University of Texas Southwestern Medical Center Dallas, TX
L. Giuliani Schmitt1, M. Dohopolski1, T. Patel2, A. R. Patel2, S. Barnett2, M. Youssef3, N. Shaikh3, X. Cai1, Z. Wardak1, R. D. Timmerman1, and T. Dan1; 1Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX, 2Department of Neurological Surgery, University of Texas Southwestern Medical Center, Dallas, TX, 3Department of Neurology, University of Texas Southwestern Medical Center, Dallas, TX
Purpose/Objective(s):Reirradiation for recurrent glioblastoma (rGBM) frequently uses traditional statichypofractionated schemes. Here we evaluate the impact of Personalized Ultra-Fractionated Stereotactic Adaptive Radiotherapy (PULSAR), our institutional adaptive treatment paradigm delivering high-dose radiation in bi-weekly to monthly pulses, on patient outcomes. We hypothesize that PULSAR will offer similar outcomes to traditional approaches.Materials/
Methods: We retrospectively reviewed rGBM patients re-irradiated on 1.5T MRI-Linac at our institution(2021-2023). Demographics, tumor and treatment characteristics were collected. Minimal clinical target volume expansions were used; planning target volume (PTV) expansions were uncommonly used. Overall survival (OS) and progression-free survival (PFS) were assessed using Kaplan-Meier analyses in statistical software. Subgroup analyses, using Log-rank tests, evaluated the impact of variables gathered. Cox proportional hazards models were used for multivariate analysis, with a p-value < 0.05 indicating statistical significance. Results: Among the 33 patients (34 treatments), median age was 52.5 years, ECOG performance status 1, and 76.5% were IDH-wild type. The interval between last RT and reirradiation averaged 13.6 months (1.6 -- 131.6 months). Surgeries included 5 biopsies, 4 subtotal resections, and 2 gross total resections. Median dose of 25 Gy (5 Gy – 36 Gy) was delivered in 5 pulses (1 -- 6) in 2–4-week intervals, with 56% patients receiving planned treatment. Median PTV were 12.9 cm³, 55.0 cm³, 108.2 cm³, and 38.0 cm³ for PTVs 35, 30, 25 and 20, with adaptations performed in 41% of pulses. Median volume changes were +90.41% (PTV 35), -11.88% (PTV 30), +53.89% (PTV 25), and +3.31% (PTV 20). Concurrent treatments included temozolomide (TMZ) for 10 patients, “other” for 21, and none for 3. Acute cerebral edema grade =3 was observed in 7 patients (median onset 70 dayspost-RT) and late cerebral edema grade 3 in one patient (220 days). Marginal progression was noted in 5 patients (median 169 days), in-field in 13 (141 days), and distant in 11 (146 days). The median follow-up, OS and PFS were 17.4, 7.3, and 5.5 months. Univariate analysis showed significant OS and PFS improvement with doses =25 Gy, completion of RT, and ECOG <2. OS and PFS improved in those with prior resection, and IDH mutation and TMZrespectively. Improved OS with MGMT methylation and surgical resection on multivariate analysis. Conclusion: PULSAR shows promising outcomes for rGBM, with improved OS and PFS in treatments = 25 Gy and completed protocols, especially for patients with better ECOG performance and concurrent TMZ. This study underscores PULSARs potential in enhancing treatment precision and patient response in a challenging cohort but further prospective research is needed.
