Feasibility and accuracy of quantitative imaging on a 1.5 T MR-linear accelerator

Abstract Purpose Systems for magnetic resonance (MR-) guided radiotherapy enable daily MR imaging of cancer patients during treatment, which is of interest for treatment response monitoring and biomarker discovery using quantitative MRI (qMRI). Here, the performance of a 1.5 T MR-linac regarding qMRI was assessed on phantoms. Additionally, we show the feasibility of qMRI in a prostate cancer patient on this system for the first time. Materials and methods Four 1.5 T MR-linac systems from four institutes were included in this study. T 1 and T 2 relaxation times, and apparent diffusion coefficient (ADC) maps, as well as dynamic contrast enhanced (DCE) images were acquired. Bland–Altman statistics were used, and accuracy, repeatability, and reproducibility were determined. Results Median accuracy for T 1 ranged over the four systems from 2.7 to 14.3%, for T 2 from 10.4 to 14.1%, and for ADC from 1.9 to 2.7%. For DCE images, the accuracy ranged from 12.8 to 35.8% for a gadolinium concentration of 0.5 mM and deteriorated for higher concentrations. Median short-term repeatability for T 1 ranged from 0.6 to 5.1%, for T 2 from 0.4 to 1.2%, and for ADC from 1.3 to 2.2%. DCE acquisitions showed a coefficient of variation of 0.1–0.6% in the signal intensity. Long-term repeatability was 1.8% for T 1 , 1.4% for T 2 , 1.7% for ADC, and 17.9% for DCE. Reproducibility was 11.2% for T 1 , 2.9% for T 2 , 2.2% for ADC, and 18.4% for DCE. Conclusion These results indicate that qMRI on the Unity MR-linac is feasible, accurate, and repeatable which is promising for treatment response monitoring and treatment plan adaptation based on daily qMRI.