SU‐E‐T‐800: Verification of Acurose XB Dose Calculation Algorithm at Air Cavity‐Tissue Interface Using Film Measurement for Small Fields of 6‐MV Flattening Filter‐Free Beams

Abstract

Purpose:To verify the dose accuracy of Acuros XB (AXB) dose calculation algorithm at air‐tissue interface using inhomogeneous phantom for 6‐MV flattening filter‐free (FFF) beams.Methods:An inhomogeneous phantom included air cavity was manufactured for verifying dose accuracy at the air‐tissue interface. The phantom was composed with 1 and 3 cm thickness of air cavity. To evaluate the central axis doses (CAD) and dose profiles of the interface, the dose calculations were performed for 3 × 3 and 4 × 4 cm2 fields of 6 MV FFF beams with AAA and AXB in Eclipse treatment plainning system. Measurements in this region were performed with Gafchromic film. The root mean square errors (RMSE) were analyzed with calculated and measured dose profile. Dose profiles were divided into inner‐dose profile (>80%) and penumbra (20% to 80%) region for evaluating RMSE. To quantify the distribution difference, gamma evaluation was used and determined the agreement with 3%/3mm criteria.Results:The percentage differences (%Diffs) between measured and calculated CAD in the interface, AXB shows more agreement than AAA. The %Diffs were increased with increasing the thickness of air cavity size and it is similar for both algorithms. In RMSEs of inner‐profile, AXB was more accurate than AAA. The difference was up to 6 times due to overestimation by AAA. RMSEs of penumbra appeared to high difference for increasing the measurement depth. Gamma agreement also presented that the passing rates decreased in penumbra.Conclusion:This study demonstrated that the dose calculation with AXB shows more accurate than with AAA for the air‐tissue interface. The 2D dose distributions with AXB for both inner‐profile and penumbra showed better agreement than with AAA relative to variation of the measurement depths and air cavity sizes.