2501 - Tumor Treating Fields Utilization for Glioblastoma at a Large Multicenter Academic Practice

D. J. Crompton¹, S. Kern², T. Burns², K. Jaeckle³, P. D. Brown⁴, A. Quinones-Jinojosa³, N. N. Laack II⁴, A. W. Bogan⁵, J. H. Uhm⁶, M. Ruff⁶, B. Do², U. Sener⁶, J. L. Peterson¹, S. A. Vora⁷, W. Breen⁴, and D. M. Trifiletti¹; ¹Department of Radiation Oncology, Mayo Clinic, Jacksonville, FL, ²Mayo Clinic, Rochester, MN, ³Mayo Clinic, Jacksonville, FL, ⁴Department of Radiation Oncology, Mayo Clinic, Rochester, MN, ⁵Department of Qualitative Health Sciences, Section of Biostatistics, Mayo Clinic, Scottsdale, AZ, ⁶Mayo Clinic, Department of Neurology, Rochester, MN, ⁷Department of Radiation Oncology, Mayo Clinic, Phoenix, AZ

Purpose/Objective(s): Glioblastoma (GBM) is the most aggressive primary brain tumor, with inevitable recurrence despite trimodality therapy. Tumor Treating Fields (TTF) are included in NCCN guidelines as standard treatment for GBM after improving overall survival in a prospective randomized trial. Still, adoption of TTF has been limited in some real world settings. In this multisite retrospective review we sought to explore the prevalence and validate the efficacy of TTF for GBM patients in a real world dataset. Materials/

Methods: We obtained institutional review board approval for this retrospective study. We identified patients with newly diagnosed GBM between 2014-2023 who received external beam radiotherapy (EBRT) at a large multisite academic institution. Data collected included extent of resection, radiotherapy dose, radiotherapy modality, utilization of tumor treating fields, and presence and location of progression (in-field, marginal, or distant) based on radiographic findings. Kaplan-Meier (KM) curves were generated for PFS and OS. Log-rank comparisons were performed with the KM curves, and location of progression (local vs. marginal vs. distant) was evaluated between the two groups using Chi-square tests.
Results: Six-hundred and seventy (670) patients were included in this retrospective study. All radiation doses and fractionations were included. Of these, one-hundred and seven (107) patients were treated with TTF, (16%). The adoption of TTF did change significantly with time, with increased utilization starting in 2019, with a rate of 20% from 2019 - 2023 (p = 0.024). PFS was significantly improved with the addition of TTF after EBRT (p=0.002), with a median PFS 12.2 months and 9.7 months with and without TTF, respectively. Similarly, overall survival was significantly improved with the addition of TTF after EBRT (p<0.001), with a median OS 24.5 months and 15.6 months with and without TTF, respectively. The location of tumor progression differed between groups, with decreased in-field and increased marginal failures in the TTF group (p = 0.002). On multivariable adjustment controlling for age, gender, ECOG, tumor location, extent of resection, IDH status, and MGMT methylation, TTF use remained associated with OS (p=0.004).
Conclusion: Despite literature demonstrating improved outcomes, widespread adoption of TTF in the treatment of GBM has been met with hesitation with less than one-fourth of modern patients agreeing to receive TTF. In this patient cohort, the prevalence has been increasing since 2019. TTF was associated with improved PFS and OS, consistent with previously published clinical trial results. Our series also suggests there may be an impact of TTF on pattern of failure, with increased marginal failures in the TTF group. Further research, including the TRIDENT study (NCT04471844), will help to understand these results.