Dosimetric validation study of a flattening filter free SABR treatment by use of a normoxic PAG gel dosimeter with MRI readout

This paper describes clinical studies of the normoxic PAG gel dosimeter with MRI readout for validation of complex flattening filter free (FFF) treatment delivery techniques. Recently our department implemented the Elekta FFF technology for stereotactic ablative radiotherapy (SABR) treatments using dynamic conformal arc (DCAT) and volumetric arc therapy (VMAT). In this study 6MV FFF DCAT and VMAT plans were analysed using 3D gel dosimetry techniques and compared against standard clinical dosimetry QA tools. Some challenges with this validation study included high dose per fraction for SABR, MRI access time and R ₂-dose calibration errors. A study of the dependency of the dose response on dose rate revealed insignificant dose rate dependence of the normoxic PAG dosimeter up to 20 Gy/min for both photon energies (6 MV and 10 MV). (paper)