1176 - Practice Variation In IMPT Treatment Planning in Oropharyngeal Cancer: Dose Differences and Expected Impact on Toxicity Outcome
Presenter(s)
J. A. Langendijk1, H. P. van der Laan2, D. Edge3, B. Vischioni4, T. Williamson5, B. Koczur6, K. C. Crama7, G. Pasqualina8, A. Goedgebeur9, J. M. Perez10, F. Pansini11, F. L. B. Garrote12, V. Jóhannesson13, F. J. P. Hoebers14, D. A. Romanello15, V. Vondracek16, U. V. Elstrøm17, J. Espen Dalen18, S. Makocki19, and T. Lomax20,21; 1Department of Radiation Oncology, University of Groningen, University Medical Center Groningen, the Netherlands, Groningen, Netherlands, 2Department of Radiation Oncology, University Medical Center Groningen, University of Groningen, Groningen, Netherlands, 3, Department of Radiotherapy University College London Hospitals NHS Foundation Trust, London, United Kingdom, 4Radiation Oncology Unit, Clinical Department, National Center for Oncological Hadrontherapy (CNAO), Pavia, Italy, 5Paul Scherrer Institute, Villigen, Switzerland, 6Heidelberg Ion Beam Therapy Center (HIT), Heidelberg, Germany, 7Holland Proton Therapy Centre Delft, Delft, Netherlands, 8Department of Radiotherapy and Radiosurgery, IRCCS Humanitas Research Hospital, Milan, Italy, 9Department Radiation Oncology, University Hospitals Leuven, Leuven, Belgium, 10Quironsalud Protontherapy Center, Madrid, Spain, 11Division of Medical Physics, IEO European Institute of Oncology IRCCS,, Milan, Italy, 12Oslo University Hospital, Oslo, Norway, 13Skåne University Hospital and Skandionkliniken, Uppsala, Sweden, 14Department of Radiation Oncology (Maastro), GROW Research Institute for Oncology and Reproduction, Maastricht, Netherlands, 15department of Radiation Oncology, MedAustron Ion Therapy Center, Wiener Neustadt, Austria, 16Ion Beam Applications, Prague, Czech Republic, 17Danish Center for Particle Therapy, Aarhus, Denmark, 18Haukeland University Hospital, Bergen, Norway, 19OncoRay – National Center for Radiation Research in Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden, Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany, 20Center for Proton Therapy, Paul Scherrer Institute, Villigen, Switzerland, 21Department of Physics, ETH Zurich, Zurich, Switzerland
Purpose/Objective(s):
Proton therapy use for head and neck cancer is increasing, yet IMPT planning varies widely across centers. Despite ICRU guidance on target coverage, no consensus exists on optimal OAR-sparing goals or how to balance competing planning priorities, leading to potential variation in plan quality and predicted toxicities. This ESTRO-EPTN (European Proton Therapy Network) project aims to map current IMPT practice to support future harmonized planning recommendations. We hypothesize that substantial inter-center variation exists in both IMPT planning strategies and NTCP-predicted toxicities for HPV-positive oropharyngeal cancer (HPV+ OPC).
Materials/Methods:
A single HPV+ OPC benchmark case with predefined targets and OARs was distributed to 18 proton centers, each generating an IMPT plan using routine practice. Dosimetric data for major OARs were collected, and clinical impact was evaluated using validated NTCP models for grade =2 and =3 dysphagia and xerostomia. Centers also completed a questionnaire on planning techniques, prioritization, robustness settings, and image-guidance practices.
Results:
Substantial inter-center variation was observed in key planning parameters, including number of fields, prioritization of OAR sparing, number of robustness scenarios, skin-avoidance methods, and the use of CBCT.
Dose distributions to major OARs, such as the pharyngeal constrictor muscles, oral cavity, and parotid and submandibular glands, showed wide variability in mean doses (Table 1).
Corresponding NTCP-analyses demonstrated notable differences in predicted risks of dysphagia grade =2 (12-30%), dysphagia grade =3 (2-9%), xerostomia=2 (39-58%) and xerostomia=3 (11-19%). Compared with a reference VMAT plan, IMPT plans were less favorable for dysphagia in 16 centers (89%) and for xerostomia in 13 centers (72%).
Conclusion:
This first phase of the ESTRO-EPTN project highlights considerable heterogeneity in IMPT planning strategies resulting in significant dose differences and expected clinical outcomes across European proton therapy centers in HPV-positive OPC. These findings emphasize the urgent need for planning harmonization. Future phases will introduce consensus-based guidelines and incorporate AI-driven planning to promote greater consistency and ultimately improve patient outcomes.