Determination and validation of photon energy absorption buildup factor in human tissues using Monte Carlo simulation

In this study, the Energy Absorption Buildup Factor (EABF) of different tissue equivalent materials have been calculated using the Monte Carlo code MCNP5. The results of MCNP5 calculations are validated against the results obtained using the Geometric Progression (G-P) fitting method. The energy range for the gamma rays was 0.1-15 MeV and penetration depth was up to 20 mfps. Chemical compositions for different tissue materials are implemented into the MCNP5 to estimate the buildup factor for each tissue type. Energy and penetration depth dependence of the EABF are also analyzed. The results show that the adipose tissue has the largest buildup factor while the bone tissue has the lowest. Comparison of MCNP5 results with the G-P fitting method demonstrated a good agreement, with 90% of all MCNP5 EABF calculated values deviating less than 5% from the G.P. The average deviation for all EABF values is 2.3%. The results from this study can be used for radiotherapy treatment, radiation dosimetry and for medical diagnostics based on the practical thicknesses and energy ranges investigated.