SU‐E‐T‐339: Dosimetric Verification of Acuros XB Dose Calculation Algorithm On An Air Cavity for 6‐MV Flattening Filter‐Free Beam

Abstract

Purpose:This study was to verify the accuracy of Acuros XB (AXB) dose calculation algorithm on an air cavity for a single radiation field using 6‐MV flattening filter‐free (FFF) beam.Methods:A rectangular slab phantom containing an air cavity was made for this study. The CT images of the phantom for dose calculation were scanned with and without film at measurement depths (4.5, 5.5, 6.5 and 7.5 cm). The central axis doses (CADs) and the off‐axis doses (OADs) were measured by film and calculated with Analytical Anisotropic Algorithm (AAA) and AXB for field sizes ranging from 2 Χ 2 to 5 Χ 5 cm2 of 6‐MV FFF beams. Both algorithms were divided into AXB_w and AAA _w when included the film in phantom for dose calculation, and AXB_w/o and AAA_w/o in calculation without film. The calculated OADs for both algorithms were compared with the measured OADs and difference values were determined using root means squares error (RMSE) and gamma evaluation.Results:The percentage differences (%Diffs) between the measured and calculated CAD for AXB_w was most agreement than others. Compared to the %Diff with and without film, the %Diffs with film were decreased than without within both algorithms. The %Diffs for both algorithms were reduced with increasing field size and increased relative to the depth increment. RMSEs of CAD for AXB_w were within 10.32% for both inner‐profile and penumbra, while the corresponding values of AAA_w appeared to 96.50%.Conclusion:This study demonstrated that the dose calculation with AXB within air cavity shows more accurate than with AAA compared to the measured dose. Furthermore, we found that the AXB_w was superior to AXB_w/o in this region when compared against the measurements.