Monte Carlo–Based Dosimetric Characterization of a Novel Holmium-166–Loaded Spiral Catheter for Beta-Emitting Brachytherapy

Abstract Brachytherapy relies on accurate spatial dose delivery and therefore requires precise modeling of radioactive sources within complex applicator geometries. In this work, we present a detailed Monte Carlo–based dosimetric analysis of a spiral catheter configuration using the Geant4 toolkit. Analytical energy-balance estimates, empirical absorbed-dose values, and full Monte Carlo energy-deposition calculations were integrated and compared as three independent approaches to validate dose estimation. The radionuclide 166 Ho was modeled by explicitly simulating its β-emission energy spectrum and physical half-life, and dose distributions were quantified using both voxelized meshes and detector-specific scoring geometries. The results demonstrate agreement within 5–7% between empirical absorbed-dose estimates and Monte Carlo calculations, supporting the accuracy of the simulation framework and the feasibility of the spiral catheter design for brachytherapy applications. High localized dose deposition was observed in the immediate vicinity of the catheter, with a delivered dose of approximately 43.0 Gy/GBq in a 0.001 g voxel, indicative of a potent and spatially confined therapeutic dose achievable in clinical practice.