Technical Note: Flattening filter free beam from Halcyon linac: Evaluation of the profile parameters for quality assurance

Abstract

Introduction: The use of flattening filter free (FFF) beams generated by standard linear accelerators is increasing in the clinical practice. The radiation intensity peaked toward the beam central axis is properly managed in the optimization process of treatment planning through intensity modulation. Specific FFF parameters for profile analysis, as unflatness and slope for FFF beams, based on the renormalization factor concept has been introduced for quality assurance purposes. Recently, Halcyon, an O-ring based linear accelerator equipped with a 6 MV FFF beam only has been introduced by Varian. Methods: Renormalization factors and related fit parameters according to Fogliata et al. ["Definition of parameters for quality assurance of FFF photon beams in radiation therapy," Med. Phys. 39, 6455-6464 (2012)] have been evaluated for the 6 MV FFF beam generated by Halcyon units. The Halcyon representative beam data provided by Varian were used. Dose fall-off at the field edges was matched with an unflattened beam generated by a 6 MV from a TrueBeam linac. Consistency of the results was evaluated against measurements on a clinical Halcyon unit, as well as a TrueBeam 6 MV FFF for comparison. Results: The five parameters in the analytical equation for estimating the renormalization factor were determined with an R 2 of 0.997. The comparison of the unflatness parameters between the Halcyon representative and hospital beam data was consistent within a range of 0.6%. Consistently with the computed parameters, the Halcyon profiles resulted in a less pronounced peak than TrueBeam. Conclusion: Renormalization factors and related fit parameters from the 6 MV FFF beam generated by the Varian Halcyon unit are provided.

Prostate SBRT using O‐Ring Halcyon Linac — Plan quality, delivery efficiency, and accuracy

“…The second constraint is the Halcyon's highest available maximal dose‐rate setting of 800 MU/min. While the Halcyon has a similar beam profile to the Truebeam Linac 23 this is significantly affecting the beam‐on time compared to the Truebeam's VMAT plans (1400 MU/min). For all Truebeam VMAT plans, the dose rate of 1400MU/min was achieved on each arc for this prescription.…”

“…The Halcyon Linac is equipped with a single-energy 6MV FFF beam with a rapid gantry rotation speed of four revolutions per minute. [23][24][25] The Halcyon mean energy and the nominal depth of maximal dose are 1.3 MeV and 1.3 cm, compared to the similar corresponding Truebeam Linac (6MV-FFF, beam) at 1.4 MeV and 1.5 cm, respectively. In contrast to Truebeam platform, the Halcyon is equipped with a newly designed double stacked and staggered 1 cm width MLC layers.…”

“…This novel linac was designed under tight performance specifications in order to improve patient safety and treatment accuracy. The Halcyon Linac is equipped with a single‐energy 6MV FFF beam with a rapid gantry rotation speed of four revolutions per minute 23–25 . The Halcyon mean energy and the nominal depth of maximal dose are 1.3 MeV and 1.3 cm, compared to the similar corresponding Truebeam Linac (6MV‐FFF, beam) at 1.4 MeV and 1.5 cm, respectively.…”

“…We have recently installed a Halcyon V2.0 Linac in our institution and initial acceptance testing and commissioning data confirmed that the machine met manufacturer specifications as described above. [22][23][24][25][26][27][28] We originally installed the Halcyon Linac for conventionally fractionated treatments but decided to commission it for extracranial SBRT treatments because of the superior image quality and performance capabilities aforementioned. To improve dose calculation accuracy, we have used the advanced AcurosXB algorithm [29][30][31] to better account for heterogeneities including SBRT board and Halcyon couch insert.…”

Clinical validation of ring‐mounted halcyon linac for lung SBRT: comparison to SBRT‐dedicated C‐arm linac treatments

“…17 The compact Halcyon Linac is equipped with 6MV FFF beam and is capable of rotating the gantry at a speed of four rotations per minute. 18,19 The mean energy and the nominal depth of maximal dose are 1. twice as fast as the standard millennium MLC, and the stacked design allow for ultralow leakage and transmission of <0.5%. 20,21 Halcyon has less penumbra with a smaller dosimetric leaf gap (DLG) of 0.1 mm compared to traditional C-arm Linacs.…”