Fiducial marker placement for hepatocellular carcinoma using magnetic resonance imaging–ultrasound fusion guidance: targeting accuracy and determinants of error (with video)

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PURPOSE: Stereotactic body radiation therapy (SBRT) is effective for hepatocellular carcinoma (HCC), and accurate fiducial marker placement is essential for motion-compensated tracking. We assessed the targeting accuracy and safety achieved with magnetic resonance imaging-ultrasound (MRI-US) fusion guidance and explored factors associated with placement error. METHODS: In this single-center cohort, 44 patients with HCC underwent SBRT with percutaneous fiducial placement under Gd-EOB-DTPA-enhanced MRI-US fusion. A region of interest (ROI) adjacent to the tumor was defined during planning, and the distance difference |A-B| between the planned tumor-ROI distance (A) and the post-procedure tumor-marker distance (B) was used as the targeting error. Predictors of error > 5 mm were explored using a random-forest model. RESULTS: Median targeting error was 6.79 mm (range: 4.06-13.19 mm). In the exploratory model, a longer ROI-tumor distance appeared to have relatively higher feature-importance values for errors > 5 mm, whereas tumor depth and sonographic visibility contributed minimally. During follow-up, four local recurrences and twenty intrahepatic metastases occurred. The cumulative incidence of intrahepatic metastasis was 14.2%, 16.7%, and 24.1% at 180, 360, and 540 days, respectively. Two patients (7.4%) progressed from Child-Pugh class A to B at 6 months. CONCLUSIONS: MRI-US fusion guidance enabled sub-centimeter fiducial placement accuracy in this cohort. A shorter tumor-ROI distance may be associated with smaller targeting error, although this remains exploratory. Tumor depth and visibility showed limited influence on placement accuracy.

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