ESTRO 2023 - Abstract Book

S540

Sunday 14 May 2023

ESTRO 2023

Oncology, Adelaide, Australia; 13 Royal Adelaide Hospital, Department of Radiation Oncology , Adelaide, Australia; 14 Sir Charles Gairdner Hospital, Department of Radiation Oncology , Nedlands, Australia; 15 Royal Brisbane Womens Hospital, Department of Radiation Oncology , Brisbane, Australia; 16 The Canberra Hospital, Department of Radiation Oncology, Canberra, Australia; 17 The Canberra Hospital, Department of Radiation Oncology , Canberra, Australia; 18 St George Hospital, Department of Radiation Oncology , Kogarah, Australia; 19 Austin Health, Department of Radiation Oncology , Heidelberg, Australia Purpose or Objective To analyse the Radiation Oncology (RO) credentialling programme data from the prospective Australian multisite trial evaluating O-(2-[18F]-fluoroethyl)-L-tyrosine Positron Emission Tomography (FET-PET) in Glioblastoma (FIG) study. [ACTRN 12619001735145]. Up to 210 GBM participants will undergo FET-PET post-surgery and pre-chemo-RT (FET-PET1), one month post chemo-RT (FET-PET2) and at suspected progression (FET-PET3) to determine FET-PET’s role in potential radiotherapy treatment planning and in identifying pseudoprogression and prognostication. Observer agreement of RO target volume delineation are reported here. Materials and Methods Radiotherapy target volumes (GTV, CTV, PTV) is per standard of care (MRI-based) with hybrid post-hoc RT volumes derived by incorporating biologic target volumes (BTV). Nineteen ROs across 10 sites completed TV-MR, TV-MR+FET and CNS organs at risk (OAR) delineation for three different FET-PET1 credentialling cases with BTV delineation by a Nuclear Medicine (NM) expert. Descriptive statistics are given as mean and standard deviation (SD). Pairwise Dice similarity coefficient (DSC) and intraclass correlation coefficient (ICC) with 95% CIs assessed volume overlap and inter-observer agreement, respectively. TV-MR and TV-MR+FET differences were assessed using Wilcoxon signed-rank test. Results GTV-MR+FET, CTV-MR+FET, and PTV-MR+FET were significantly larger (p<0.001) than GTV-MR, CTV-MR, PTV-MR (Table 1). Volume agreement between n=19 ROs was moderate to excellent for GTV-MR (ICC = 0.90; 95% CIs, 0.69-1.00) and good to excellent for GTV-MR+FET (ICC = 0.97; 95% CIs, 0.87-1.00). Observer pairwise DSC calculated for each set of target volumes was >0.80 for each credentialling case. OAR mean DSC was highest for brainstem (0.86 ± 0.06) and eyes (left, 0.91 ± 0.03; right, 0.92 ± 0.02) but lowest for optic chiasm (0.46 ± 0.24). Table 1. Summary of RO target volumes comparing MRI-derived versus MR-FET (mean and standard deviation) for three credentialling cases from the FIG trial demonstrating the hybrid volumes were larger than MRI-only volumes (p<0.001). Conclusion Multi-observer hybrid RT volumes were systematically larger than MR-only derived volumes. The incorporation of the BTV increased GTV agreement. Optic chiasm delineation requires greater consistency. This represents one of the largest credentialling multi-site programmes for RO FET-PET volume analysis in GBM RT contouring. This has resulted in increased national expertise in FET-PET interpretation and incorporation into RT planning in preparation for the prospective FIG trial recruitment phase. PD-0649 Temozolomide and hypofractionated RT versus standard of care in the post-operative setting of GBM. M. Ferro 1,1 , G. Macchia 1 , D. Pezzulla 1 , S. Cilla 2 , C. Romano 2 , S. Cammelli 3,4 , E. Cucci 5 , D. Vallerossa 3 , A. Benini 3 , M. Buwenge 3 , M. Boccardi 1 , A.G. Morganti 3,4 , G.P. Frezza 6 , F. Deodato 1,7 1 Gemelli Molise Hospital – Università Cattolica del Sacro Cuore, Radiation Oncology Unit, Campobasso, Italy; 2 Gemelli Molise Hospital – Università Cattolica del Sacro Cuore, Medical Physics Unit, Campobasso, Italy; 3 IRCCS Azienda Ospedaliero-Universitaria di Bologna, Radiation Oncology, Bologna, Italy; 4 Alma Mater Studiorum Bologna University, Department of Experimental, Diagnostic, and Specialty Medicine - DIMES, Bologna, Italy; 5 Gemelli Molise Hospital – Università Cattolica del Sacro Cuore, Radiology Unit, Campobasso, Italy; 6 Bellaria Hospital, Radiation Oncology Unit, Bologna, Italy; 7 Università Cattolica del Sacro Cuore, Istituto di Radiologia, Roma, Italy Purpose or Objective Adjuvant radiation treatment with standard fractionation (SFRT) and short course hypofractionated radiotherapy (hRT) for elderly and/or poorly performing patients in combination with Temozolomide (TMZ) are the standard of care (SC) for patients with newly diagnosed glioblastoma (GBM). Long-course hRT represents a reliable option that has recently demonstrated excellent tolerance and encouraging outcomes in several phase-I studies, even in younger and fit patients. This retrospective multicenter analysis compares safety and effectiveness of SC versus long course hRT on real world large series of GBM patients regardless of age and performance status. Materials and Methods The study included GBM patients who received SC or long course hRT in the postoperative setting between 2004 and 2021. SC treatment consisted in 60 Gy/30 fractions or 40 Gy/15 fractions according to age, performance status and physician choice. Long-course hRT was delivered into 25 daily fractions with total doses ranging from 60 to 82.5 Gy. Results A total of 265 patients were evaluated retrospectively. One hundred twenty-two patients received SC (96 SFRT and 26 short course hRT) and 143 received long course hRT. Seventy-four percent of SC patients were given TMZ, compared to 99% of those who were given long-term hRT. Patients who received SC were somewhat older than those who did not (median, 62 vs 60 years). The intensity modulated radiation treatment (IMRT) technique was used to treat all of the patients. Patients who received SC had a median overall survival of 18 months against 17 months (p=0.11) when compared to those who