MR-Guided Focused Ultrasound-Enhanced Liquid Biopsy (Sonobiopsy) for the Definitive Differentiation of True Progression from Pseudoprogression in Glioblastoma: A Prospective Phase II Clinical Trial

Abstract

Abstract Background Distinguishing true tumor progression (PD) from treatment-induced pseudoprogression (PsP) in glioblastoma (GBM) remains a critical imaging challenge. While liquid biopsy offers a potential non-invasive solution, its sensitivity in central nervous system malignancies is restricted by low biomarkers shedding across the blood-brain barrier (BBB). We evaluated the diagnostic efficacy of magnetic resonance-guided focused ultrasound (MRg-FUS)-enhanced liquid biopsy (Sonobiopsy) to transiently open the BBB and enrich plasma circulating tumor DNA (ctDNA) for definitive PD vs. PsP differentiation. Methods In this prospective, single-arm, phase II clinical trial, 42 patients with \(\:IDH\text{-wildtype}\) GBM presenting with ambiguous radiological progression within 12 weeks of completing chemoradiotherapy were enrolled. Low-intensity focused ultrasound (LIFU, 220 kHz) combined with intravenous microbubbles was applied to the region of suspected recurrence. Serial plasma samples were collected pre-sonication and at dedicated post-FUS intervals. Patient-specific \(\:TERT\) promoter mutations and \(\:EGFRvIII\) variants were tracked via droplet digital PCR (ddPCR). The reference standard was established via histopathology or 6-month clinical/radiological follow-up. Results Localized BBB opening was successfully achieved in 100% of procedures. Sonobiopsy induced a significant surge in plasma ctDNA levels, peaking at 30 minutes post-FUS with a median 6.8-fold increase from baseline (\(\:P0.93 (95% CI: 0.84–0.99). No Grade \(\:\ge\:3\) adverse events or intracranial macro-hemorrhages were observed. Conclusions MRg-FUS-mediated Sonobiopsy is a safe, feasible, and highly accurate diagnostic platform that overcomes the limitations of the BBB, enabling precise non-invasive differentiation between true progression and pseudoprogression in glioblastoma patients.