Author: Albert Admasu, Kayla Alfonso, Maria de la Luz De Ornelas, Nesrin Dogan, Eric Mellon, Yunze Yang 👨🔬
Affiliation: University of Miami, Department of Radiation Oncology, University of Miami, University of Miami Sylvester Comprehensive Cancer Center 🌍
Purpose: Rotational uncertainties in single-isocenter multi-target (SIMT) stereotactic radiosurgery (SRS) HyperArc treatments can cause additional target displacement, potentially degrading overall plan quality. The degree of this deterioration varies among individual metastases. In this exploratory study, we aim to evaluate the dosimetric impact and assess robustness against rotational uncertainties.
Methods: Ten patients who underwent SIMT SRS HyperArc treatments were included in the study. Six synthetic CT datasets were generated from the original simulation CT. In each scenario, a ±1-degree rotation about the isocenter was applied along one of the three rotational axes (yaw, pitch, or roll), resulting in six unique simulated cases representing patient orientation deviations. Dose calculations were performed for all scenarios. Dose volume histogram (DVH) indices from the planning target volume (PTV), including D99% and D1%, were extracted and compared with those from the original treatment plan using the Wilcoxon signed-rank test. The worst-case scenario was analyzed, and its relationship to target volume was investigated.
Results: Twenty-nine metastatic lesions were observed across 10 patients, with a median volume of 0.7 cm³ (range: 0.1–20.7 cm³). D99% of the PTV was significantly reduced in scenarios compared to the original plan (p < 0.001). However, no significant differences were found between scenarios (p-value range: 0.009–0.871). In the worst-case scenario, PTV D99% decreased by 7.2 ± 3.6% (mean ± std) compared to the original plan. A weak negative correlation was observed between the drop in D99% and target volume (r = -0.25). No significance was found across scenarios for PTV D1% (p-value range: 0.056–0.905).
Conclusion: This study provides a comprehensive evaluation of rotational uncertainties in SIMT SRS treatments. The findings emphasize the need to account for these uncertainties per target. These results provide a foundation for future research focused on minimizing uncertainties optimized isocenter placement and robust treatment planning.