1. Energy deposition and neutron background studies for a low energy proton therapy facility Roxana Rata*, Roger Barlow* * International Institute for Accelerator Applications (IIAA) Abstract Proton therapy is important in the fight agains cancer, because the Bragg peak delivers the dose within the tumour and spares the surrounding tissue. Proton beams from cyclotrons are delivered through passive scattering which requires several studies to calculate the dose in the tumour and in the surrounding tissue. For this study, using FLUKA Monte Carlo code, we simulated a 60 MeV proton beam used to treat ocular tumours at Clatterbridge Centre for Oncology. Many elements of the beam line, such as : nozzle, collimator, water phantom, were modelled. A simple geometry was considered for this set of simulations. The proton energy deposition and the proton fluence in the water phantom were studied, together with secondary neutron energy deposition and secondary neutron fluence for a better understanding of the contribution of the total dose in the target volume. 1. Introduction and Objectives 2. Methods 3. Results The main challenge of conventional radiotherapy is to minimize the dose to healthy tissue. Proton therapy has this advantage of sparing the surrounding organs, reducing the side effects. The proton beams are mainly delivered through passive scattering which causes beam loss in the beam line components, therefore secondary neutron radiation is produced. The neutrons generated during treatment can contribute to the total dose in the target volume and far beyond. The purpose of this work is to calculate and study the dose for protons and also the secondary neutron fluence and the neutron dose in patients, by performing Monte Carlo simulations for Clatterbridge Centre for Oncology. The simulations were performed with FLUKA Monte Carlo code. FLUKA is a powerful tool which can be also used in high-energy physics, shielding, dosimetry, calorimetry etc. The beam used in this simulation was a 60 MeV proton beam. A simple geometry was considered for this initial work: the nozzle, the patient collimator and a water phantom. The proton and the neutron dose and fluence were calculated in the water phantom which simulates the eye tissue (Fig. 1). Fig.1 3D- View of the simulation geometry Fig.2 Neutron fluence in the nozzle Fig.3 Neutron fluence in the water phantom Fig.4 Proton fluence in the nozzle Fig.5 Proton dose in the water phantom The results of the neutron fluence in the nozzle and in the water phantom are plotted in Fig.2 and Fig.3 as function of the depth. It can be seen that the neutron fluence reaches a maximum at the exit of the nozzle, and at the entrance of the water phantom. Fig. 4 represents the proton fluence along the nozzle. Fig. 5 plots the proton dose deposited in the water phantom. The Bragg peak (maximum value) was found at 3 cm depth. As the beam is completely stopped, only secondaries deliver a dose in the rest of the water phantom. Contacts: a.b.surname@hud.ac.uk