Evaluation of Multiple Planning Strategies for Lung SBRT Using Version 18 of Eclipse
Abstract
Purpose
To identify a preferred institutional strategy for planning LUNG SBRT cases on version 18 of ECLIPSE using the photon optimizer (PO), four planning strategies were compared. The first strategy involved limiting the number of monitor units during optimization and the use of Varian SBRT NTO (LiMU+NTO). The second strategy consisted of limited inverse optimization on a manually planned conformal arc using the SBRT NTO at the final resolution levels (CARC+NTO). The third strategy used Varian Aperture Shape Control (ASC) configured to “very high” with the SBRT NTO throughout optimization (ASC+NTO). The final strategy involved only the SBRT NTO with high priority (NTO). Strategies were compared within the treatment planning system to identify possible dosimetric advantages over the current institutional strategy and were end‑to‑end tested.
Methods
Thirteen previously treated lung cancer cases were re-planned with all strategies, and the resulting plans were compared with the delivered plan. Strategies were evaluated in terms of median dose spillage (ΔV50%), conformity index of the 100% isodose volume (CI), difference in monitor units (ΔMU%), modulation complexity score (MCS), and dose-to-OARs. Additionally, radiochromic film measurements were acquired using the Quasar Motion Phantom (QMP) (Modus Medical Devices Inc, London, ON) with a cedar film insert with an acrylic sphere acting as a target. The QMP was set up to follow a sinusoidal trace, and an irregular breathing cycle will also be used for comparison.
Results
All strategies except ASC+NTO produced clinically acceptable plans in terms of organ‑at‑risk sparing and V50%. Additionally, the SBRT NTO and CARC+NTO strategies improved CI while decreasing MSC and increasing MUs. Only SBRT NTO consistently decreased V50%.
Conclusion
The SBRT NTO strategy yields clinically superior lung SBRT plans with highly conformal target doses while decreasing median dose spillage and improving OAR sparing; however, it increases the number of MUs and plan complexity.