Adaptive Radiotherapy (ART) Using In Vivo Portal Dosimetry Constancy on Halcyon LINAC for Head and Neck Cancer VMAT

Introduction: This study evaluated the potential of the Varian Halcyon LINAC and its associated Portal Dosimetry (PD) software, using in vivo megavoltage portal images, as a tool for in vivo portal dosimetry constancy (IVDc) in head and neck cancer (HNC) patients receiving volumetric modulated arc therapy (VMAT).Material and Methods: A retrospective study included ۱۰۰ HNC patients (mean age ۵۸.۴ ± ۹.۲ years; ۷۲ males, ۲۸ females) treated with three arc VMAT plans on the Halcyon LINAC. A prescription dose of ۷۰۰۰ cGy was delivered over ۳۵ fractions to high risk volumes and ۶۳۰۰ cGy to intermediate risk volumes. Portal images from all fractions (۳۵۰۰) and arcs (۱۰,۵۰۰) were compared to first fraction baselines via gamma analysis with a ۳%/۲ mm criterion and ۹۵% passing threshold. Phantom tests evaluated sensitivity to thickness changes.Results: Gamma passing rates exhibited a steady decline over the treatment course (R²=۰.۹۷۲۴), with an average ۹۳.۹ ± ۳.۶% passing rate, dropping below ۹۰% after ۲۵ fractions. Failures correlated with thickness variations exceeding ۱ cm, which were detected with high accuracy during phantom tests. Pretreatment patient-specific QA yielded ۱۰۰% pass rates.Conclusion: This study demonstrates the potential of the Halcyon LINAC's integrated PD system and Varian PD software for IVDc in HNC patients treated with VMAT. The results confirm the feasibility of using in vivo MV portal images acquired on the Halcyon LINAC to assess dose consistency throughout treatment.

کلیدواژه ها:

Head and Neck Neoplasms Radiotherapy Intensity ، Modulated Radiotherapy Planning Computer ، Assisted