Hamamatsu News 1 / 2020

11 News 2020 Vol.1 Application Report SiPM Technology Increases the Safety of Charged Particle Therapy through Improved Beam Range Verification Introduction Charged particle therapy (CPT), or hadrontherapy, is an advanced radiotherapy technique that uses accelerated proton or carbon ion beams to treat solid tumors with extreme precision. Charged particles release most of their energy at the end of their path (in the region called the Bragg peak) which is dependent on the energy of the particles. This property allows healthcare staff to target cancer cells very specifically, significantly reducing the dose to the surrounding healthy tissue. To verify that the treatment has been delivered according to plan, instruments indirectly measure the position of the Bragg peak in a process called “beam range verification”. The most widely used approach for proton CPT is Positron Emission Tomography (PET). This technique measures the activity of the posi­ tron emitting radionuclides produced by the nuclear interactions between the beam and the traversed tissue. In carbon ion therapy, Interaction Vertex Imaging (IVI) is a promising technique but it is so far clinically unexplored. IVI exploits the production of secondary charged particles upon the nuclear fragmentation of carbon ions in tissue. The charged fragments, emitted at almost the same velocity of the primary ion, exit the patient and pass through a tracking system that reconstructs their emission point and provides information of the primary ion beam’s range. INSIDE (INnovative SolutIons for Dosimetry in hadronthErapy) [1] is an innovative beam range verification system based on the complementary information provided by two different detection systems, a PET scanner and an IVI system called a dose profiler (DP). The INSIDE detector technology is based on inorganic scintillating crystals (for the PET detector) and scintillating fibers (for the DP detector), with read-outs based on Hamamatsu MPPC SiPMs. SiPMs have many properties that make them ideally suited for such a demanding application. Because of their small size and flexibility when designing the sensor, it is straightforward to build a detector configuration optimized for the constraints on the patient set-up and on that beam. The pixel dimension can be adjusted during manufacture to set the desired spatial resolution of ~2 mm. SiPMs have a fast response time which, when coupled with the appropriate electronics read-out scheme, means that data can be processed at the rates on the order of hundreds of kHz. Finally, SiPM technology is fully compatible with the safety requirements of a treatment room, as no high voltages are needed. The first phase of the INSIDE project, which focused on the develop­ ment of the two detectors, was carried out between 2013 and 2016. Patient experimentation and clinical studies represent the second phase of the INSIDE project. These took place in one of the three CNAO treatment rooms where the two detectors have been installed on a movable cart that can be positioned next to the patient bed without interfering with the treatment beam (figure 1). The third phase of the project is full clinical trials. Abstract In charged particle therapy, it is of great importance to monitor the range of the ion beam within patients to guarantee the safety and effectiveness of the treatment. An innovative bi-modal system based on Hamamatsu MPPC Silicon Photo Multipliers (SiPM) technology was developed to monitor range variations and check compliance with the planned treatment. The system is based on the detection of the secondary radiation emitted by nuclear interactions of the beam with the patient’s body. The system, named INSIDE, is the result of a collaboration between the Universities of Pisa, Sapienza Roma, Torino, Bari Polytechnic, the National Institute for Nuclear Physics (INFN), Historical Museum of Physics and the Enrico Fermi Study and Research Center (CREF), the Center of Oncological Hadrontherapy (CNAO). The INSIDE system is now undergoing clinical trials at CNAO.