ESTRO 2020 Abstract book

S773 ESTRO 2020

metric (dose difference> 3%)

PO‐1366 Comparison of Acuros and Anisotropic Analytical Algorithm for dose calculations in VMAT treatments E.M. Ambroa Rey 1 , P. Rodríguez Meijide 1 , M. Pérez Fernández 1 , M. López Sánchez 1 1 Hospital Universitario Lucus Augusti, Medical Physics, Lugo, Spain Purpose or Objective The purpose of this study is to compare the algorithm Acuros XB and AAA for dose calculations in heterogeneous pathologies such as head and neck (H&N), esophagus and 70 VMAT patients were selected for this study (24 lung, 24 H&N and 22 esophagus). Plans were calculated in Eclipse (v13.6). Treatments plans originally calculated with AAA algorithm were recalculated using Acuros XB (V13.6) using the same number of monitor units (MU) and multileaf collimator as the original plan. No other parameters were changed or twiked during the optimization. Dose differences in PTV coverage and other dosimetric values were compared for both algorithms. Due to the small sample a Kruskal-Wallis test was performed to analyzed the differences between the two calculations. To estimated precisely how important these differences are, the effect size was also studied. Results Table I shows PTV coverage (V95%), minimum and maximum dose to the PTV. The major differences in the V95% were shown for the H&N treatments, where there is a 3% difference, in average. For the esophagus and lung treatments this difference was 2.8% and a 1.1% respectively. Differences in V95% were statistically significant for H&N and esophagus treatments, but not for the lung cases. lung VMAT treatments. Material and Methods

According to Cohen criteria, the effect size of these significance was medium (d=0.5) for esophagus treatments and large effect (d=0.7) for HN treatments. Figure I shows the dosimetric differences between the AAA and Acuros algorithm for the three pathologies.

Conclusion The PerFRACTION module for 2D IVD performs well regardless of the treatment technique, being capable of identifying all the changes imposed on the phantom. However, the systematic shift from predicted to measured 2D dose must be minimized to use predicted 2D dose as the reference. The sensitivity of the system to detect clinically relevant changes depends on the dose distribution with respect to the volumes of interest and changes. Increasing the distribution of beam portals increases this sensitivity. From this phantom study it can be concluded that even if large differences in 2D passing rates (pass rate<50%) correctly identify dose differences larger than 4%, to track smaller changes, moving to other approaches other than the current dose or DTA metrics is needed.

Furthermore, calculations with Acuros XB shown a higher maximum dose (3% for esophagus, 2.1% for H&N and 2.7% for lung treatments) and a lower minimum dose (in