MAGAT Gel Dosimetry Validation in RapidArc^TM Treatment Using Cone-beam CT

Abstract

This study presents the three-dimensional (3D) measurement of the dose distribution delivered using the RapidArc^TM technique and MAGAT polymer gel with cone-beam CT (CBCT) as the dose reading tool. 3D verification of clinical prostate quality assurance (QA) plan was performed and analyzed. The MAGAT normoxic polymer gel consisted of methacrylic acid (monomer purity ＞ 98%), gelatin from procine skin (type A, Sigma Aldrich), and tetrakis (hydroxymethyl) phosphonium choloride (THPC) (80% solution in water). A linear accelerator (Varian) with CBCT was used for radiation delivered and CBCT as dose reader. Corresponding QA plans of RapidArc^TM plans of two prostate cancer cases were selected for dose comparison measurements. 3D gamma comparisons, dose profiles, and 3D volumes were used for evaluation. The dose response curve of the MAGAT polymer gel was acquired as x = 9.79y-13154 with R^2 = 0.9794, where y is the CT number and x is the radiation dose in cGy. The 3D gamma analysis was performed using comparisons of volumes in 90% and 80% isodose between treatment planning system calculation and gel phantom measurement for the prostate cases. In the 90% isodose covered volume, 96.3% of points were within 5%/5 mm (dose difference/distance to agreement) and 91.2% of points were within 3%/3 mm. In the 80% isodose volume, the pass rates were 98.7% and 96.1%, respectively. Excellent 3D dose measurement quality for the RapidArc^TM delivery technique was achieved with the MAGAT polymer gel and CBCT scan.