Purpose: To investigate the current practice patterns in image-guided proton therapy (IGPT) for brain tumours.

Methods: A multi-institutional survey was distributed to European particle therapy centres to analyse the current practice of IGPT for neuro-oncology. The survey was subsequently used for driving a DELPHI consensus analysis aiming at defining the minimum requirements and the optimal workflow.

Results: Seven centres participated in the survey on proton therapy for brain tumours. All reported access to pencil beam scanning and rotating gantries; one also used passive scattering. Supine positioning with standard immobilisation tools was common, while prone and paediatric-specific methods were rare. Multimodal imaging with CT and MRI was standard; PET use was limited and SPECT absent. Rigid registration between imaging modalities was widely used, though MR imaging in treatment position was uncommon. Verification practices varied. Six centres joined the DELPHI consensus, reaching agreement on minimum requirements for immobilisation, imaging for treatment planning, image registration and pre-treatment setup. Disagreement remained on robustness criteria, imaging frequency, and dose tracking, highlighting the need for unified clinical guidelines and workflow optimisation.

Conclusion: There is generally agreement across European proton centres, but variability remained in key components of treatment planning, verification and workflow optimisation, including the frequency and modality of control imaging, plan robustness criteria, and treatment position imaging protocols. These differences reflect both local resource availability and the absence of harmonised guidelines. The minimal requirements for image guidance in brain proton therapy achieved good consensus level and will be very useful for new centres.