Evaluating the accuracy of a three-term pencil beam algorithm in heterogeneous media. (16th January 2017)

• Record Type: Journal Article
• Authors: Chapman, J W; Knutson, N C; Fontenot, J D; Newhauser, W D; Hogstrom, K R
• Is Part Of: Physics in medicine & biology. Volume 62:Number 3(2017:Feb.)
• Page Start: 1172
• Page End: 1191
• Publication Date: 2017-01-16
• Subjects: pencil beam algorithm -- nuclear halo -- proton -- dose calculation -- Monte Carlo -- MCNPX; Biophysics -- Periodicals; Medical physics -- Periodicals; 610.153
• DOI: 10.1088/1361-6560/aa51aa
• Languages: English
• ISSNs: 0031-9155

Abstract

Abstract: The goal of this work was to evaluate the accuracy of our in-house analytical dose calculation code against MCNPX data in heterogeneous phantoms. The analytical model utilizes a pencil beam model based on Fermi–Eyges theory to account for multiple Coulomb scattering and a least-squares fit to Monte Carlo data to account for nonelastic nuclear interactions as well as any remaining, uncharacterized scatter (the 'nuclear halo'). The model characterized dose accurately (up to 1% of maximum dose in broad fields (4 × 4 cm 2 and 10 × 10 cm 2 ) and up to 0.01% in a narrow field (0.1 × 0.1 cm 2 ) fit to MCNPX data). The accuracy of the model was benchmarked in three types of stylized phantoms: (1) homogeneous, (2) laterally infinite slab heterogeneities, and (3) laterally finite slab heterogeneities. Results from homogeneous phantoms and laterally infinite slab heterogeneities showed high levels of accuracy (>98% of points within 2% or 0.1 cm distance-to-agreement (DTA)). However, because range straggling and secondary particle production were not included in our model, central-axis dose differences of 2–4% were observed in laterally infinite slab heterogeneities when compared to Monte Carlo dose. In the presence of laterally finite slab heterogeneities, the analytical model resulted in lower pass rates (>96% of points within 2% or 0.1 cm DTA), which was attributed to the use of the central-axis approximation.