RadCalc as a calculation-based PSQA solution for online Adaptive RT with Elekta Unity MR-Linac

Abstract
 

Purpose: MR Linac offers Online Adaptive RT (oART) which improves treatment accuracy by modifying initial treatment plan to the anatomy of the day. Calculation-based PSQA on daily MR images is the preferred method for oART. RadCalc enables beam modelling that considers characteristics of 1.5T magnetic field and no other commercial secondary dose calculation software considers the MR effect in dose calculations.

Methods: 6 different ELEKTA MRL models are configured in RadCalc. 1 model is using pre-configured data from RadCalc, and the other 5 models are using the same beam data except for the PDD data. Due to the design of the bore, beam data are not only collected at 0 degrees but also at 270 degrees. Some of the models use PDD data from the TPS, while some are using PDD acquired at 0degrees, 270degrees and both 0 and 270 degrees. Point dose comparison at the centre of target between RadCalc MCI and MONACO TPS was performed. 577 daily adaptive plans were evaluated. Point dose comparison between RadCalc MCI and ion chamber measurements in ArcCheckMR was also performed.

Results: Average differences from calculated PDD data were below 1% which indicates that RadCalc accurately accounts for MR effects in homogenous materials. Comparison between measured PDD and calculated PDD shows strong correspondence in overlapping regions which suggests that calculated PDD can effectively substitute measured PDD data. Doses calculated using RadCalc demonstrated similar trends to those of PSQA-based measurements.

Conclusion: Accuracy of RadCalc for MR-Linac has been verified and it is a reliable and effective tool for PSQA in adaptive plans.

Reference:

Sung, J., Cho, Y., Kim, J. W., & Lee, H. (2024). Dose calculation accuracy of beam models in RadCalc for a 1.5 t MR-Linac. Cancers, 16(3), 526. https://doi.org/10.3390/cancers16030526