Feasibility of intracranial stereotactic radiotherapy on Halcyon™ with SGRT and open-face masks

PURPOSE: To assess the clinical feasibility and setup accuracy of using open-face masks in combination with the AlignRT® InBore surface-guided radiation therapy (SGRT) system on the Halcyon™ for intracranial stereotactic radiotherapy (SRT), in the absence of a six degrees-of-freedom (6DoF) couch. MATERIALS AND METHODS: A total of 150 treatment fractions for single brain lesions > 1 cm, across four institutions within the same healthcare organization were retrospectively and prospectively analyzed while splitting patients into four groups: closed-face masks without SGRT on Halcyon™ (G1), closed-face masks with SGRT on Halcyon (G2), open-face mask with SGRT on Halcyon (G3), and open-face mask with SGRT on TrueBeam™ with 6DoF couch (G4). For each group, patient's positioning accuracy was assessed in terms of residual rotational errors extracted following offline rigid registration between the daily CBCTs and the planning CT performed with Eclipse. RESULTS: SGRT significantly reduced residual rotational errors, particularly in yaw and pitch. The use of open-face masks combined with SGRT on Halcyon™ achieved rotational errors (yaw: 0.3 ± 0.3°, pitch: 0.5 ± 0.5°, roll: 0.4 ± 0.3°) approaching those observed with a TrueBeam™ and a 6DoF couch (0.2 ± 0.3° in yaw - p = 0.059, 0.3 ± 0.5° in pitch - p = 0.004, and 0.2 ± 0.3° in roll - p = 0.002). CONCLUSION: This study demonstrates the feasibility and clinically acceptable dosimetry of SRT on Halcyon™ when combining open-face masks with the AlignRT® InBore system under the evaluated clinical conditions in the absence of dedicated SRT systems.