Optimization of a general-purpose, actively scanned proton beamline for ocular treatments: Geant4 simulations.

The Italian National Center for Hadrontherapy (CNAO, Centro Nazionale di Adroterapia Oncologica), a synchrotron-based hospital facility, started the treatment of patients within selected clinical trials in late 2011 and 2012 with actively scanned proton and carbon ion beams, respectively. The activation of a new clinical protocol for the irradiation of uveal melanoma using the existing general-purpose proton beamline is foreseen for late 2014. Beam characteristics and patient treatment setup need to be tuned to meet the specific requirements for such a type of treatment technique. The aim of this study is to optimize the CNAO transport beamline by adding passive components and minimizing air gap to achieve the optimal conditions for ocular tumor irradiation. The CNAO setup with the active and passive components along the transport beamline, as well as a human eye-modeled detector also including a realistic target volume, were simulated using the Monte Carlo Geant4 toolkit. The strong reduction of the air gap between the nozzle and patient skin, as well as the insertion of a range shifter plus a patient-specific brass collimator at a short distance from the eye, were found to be effective tools to be implemented. In perspective, this simulation toolkit could also be used as a benchmark for future developments and testing purposes on commercial treatment planning systems.

Abstract ID: 241 Geant4 simulation studies of secondary particles emission in hadrontherapy treatments.

The aim of this work is the full simulation with Geant4 (vs. 10.0.p03) of secondary particles emitted during an hadrontherapy treatment with 12C. An accurate study of the ion beam fragmentation is important for both the evaluation of secondaries field inside and outside the target volume (i.e. for radioprotection and biological effects evaluation) and the prediction of nuclear particle interactions and their reaction products. In this study we investigate the depth energy deposition (Bragg curve) and the rate of secondary particles produced in the interaction between 12C and targets of different materials (water and Plexiglas). Simple irradiation setup was first implemented for a preliminary comparison of the Geant4 code with literature studies [1,2]. A good agreement (∼0.04%) was found for the Bragg peak position and the peak-to-plateau ratio (∼0.3%). The complete CNAO [3] (Centro Nazionale di Adroterapia Oncologica) extraction beamline with the target water phantom was then simulated for a characterization of secondary particles energy deposition along the beam axis, angular distributions for outgoing protons, neutrons, heavy secondary particles and prompt gammas. An agreement within 0.03% was found for the Bragg peak position with respect to CNAO data and Fluka simulation for 279.97 MeV/u 12C, highlighting the reliability of the Geant4 simulation. Preliminary results agree with literature studies but experimental data are needed to validate the code. Comparisons with additional simulation codes are foreseen. Geant4 simulations studies to predict the development of different physical processes as a function of the beam energy are also ongoing for both protons and carbon ions.