Application of the accelerator log file combined with the film to verify the accuracy of AAA and AXB algorithms in the heterogeneous medium / 中华放射肿瘤学杂志

ABSTRACT

Objective The accelerometer log files generated when the simulation plans were executed on the chest phantom,the modified log files including multi-leaf collimator (MLC) and Gap motion error were imported into the treatment planning system and then the dose was reconstructed by Analytical Anisotropic Algorithm (AAA) and Acuros XB (AXB) algorithms.The calculation accuracy of these two algorithms was analyzed according to the measured value of film.Methods The targets and organs at risk (OARs) of the mediastinum and peripheral lung cancer were contoured on the chest phantom,intensity-modulated radiation therapy (IMRT) plans were designed and then the dose was calculated with the AAA and AXB algorithms.The films were placed in the phantom to measure the dose when the simulation plans were executed through the accelerator.The log files were extracted by Varian Argus software and the MLC,Gap motion deviation information was imported into the treatment planning system.The dose was reconstructed by two algorithms.The differences of target dose (D2,D98,Dmax,Vprescrited) and OAR dose (lungV5,V10,V20,Dmean;HeartV30,Dmean;Spinal cordDmax) were statistically compared between two algorithms.The measured dose of film was compared with the isocenter doses of the two algorithms.3mm/3％ standard was adopted to analyze the gamma-pass rates.Pass rates of high-dose region (target region) and low-dose region (upper,lower,left and right directions outside the target region) were analyzed with different size matrices.Results The dose differences were detected in the simulation plans of mediastinum and peripheral lung cancer by using the AAA and AXB algorithms.The maximum dose differences of the two targets were D98(2.47％) and Vprescribed (4.21％) using the AAA and AXB algorithms.The maximum differences of the OARs were the left lung (D =3.58％、V10 =-2.76％),the right lung (V5=-1.96％,D mean =0.18％),the heart (D =1.15％,D =0.18％) and the spinal cord (Dmax =-3.34％,1.79％),respectively.Compared with the measured dose of filn,the average gammapass rate in the mediastinum and peripheral lung cancer by using two algorithms of different sizes of matrix were 94.07％± 1.32％ (AAA),93.81％± 1.43％ (AXB) and 93.73％± 1.31％ (AAA),94.39％± 1.32％ (AXB).In the low dose region of the two targets,the average gamma-pass rate by the AXB algorithm was higher than that by the AAA algorithm.Conclusions The AAA and AXB algorithms differ in the calculation of target areas for the mediastinum and peripheral lung cancer simulated on the chest phantom.The average gamma-pass rate of the AXB algorithm is better compared with that of the AAA algorithm referring to the measured dose of the film,which is closer to the measured value of the film in the cavity.