Dose Calculation Accuracy of Beam Models in RadCalc for a 1.5 T MR-Linac

Simple Summary The recent advancement to RadCalc version 7.1.4 marks a significant milestone as an independent dose verification tool tailored to encompass both mechanical and dosimetric intricacies of MR-linacs. Although previous assessments successfully validated the software's efficacy on a 0.35 T MR-linac using v7.1.4, its validation for a 1.5 T MR-linac was restricted to v6.3. This discrepancy prompted an investigation into the software's performance on a 1.5 T MR-linac due to the absence of a specific MR-linac beam-modeling protocol within RadCalc. This study's novelty lies in the rigorous evaluation of calculation accuracy utilizing diverse beam-modeling techniques for the 1.5 T MR-linac. Results of this comprehensive analysis, showcasing RadCalc's calculated doses and their alignment with expected measurements, robustly affirm its credibility and accuracy in dose calculations, particularly within the complex setting of the 1.5 T magnetic field.Abstract The purpose of this study is to evaluate RadCalc, an independent dose verification software, for patient-specific quality assurance (PSQA) in online adaptive planning with a magnetic resonance linear accelerator (MR-linac) of a 1.5 T. Version 7.1.4 of RadCalc to introduce the capability to establish a beam model that incorporates MR field characteristics. A total of six models were established, with one using manufacturer-provided data and the others differing in percentage depth dose (PDD) data sources. Overall, two models utilized PDD data from the treatment planning system (TPS), and three used commissioned PDD data from gantry angles of 0 degrees and 270 degrees. Simple tests on a virtual water phantom assessed dose-calculation accuracy, revealing percentage differences ranging from -0.5% to -20.6%. Excluding models with significant differences, clinical tests on 575 adaptive plans (prostate, liver, and breast) showed percentage differences of -0.51%, 1.12%, and 4.10%, respectively. The doses calculated using RadCalc demonstrated similar trends to those of the PSQA-based measurements. The newly released version of RadCalc enables beam modeling that considers the characteristics of the 1.5 T magnetic field. The accuracy of the software in calculating doses at 1.5 T magnetic fields has been verified, thereby making it a reliable and effective tool for PSQA in adaptive plans.