Entrance surface dose as a good radiation dose descriptor is used in dose optimization and radiation protection. These two parameters are very important and should not be compromised during radiological examination. This study examined equivalent entrance surface dose and film surface entrance dose in adult patients with average weight and body mass index (BMI) of 69.2±0.4 kg and 24.9±0.6 kgm^-2 respectively. The study was carried out during routine diagnostic imaging of pelvis in some hospitals in Lagos Metropolis. Indirect dose measurement method was used to assess the dose. Entrance surface doses and patient thicknesses were determined using parametric method. The equivalent entrance surface doses were obtained with help of mathematical models which employed both homogenous and non–homogenous attenuation coefficients of the exposed tissue. Varied values of were obtained for male and female subjects. The ratio factors of the calculated film surface entrance doses to the patient entrance surface doses were found to be 20.12 and 0.012 for pelvis AP and LAT when homogenous attenuation coefficient was used. The ratio factor was 23.88 and 0.004 for pelvis AP and LAT respectively when non-homogenous attenuation coefficients of the exposed tissue were used. The study showed the possible range of values expected as the dose to film, especially during pelvis examination. It also established that a substantial amount of ESD is deposited in the tissue rather than being used for image formation thereby necessitating the need for dose optimization and effective filtration.

Keywords: film surface entrance dose, attenuation coefficient radiological examination, antero-posterior, lateral, pelvis