Secondary Gamma-ray test by Cadmium Zinc Telluride detector for Carbon Ion Radiotherapy

Carbon ion therapy is one of the most advanced radiotherapy techniques owing to its precise energy deposition in tissue. Accurate verification of particle range is critical for ensuring precise dose delivery to the target volume while minimizing damage to surrounding healthy tissues. Currently, slit-promoted prompt gamma imaging (PGI) methods are being explored in research trials, but no mature clinical applications are available. To address this limitation, a Cadmium Zinc Telluride (CZT) semiconductor detector was developed to determine the particle range and delivered dose distribution by monitoring secondary particles generated during carbon ion therapy. The CZT detector, measuring 18 × 18 × 5 mm 3 , utilizes orthogonal anode and cathode strips (16 strips, each 16.4 mm× 0.9 mm), yielding 32 signals. These signals are sequentially processed through a charge-sensitive preamplifier circuit, a filter-forming amplifier circuit, and a data acquisition system. Full-energy peaks at 511 keV were clearly observed in both the in-beam and off-beam regions at 190.19 MeV/u, with energy resolutions of 7.2% and 4.0%, respectively. The distribution of secondary particles was determined using positional formulas. The Bragg peak range was verified based on the secondary particle count distribution, and the total secondary particle count was used for dose validation. This paper illustrates the feasibility of the CZT detector for secondary particle monitoring during carbon ion therapy.