Purpose: To propose equivalent guidelines for lung SBRT when using Acuros XB to RTOG guidelines, suited for convolution algorithms such as AAA, considering the difference between the algorithms and its biological impact.
Methods: A retrospective analysis was performed on 30 lung patients previously treated with SBRT by generating two sets of plans. The first set compared the original AAA plans, based on dynamic-conformal arcs (DCAs), to new plans first recalculated and then renormalized for PTV coverage using AXB. The second set was calculated in AXB based on DCAs and additional static beams, and then recalculated and renormalized in AAA. The recalculated and renormalized plans were compared to the original plans based on V100 and V90 PTV coverage as well as V105, conformality index, D2cm, Rx/Dmax, R50, and Dmin. These metrics were analyzed both nominally and based on variations according to RTOG guidelines.
Results: AAA plans recalculated in AXB had a significant reduction in most dosimetric metrics with extreme changes in V100 (4%) and the conformality index (7.5%). To achieve equal PTV coverage, AXB required an average of 1.8% more MU. Based on the relative differences between AAA and AXB in the above criteria, new guidelines for AXB, equivalent to RTOG guidelines, have been developed. Minor violations of the new guidelines by AXB plans of the 1st set were found to have significantly increased from those of the RTOG guidelines, with no change in major violations, by 19 and 34% for recalculated and renormalized plans, respectively. The violations became comparable to those of AAA plans against the RTOG guidelines. A similar trend was found for the second set (original) by 225%. The number of violations of the two sets against the new guidelines were similar to each other.
Conclusion: The new guidelines are recommended for planning with AXB.