Estimation of organ and effective dose due to Compton backscatter security scans

Abstract

Purpose: To estimate organ and effective radiation doses due to backscatter security scanners using Monte Carlo simulations and a voxelized phantom set. Methods:Voxelized phantoms of male and female adults and children were used with theGEANT4 toolkit to simulate a backscatter security scan. The backscatter system was modeled based on specifications available in the literature. The simulations modeled a 50 kVp spectrum with 1.0 mmaluminum-equivalent filtration and a previously measured exposure of approximately 4.6 μR at 30 cm from the source. Photons and secondary interactions were tracked from the source until they reached zero kinetic energy or exited from the simulation's boundaries. The energy deposited in the phantoms' respective organs was tallied and used to calculate total organ dose and total effective dose for frontal, rear, and full scans with subjects located 30 and 75 cm from the source.

Locally optimized non-local means denoising for low-dose X-ray backscatter imagery

“…In [37], Rez et al measured the noise in publicly available XBS images and, assuming the noise is described by Poisson statistics, estimated the X-ray dose needed to generate the observed noise. This led to estimates higher than those reported by manufacturers or the government, though other investigators have estimated lower dosages [38]. In the context of the work presented here, it is important to note that estimating X-ray dose from the denoised images presented above would lead to a significant over-estimate; while the denoised images have noticeably lower noise than the raw data, this is clearly due to post-processing effects.…”

Response to “Comment on ‘Estimation of organ and effective dose due to Compton backscatter security scans’” [Med. Phys., 39, 3396 (2012)]

“…Since both errors affect the photon fluence modeled in our simulations, but not the simulated geometry, this scaling factor can be applied to the organ and effective dose estimates reported in our study. 2 Overall, the corrections result in new dose estimates that are 20%-40% less than those published in our original study. For clarity, we report the dose estimates reduced by 40% (for subject position 75-cm from the source) in Tables I-IV.…”

“…2 We welcome the opportunity to improve the accuracy of our dose estimates. Our study included and discussed numerous assumptions that limited the accuracy of the results.…”

“…Overall, as described below, corrections based on the information provided by Glover and Hudson suggest that the organ and effective doses as estimated by our methods are 20%-40% less than those reported in our original study. 2 Glover and Hudson state two errors in our simulations that determined the photon fluence that provides the exposure as previously measured according to the ANSI N43.17-2009 standard. One error was the position at which we modeled the ionization chamber.…”

Comment on “Estimation of organ and effective dose due to Compton backscatter security scans” [Med. Phys., 39, 3396 (2012)]

“…We also implemented a third method that most resembled that undertaken by Ref. 1. In this case, the conversion coefficients were calculated using the voxelized phantom results from ICRU-ICRP 116 (Ref.…”