Acuros-Based Planning with Density Override for Lung SBRT by a Dynamic Conformal Arc Technique: Comparative Evaluation with AAA-Based Planning in Four-Dimensional Dose

The purpose of this study was to evaluate a planning strategy based on Acuros with density override in comparison with AAA without and with the override. Ten lung-tumor patients were selected with each PTV size around 2 - 4 cm and were imaged using slow scan, followed by four-dimensional (4D) imaging limited to the target. On each phase-specific image, gross tumor volume (GTV) was contoured. Summed over all phases, an integrated GTV (iGTV) was generated and copied to the slow scan. A treatment plan was created using a dynamic-conformal-arc technique with AAA to prescribe 60 Gy to 95% of PTV (iGTV + 0.5 cm). Each AAA-based plan was regenerated by overriding the density of the setup margin of PTV by GTV density (modeling tumor-position uncertainty). It was also regenerated with Acuros and the override. The three plans were validated in 4D dose to PTV, after similarly overriding PTV density (phase-specific), accurately calculating with Acuros, and summing the phase-specific plans through organ/dose registration. The Acuros-based plan with the override, the AAA-based plan, and the AAA-based plan with the override provided 4D PTV doses of 63.9, 67.9, and 62 Gy at D95%, respectively, averaged over all patients. The override with Acuros and AAA produced lesser 4D doses, closer to the associated 3D doses, respectively, than that without the override, with better conformity and inhomogeneity. With the override in common, Acuros provided a greater dose to PTV than that by AAA. The Acuros with the override, which was more accurate than the AAA without the override, is clinically recommended.