Gadolinium dose enhancement determination by unlaminated EBT3 films irradiated with 192Ir brachytherapy source

Abstract

In this work, Gafchromic® EBT3 films were carefully delaminated and resealed with a thin mylar film of 12 μm for implementing accuracy measurements of Gd dose enhancement by a192Ir brachytherapy source. The intervened dosimeters were previously characterized in terms of their quality intervention (mechanical damage and dosimetry modification). The dose enhancement measurements were implemented in a phantom formed by a set of acrylic slabs of 30 × 30 × 0.5 cm3 machined to contain in the central axis 2 vials of 1.25 × 1.25 × 4.5 cm3 which were filled with a 20 mg/ml solution of Gd agents and with water simulating a tumoral phantom doped and undoped with Gd. In the center of the phantom, a machined acrylic slab was placed to introduce the 2.5 mm flexible guide of GammaMedplus iX equipment to position the source. Fragments of delaminated and resealed EBT3 of 0.9 × 4 cm2 were placed inside the second vial and 0.5 cm away from it, at 1.95 cm and 3.55 cm from the radioactive source respectively, to measure simultaneously the tumor dose enhancement and the radiation shielding produced at a proximal zone. CT images of the phantom were taken to prescribe 5 Gy to 1.95 cm (EBT3 film position) using a Varian BrachyVision™ planning system. Films were read out by a flatbed scanner Epson V750 PRO, 48 h after irradiation. The measurements in both tumor and healthy tissue were repeated ten times in each condition to analyze the uncertainties of the complete experimental realization. The results showed variations in the response of the intervened dosimeters, less than 1.7% for the range of interest and average fluctuations in the readout of 4.6%. The implemented dosimeter showed the feasibility of measuring dose enhancement by 192Ir source of 13 ± 7% for the concentration studied. Additionally, radiation shielding up to 6% was obtained, consistent with what has been reported in the literature.