He-Check: verification of the repeatability of dose delivery based on the simultaneous acceleration of helium and carbon ions

Radiation therapy is a cancer treatment technique that uses particle radiation to either kill or control the growth of malignant cells. One of the most promising radiotherapy techniques is hadrontherapy, which uses heavy particles, such as protons and carbon ions, to offer both physical and biological advantages in the treatment of localized tumors. The heavy charged particles have the peculiar characteristic of depositing a large part of their energy at a controlled depth, resulting in the characteristic Bragg's peak. This leads to highly accurate targeting of tumors while sparing the surrounding healthy tissues. Due to the localized energy deposition of charged particles, high precision is demanded. Range and energy uncertainties make this challenging and affect treatment precision. To address these challenges, advanced techniques like real-time verification methods are required. These methods aim to provide dynamic feedback on patient position and delivered dose, enhancing treatment safety and precision. At CNAO (Centro Nazionale di Adroterapia Oncologica), one of the few facilities offering dual treatment capabilities with protons and carbon ions, a novel system for the real-time verification of the patient position during beam delivery is under development. The system, called He-Check, employs an ion beam to evaluate the variation of the patient's anatomy during treatment. To this purpose, a fraction of helium ions are accelerated in combination with the primary carbon-12 beam used for therapy. This characteristic permits the joint acceleration of the two ion species. Helium ions possess almost identical magnetic rigidity at the same velocity and three times the range of carbon ions. By correctly dosing the helium the increase in the dose administered to the patient can be kept under control. The system exploits a plastic scintillator that, once exposed to the helium beam, generates optic photons detected by a sCMOS sensor. The present work is focused on the analysis of the spatial and temporal resolution of the system, with a particular focus on the characterization of the repeatability of measurements. Spatial resolution was assessed by capturing images at various depths to establish the maximum achievable resolution of the system. Additionally, a mirror was introduced along the axis of the scintillator to have a three-dimensional measurement of the beam. Repeatably and resolution can be assessed by subtracting images, either by administering the same plan or by administering plans with known differences. Furthermore, a comprehensive evaluation of various acquisition modalities for the sCMOS camera was conducted. The primary objective was to synchronize the proposed acquisition system with the beam time necessary to irradiate a single slice during treatments. To achieve this synchronization, the output signal from the Dose Delivery System (DDS), which operates in synchrony with the beam-on signal, interfaces with an Arduino device. The DDS generates a 5V digital signal, detected by the Arduino, which subsequently generates a pulse train tailored to trigger the sCMOS camera. Overall, the proposed system takes another step in the direction of proposing a robust solution for real-time imaging during particle therapy treatments.