Speaker
Dr
Matteo Morrocchi
(INFN - Sezione di Pisa)
Description
Hadrontherapy is a powerful radiotherapy technique characterized by a dose deposition highly localized in the tumor target and by a minimal dose released to the surrounding healthy tissues. However, on the path inside the patient, nuclear interactions of the beam with the tissues produce fragments with high Relative Biological Efficiency (RBE). An accurate measurement of fragments production is needed to improve the RBE models and, ultimately, the clinical treatment plans.
The FOOT (FragmentatiOn Of Target) experiment aims at identifying the fragments produced in the human body during hadrontherapy and at measuring their cross sections. A dedicated experimental apparatus is being designed to fully characterize the fragments produced by therapeutical beams on hydrogenated targets. The apparatus is composed of a start counter that provides the trigger information and the start of the time-of-flight (TOF) measurement when crossed by a primary particle. A beam monitoring drift chamber reconstructs the direction and impinging point of the ion beam on the target. A series of silicon pixel detectors track the fragments after the target. Then, a dedicated magnetic spectrometer separates the fragments and a silicon strip detector measures the momentum and allows matching the tracks with the hits occurring in the last two elements in the detection chain dedicated to the particles identification: a ΔE-TOF detector, which measures the energy released in a thin plastic scintillator and the stop of the TOF, and a calorimeter, which measures the kinetic energy of the fragments. In addition, an emulsion spectrometer can be inserted after the target (replacing the magnetic silicon tracker subsystems) to characterize the production of low Z fragments.
The final goal of the FOOT experiment is to measure the differential cross section with 5% uncertainty for ions beams impinging on different targets (e.g., C, C$_2$H$_2$) to be obtained after inverse kinematics reconstruction. The required resolutions to achieve these experimental goals have been estimated by means of a Monte Carlo simulation of the apparatus. In particular, a time resolution σ of approximately 100 ps and a energy resolution of a few % should be accomplished by the final ΔE-TOF detector to comply with the general experimental requirements, the momentum of the fragments should be known with a 5% resolution, and the kinetic energy should be determined by the calorimeter with a 2% resolution.
A large effort has been dedicated to optimize the design of the experiment by means of simulations and first prototypes, which are being developed and characterized with test beams. In this work, the experimental design and the requirements of the FOOT experiment will be discussed, and the first results on the experimental studies that were performed will be presented. In particular, for the ΔE-TOF detector a first prototype was developed and characterized in terms of energy and time resolution, by irradiating it with proton beams of different energies. An energy resolution of 8% and a time resolution of 140 ps were obtained with a 70 MeV proton beam. Even though the performances tended to deviate from the experiment requirements for higher beam energies, they are expected to improve for heavier ions, due to the increase in the released energy. The results of this first prototype are currently being used to improve the design of the ΔE-TOF detector (i.e, bar readout, coupling and wrapping). The limitations and the ongoing improvements will be shown and discussed.
Primary author
Dr
Matteo Morrocchi
(INFN - Sezione di Pisa)
