Room: Exhibit Hall
Purpose: Halcyon is a single-energy 6 MV, flattening-filter-free (FFF), enclosed-bore linac used clinically for the first time in September 2017. Halcyon has a rigid workflow and fewer moving parts to be better suited for clinics with limited access to vendor support and radiation therapy training. The planning system uses a closed beam model and there are no user-tunable parameters. A Halcyon accelerator was installed and commissioned at our center using a subset of traditional commissioning tests in an effort to expedite the process. Tests were selected to be simple and sensitive to deficiencies or discrepancies in machine or model performance, and included TG-51 reference dosimetry, profile measurements and End-to-End tests.
Methods: Halcyon is TG-51 compliant, and reference dosimetry was performed in a water-tank using a Farmer chamber. Profiles were acquired using an IC Profiler ion chamber array for 10x10 and 28x28 cmÂ² fields. End-to-end tests were performed using a water-equivalent CIRS phantom with PinPoint and Farmer ion chambers and EBT3 film. Two VMAT plans were delivered for each of brain, head and neck, spine, GYN and prostate treatment sites.
Results: Variation of the Halcyon beam over the active volume of the Farmer chamber was less than 0.5% and omission of lead filtering in determination of the beam quality factor resulted in a 0.1% difference in output. End-to-End testing detected a systematic point-dose discrepancy of up to 5.5% resulting from MLC leaf end and edge modeling deficiencies. This modeling deficiency was confirmed through targeted testing.
Conclusion: We commissioned Halcyon within a week and End-to-End testing was sensitive enough to detect an issue in the beam model. TG-51 reference dosimetry was accurately performed without specialized chambers or lead filtering with minimal dosimetric impact. This expedited, Halcyon-specific commissioning approach is simple and accessible to clinics with limited access to physics support or training.