A novel end-to-end test for combined dosimetric and geometric treatment verification using a 3D-printed phantom

The dosimetric and geometric accuracy are important components to ensure safe patient treatment in radiation therapy. Therefore, these components must be checked during quality control. This work presents a possible solution for the determination of the geometric isocenter deviation in the entire treatment chain. Additionally, the dose measurement of the established end-to-end test workflow measured in the same procedure as the geometric deviation is described. An in-house designed end-to-end test phantom went through the entire procedure of a standard patient treatment and the dosimetric and geometric accuracy were determined. At 3 linear accelerators (linac), the phantom was positioned either with cone beam computed tomography or with surface guidance. In this position, a Winston-Lutz test was performed and the deviations of the gantry, collimator and couch isocenter measurements to the phantom position were determined. Additionally, a dose measurement in the phantom was performed and compared to the dose predicted in the treatment planning system. To validate the results obtained with the in-house designed phantom, comparative measurements with commercial phantoms were performed. According to the performed end-to-end test, 2 out of the 3 linacs showed isocenter variations larger than 1 mm for collimator and gantry rotations and larger than 2 mm for couch rotations. With an isocenter variation of less than 1 mm for collimator and gantry rotations, 1 linac fulfilled the tolerance for stereotactic treatments without couch rotation. With couch rotation, an isocenter variation of less than 2 mm was detected at this linac, which fulfilled the tolerance for IMRT treatments. The mean dose deviation between measurement and treatment planning system was 1.82% ± 1.03%. The results acquired with the UMM phantom did not show statistically significant deviations to those acquired with relevant other commercial phantoms. The novel end-to-end test procedure allows for a combined dosimetric and geometric treatment evaluation. Besides the commonly performed dose end-to-end test the geometric isocenter deviation within a patient treatment workflow was evaluated and categorized for IMRT or SBRT.