Dosimetric and energy deposition evaluation of the dual-microcavity capsule structure for glioma 125I brachytherapy using Monte Carlo simulation

Abstract

Brachytherapy has emerged as a primary approach for tumor treatment, and determining the dosimetric parameters of the radiation source is a critical step in radiation therapy, as recommended by the American Association of Physicists in Medicine (AAPM). This study investigates a novel dual-cavity capsule for combined radiotherapy and chemotherapy treatment. Monte Carlo simulations were used to obtain the dosimetric parameters and energy deposition distribution of the dual-cavity structure within a water phantom. The simulation results were then compared with published data for other commercial ¹²⁵I seeds. The results show that the dose-rate constant for the dual-cavity capsule is (0.984 ± 0.020) cGy·h⁻¹U⁻¹, which aligns with values reported for other commercial ¹²⁵I seeds. The radial dose function and anisotropy function of the dual-cavity capsule generally match reference data for these seeds, though notable differences were observed at specific positions. When the source activity was set to 1 mCi, the dose rate at the center of the dual-cavity capsule was 12.40 cGy/h, compared to 13.07 cGy/h for a single-cavity structure containing only a radiotherapy channel, showing a dose rate difference of approximately 5 %. The presence of the chemotherapy channel caused a shift in the peak dose rate within the dual-cavity structure but had minimal effect on the overall radiotherapy dose distribution. The dual-cavity capsule demonstrates a high central dose rate, with a rapid dose fall-off toward the periphery. Due to structural and material modifications, the radial dose function and anisotropy function of the dual-cavity capsule deviate from the assumptions of the AAPM TG-43U1 formalism, indicating that the TG-43U1 two-dimensional dose-rate equations may not fully apply to this novel design. This study serves as a valuable reference for establishing spatial dosimetric parameters for the dual-cavity capsule structure in clinical practice.