P160] From anisotropical analytical algorithm to acuros XB: Clinical implications in vmat technique for lung, head&neck and prostate treatments

Abstract

Purpose To determine the dose differences and clinical implications of using a high accuracy algorithm, AcurosXB (AXB), instead of the Anisotropic Analytical Algorithm (AAA), for three different treatment sites with VMAT technique, in order to use AXB as routine algorithm. Methods We selected fifteen prostate and head&neck cancer patients, and seventeen lung cancer patients. All of them had been optimized with the Photon Optimizer algorithm and calculated with AAA. These plans were recalculated with AXB to quantify dose differences in significant points of the DVH: coverage and maximum dose criteria for the PTV, and several dose-volume constraints for the involved Organs at Risk (OAR). All data were statistically treated. For the PTV, we analyzed clinical consequences in terms of coverage and homogeneity. For the OAR, it is well known that classic dose tolerances have been stated based on AAA or even simpler algorithms. In our study, we identified those dose-volume points in which AXB provides lower calculated doses than AAA. In these cases, it wouldn’t be safe to plan with AXB according to classic dose tolerances, since it might imply that these criteria weren’t met with AAA. To prevent this, an additional statistically derived restriction to tolerance constrains is proposed when using AXB. Results PTV: For lung and head&neck patients, due to the high heterogeneity involved, we observe a worse coverage and homogeneity in plans recalculated with AXB. Consequently, if we use AXB in our practice, a more demanding optimization is needed to meet objectives, implying a better local control disease. OAR: for most of the dose-volume points studied the differences found are statistically significant. Some of them might lead to clinical consequences for serial OAR. In these cases, we encourage to restrict Dmax tolerance when AXB is used, as discussed above. Conclusions The results obtained with AXB differ from those obtained with AAA. Since AXB is more accurate, we propose using it in clinical practice. Nevertheless, we strongly recommend being cautious about OAR tolerances, setting an additional restriction to the tolerance criteria when required, until these are reviewed and an international consensus is adopted taking into account the new algorithms.