Stability of liver position in a shuttle-based workflow for daily online magnetic resonance imaging-guided particle...

Online adaptive particle therapy makes it possible to consider interfractional changes during treatment, and therefore may lead to improved treatment outcomes. The advantages of online adaptive particle therapy may be realized with minimal workflow disruption by employing a shuttle-based daily quasi-online magnetic resonance imaging (MRI)-guided strategy, where the patient remains in the treatment position on a transfer table for MRI at a diagnostic device and subsequent treatment delivery. This study investigated potential liver displacement and deformation while using a shuttle-based workflow.

Fourteen healthy volunteers each underwent four MRI scans in a 1.5 T MRI scanner, with intra-hospital transport simulations between MRI scans. The study proceeded in the following steps: volunteer positioning, first MRI scan (MRI 1), ten-minute time control phase, second MRI scan (MRI 2), short transport phase, third MRI scan (MRI 3), long transport phase, and finally the last MRI scan (MRI 4). In each MRI set, the liver and relevant external outline were contoured. Dice similarity coefficient (DSC) and mean distance to agreement (MDA) were calculated to quantify consecutive shifts between image sets and accumulative shifts over the course of the study.

Median MDA values for the liver (and for the external) contour were 0.6 mm (0.4 mm) for MRI 1 - MRI 2, 0.4 mm (0.5 mm) for MRI 2 - MRI 3, and 0.3 mm (0.7 mm) for MRI 3 - MRI 4. All subjects exhibited MDA values of <1.0 mm (<1.5 mm) and DSC values of >0.97 (>0.98) during transport phases. Outliers for the accumulative shift from MRI 1 - MRI 4 remained at <2.0 mm (<1.8 mm) after approximately 75 minutes.

The study demonstrated the high stability of the liver position in a shuttle-based workflow, a finding that can be used to enhance MRI-guided adaptive treatment strategies in radiotherapy.