This study aimed to investigate the radiation absorption effects of the humeral locking plate system on breast tissue in different radiological energy ranges using MCNPX (Monte Carlo N-Particle Extended Transport Code System, version 2.6.0) general-purpose Monte Carlo code. In the present study, a novel MCNPX simulation setup has been generated considering the elemental mass fractions of investigated materials and biological structures. The validation of MCNPX simulation geometry used in this study has been provided by comparing the results with standard XCOM data for mass attenuation coefficients of Ti-6Al-4V alloy. A very good match between XCOM and MCNPX data has been achieved. Therefore, validated simulation input has been employed for further investigations of the present study. Our findings showed that the amount of absorbed energy that was measured in breast tissue with the humeral locking plate was higher than that without humeral locking plate for the same radiological energy value. Our results would be beneficial to use the present simulation technique and mass attenuation coefficients for radiation physics and medical applications, especially for assessments of breast cancer risk.