ESTRO 2025 - Abstract Book

S2912

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2025

3946

Digital Poster Unlocking the potential of highly conformal external beam radiotherapy planning for locally advanced cervical cancer: Results from EMBRACE-II Anna K Clark 1 , Peter J Hoskin 2,3 , Marianne Assenholt 4 , Peter Bownes 1 , Yvette Seppenwoolde 5 , Monica Serban 6 , Astrid L.H.M.W. van Lier 7 , Mayuri Charnalia 8 , Taran P Hellebust 9 , Barbara Segedin 10 , Supriya Chopra 11 , Jorrit Visser 12 , Geetha Menon 13 , Daniil Zolotuhhin 14 , Laura A Velema 15 , Cornelia G Verhoef 16 , Li Tee Tan 17 , Hanne F Mathiesen 18 , Rachel A Cooper 19 , Ina M Jürgenliemk-Schulz 20 , Christian Kirisits 21 , Jacob C Lindegaard 22 , Remi Nout 5 , Richard Pötter 21 , Kari Tanderup 8,23 1 Department of Medical Physics, Leeds Cancer Centre, St James's University Hospital, Leeds, United Kingdom. 2 Department of Radiation Oncology, Mount Vernon Cancer Centre, Northwood, United Kingdom. 3 Department of Clinical Oncology, The Christie NHS Foundation Trust, Manchester, United Kingdom. 4 Department of Medical Physics, Aarhus University Hospital, Aarhus, Denmark. 5 Department of Radiotherapy, Erasmus MC Cancer Institute, Rotterdam, Netherlands. 6 Radiation Medicine Program, Princess Margaret Cancer Centre, Toronto, Canada. 7 Department of Radiotherapy, University Medical Centre Utrecht, Utrecht, Netherlands. 8 Danish Center for Particle Therapy, Aarhus University Hospital, Aarhus, Denmark. 9 Department of Medical Physics, Oslo University Hospital, Oslo, Norway. 10 Department of Radiotherapy, Institute of Oncology, Ljubljana, Slovenia. 11 Department of Radiation Oncology, Tata Memorial Centre, Mumbai, India. 12 Department of Radiotherapy, Amsterdam University Medical Center, Amsterdam, Netherlands. 13 Department of Oncology, Cross Cancer Institute, University of Alberta, Edmonton, Canada. 14 Department of Radiotherapy, North Estonian Medical Centre, Tallinn, Estonia. 15 Department of Radiation Oncology, Leiden University Medical Center, Leiden, Netherlands. 16 Department of Radiotherapy, Radboud University Medical Center, Nijmegen, Netherlands. 17 Department of Oncology, Cambridge University Hospitals NHS Foundation Trust, Cambridge, United Kingdom. 18 Department of Oncology, Rigshospitalet, Copenhagen, Denmark. 19 Department of Radiation Oncology, Leeds Cancer Centre, St James's University Hospital, Leeds, United Kingdom. 20 Department of Radiation Oncology, University Medical Centre Utrecht, Utrecht, Netherlands. 21 Department of Radiation Oncology, Comprehensive Cancer Center, Medical University of Vienna, Vienna, Austria. 22 Department of Oncology, Aarhus University Hospital, Aarhus, Denmark. 23 Department of Clinical Medicine, Aarhus University, Aarhus, Denmark Purpose/Objective: Technical advancements have driven plan optimisation of external beam radiotherapy (EBRT) for locally advanced cervical cancer (LACC) towards increasing dose conformity. The EMBRACE-II study introduced innovations such as the coverage probability (CovP) technique for simultaneous integrated boost (SIB) of pathological lymph nodes aiming to reduce normal tissue dose [1,2]. This work presents an evaluation of EBRT plan dosimetry achieved in EMBRACE-II. Material/Methods: 1366 patients with LACC treated with chemoradiation according to the EMBRACE-II protocol are included in this analysis. EBRT elective target volume was chosen based on nodal status; categories were small pelvis (N0), large pelvis (N0 or N1 with ≤ 2 pelvic nodes) and large pelvis + para-aortic region (N1 with ≥ 3 nodes or at least one common iliac node or above). Pathological nodes were treated using SIB and CovP. Nodal dose prescription was based on institutional practice with recommended total EBRT + brachytherapy dose of 55-65Gy EQD2 10 . Nodal planning target volume (PTV) margin was 5mm. The CovP technique creates a heterogenous nodal dose distribution, so the centre of the target receives ≥100% and the edge is reduced to 90% of the prescription dose [1,2]. Five groups were defined according to extension of elective target volume and nodal boost location (figure 1). Planning volumes and dose conformity were compared between groups and to patients treated with the same dose and treatment modality in the EMBRACE–I study [3].

Results: Primary PTV volume and volume irradiated to 43Gy (V43Gy) are shown in table 1. V43Gy/PTV dose conformity was