by CCC, Acuros Dw,m and Acuros Dm,m were visually compared as well. RESULTS Differences between PTV V100 calculated by CCC and Acuros XB Dm,m varies from 13.2% to 0.4% with a mean value of 4.3%, while the differences between PTV V100 calculated by CCC and Acuros XB Dw,m varies from 4.2% to 0.6% with a mean value of 2.2%. The differences between PTV V100 calculated by Acuros XB Dm,m and Acuros XB Dw,m varies from 14.6% to 0.1% with a mean value of 3.9%. When GTV D98 is evaluated, the largest difference between CCC and Acuros XB Dm,m is 4.53% with mean value of 2.43%, while the largest difference between CCC and Acuros XB Dw,m is 4.11% with mean value of 1.77%. For all the cases, GTV D98 calculated by CCC is closer to the ones calculated by Acuros XB Dw,m. CONCLUSION The present study shows that the differences in dose calculated by CCC and Acuros Dm,m are larger than the dose differences between CCC and Acuros Dw,m. This difference will cause significant discrepancies if both CCC and Acuros Dm,m are used in clinical trials. This study indicates that Acuros Dw,m should be used to be consistent with CCC, however, this contradicts current recommendations in literature. Hence, further investigation and clarification are needed about which dose reporting mode should be used.