Room: ePoster Forums
Purpose: The purpose of this study is to evaluate the robustness of three optimization methods for the spot position errors in spot scanning proton therapy.
Methods: We assumed several model errors for the spot position on the spot scanning system in Nagoya Proton Therapy Center (NPTC). We created treatment plans with the model errors and evaluated the dose impact to target and OARs using the treatment planning system (VQA ver. 3.0.1) and evaluated the robustness of three optimization methods. Model errors were 4 patterns that were Â± 1 mm in the perpendicular to the beam. We created treatment plans for head and neck cancer treated with Single Field Uniform Dose (SFUD) and Intensity Modulated Proton Therapy (IMPT). For IMPT, we also compared worst case optimization (WCO) plans with no WCO plans. We evaluated 4 SFUD and 4 IMPT plans of head and neck cancer.
Results: We compared dose to target and OARs and investigated several dose indexes of all plans. The maximum absolute error in PTV (D98) for SFUD, WCO IMPT and no WCO IMPT were 0.59Â±0.23 Gy, 0.98Â±0.33 Gy, 1.05Â±0.52 Gy, respectively. The maximum absolute error in optic nerve (Dmax) were 1.26Â±0.82 Gy, 1.58Â±0.67 Gy, 1.94Â±1.18 Gy. The maximum absolute error in chiasm (Dmax) were 1.49Â±0.38 Gy, 1.55Â±0.83 Gy, 1.84Â±0.94 Gy. From the analysis of DVHs, WCO IMPT was more robust than no WCO IMPT, but SFUD was the most robust to spot position errors.
Conclusion: We evaluated the robustness of three optimization methods to spot position errors in spot scanning proton therapy. Although IMPT had a better dose distribution than SFUD, SFUD was the most robust to spot position errors.