| Sumario: | Simple Summary: A new planning and optimization algorithm, VOLOTM Ultra, has been introduced for tomotherapy planning. This algorithm includes new features that significantly changed how treatments are planned and optimized. We have reoptimized 1056 treatment plans for 36 patients and six anatomical locations (breast with and without nodes, head and neck, cervix, esophagus, and hypofractionated). The results allowed us to characterize the impact of the accelerated treatment, leaf open/close time cutoff, normal tissue objective weight, number of optimization rounds, and use of rings on dosimetric quality and beam on time. The aim was to give a better understanding of the impact of the planning parameters on tomotherapy treatments to improve the quality of treatment for patients undergoing tomotherapy. Background: This work aimed to determine the optimum VOLOTM Ultra algorithm parameters for tomotherapy treatments. Methods: 1056 treatment plans were generated with VOLOTM Ultra for 36 patients and six anatomical locations. The impact of varying four parameters was studied: the accelerated treatment (AT), leaf open/close time (LOT) cutoff, normal tissue objective (NTO) weight, and number of iterations. The beam-on time and dosimetric metrics were quantified for the target volumes and organs at risk (OARs). Delivery quality assurance measurements were obtained for 36 plans to assess the delivery accuracy. Results: The mean beam-on time for the helical tomotherapy and TomoDirect (TD) plans decreased by 26.6 ± 2.8% and 17.4 ± 4.3%, respectively, when the accelerated treatment parameter was increased from 0 to 10, at the expense of the planning target volume (PTV) coverage (2% lower D98%) and OAR dose (up to 15% increase). For TD plans, it seems preferable to systematically use an AT value of 10. Increasing the number of iterations beyond six seems unnecessary. In this study, an NTO weight of approximately 10 appears to be ideal and eliminates the need to use rings in the treatment plan. Finally, no correlation was found between the leaf open/close time cutoff and the delivery accuracy, while a leaf open/close cutoff of 60 ms seemed to degrade dosimetry quality. Conclusion: Optimal values for the AT, LOT cutoff, NTO weight, and number of optimization rounds were identified and should help improve the management of patients whose tomotherapy treatments are planned with VOLOTM Ultra.
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