New quality control phantom for stereotactic body radiation therapy using radiochromic EBT3 film

Abstract

Introduction Stereotactic Body Radiation Therapy (SBRT) is an increasingly used technique. Due to its particular characteristics a patient specific quality control (QC) is mandatory to ensure an accurate dose delivery. Purpose To develop a dosimetry system consisting of a phantom for insertion of radiochromic films positioned in orthogonal directions for dose measurements. Materials and methods A full film characterization was performed, evaluating megavoltage radiation response, scanning symmetry, angle positioning, after radiation time dependence. Sensitometric curves were performed for a high dose range (1–40 Gy) with 6 MV photons. A PMMA homogeneous and spherical shape phantom was developed, divided in four identical pieces allowing the positioning of the radiochromic films in an orthogonal disposal. Several SBRT treatment plans (conformal, IMRT and VMAT) were measured for validation purpose. The comparison between the calculated and measured doses was made using the gamma index criteria (3%/3 mm) in an in-house software and compared with the results of a commercial system. Results Optimal conditions for film transmission scanning were obtained as well as the correction factors for high uniformity achievement. The spherical shape of the phantom revealed to be advantageous allowing several non-coplanar irradiation angles. Due to the homogeneity of this phantom, heterogeneities problems associated to other commercial systems are not relevant. The passing rate for the gamma index was >95% for the total points analyzed. Conclusions The developed phantom and the system characterization result in a suitable phantom/radiochromic system for SBRT plan dose QC. With a single irradiation, dose distribution in orthogonal planes is obtained, with the characteristic high spatial resolution of these films. Disclosure The authors have no relevant financial or non-financial relationships to disclose.