Chest wall thickness measurements of the LLNL and JAERI torso phantoms for germanium detector counting. Lawrence Livermore National Laboratory and Japanese Atomic Energy Research Institute.

Abstract

The Lawrence Livermore National Laboratory and Japanese Atomic Energy Research Institute torso phantoms were developed to calibrate lung counting systems that are used to estimate plutonium and other radionuclides deposited in the lung. Originally, low energy photon counting systems consisted of phoswich detectors. The average chest wall thicknesses and individual measurement points of the Lawrence Livermore National Laboratory phantom and its overlay plates in the regions covered by these detectors were provided by the manufacturer. Germanium detectors are of a different size and are placed in different locations on the phantom so that the manufacturer's data are no longer applicable for the locations of the germanium detectors on the phantom. The Human Monitoring Laboratory has re-evaluated the chest wall thickness of both the Lawrence Livermore National Laboratory and Japanese Atomic Energy Research Institute phantoms and their overlay plates for its germanium lung counting system. The measurements were made in the upper right, lower right, upper left, and lower left positions on the phantom's torso plate above the lungs. The effective chest wall thicknesses (17 keV) for the Lawrence Livermore National Laboratory torso plate are 1.46 cm, 1.43 cm, 1.66 cm, 1.48 cm, respectively. The manufacturer's quoted average effective chest wall thickness for a pair of phoswich detectors is 1.63 cm. The measured effective chest wall thicknesses (17 keV) for the JAERI's torso plate are 1.76 cm, 2.15 cm, 1.79 cm, 2.15 cm, respectively. The manufacturer's quoted average chest wall thickness for an unspecified region of the chest is 1.50 cm. This paper presents effective chest wall thickness data for the phantoms with and without their overlay plates at 17 keV, 60 keV, 200 keV and 1,500 keV. The uncertainties involved in determining the effective chest wall thickness have shown that there is no significant difference between the effective chest wall thickness and the physical chest wall thickness.