2570 - Reduced Treatment Volumes for Glioblastoma Result in Lower Rates of Radionecrosis and Lymphopenia: A Pooled Analysis

J. K. Matsui¹, D. Swanson², P. K. Allen², H. K. Perlow³, J. Bradshaw¹, T. Beckham⁴, M. C. Tom⁴, C. Wang⁴, S. Perni⁴, D. N. Yeboa⁴, A. J. Ghia⁴, M. F. McAleer⁴, J. Li⁴, J. D. Palmer⁵, and S. L. McGovern⁴; ¹The Ohio State University College of Medicine, Columbus, OH, ²The University of Texas MD Anderson Cancer Center, Houston, TX, ³Department of Radiation Oncology, The Ohio State University Wexner Medical Center, Columbus, OH, ⁴Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, ⁵Department of Radiation Oncology, The James Cancer Center, Ohio State University Wexner Medical Center, Columbus, OH

Purpose/Objective(s): There is marked variability defining treatment fields for the treatment of glioblastoma (GBM). We performed a retrospective study comparing outcomes of patients treated according to the MD Anderson Cancer Center (MDACC) or Radiation Therapy Oncology Group (RTOG) guidelines and identified differences in treatment-related toxicity. Materials/

Methods: Adult patients with GBM treated with surgery and adjuvant radiation treatment (RT) between 2013–2016 were included in this study. Patients were treated according to institutional preference. Primary outcomes were local control rates, survival outcomes, and radiation-related toxicity. Radionecrosis was characterized through either surgical pathology or MRI, utilizing available perfusion and diffusion techniques. Progression-free survival (PFS) and overall survival (OS) were calculated using the Kaplan-Meier estimator. Univariate and multivariate analyses were conducted using the Cox regression models.
Results: In our study, 257 patients met inclusion criteria with a median age of 60.1 at the time of diagnosis. There were 162 and 95 patients treated according to the MDACC and RTOG guidelines, respectively. Although the gross tumor volumes were similar between the groups, the RTOG cohort had a larger median planning target volume (303.2 cc vs 430.7 cc, P = <.001) and worse PFS (P = .031). There was not a statistically significant difference in OS between treatment strata. Patients treated according to the RTOG protocol experienced higher rates of radionecrosis (34% vs 21%, P = .024) and grade 3+ lymphopenia (15% vs 7%, P = .044).
Conclusion: Patients treated according to the MDACC protocol had smaller treatment volumes, improved PFS, and lower rates of radiation-related toxicity. Prospective investigation is warranted to confirm the differences in outcomes.