Using Monte Carlo Method for estimation of Absorbed Dose in Mammography

Mammography is the best method for diagnosis of breast cancer in which the received radiation dose to the patient during imaging increases the risk of cancer. Therefore, it is necessary to evaluate irradiation device and estimate the patient dose during mammography. In this study Mean Glandular Dose (MGD) and ESD have been calculated by Monte Carlo method-MCNP4C code. Suitable models for X-ray tube components and patient's breast are considered. In order to simulate Xray spectra, the accelerating electrons were transported until they slow down and stop in the target. To achieve error less than 2% in this work 2x10(8) electrons have been transported and both bremsstrahlung and characteristic X-ray production have been considered and compared with IPEM. Various target/filter combinations and kVps were focused to investigate all device condition effect on the absorbed dose. The breast is simulated as a semi cylinder with 16 cm diameter and 4 cm thickness. After transporting 2x10(8) photons, MGD and ESD have been obtained with error less than 2%. The simulation results show that the relationship between MGD and kVp is linear and the equation is y = 0.127 x -1.544. The results illustrate that for a 4 cm breast MGD is variable between 1.38 and 1.76 mGy in kVp range of 23 to 26. According to simulation, ESD varies from 2.23 to 2.92 mGy for a 4- cm thick breast in kVp range of 23 to 26.