2611 - Monitoring Glioblastoma Dynamics during Chemoradiation on the 1.5T Magnetic Resonance Imaging-Linear Accelerator
Presenter(s)
K. E. Jamora1, D. Mathieu1,2, S. C. Fong1,3, M. Wada1, R. Khor1, M. Tacey1, B. Harris1, S. Fisher1, B. Geary1, H. Gan4, L. Cher4, E. Lau5, A. Gonzalvo6, R. O'Brien7, D. Wilding-McBride7, A. Scott8, and S. P. Ng1; 1Department of Radiation Oncology, Austin Health, Melbourne, VIC, Australia, 2Centre hospitalier de l'Universite de Montreal, Montreal, QC, Canada, 3Department of Radiation Oncology, Peter MacCallum Cancer Centre, Melbourne, VIC, Australia, 4Department of Medical Oncology, Austin Health, Melbourne, VIC, Australia, 5Department of Radiology, Austin Health, Melbourne, VIC, Australia, 6Department of Neurosurgery, Austin Health, Melbourne, VIC, Australia, 7Medical Radiations, School of Health and Biomedical Sciences, RMIT University, Bundoora, VIC, Australia, 8Department of Molecular Imaging and Therapy, Austin Health, Melbourne, VIC, Australia
Purpose/Objective(s): Glioblastoma (GBM) changes during chemoradiation are typically assessed using pre- and post-treatment magnetic resonance imaging (MRI), but frequent imaging remains challenging. MRI-guided radiation therapy (MRgRT) enables real-time monitoring of tumor dynamics throughout treatment. This study utilizes an MRI-linear accelerator (MR-linac) to quantify daily interfraction variations in tumor volume and position during treatment.
Materials/Methods: GBM patients suitable for chemoradiation using a 1.5T MR-linac were enrolled in a prospective study. T2/FLAIR hyperintensity regions were contoured at baseline and succeeding fractions. Tumor dynamics were assessed using absolute volume, percentage change in volume relative to fraction 0 (V%), and migration distance representing the linear displacement of volume relative to fraction 0. Tumor changes were compared between patients with early progression (defined as progression within 6 months post-treatment) and those without early progression, as well as between methylated and unmethylated/unknown MGMT promoter status groups.
Results: Among 26 patients, 10 received 4005 cGy/15 fractions, and 16 received 6000 cGy/30 fractions of chemoradiation. The mean absolute volumes at Fx0, Fx1, Fx10, Fx15, Fx20, and Fx30 were 60.53 cm³, 62.14 cm³, 60.24 cm³, 57.10 cm³, 61.19 cm³, and 65.90 cm³. The corresponding mean V% at Fx1, Fx10, Fx15, Fx20, and Fx30 were 3.93%, 8.56%, 8.60%, 17.14%, and 39.24%. In early progressors, V% at these fractions were 7.76%, 22.79%, 31.44%, 57.63%, and 108.57%, while in non-early progressors, values were 3.01%, 3.12%, -1.55%, -11.04%, and -10.70%. Among methylated tumors, V% were 7.72%, 9.64%, 0.93%, -11.43%, and -7.67%, while unmethylated/unknown tumors had 1.61%, 7.89%, 13.4%, 30.13%, and 60.57%. The mean migration distances at Fx1, Fx10, Fx15, Fx20, and Fx30 were 0.96 mm, 3.25 mm, 4.89 mm, 7.07 mm, and 7.68 mm. In early progressors, migration distances were 0.94 mm, 2.70 mm, 4.42 mm, 4.96 mm, and 6.04 mm, while in non-early progressors, values were 0.91 mm, 3.50 mm, 5.14 mm, 9.47 mm, and 9.79 mm.
Conclusion: Tumor dynamics during chemoradiation may vary based on MGMT methylation status and could potentially serve as an indicator of early post-treatment progression. Early progressors showed greater volume increases, particularly after Fx10, while treatment responders had stable or decreasing volumes. Methylated tumors showed a trend toward volume stability or reduction, whereas unmethylated/unknown tumors exhibited progressive growth. Migration distance was greater in treatment responders, suggesting possible tumor deformation, while early progressors had lower migration, possibly due to continuous expansion. These findings suggest distinct tumor evolution patterns, with potential implications for treatment adaptation and response monitoring.