Room: AAPM ePoster Library
Purpose: estimate the dosimetric differences of various energies in case of Lung Stereotactic body radiotherapy (SBRT) volumetric modulated arc therapy (VMAT) treatment planning.
Methods: patients of stage I non-small cell lung cancer (33 plans) having planning target volume (PTV) from 63.3cc to 240cc were selected for this study retrospectively. All patients were planned thrice for Truebeam using 6XFF, 6XFFF and 10XFFF energies having similar optimization constraints with their maximum available dose rates 600, 1400 and 2400 MU/min respectively. Dose prescription was 60Gy in 8 fractions and planned with two partial arcs on Eclipse TPS. Progressive resolution optimizer (PRO) and Acuros algorithm were employed for optimization and dose calculation respectively. Each plan evaluation was carried out qualitatively and quantitatively for PTV and organ at risk (OARs) doses as per RTOG guidelines (0813/0913). All 6XFFF and 10XFFF plans were scaled w.r.t. 6XFF plans for OARs comparison. Delivery quality assurance (DQA) for each plan was performed with PTW Octavious-4D Phantom. In addition, point dose was verified with thimble ion chamber.
Results: coverage Index (CI) (p<0.05) was found same (96% ±0.008) for 6XFF and 6XFFF, while 94%±0.012 for 10XFFF. Mean conformity Index (COIN) (p>0.05) for 6XFF, 6XFFF and 10XFFF was 0.956±0.036, 0.957±0.037 and 0.936±0.043 respectively. Mean treatment time (p<0.05) for 6XFF, 6XFFF and 10XFFF was 3.7±0.41, 1.55±0.21 and 1.13±0.13 minutes respectively. Mean gamma (3%,3mm) was 96.5±1.12(94.7 to 98.7), 96.3±1.03(94 to 97.5) and 97.4±1.3(94.1 to 99.2) for 6XFF, 6XFFF and 10XFFF respectively. Mean point dose (%) difference between TPS and measurement was 2.2±0.4(1.16 to 3.08), 2.4±0.9(1.06 to 4.15) and 2.68±0.9(0.75 to 4.2) for 6XFF, 6XFFF and 10XFFF respectively.
Conclusion: was found to be optimal choice based on OAR sparing with no compromise on CI and COIN. However gamma evaluation was relatively better (1.14%) during DQA for 10XFFF over both the energies.