Evaluation of a novel MR-compatible 3D scanner
Kim J, Mertens T, Du D, Doemer A, Dolan J, Xhaferllari I, Chetty I, and Wen N. Evaluation of a novel MR-compatible 3D scanner. J Med Phys 2019; 46(6):e412.
J Med Phys
Purpose: In MR-guided radiotherapy, there exists an unmet need for robust, 3D scanning equipment that can be used for data acquisition during acceptance/ commissioning and periodic QA testing. Avendor-provided MR-conditional prototype 3D scanning system was recently developed and tested on a clinical MR-guided Linac. Methods: Tests were performed using a 0.35 T MR-Linac delivering a 6 MV flattening filter-free beam with a bore diameter of 70 cm. The certified MR-conditional scanning system comprises webbased software, a water reservoir, an electronics control box, a hand pendant, and a 3D rectangular water tank. Scanning was performed over three sessions using 85 and 80 cm SSDs, 5 and 10 cm depths, and field sizes (FS) ranging from 0.4 × 0.2 cm2 to 27.2 × 24.1 cm2. MR-compatible A26 (field) and A1SL (reference) ionization chambers were used for FS > 2.5 × 2.5 cm2 and an Edge diode detector for smaller FS. For each session, inline and crossline profiles as well as percent depth dose (PDD) measurements were acquired. Profiles and PDDs were compared across sessions and to Monte Carlo simulations and commissioning measurements acquired using either a 1D tank with manual changes in detector position applied between measurements or 2D ion chamber array. Results: For PDDs at 10 × 10 cm2 FS, dmax was constant and PDD10x was within 1% (mean: 1.4 cm and 61.6%, respectively) across all sessions. At 80 cm SSD, dmax was within 0.5 mm and PDD10x within 1% of baseline commissioning measurements. Both crossline and inline flatness and symmetry at 10 × 10 cm2 and 27.2 × 24.1 cm2 FS were within 1% of baseline measurements acquired during commissioning and field widths for all FS were within 1 mm of nominal values. Conclusion: Performance of a novel, MR-compatible 3D scanning water tank was assessed in a clinical MR-Linac system. Profile and PDD measurements were acquired using ion chambers and diodes. Data was consistent between scanning sessions and with previously acquired commissioning data.