Airport Passenger Screening Using Backscatter X-Ray Machines: Compliance with Standards by Committee on Airport Passenger Screening: Backscatter X-Ray Machines

Author:Committee on Airport Passenger Screening: Backscatter X-Ray Machines
Language: eng
Format: epub
Publisher: The National Academies Press
Published: 2015-12-23T00:00:00+00:00

Estimation of Organ and Effective Dose Due to Compton Backscatter Security Scans

Hoppe and Schmidt27 calculated the organ and effective doses for four voxelized phantoms using published data for incident kerma and X-ray filtration. They did the calculations for a 34-year-old male, a 26-year-old female, an 11-year-old female, and a 6-year-old male, all using 2 mm cubic voxels. They used the air kerma values provided by the JHU/APL report cited above, 41 nGy, to determine the photon fluence. They estimated the photon spectrum using the SPEC78 software assuming the X-ray anode voltage of 50 kV, tube description, and filtration of 1.0 mm of aluminum, the minimum consistent with the ANSI/HPS N43.17-2009 reference effective dose method. They used the estimated photon spectrum to calculate energy deposited in the 1800 cc ion chamber used by JHU/APL in order to determine the kerma to fluence conversion, but they did not do additional calculations to test the accuracy of the photon spectrum. This process has been contested because the ion chamber was simulated as a water cylinder instead of air, which results in an overestimate by a factor of about 3 in the source fluence.28 They found the effective dose for a person at 30 cm from the beam exit surface to range from 50 nSv for an adult male to 70 nSv for the 6-year-old male child. The other two phantoms, female adult and child, both showed 60 nSv per screening. They found the highest organ doses in the adipose tissue, ranging from 37.3 nGy in the adult male to 63.3 nGy in the female child, per scan. They present numbers for the skin, but the 2 mm pixel size averages the skin dose with that of adjacent tissue and introduces significant errors due to partial pixels in the field, so these numbers are not reliable.

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