S376
Clinical - CNS
ESTRO 2026
Mayo Clinic, Rochester, USA. 7 Research, Mayo Clinic, Rochester, USA. 8 Radiation Oncology, University of Florida, St. Johns, USA. 9 Radiation Oncology, UCSF, San Francisco, USA Purpose/Objective: A phase II clinical trial utilizing 18F-DOPA-PET-guided dose escalation radiation therapy (DERT) for glioblastoma demonstrated improved PFS in MGMT- unmethylated patients and OS in MGMT-methylated patients compared to historical controls.1 There are limited previous studies reporting on POF after PET- guided DERT, mixed reports regarding the impact of incorporating PET-guidance on POF, and limited comparative data on recurrence patterns defined by MR vs PET.2-4 This planned secondary analysis sought to compare concordance and discordance between MR and PET recurrence volumes and dosimetric patterns of failure in the setting of AA-PET-guided DERT for glioblastoma and this is the first time the post-treatment PET-defined patterns of failure are reported. Material/Methods: Post-treatment recurrences were delineated on MRI (MRIrecvol) and 18F-DOPA PET (PETrecvol) for the 61 patients who had both imaging series at the MR-RANO timepoint out of the 75 glioblastoma patients treated on the PET-guided DERT clinical trial. MR and PET recurrence volumes were rigidly registered to initial treatment volumes and dose distributions, spatial concordance was quantified, and recurrences were classified as central, in-field, marginal or out-of-field with respect to each of the 3 isodose levels prescribed in the trial. Results: Of the 61 evaluable patients, 92% had at least 1cc of PETrecvol extending outside of the MRrecvol (range 0.1 to 103.6cc). Central failures as determined by MR vs PET at the MR-RANO timepoint were 95% vs 80%, 89% vs 67%, and 49% vs 15% for the 5100cGy, 6000cGy, and 7600cGy isodose levels, respectively. In- field, marginal and distant failures per MR vs PET for the 7600cGy isodose level were 21% vs 25%, 23% vs 46% and 7% vs 15%. The mean concordance of preDERT GTV volumes with the MRrecvol was 0.22, 0.61, and 0.66 for PEThigh(TBR>2.0), MRT1CE+cavity, and the combined PEThigh+MRT1CE+cavity, respectively. The mean concordance of preDERT GTV7600 volumes with the PETrecvol was 0.19, 0.38, and 0.46 for PEThigh, MRT1CE+cavity, and the combined PEThigh+MRT1CE+cavity, respectively. The mean concordance of the preRT PETlow(mean TBR=1.6) volume included in GTV5100 for the DERT trial was 0.48, statistically significantly different than PEThigh (<0.0001). Conclusion: These findings indicate that PET-guided DERT impacts
Conclusion: Significant associations were observed between stress, fatigue, physical activity, KPS and StepCount in patients with GBM before the start of chemoradiotherapy. Fatigue emerged as the primary contributor to perceived stress within this population. Future analyses will explore longitudinal patterns and examine the relationship between stress and progression-free survival upon completion of follow- up. Keywords: Glioblastoma, Stress, Physical activity Comparing MR and PET recurrence volumes and patterns of failure for a phase II glioblastoma clinical trial of 18 F-DOPA-PET directed dose escalated RT Debra H Brinkmann 1 , Deanna Hasenauer 2 , Nadia N Laack 1 , Brian F Kabat 3 , Christopher H Hunt 4 , Val Lowe 4 , Timothy J Kaufmann 4 , Katharine Dooley 3 , Elizabeth Yan 1 , Jann N Sarkaria 1 , Paul D Brown 1 , Sani H Kizilbash 5 , Uhm H Joon 6 , Michael W Ruff 6 , Jing Qian 1 , Diane Vogen 7 , Mark Zakhary 8 , Yan Zhang 1 , Maasa Seaberg 9 , Hok Wan Chan Tseung 1 , Brad J Kemp 1 , Derek R Johnson 4 , William Breen 1 Digital Poster 3002 1 Radiation Oncology, Mayo Clinic, Rochester, USA. 2 Radiation Oncology, Mayo Clinic, Jacksonville, USA. 3 Quantitative Health Sciences, Mayo Clinic, Rochester, USA. 4 Radiology, Mayo Clinic, Rochester, USA. 5 Medical Oncology, Mayo Clinic, Rochester, USA. 6 Neurology,
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