ESTRO 2023 - Abstract Book

S539

Sunday 14 May 2023

ESTRO 2023

Conclusion We present a large cohort of patients with CRC BM treated with SRS. Uncontrolled extracranial disease at the time of BM diagnosis was associated with both poorer OS and higher risk of intracranial progression. Higher BED was correlated with better local control, independent of tumor size. Future analyses will explore the genomic features that may further explain differences in oncologic outcomes. PD-0647 Conventionally fractionated versus hypofractionated radiotherapy in elderly glioblastoma patients H.I. Lee 1 , J. Kim 2 , I.A. Kim 3 , J.H. Lee 1 , H.I. Yoon 2 , C.W. Wee 4 1 Seoul National University Hospital, Department of Radiation Oncology, Seoul, Korea Republic of; 2 Yonsei Cancer Center, Department of Radiation Oncology, Seoul, Korea Republic of; 3 Seoul National University Bundang Hospital, Department of Radiation Oncology, Seongnam, Korea Republic of; 4 SMG-SNU Boramae Medical Center, Department of Radiation Oncology, Seoul, Korea Republic of Purpose or Objective This study aimed to compare the outcomes of conventionally fractionated radiotherapy (CFRT) and hypofractionated radiotherapy (HFRT) in elderly glioblastoma (e-GBM) patients and identify subgroups who may benefit from CFRT. Materials and Methods Patients aged 65 years or older underwent surgical resection and radiotherapy for newly diagnosed IDH-wildtype e-GBM between 2006 and 2021 were included in this multicenter cohort study. Patients who were planned for a ≥ 6-week or ≤ 4- week radiotherapy were regarded as being treated with CFRT or HFRT, respectively. The median radiotherapy dose in the CFRT and HFRT group were 60 Gy in 30 fractions and 45 Gy in 15 fractions, respectively. Median survival (MS) was calculated from the date of surgery. Results A total of 239 and 221 patients who underwent CFRT and HFRT were included, respectively. 84% of patients were treated with temozolomide (TMZ)-based chemoradiation. With a median follow-up of 17.7 months (range, 3.3–149.9) for survivors, the MS was 17.5 months for CFRT group and 13.5 months for HFRT group, respectively (p<0.001). In multivariate analysis, CFRT (vs. HFRT) was a significantly favorable factor for overall survival in both patients older than 65 years (p=0.020) and 70 years (p=0.021). TERT promoter mutation (p=0.028) and TP53 mutation (p<0.001) were significantly adverse genetic factors for survival. In patients with unmethylated MGMT promoters, TMZ marginally improved MS compared to RT alone (14.1 vs. 10.7 months; p=0.072) in univariate analysis. However, in multivariate analysis of these patients, only the use of CFRT over HFRT significantly improved MS (p=0.003). Finally, recursive partitioning analysis identified three prognostic subgroups; class I = MGMTmeth/KPS ≥ 70; class II = MGMTmeth/KPS<70 or MGMTunmeth/GTR; class III = MGMTunmeth/residual disease (p<0.001). Compared to HFRT, CFRT significantly improved MS in class I (39.7 vs. 22.5 months; p=0.003) and class II (16.9 vs. 13.5 months; p=0.001), but not in class III (10.8 vs. 10.4 months; p=0.637). Conclusion Compared to HFRT, CFRT can be a more effective strategy for selected e-GBM patients. Further prospective studies are needed to establish an optimal guideline for e-GBM patients. PD-0648 FET-PET incorporation for GBM radiotherapy planning: multi-site FIG Study credentialling programme E. Koh 1 , N. Barry 2 , M.A. Ebert 3 , A. Moore 4 , R.J. Francis 5 , S.P. Ng 6 , M. Back 7 , B. Chua 8 , M. Pinkham 9 , A. Pullar 9 , C. Phillips 10 , J. Sia 11 , P. Gorayski 12 , H. Le 13 , S. Gill 3 , J. Croker 14 , N. Bucknell 3 , C. Bettington 15 , F. Syed 16 , K. Jung 17 , J. Chang 1 , A. Bece 18 , C. Clark 18 , M. Wada 19 , A.M. Scott 19 1 University of New South Wales, Radiation Oncology, Liverpool Hospital, New South Wales, Sydney, Australia; 2 The University of Western Australia, School of Physics, Mathematics and Computing, Crawley, Australia; 3 Sir Charles Gairdner Hospital, Department of Radiation Oncology, Nedlands, Australia; 4 Trans Tasman Radiation Oncology Group, TROG Cancer Research, Newcastle, Australia; 5 Sir Charles Gairdner Hospital, Department of Nuclear Medicine, Nedlands, Australia; 6 Austin Health, Department of Radiation Oncology, Heidelberg, Australia; 7 Royal North Shore Hospital, Department of Radiation Oncology, Sydney, Australia; 8 Royal Brisbane Womens Hospital, Department of Radiation Oncology, Brisbane, Australia; 9 Princess Alexandra Hospital, Department of Radiation Oncology, Brisbane, Australia; 10 Peter MacCallum Cancer Centre, Department of Radiation Oncology, Melbourne, Australia; 11 Peter MacCallum Cancer Centre, Department of Radiation Oncology , Melbourne, Australia; 12 Royal Adelaide Hospital, Department of Radiation