Free-breathing GRASP MRI Shows Limited Ability to Represent Full Respiratory Motion in Liver Cancer Radiotherapy
A retrospective study of 54 liver cancer patients found that free-breathing GRASP MRI best matches the mid-respiratory phases (30%–60%) of 4D-CT, with optimal alignment at the 50% phase. 4D-CT is the established gold standard for assessing respiratory-induced organ motion in stereotactic body radiation therapy (SBRT). The findings suggest GRASP MRI should be combined with 4D-CT rather than used alone to ensure accurate tumor target delineation during liver SBRT planning.
Researchers conducted a retrospective analysis of 54 patients undergoing liver stereotactic body radiation therapy (SBRT) to evaluate whether free-breathing golden-angle radial sparse parallel (GRASP) MRI can adequately represent respiratory-induced organ motion across all breathing phases. Image fusion between GRASP MRI and each respiratory phase of 4D-CT was performed using an in-house registration program, with fusion quality measured by maximum cross-correlation coefficient (MCC). The 50% respiratory phase of 4D-CT showed the highest fusion quality with GRASP MRI, and no statistically significant differences were found compared to the 30%, 40%, and 60% phases. However, fusion quality declined significantly outside the mid-respiratory window, with poor alignment observed at the 0%, 10%, 20%, 80%, and 90% phases (P < 0.001). Two blinded radiation oncologists independently validated these results, with subjective clinical relevance scores remaining above 4 out of 5 for phases 30%–70% but falling below 4 for extreme respiratory phases. The authors conclude that GRASP MRI alone cannot represent the full range of respiratory motion and should be supplemented with 4D-CT or other dynamic imaging modalities to ensure comprehensive motion assessment and accurate target volume definition in liver SBRT.
What's missing
The study is retrospective and limited to 54 patients from a single institution, which may limit generalizability. It does not report inter-observer variability between the two radiation oncologists or address how different liver tumor sizes, locations, or patient breathing patterns may affect GRASP MRI performance. The clinical impact of using only mid-respiratory phase matching on actual treatment outcomes (e.g., local control rates, toxicity) is not assessed. Additionally, comparisons with other MRI acquisition techniques are absent.
What different sources said
- arXiv physicsCenter
The Role of Free-breathing GRASP MRI in Accurate Phase Matching with 4D-CT for Motion Representation in Liver Cancer Radiotherapy
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