Patient-specific quality assurance in SBRT treatments using 3D polymer gel dosimetry

Abstract

In stereotactic body radiation therapy (SBRT), patient-specific quality assurance (PSQA) is required due to the complex dose distributions delivered. In this context, polymer gels are considered reliable as a three-dimensional dosimeter. This work used polymer MAGIC-gel sealed in 2 mm thin-wall glass spheres to assess the three-dimensional (3D) dose distribution imparted to patients and compared the results with that provided by the treatment planning system. Four SBRT treatments targeting vertebral, ilium, pelvic lymph node and lung regions were selected for this study. A computed tomography (CT) scan of each glass sphere was obtained, and the patient treatment plan was superimposed on the glass sphere CT image. Thereafter, the spheres were irradiated under similar conditions to the patient using a Varian TrueBeam linear accelerator. A high-spatial resolution optical CT scanner was used to read the glass sphere containing the gel. Planned and delivered 3D dose distributions were compared quantitatively through 3D gamma passing rates at several selected acceptance criteria and qualitatively through the evaluation of dose-profiles, isodose-curves, and dose-volume histograms. We observed that the overall 3D gamma passing rate exceeded 90% at acceptance criteria of 2% dose difference and 2 mm distance-to-agreement for a dose threshold of 20%. The results of this study suggest that the polymer MAGIC-gel sealed in thin-wall glass spheres in conjunction with the optical CT readout method is a suitable PSQA system for SBRT treatments.