1. Center of Molecular Imaging; Radiotherapy and Oncology; Institut de Recherche Expérimentale et Clinique; Université catholique de Louvain; Brussels 1200 Belgium
2. INFN-Dipartimento di Ingegneria Industriale; Università di Roma “Tor Vergata”; Roma 00173 Italy
3. Laboratori Nazionali del Sud; Istituto Nazionale di Fisica Nucleare; Catania 95125 Sicily Italy
4. National Eye Proton Therapy Centre; Clatterbridge Cancer Centre; Wirral CH63 4JY UK
5. Department of Radiotherapy and Oncology; Cliniques Universitaires Saint-Luc; Brussels 1200 Belgium
6. National Physical Laboratory; Acoustics and Ionising Radiation Division; Teddington TW11 0LW UK
7. EBG MedAustron GmbH; Wiener Neustadt 2700 Austria