Clinical experience of the normoxic PAG gel dosimeter using a flattening filter free beam for SABR treatments with MRI readout

Abstract

Three-dimensional dosimeters are of great interest in a progressive radiotherapy facility utilising complex and advanced treatment techniques such as high dose rate dynamic stereotactic ablative radiotherapy (SABR). In our Centre we recently introduced 6 MV flattening filter free (FFF) dynamic conformal arc (DCAT) and volumetric arc therapy (VMAT) as treatment options for our lung patients using 4D-IGRT on the Elekta platform. Treatments of this nature however, are difficult and complex to validate and mainstream quality assurance tools are often limited in their ability to satisfy clinical demands. Clinical requirements dictate that for short fractionation high dose regimes such as SABR that the geometric and dosimetric parameters of a plan are well known and within tight tolerances. Three-dimensional polymer gel dosimeters offer significant advantages for encapsulating and validating steep 3D dose distributions of this complexity. This paper describes clinical studies of the normoxic PAG gel dosimeter (Venning et al., 2005) with MRI readout for validation of complex FFF treatment delivery techniques. Patient plans were analysed using 3D gel dosimetry techniques and compared against standard clinical dosimetry QA tools. There are numerous challenges involved when operating a clinical gel dosimetry service including high dose per fraction for SABR leading to dosimeter saturation, MRI access, expertise and time. These issues will be covered in the presentation.