Newly introduced hybrid systems that combine an MRI scanner with a linear accelerator for radiation treatment, called MR-linacs, provide an opportunity for the daily acquisition of quantitative MRI... Show moreNewly introduced hybrid systems that combine an MRI scanner with a linear accelerator for radiation treatment, called MR-linacs, provide an opportunity for the daily acquisition of quantitative MRI (qMRI) without increasing patient burden. This allows for the measurement of changes in quantitative MRI biomarkers over time, that may indicate a response to the radiation treatment. In this thesis, the performance of the Unity MR-linac with regards to several qMRI sequences was characterized, showing results similar to diagnostic systems in terms of accuracy and repeatability. Additionally, we found changes in qMRI parameters in patients early during treatment, which indicates potential as biomarkers for treatment outcome. Show less
PurposeSystems 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... Show morePurposeSystems 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 methodsFour 1.5 T MR-linac systems from four institutes were included in this study. T1 and T2 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.ResultsMedian accuracy for T1 ranged over the four systems from 2.7 to 14.3%, for T2 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 T1 ranged from 0.6 to 5.1%, for T2 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 T1, 1.4% for T2, 1.7% for ADC, and 17.9% for DCE. Reproducibility was 11.2% for T1, 2.9% for T2, 2.2% for ADC, and 18.4% for DCE.ConclusionThese 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. Show less
