Body size-dependent patient effective dose for diagnostic radiography

The health-related mean absorbed dose to organs and tissues and the effective dose were usually calculated from the entrance surface dose (ESD) using computational phantoms by the Monte Carlo method. Because these phantoms represented an average adult with simplified organ shape and position within the body, the calculated results were hypothetical doses to the phantom but not to the patient. In order to determine the patient doses, the body size of individual patients should be taken into consideration. In the present work, two approaches were adopted to estimate the radiological thickness of a patient which determined the overlying tissue shielding and photon attenuation in the calculation of organ and effective doses. The first approach involved the determination of this thickness from patient body weight and height. It was found that the body mass index (BMI) was approximately linearly proportional to the body thickness. Therefore, the BMI was used to determine the size-dependent organ and effective doses from patient ESDs measured by the thermoluminescent dosimeters. To verify the applicability of BMI, WinODS software was employed to compute the organ and effective doses using the size- and sex-adjustable anthropomorphic phantom. The second approach involved the estimate of body thickness from the transmission factor, defined as the ratio of exit surface dose to ESD. The transmission factor was measured using polyethylene phantoms of varying thicknesses. Also, a backscatter factor, defined as the ratio of ESDs with and without the presence of patient, was measured using polyethylene phantoms of varying thicknesses.