Priyanka Agarwal*, Rajesh Kinhikar, Rakhi Berman, Naveen Mummudi, Shrikant Kale and Jaiprakash Agarwal
Aim: To study the dosimetric differences of using different energy in the case of lung SBRT VMAT treatment planning.
Materials & Methods: A total of 12 patients with stage I non-small cell lung cancer (36 plans) with PTV of 63.3cc to 115.4cc were selected for this study retrospectively. Three different treatment plans were generated using 6XFF, 6XFFF, and 10XFFF energies with same optimization constraints to deliver 60Gy in 8 fractions with two partial arcs on Eclipse TPS. A progressive resolution optimizer and Acuros algorithm were employed for optimization and dose calculation, respectively. Planning evaluation was carried out qualitatively and quantitatively for PTV and OARs doses, as per RTOG guidelines (0813/0915). Delivery quality assurance for each plan was performed using the PTW Octavious-4D phantom. In addition, the point dose was verified using a thimble ion chamber.
Results: The Coverage Index (CI) (p<0.05) was the same 96%±0.008 for 6XFF and 6XFFF, while 94% ± 0.012 for 10XFFF. The 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, 96.3 ± 1.03 and 97.4 ± 1.3 for 6XFF, 6XFFF and 10XFFF, respectively. Mean point dose difference in % between TPS and measurement was 2.2 ± 0.4, 2.4 ± 0.9 and 2.68 ± 0.9 for 6XFF, 6XFFF and 10XFFF respectively.
Conclusion: We found 6XFFF to be the optimal choice based on OAR sparing with no compromise for coverage and conformity index.
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