BACKGROUND AND PURPOSE: As no guidelines for pencil beam scanning (PBS) proton therapy (PT) of paediatric posterior fossa (PF) tumours exist to date, this study investigated planning techniques across European PT centres, with special considerations for brainstem and spinal cord sparing. MATERIALS AND METHODS: A survey and a treatment planning comparison were initiated across nineteen European PBS-PT centres treating paediatric patients. The survey assessed all aspects of the treatment chain, including but not limited to delineations, dose constraints and treatment planning. Each centre planned two PF tumour cases for focal irradiation, according to their own clinical practice but based on common delineations. The prescription dose was 54 Gy(RBE) for Case 1 and 59.4 Gy(RBE) for Case 2. For both cases, planning strategies and relevant dose metrics were compared. RESULTS: Seventeen (89 %) centres answered the survey, and sixteen (80 %) participated in the treatment planning comparison. In the survey, thirteen (68 %) centres reported using the European Particle Therapy Network definition for brainstem delineation. In the treatment planning study, while most centres used three beam directions, their configurations varied widely across centres. Large variations were also seen in brainstem doses, with a brainstem near maximum dose (D2%) ranging from 52.7 Gy(RBE) to 55.7 Gy(RBE) (Case 1), and from 56.8 Gy(RBE) to 60.9 Gy(RBE) (Case 2). CONCLUSION: This study assessed the European PBS-PT planning of paediatric PF tumours. Agreement was achieved in e.g. delineation-practice, while wider variations were observed in planning approach and consequently dose to organs at risk. Collaboration between centres is still ongoing, striving towards common guidelines.

Centre Antoine Lacassagne Department of Radiation Oncology Nice France

Centre Regional Francois Baclesse Department of Radiation Oncology Caen France

Centre Regional Francois Baclesse Department of Radiation Oncology Caen France; Angers University Hospital Department of Paediatric Oncology Angers France

Centro de Protonterapia Quironsalud Madrid Spain

Clínica Universidad de Navarra Proton Therapy Unit Madrid Spain

Danish Centre for Particle Therapy Aarhus University Hospital Aarhus N Denmark

Danish Centre for Particle Therapy Aarhus University Hospital Aarhus N Denmark; Aarhus University Department of Clinical Medicine Aarhus N Denmark

Heidelberg Ion Beam Therapy Centre University Hospital Heidelberg Department of Radiation Oncology Heidelberg Germany

Hospital S Chiara APSS Medical Physics Unit Trento Italy

Institut Curie Department of Radiation Oncology and Proton Centre Paris France

Institut Curie Department of Radiation Oncology and Proton Centre Paris France; Institut Gustave Roussy Department of Radiation Oncology Villejuif France; Centro de Protonterapia Quironsalud Madrid Spain

Institute of Nuclear Physics Polish Academy of Sciences Kraków Poland

Karolinska University Hospital Department of Radiotherapy Physics and Engineering Stockholm Sweden

Karolinska University Hospital Department of Radiotherapy Stockholm Sweden

MedAustron Ion Therapy Centre Department of Radiation Oncology Wiener Neustadt Austria

National Research Institute of Oncology Kraków Gliwice branch Department of Radiation Oncology Kraków Poland

Paediatric Radiotherapy Unit IRCCS Foundation Institute of Cancer Milano Italy

PARTICLE Proton Therapy Centre University Hospital Leuven Department of Radiation Oncology Leuven Belgium

Paul Scherrer Institute Centre for Proton Therapy ETH Domain Villigen Switzerland

Proton Therapy Centre Czech Department of Radiation Oncology Prague Czech Republic

Radiation Oncology Unit Clinical Department National Centre for Oncological Hadrontherapy Pavia Italy

Radiation Oncology Unit Clinical Department National Centre for Oncological Hadrontherapy Pavia Italy; University of Pavia Department of Clinical Surgical Diagnostic and Pediatric Sciences Pavia Italy

Sahlgrenska University Hospital Department of Therapeutic Radiation Physics Medical Physics and Biomedical Engineering Gothenburg Sweden; Institute of Clinical Sciences Sahlgrenska Academy University of Gothenburg Department of Medical Radiation Sciences Gothenburg Sweden

Skåne University Hospital Hematology Oncology and Radiation Physics Lund Sweden

Trento Proton Therapy Centre epartment of Radiation Oncology APSS Trento Italy

University of Groningen University Medical Centre Groningen Department of Radiation Oncology Groningen the Netherlands

University of Manchester The Christie NHS Foundation Trust Manchester Academic Health Science Centre Manchester United Kingdom

University of Manchester The Christie NHS Foundation Trust Manchester Academic Health Science Centre Manchester United Kingdom; University of Manchester Royal Manchester Children's Hospital The Children's Brain Tumour Research Network Manchester United Kingdom

West German Proton Therapy Centre Essen Essen Germany

West German Proton Therapy Centre Essen Essen University Hospital Essen Germany

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