Evaluation of the analytical anisotropic algorithm (AAA) in an extreme water-lung interface phantom using Monte Carlo dose calculations

Abstract

This study compares the performance of the analytical anisotropic algorithm (AAA), a new superposition-convolution algorithm recently implemented in EclipseTM Integrated Treatment Planning System (TPS), to that of the pencil beam convolution (PBC) algorithm in an extreme (c-shaped, horizontal and vertical boundaries) water-lung interface phantom. Monte Carlo (MC) calculated dose distributions for a variety of clinical beam configurations at nominal energies of 6MV and 18 MV are used as benchmarks in the comparison. Dose profiles extracted at three depths (4, 10 & 16 cm), 2-D maps of the dose difference and dose difference statistics are used to quantify the accuracy of both photon dose calculation algorithms. Results show that AAA is considerably more accurate than the PBC algorithm, with the standard deviation of the dose differences within a region encompassing the lung block reduced by a factor of two and more. Confidence limits with AAA were ≤ 4% for all beam configurations investigated while they ranged from 3.5% to 11.2% with the PBC algorithm. Finally, AAA calculations for the small 4×4 ? 18 MV beam, which is poorly modeled by PBC (with the dose differences as high as 16.1%), provided the same accuracy as the PBC model of 6 MV beams commonly acceptable in clinical situation.