Feasibility Study of Transit Dosimetry (TD) with an Electronic Portal Imaging Device (EPID) in volumetric arc therapy (VMAT) for head and neck cancer (HNC)

Abstract

Introduction: The progress in radiotherapy treatment modalities, such as Intensity Modulated Radiotherapy (IMRT) and Volumetric Arc Therapy (VMAT), introduces considerable complexity. Consequently, the precision of dose delivery in treatment becomes crucial. This dosimetric investigation aims to integrate transit dosimetry into routine clinical procedures and assess outcomes using the gamma analysis methodology.Material and Methods: This dosimetric investigation selected a cohort comprising 30 patients diagnosed with head and neck cancer (HNC) and treated using TruebeamTM & HalcyonTM medical linear accelerators (Varian Medical Systems, Palo Alto, CA). Nine hundred forty-two treatment fluence maps were generated using transit dosimetry and evaluated with gamma analysis. The dosimetry was performed using amorphous silicon (a-Si 1000 and a-Si 1200) electronic portal imaging devices (EPIDs), with gamma analysis criteria of 2% dose difference (DD) and 2 mm distance to agreement (DTA), as well as 3% DD and 3 mm DTA.Results: Daily treatment consistency was assessed by establishing the initial-day fluence as the reference for the entire treatment regimen. In all instances, it was observed that the area gamma value was <1, exceeding 95% compliance when applying the 2%, 2 mm, and 3%, 3 mm criteria. This indicates a favourable agreement between the fluence of the reference day and subsequent treatment sessions throughout the course of treatment.Conclusion: The findings of this dosimetric investigation demonstrate the successful integration of transit dosimetry into routine clinical procedures, providing assurance in dose verification without imparting additional doses to patients. Consequently, this dosimetric approach exhibits potential efficacy for dose verification purposes within clinical settings.