ESTRO 2023 - Abstract Book

S902

Digital Posters

ESTRO 2023

The median follow-up duration was 56.0 months. The median ART dose delivered was 61.2 Gy (range 45.0–66.0Gy) in 24–34 daily fractions, corresponding to a median EQD2 of 59.16 Gy (range, 43.50–69.12 Gy). In multivariate analysis, larger and higher mitotic count significantly reduced LC (P < 0.001 and P = 0.002), PFS (P < 0.001 and P = 0.006), and OS (P = 0.006 and P = 0.001). Meanwhile, a higher RT dose was significantly associated with improved LC, PFS, and OS. In addition, RT showed a dose-dependent effect on LC, PFS, and OS; local failure, tumor progression, and death were reduced by 12%, 12%, and 16%, respectively, per 1 Gy increase in the dose (EQD2). Conclusion Our results indicate that the dose of ART in AM has a dose-response relationship with LC and survival outcomes.

PO-1128 Pattern of care and post-progression survival in recurrent GBM after TMZ-based chemoradiation

D. Kim 1,2 , J.H. Lee 3,2 , H.I. Yoon 4 , N. Kim 5 , D.H. Lim 5 , J.H. Song 6 , C.W. Wee 7,3 , I.A. Kim 8,3

1 Seoul National University College of Medicine, Radiation Oncology, Seoul, Korea Republic of; 2 Seoul National University Hospital, Radiation Oncology, Seoul, Korea Republic of; 3 Seoul National University College of Medicine, Radiation Oncology, Seoul, Korea Republic of; 4 Yonsei Cancer Center, Yonsei University College of Medicine, Radiation Oncology, Seoul, Korea Republic of; 5 Samsung Medical Center, Sungkyunkwan University School of Medicine, Radiation Oncology, Seoul, Korea Republic of; 6 Seoul St. Mary’s Hospital, College of Medicine, The Catholic University, Radiation Oncology, Seoul, Korea Republic of; 7 SMG-SNU Boramae Medical Center, Radiation Oncology, Seoul, Korea Republic of; 8 Seoul National University Bundang Hospital, Radiation Oncology, Seongnam, Korea Republic of Purpose or Objective This multicenter study aimed to evaluate post-progression survival (PPS) according to the pattern of care in recurrent glioblastoma (rGBM) incorporating molecular genetics. Materials and Methods We evaluated 443 adult patients diagnosed as rGBM after standard temozolomide-based chemoradiation between 2013– 2019 (radiotherapy [RT] dose ≥ 50 Gy). Survival probabilities were evaluated using the Kaplan-Meier method and Cox regression was used to identify the effect of predictors on PPS in isocitrate dehydrogenase wild type (IDH-WT) rGBM patients (n = 414) according to the 2021 WHO classification. Subgroup analyses including propensity score matching (PSM) were performed. In addition, we evaluated the effect of molecular biomarkers on PPS in 315 patients for which molecular data were available. Results Post-progression median follow-up in survivors was 8.4 months (interquartile range 4.6–21.7 months). At first recurrence, 18.6%, 25.8%, 40.1%, and 15.5% underwent best supportive care (no-therapy group), surgery with or without adjuvant therapy (surgery group), chemotherapy (CTx) alone (CTx group), re-RT with or without CTx (re-RT group), respectively. The median PPS was 3.4 months, 13.9 months, 6.6 months, and 10.5 months for no-therapy group, surgery group, CTx group, and re-RT group, respectively (all p < 0.05 between groups). In multivariate analysis for the surgery subgroup (n = 107), surgery with CTx (p = 0.02) and surgery with re-RT (with or without CTx) (p = 0.03) showed significantly improved PPS compared to surgery alone. Surgery with re-RT (with or without CTx) also demonstrated better PPS than surgery with CTx (median PPS 18.6 months vs. 11.2 months; p = 0.07). In multivariate analysis of the no surgery group (n = 230), the re-RT group (with or without CTx) was associated with an improved PPS compared to the CTx alone group (p = 0.01). In the PSM analysis, re-RT with CTx compared to CTx, demonstrated significantly improved PPS (p = 0.03). Genetic analysis revealed that re-RT improved PPS in patients with methylated MGMT promoter (p = 0.01) or homozygous deletion of CDKN2A/B (p = 0.003) in the surgery group. In the no surgery group, PPS was improved by re-RT in patients with WT TERT promoters (p = 0.04). Conclusion In patients with rGBM, surgical resection plus re-RT significantly improved PPS compared to other treatment combinations. For those who are not candidates for surgery, re-RT should also be strongly considered when feasible. Genetic features can further guide who would benefit the most with re-RT in rGBM. C. Chissotti 1,2 , M. Torrisi 1,2 , A. Fodor 1 , C.L. Deantoni 1 , S. Broggi 3 , F. Ferrario 1,2 , L. Giannini 1,2 , S.L. Villa 1,1 , M. Midulla 1,1 , C.R. Gigliotti 3 , I. Dell'Oca 1 , R. Castriconi 3 , F. Zerbetto 1 , C. Fiorino 3 , A. Del Vecchio 3 , S. Arcangeli 4,2 , N.G. Di Muzio 1,5 1 IRCCS San Raffaele Scientific Institute, Department of Radiation Oncology, Milan, Italy; 2 Università degli Studi di Milano Bicocca, School of Radiation Oncology, Milan, Italy; 3 IRCCS San Raffaele Scientific Institute, Medical Physics, Milan, Italy; 4 ASST Monza, Department od Radiation Oncology, Monza, Italy; 5 Università Vita-Salute San Raffaele, Medicine and Surgery, Milan, Italy Purpose or Objective Recurrent primary brain tumors or metastases (mts) are challenging and stereotactic re-irradiation is increasingly used as a salvage treatment. Here we report the experience of our Institute with stereotactic reirradiation in pts with intracranial recurrence. PO-1129 Stereotactic re-irradiation of relapsed intracranic lesions: a monoinstitutional experience

Materials and Methods