Evaluation of the scattered radiations of lead and lead-free aprons in diagnostic radiology by MCNPX

BACKGROUND: Over the past few years, because of high attenuation and lightweight, non-toxic, lead-free aprons (LFAs) have been replaced by lead aprons (LAs). Lots of studies declared that this fact was based on the interactions of diagnostic X-ray with material such as the photoelectric effect (PE) and Compton scattering. These studies have demonstrated that in these types of aprons, due to the presence of different K-edge absorption, PE has a wide absorption in various metals with divers K-edges. The measurement geometry in most of these studies was narrow beam geometry, i.e. a collimated source and a collimated detector with a large source-detector distance.

OBJECTIVE: The present study intended to evaluate the attenuation of radiology scattered radiations in LAs and LFAs in both narrow and broad beam geometries, which is a more realistic situation, in order to check whether or not the higher attenuation is valid.

METHODS: In this study, a lead apron contains (Pb + EPV) and two non-lead compounds of (W + Sn + EPVC) with different weight percent (Wt%) were evaluated in the energy range of diagnostic radiology (100 kVp). The MCNPX code was applied to simulate broad - and narrow-beam measurement geometries. The evaluations have been performed in three situations: 1^st) the same density thickness of LA and LFAs 2^nd) same line thickness of LA and LFAs 3^rd) considering the thickness of LFAs which has the same attenuation with LAs i.e. lead equivalent thickness for LFAs in the narrow beam. Finally, the x-ray transmission ratio (I/I_0) of LAs and LFAs was compared in 100 kVp for three mentioned conditions.

RESULTS: Our results indicated that LFAs had more radiation attenuation rather than LA in the 1^st and 2^nd conditions with both geometries. However, LFAs had lower attenuation in comparison to LAs in the 3^rd condition with broad beam geometry. More importantly, the transmission ratio (I/I_0) of LFAs in the broad beam condition was more significant than LA.

CONCLUSION: The scattered radiations produced by LFAs are more than LAs because of the production of characteristic radiations resulted from K-edge absorption in composited aprons. Consequently, the LFAs should be evaluated in both narrow and broad beam situation using the lead equivalent thickness of LFAs to make sure that the non-lead aprons do not increase the radiation dose of the user.