Marco Pullia

We developed a novel gamma-ray detection system (TIARA) for range monitoring in Particle Therapy. The system employs Cherenkov-based gamma-ray detection modules arranged around the target or patient, operated in time coincidence with a fast plastic beam monitor (described in a separate paper). This work focuses on the design and comprehensive characterization of the gamma-ray detection module. It consists of a monolithic PbF2 crystal (2 × 1.5 × 1.5 cm³) coupled to a 2 × 2 SiPM matrix from Hamamatsu. A series of beam tests at different clinical facilities (MEDICYC and ProteusOne in France, CNAO in Italy) enabled the determination of the detector time resolution under various conditions, with values ranging from 222 to 283 ps FWHM (Full Width Half Maximum). Monte Carlo simulations including the optical response of PbF₂ allowed for the determination of the detection efficiency as a function of particle type and energy. For the final TIARA prototype, which will be composed of 30 modules, an overall detection efficiency of 0.45% is expected. Comparison with experimental data confirmed that the modules are effectively insensitive to neutrons, yielding an excellent signal-to-noise ratio (SNR), with an estimated SNR of 17 for a module placed at 25 cm from the 148 MeV proton beam axis. These features translate into high range accuracy: while the performance varies with beam energy and irradiation conditions, a range accuracy of 3.3 mm at 2σ significance level was achieved at low intensity with 63 MeV protons at MEDICYC, for a small irradiation spot of ~ 10⁷ protons.

Objective. Prompt-gamma imaging is a promising technique for in-situ range verification during proton therapy, with the potential to reduce range uncertainties. Current prompt-gamma cameras typically rely on mechanical collimators, among which the knife-edge slit (KES) and multi-parallel slit (MPS) collimators are the two most widely studied concepts. In this work, we propose a novel inverted (INV) collimator concept that uses a single bar of high-density material to cast a gamma-ray shadow onto the central region of a pixelated scintillation detector. In addition to advantageous properties such as a high efficiency and a large field of view, the INV collimator also features a significantly reduced weight compared to the KES and MPS collimators. Approach. We optimized and compared the different collimator designs with respect to their simulated statistical range retrieval precision. To overcome the computational time limitations associated with full Monte Carlo (MC) simulations, we developed a new hybrid simulation tool based on a dedicated fixed-ray calculation of the collimator combined with precalculated MC simulations of prompt-gamma emission and detection. This approach enables rapid parameter optimization while incorporating all experimentally relevant effects, such as the detector spectral response and an empirical neutron background. Main results. We present optimized collimator geometries for the MPS, KES, and the novel INV collimator. The INV collimator achieves a statistical range retrieval precision (2 σ ) of 2.2 mm at a proton beam energy of 100 MeV and 2.4 mm at 150 MeV for 10 8 protons irradiating a homogeneous tissue-equivalent phantom, demonstrating performance comparable to the optimized KES design. In addition, we present a first experimental validation of the INV collimator concept at the CNAO hadron therapy facility in Pavia, Italy, demonstrating agreement between the hybrid simulation and measurements. Significance. These results suggest that the INV collimator is a promising concept for future prompt-gamma cameras, offering competitive performance and facilitating clinical implementation due to its reduced device weight.

Prompt Gamma Timing (PGT) is a promising technique for in vivo range verification in particle therapy, exploiting the time-of-flight between primary particles and prompt gamma rays emitted by nuclear interactions. PGT distribution is highly sensitive to beam energy and target density, which, under controlled detector positioning, enables real-time monitoring of particle range, detection of morphological changes, and support for adaptive treatment strategies. Objective: This study investigates for the first time the application of PGT in carbon ion therapy. Approach: Measurements were performed using a dedicated detection system composed of a silicon strip sensor for primary ion timing and a LaBr3(Ce) scintillator read out by a SiPM matrix for secondary radiation. Carbon ion beams with energies of 166.41, 268.86, and 398.84 MeV/u irradiated a homogeneous 30.0 cm PMMA target at CNAO (Pavia, Italy). The secondary radiation detector was positioned at four off-beam positions to assess the robustness of the PGT technique. Monte Carlo simulations based on Geant4 were conducted for all configurations to evaluate agreement and predictive capability. Main Results: A quantitative bin-by-bin comparison of experimental and simulated PGT intensities demonstrated strong agreement within the 95% confidence interval, with no incompatible bins at 166.41 MeV/u, at most 1% at 268.86 MeV/u, and up to 8% at 398.84 MeV/u, depending on detector position. Prompt gammas were identified as the dominant contribution to the detected signals, particularly for detector positions upstream with respect to the primary particle beam, minimizing signal contamination from neutrons and charged fragments. Significance: The validated experimental - simulation framework confirms the capability of the proposed PGT system to resolve energy-dependent differences and highlights its potential for detecting clinically relevant changes in the particle beam range, supporting further development toward real-time monitoring in carbon ion therapy.

The Superconducting Ion Gantry (SIG) project, developed in collaboration with INFN, CERN, CNAO, MedAustron and FEAC Engineering, aims to improve cancer treatment by creating compact and lightweight ion gantries. These systems allow for precise, non-coplanar irradiation while reducing damage to surrounding healthy tissues. A key element of this project is a 4 T curved superconducting dipole magnet, made with Nb-Ti Rutherford cables, featuring a 1.65 m curvature radius and an 80 mm aperture, designed for a 430 MeV/u carbon ion gantry. This study addresses the mechanical challenges of the magnet's curvature, maintained by two curved steel clamps, and the use of an indirect cooling system. To test the design and assembly process, a 30$^\circ$ demonstrator is being developed as a step toward the final 45$^\circ$ dipole. Building on previous 2D mechanical studies of the SIG curved dipole, this work presents a 3D FEM analysis of the magnet support structure. The vertical preload system aims to maximize the contact between the coil, collars, and yoke, evaluated through the percentage of elements in contact during assembly, cooldown, and energization. At the coil ends, the longitudinal preload system provides restraint and prevents additional movements during powering. All stresses remain within allowable limits, supporting the development of a design compatible with indirect cooling.

In the context of the HITRI project and EuroSIG international collaboration, a carbon-ion gantry is being designed for possible installation at the National Center for Oncological Hadrontherapy (CNAO), Pavia, Italy. The design is based on superconducting (SC) magnet technology for the dipoles, in order to reduce gantry dimensions and weight. Unlike normal-conducting magnets, SC magnets are sensitive to local beam losses, which can lead to local energy deposition and potential quenches, thus inducing considerable gantry downtime. This contribution presents exploratory studies of energy deposition in the SC dipole magnets currently foreseen for the gantry. The studies are carried out by means of Monte Carlo simulations, using the code to characterize ruling factors such as beam spot size and impact angle. In this exploratory phase, simulations were carried out assuming simplified beam impact conditions.

This paper reports on the updated status and manufacturing results of the EuroSIG Superconducting dipole Demonstrator Magnet (SDM-c). The SDM-c is one of the key technologies for the next-generation European heavy-ion gantry and consists of a curved cos−θ NbTi dipole with a 30° magnetic length over a 1.65 m curvature radius and a 0.15 Ts⁻¹ ramp-rate. We summarize the milestones reached in the last year, including the production of the curved dummy coil, employed to validate the manufacturing tooling and procedures, the production of the first curved NbTi coil, and the engineering and procurement of the mechanical structure, which was also complicated by the curvature. The results show that the project is in good track to prove the feasibility of the bending magnet concept. The paper includes a discussion of the remaining challenges for the final prototype magnet, which has a 45° magnetic length and a 0.4 Ts⁻¹ ramp-rate.

Machine learning (ML) models are able to process complex images, providing state-of-the-art performance in tasks such as image classification and semantic segmentation. These models can be mapped to highly efficient commercial-off-the-shelf (COTS) specialized hardware accelerators, whose reliability should be carefully evaluated before deployment. Unfortunately, given the large number of ML model architectures, possible configurations or input selections, and the numerous COTS accelerator architectures available, exhaustively testing every model-accelerator combination with beam experiments is unfeasible. Additionally, the radiation data obtained with a specific combination can hardly be extended to different configurations. In this paper, we test vision transformer (ViT) and segmentation convolutional neural network (CNN) models, in addition to several ML micro-benchmarks, on the Google Coral Edge TPU at 6 different radiation facilities, investigating particle-, software-, and hardware-dependent reliability behaviors. Our experimental results show that, while the cross section for radiation-induced silent data corruption (SDCs) can be up to 8 orders-of-magnitude higher when testing with high-LET heavy ions compared to atmospheric neutrons, the characteristics of the SDCs are similar across all types of radiation tested. Instead, the most impactful factors that lead to misclassifications in beam tests are actually the model complexity and the input selection. These results can be leveraged to more efficiently plan and utilize the beam time available in radiation experiments, thus improving the understanding of the fault models affecting the software, while also characterizing the reliability of the underlying hardware accelerator.

Pulsed particle beams in hadron therapy treatments generate ionoacoustic signals (10-250 kHz ultrasound) that contain morphological and dosimetric information about the deposited dose, with accuracies superior to traditional nuclear imaging techniques. However, the application of this technique is limited by the immature detector technology that cannot acquire the weak signals (fractions of Pa) of clinical treatments. This paper aims to overcome this limitation by developing the first dedicated Active Ionoacoustic Sensor (AIS), composed of a piezoelectric Polyvinyldene Fluoride and a dedicated Low-Noise Amplifier in 28 nm CMOS technology. The AIS prototype is characterized in the electrical and acoustic domain, and its noise and imaging performances allow to reconstruct the dose deposition of a simulated 200 MeV proton beam with a gamma index 3%/3 mm higher than 95% with a Bragg Peak dose as low as 25 mGy.