SU-FF-T-649: A Comparison of Constant Dose Rate SmartArc and Helical Tomotherapy

Abstract

Purpose: The purpose of this study was to compare constant dose rate and gantry rotation speed intensity modulated arc delivery planned with the new Pinnacle SmartArc planning system and delivered on a Varian 21EX with helical tomotherapy (HT). Materials and Methods: A series of thirty patients that were treated with HT were randomly selected and re‐planned for SmartArc treatment delivery on a Varian 21EX equipped with a 120‐leaf MLC. All SmartArc plans were optimized for delivery using a constant dose rate and gantry speed, which eliminated the need for special VMAT licensees. The same contours, objectives, and prescriptions were used for the HT and SmartArc plans. SmartArc dosimetric verification was performed using a cylindrical solid water phantom with radiographic film and with an ionization chamber array. The MLC log files for the SmartArc treatment deliveries were also downloaded and analyzed. Results: 25 of the test cases were planned with a single arc, while 5 cases were planned with double arcs. The mean delivery time was 2.5 minutes, and the mean number of monitor units was 547. For the prostate test cases, the SmartArc plans were remarkably similar to the tomotherapy plans. The dose uniformity of the PTV for the SmartArc cases was actually superior to the tomotherapy dose uniformity for most of the prostate cases. For both the lung cases and H&N cases, the PTV uniformity and normal tissue DVHs were slight worse in the SmarArc plans as compared to the HT plans. Conclusion: SmartArc treatment plans can be created for delivery using a constant dose rate and gantry rotation speed that are very similar to helical tomotherapy plans for prostate, lung, and simple H&N patients. These plans can be delivered in 2–3 minutes per arc without the need to purchase special VMAT licenses on most accelerators.