ESTRO 2021 Abstract Book

S1661

ESTRO 2021

registrations per patient. All observers received an initial overview of Monaco functionality, and an introduction to MRI- based gynaecological anatomy. Rigid translational registrations were undertaken independently using soft tissue alignment of the cervix in all three planes.

Resulting translations, time taken for registration and confidence scores using Likert scale of 1(not confident) to 5 (extremely confident) were recorded and compared between cohorts (RT MR , RT CT , RT I ) using descriptive statistics. Following a 14 day break, the process was repeated with an education guide (developed by a multi-disciplinary team including therapeutic/diagnostic radiographers and clinicians) being introduced aiming to standardize image registration by highlighting the most relevant anatomic regions. Results Collation of the post-intervention registrations for RT MR and RT CT cohorts is on on-going. However, the initial mean registration confidence was higher in the RT MR group for MR-CT and MR-MR registrations, 2.8 and 3.2 respectively compared to the RT CT group 2.6 and 2.8. The RT CT group were more confident with CBCT-CT registrations (mean 2.1(RT CT ) vs 1.7 (RT MR )).

The mean pre-intervention MR-CT registration confidence levels for RT I cohort slightly lower (2.6). There was no statistically significant difference in registration time between all cohorts and all registration methods, with combined group mean registration times of 2.3 (1.0, 2-5), 2.4 (1.9, 1-10), 2.1(0.6, 1-4) minutes for CBCT-CT, MR-CT and MR-MR respectively. Variation in inter-observer registration was smallest in like-for-like image registration methodologies (CBCT-CT and MR-MR) for the RT MR cohort and in the CT guided methodologies in the RT CT cohort. Table 1 summarizes pre intervention inter-observer registration variations for the RT CT and RT MR cohorts. Conclusion Based on preliminary data it is anticipated that the combination of both a dedicated image registration guide and familiarity with MRI and the MRL specific software will reduce inter-observer variation and time while increasing confidence in undertaking at-treatment MR-CT and MR-MR registrations. are similar to RT MR (3.2 vs 2.8) with the RT CT PO-1950 Added value of FDOPA PET to radiotherapy of glioblastoma multiforme: Single institution experience D. Sipos 1,2,3 , Z. Laszlo 2 , Z. Toth 3,4 , P. Kovacs 2,2 , A. Gulyban 5 , I. Repa 2,2 , A. Kovacs 3,1,6 , F. Lakosi 2,1 1 University of Pécs, Department of Medical Imaging, Kaposvár, Hungary; 2 “Moritz Kaposi” Teaching Hospital, Dr. József Baka Diagnostic, Radiation Oncology, Research and Teaching Center, Kaposvár, Hungary; 3 University of Pécs, Doctoral School of Health Sciences, Pécs, Hungary; 4 ., Somogy County Moritz Kaposi Teaching Hospital, MEDICOPUS Healthcare Provider and Public Nonprofit Ltd., Kaposvár, Hungary; 5 Institut Jules Bordet, Medical Physics Department, Bruxelles, Belgium; 6 University of Debrecen, Department of Oncoradiology, Debrecen, Hungary Purpose or Objective To investigate the added value of 6- [18F] -fluoro-L-3,4-dihydroxyphenylalanine (FDOPA) PET to radiotherapy planning in glioblastoma multiforme (GBM). Materials and Methods From September 2017 to December 2020 17 patients with GBM received external beam radiotherapy up to 60 Gy with concurrent and adjuvant temozolamide. Target volume delineations followed the European guideline with 2 cm safety margin (CTV) around the contrast enhanced lesion+resection cavity on MRI (GTV). All patients had FDOPA hybrid PET/MRI followed by PET/CT before radiotherapy planning. PET/CT data was co-registered rigidly to the planning CT/MRI. PET segmentation followed international recommendation: T/N 1.7 (BTV1.7) and T/N 2 (BTV2.0) SUV thresholds were used for biological target volume (BTV) delineation. Direct use of PET/MRI images in the TPS was not feasible, thus PET/MRI and PET/CT based segmentation were compared with linear regression analysis MICE Toolkit (version 1.0.6, NONPI Medical AB,