Optimum X-ray energy in diagnostic radiology: Monte Carlo simulation studies

Diagnostic X-ray examinations are the principal source of population exposure to ionizing radiation. ICRP recommends the limits in dose equivalent that are based on the risk estimates for each organ and tissue. For this reason a realistic knowledge of dose values to the organs involved in X-ray examinations and more efficient methods for dose reduction and image optimization are necessary. In this work a new methodology is proposed to correlate organ dose with irradiation photon energy and image quality. A Monte Carlo method has been applied to the mathematical models to calculate organ doses and to evaluate the quantity of photons impinging on radiographic plane in diagnostic radiology under conditions of partial body irradiation. The technical parameters for a typical radiographic technique have been reproduced. External irradiation with monochromatic photo energies have been considered in the range 20-100 keV. Organ dose values have been normalised to the number of photons transmitted without interactions on radiographic plane. The doses so obtained against photon energy have been considered as ones necessary to produce the same useful diagnostic information. Moreover the ratio between the number od scattered and transmitted photons on radiographic plane have been calculated. Finally a discussion on the optimum photon energy for every organ has been carried out comparing these data