A dosimetric and treatment delivery comparisons of the Halcyon and TrueBeam stereotactic plans for one or more brain metastases.

Background: The purpose of this investigation was to determine if the Halcyon linear accelerator could provide a comparable level of treatment quality and efficiency to the TrueBeam linear accelerator when used for brain stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT) in individuals with multiple brain metastases. The goal was to evaluate Halcyon as a potential substitute for TrueBeam. Materials and methods: A review of prior treatments was performed, examining data from 30 individuals (encompassing 64 lesions) who had undergone TrueBeam SRS and SRT procedures. These existing treatment plans were then replanned for the Halcyon platform. Both treatment platforms employed 6 MV-FFF beams; however, the TrueBeam utilized a maximum dose rate of 1400 MU/min, while the Halcyon operated at 800 MU/min. Various dosimetric parameters, such as target coverage, doses to organs at risk, and gradient index, were compared, along with treatment delivery efficiency metrics, including monitor units and beam-on time. Statistical analysis was used for comparisons. Portal dosimetry was implemented for quality assurance. Results: Both platforms achieved comparable target coverage and organ at risk (OAR) sparing, meeting Hypofractionated Treatment Effects in the Clinic (HyTEC), Quantitative Analyses of Normal Tissue Effects in the Clinic (QUANTEC), and the American Association of Physicists in Medicine Task Group 101 (AAPM TG-101) guidelines. Halcyon showed statistically equivalent gros tumor volume/planning target volume (GTV/PTV) doses, but a slightly higher gradient index (clinically insignificant). Beam-on time was longer for Halcyon due to its lower dose rate, but overall treatment time was potentially shorter due to efficient setup. Halcyon exhibited better QA pass rates. Conclusion: Halcyon offers comparable dosimetric quality and treatment efficiency to TrueBeam for brain SRS/SRT. Its streamlined workflow and reduced setup time offer clinical advantages in high-volume centers, despite limitations like the lack of rotational couch correction and lower maximum dose rate.