Room: Exhibit Hall
Purpose: To determine photon plan delivery reproducibility improvement by utilizing robust optimization in lung SBRT. Robust optimization involves allowing the optimizer to consider possible scenarios due to localization uncertainties.
Methods: Eleven SBRT lung patients were planned using VMAT beams. The PTV consisted of five millimeter expansion in all directions from the ITV. Each case was optimized using PTV planning objectives (â€œstandard planâ€?). A second plan was optimized using robust ITV objectives with values of five millimeters isotropically (â€œrobust planâ€?). A satisfactory plan was reached when the dose criteria as defined by NRG protocols was met. The normalization for all plans was D95 of PTV equals 5400 cGy.Each plan was evaluated by recalculating the beams using isocenter perturbations of five millimeters along all major axes. Dose statistics for the eight evaluation studies were averaged and the ratio of that average to the optimized plan value was used for comparison. Dose to 99% (â€œD99â€?) of ITV and maximum dose to the ITV was considered.
Results: The D99 for the averaged evaluated studies more closely matched the robust plans than the standard plans. The average for D99 for robust plans was 0.83 Â± 0.05 vs 0.81 Â± 0.05 for the standard plans. When comparing maximum dose, the ratio for robust plans was 1.03 Â± 0.02 vs 1.01 Â± 0.03 for the standard plans.
Conclusion: Robust planning shows promise as an acceptable way to achieve target coverage when considering localization uncertainties. Robust plans can result in a higher maximum dose. With further development, robust optimization can become an integral part of the planning process.