2579 - Conventional Target Volume Delineation in Glioblastoma: Insights from a Large Multicenter Academic Practice
Presenter(s)
D. J. Crompton1, S. Agarwal2, S. Kern3, V. Munlapudi4, S. A. Vora5, P. D. Brown6, N. N. Laack II7, J. L. Peterson1, W. Breen7, and D. M. Trifiletti1; 1Department of Radiation Oncology, Mayo Clinic, Jacksonville, FL, 2Tata Memorial Hospital (Mumbai Maharashtra), Mumbai, Maharashtr, India, 3Mayo Clinic, Rochester, MN, 4Florida Atlantic University, Boca Raton, FL, 5Mayo Clinic, Phoenix, AZ, 6Mayo Clinic Cancer Center, Rochester, MN, 7Department of Radiation Oncology, Mayo Clinic, Rochester, MN
Purpose/Objective(s): Glioblastoma (GBM) is the most aggressive primary brain tumor, with inevitable recurrence despite trimodality therapy. The two most common guidelines to define treatment volumes when delivering radiotherapy for GBM have been published by RTOG and EORTC. The impact of these different treatment techniques on pattern of failure (POF), progression-free survival (PFS), and overall survival (OS) remains unclear. We sought to analyze treatment volume delineation difference in patients treated with GBM and the role these differences might play in POF, PFS, and OS.
Materials/Methods: We identified 364 patients with GBM who underwent external beam radiotherapy (EBRT) to a dose of 60 Gy in 30 fractions from 2014–2023 across our three sites. Data were collected through chart review and included patient/tumor characteristics such as age, ECOG, sex, extent of resection, MGMT status, as well as treatment planning data including target volume delineation technique (EORTC vs. RTOG) and linear distance from GTV to PTV (prior to editing for barriers to tumor spread). Kaplan-Meier curves were generated for PFS and OS with log-rank comparisons, and location of failure (local vs. marginal vs. distant relative to the 60 Gy volume) was compared using Chi-square tests. Cox proportional hazards model was performed for multivariate analysis.
Results: 287 (79%) of the 364 total patients were treated with a boost volume to 60 Gy (RTOG) and 76 (21%) planned with a single prescription dose volume to 60 Gy (EORTC). There was no difference in location of failures between groups (p=0.264). Time to intracranial tumor progression was not significantly different between patients planned with RTOG versus EORTC (median 11.6 vs. 12.3 months, respectively; p=0.642). OS was not significantly different between the two groups (median 22.2 vs. 19.4 months, respectively; p=0.884). There was no difference in PFS or OS with increasing linear distance [95% CI 5-25mm] from GTV to PTV-60Gy (p=0.74 and p=0.20, respectively). In patients treated with a boost volume, there was no difference in PFS or OS with increasing linear distance from GTV to PTV-46Gy [95% CI 13-25mm] (p=0.30 and p=0.26, respectively).
Conclusion: This is the largest retrospective series seeking to analyze treatment outcomes between RTOG and EORTC guidelines in GBM. Our analysis revealed no significant differences in PFS or OS between the two approaches. There was also no statistically significant difference in pattern of failure. Linear expansion distance from the GTV to both the low- and high- dose PTVs were not significantly associated with PFS or OS. Ultimately this retrospective study is consistent with previously published literature which suggests that there is no conventional MRI-guided target delineation method which appears superior. Ongoing studies evaluating novel MR techniques and radiotracers in radiotherapy target delineation are warranted.