Investigation of the Effect of Different Voxel Sizes and Beam Fields on Dose Distribution in Small-Field Radiotherapy Treatment

This study investigates the influence of voxel size and small photon beam fields on dose distribution to determine optimal dosimetric parameters for accurate calculations in radiotherapy. Dose distributions were computed in a homogeneous water phantom using the Monte Carlo–based EGSnrc/DOSXYZnrc system with a 1 MeV photon source and beam sizes from 0.5 × 0.5 to 3 × 3 cm². Analyses at clinically relevant surface depths (0.007–0.1 cm) showed that a voxel size of 0.01 cm provides optimal accuracy across all field sizes. Beyond 0.1 cm depth, the ideal voxel size increased proportionally with both depth and beam field, ranging from 0.05 to 0.25 cm. Larger voxels caused substantial errors, reaching 5–34% in dose calculations. These findings highlight voxel size as a critical factor in small-field dosimetry and emphasize that selecting depth- and field-specific voxel dimensions can enhance dose accuracy and potentially reduce radiation-induced skin toxicity in precision radiotherapy.