There is a concern for dose calculation in highly heterogenous environments such as the thorax region. This study compares the quality of treatment plans of peripheral non-small cell lung cancer (NSCLC) stereotactic body radiation therapy (SBRT) using 2 calculation algorithms, namely, Eclipse Anisotropic Analytical Algorithm (AAA) and Acuros External Beam (AXB), for 3-dimensional conformal radiation therapy (3DCRT) and volumetric-modulated arc therapy (VMAT). Four-dimensional computed tomography (4DCT) data from 20 anonymized patients were studied using Varian Eclipse planning system, AXB, and AAA version 10.0.28. A 3DCRT plan and a VMAT plan were generated using AAA and AXB with constant plan parameters for each patient. The prescription and dose constraints were benchmarked against Radiation Therapy Oncology Group (RTOG) 0915 protocol. Planning parameters of the plan were compared statistically using Mann-Whitney U tests. Results showed that 3DCRT and VMAT plans have a lower target coverage up to 8% when calculated using AXB as compared with AAA. The conformity index (CI) for AXB plans was 4.7% lower than AAA plans, but was closer to unity, which indicated better target conformity. AXB produced plans with global maximum doses which were, on average, 2% hotter than AAA plans. Both 3DCRT and VMAT plans were able to achieve D95%. VMAT plans were shown to be more conformal (CI = 1.01) and were at least 3.2% and 1.5% lower in terms of PTV maximum and mean dose, respectively. There was no statistically significant difference for doses received by organs at risk (OARs) regardless of calculation algorithms and treatment techniques. In general, the difference in tissue modeling for AXB and AAA algorithm is responsible for the dose distribution between the AXB and the AAA algorithms. The AXB VMAT plans could be used to benefit patients receiving peripheral NSCLC SBRT.

The purpose of this study was to investigate the characteristics of electron contamination and Output Factors (OFs) from Varian Trilogy Clinac iX 6 MV photon beam at small field sizes. EGSnrc Monte Carlo (MC) code system was used to model the photon beam for this Linear Accelerator (Linac) head and analyze the electron contamination and OFs from this treatment head. The electron contamination was analyzed for field sizes of 1 × 1, 2 × 2, 3 × 3, 4 × 4, and 5 × 5 cm 2 . The number of electron contamination increases with increasing field sizes, but the maximum energy of the electron contamination stays constant (at around 1.87 MeV for each field size). The contaminants contribute to the dose at the surface of the water phantom (1-5 cm from the surface) for field size 4 × 4 and 5 × 5 cm 2 and this dose decreases with depth. The OFs are simulated by EGSnrc code system and have a good agreement with measurement (deviation 3.45, 1.76, and 0.86 for field of 2, 3 and 4, respectively). This study presented that MC methods have great potential to accurately predict the electron contamination and OFs for 6 MV photon beam.

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The presence of the moving chest wall was capable of identifying depth dose differences between the two versions of the algorithms. These differences could not be identified in the static chest wall as shown in the anterior beam depth dose calculations.