Quantitating Inter-fraction Target Dynamics during Concurrent Chemoradiation for Glioblastoma: A Prospective Serial Imaging Study.

Abstract Background Magnetic Resonance Image-guided Radiotherapy (MRIgRT) has the potential to improve outcomes for glioblastoma (GBM) by adapting to tumor changes during RT. This study quantifies inter-fraction dynamics (tumor size, position, and geometry) based on sequential MRIs obtained during standard 6 week chemoradiation (CRT). Methods Sixty-one patients were prospectively imaged with gadolinium-enhanced T1 (T1c) and T2/FLAIR axial sequences at planning (Fx0), fraction 10 (Fx10), fraction 20 (Fx20), and one-month post CRT (P1M). Gross tumor volumes (GTV) and clinical target volumes (CTV) were contoured at all time points. Target dynamics were quantified by absolute volume (V), volume relative to Fx0 (Vrel), and the migration distance (dmigrate; the linear displacement of the GTV or CTV relative to Fx0). Temporal changes were assessed using a linear mixed effect model. Results Median V at Fx0, Fx10, Fx20, and at P1M for the GTV were 18.4 cm3 (range: 1.1–110.5 cm3), 14.7 cm3 (range: 0.9-115.1 cm3), 13.7 cm3 (range: 0.6-174.2 cm3) and 13.0 cm3 (range: 0.9-76.3 cm3), respectively, with corresponding median Vrel of 0.88, 0.77 and 0.71 at Fx10, Fx20 and P1M (relative to Fx0, p 5 mm during CRT. Conclusions Clinically meaningful tumor dynamics were observed during CRT for GBM, supporting evaluation of daily MRIgRT and treatment plan adaptation.