Speaker
Description
Carbon-ion radiotherapy (CIRT) is capable of delivering a precise dose distribution using the Bragg peak. However, the generation of secondary neutrons and the uncertainty of the beam range can potentially affect the efficacy of the treatment and could also result in damage to surrounding organs at risk (OAR). In order to ensure patient safety, it is essential to accurately characterize secondary neutrons and implement real-time dose verification. Carbon ion beams have been observed to produce significantly higher secondary neutron emissions relative to prompt gamma rays compared to proton beams. The use of neutron measurement techniques in CIRT can improve detection efficiency due to the high neutron production rate and contribute to higher accuracy. In this study, the design of a neutron scatter imager for carbon beam range verification was optimized using Geant4-based Monte Carlo simulations. A carbon beam with an energy range of 56–430 MeV/u and a water phantom with dimensions of 10×10×40 cm³ were employed in Geant4 simulations (Fig.1). The neutron scatter imager, which consists of two pixelated plastic scintillator detectors (EJ-276), was optimized for three key parameters: detector thickness (0.5–5 cm), inter-detector distance (5–20 cm), and pixel size (1–10 mm). Furthermore, the effectiveness of lead (Pb) shield in reducing the gamma-ray effect was evaluated. To achieve effective image reconstruction in fast neutron scatter imaging, it is necessary that single scattering occurs in each detector. Accordingly, the optimal thickness of the detector was determined to be 1 cm by considering the probability of single scattering and multiple scattering. An inter-detector distance of 10 cm was selected based on considerations of resolution and efficiency, facilitating suitability for real-time imaging. A pixel size of 3 mm was determined to be optimal imaging resolution, and a 5 cm Pb-shield was found to reduce gamma-ray transmission to below 20% while maintaining neutron detection efficiency. In the present study, a neutron scatter imager for CIRT beam range verification was optimized using Geant4 simulations. The identified parameters (detector thickness, inter-detector distance, pixel size, and Pb-shield thickness) enable precise neutron imaging, thereby enhancing the accuracy of the treatment and patient safety.
| Workshop topics | Detector systems |
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