Reconstruction of a Human Skull Calibration Phantom Using Bone Sections From an 241Am Exposure Case

Abstract

New York University Medical Center's Institute of Environmental Medicine (NYUMC/IEM) was called upon by representatives of the United States Transuranic Registry to reconstruct a human skull phantom for the purpose of producing a calibration structure to be used for determining 241Am skeletal content from in vivo measurements. The human skull represented a deposition pattern of 241Am in the bone matrix which had accumulated into the bone via natural metabolic processes after an accidental intake. Soon after death, the skull was sagittally divided and the left lateral side was analyzed radiochemically. Assuming symmetry of deposition, and based on measurements of the right lateral side of the skull performed at NYUMC/IEM as well as results of radiochemical analysis of sections of the left side, the activity content of the right side was estimated to be 307 +/- 4 Bq (8.3 +/- 0.1 nCi). The right side was subsequently paired with a blank left lateral of a control skull and embedded into tissue-equivalent material. The reconstructed skull phantom was then evaluated to determine its applicability as a calibration phantom which could be used to estimate skeletal burdens of 241Am.

EURADOS 241Am skull measurement intercomparison

“…The laboratories which used calibration phantoms with different source distributions than the measured one introduced this bias into their estimates. Additionally in a real 241 Am incorporation, the activity is present both in the cortical and in the trabecular bone and there can be bone remodelling which may result in 241 Am activity patterns as those measured by Hickman and Cohen (1988) in the construction of the USTUR skull phantom.…”

“…The skeleton divided postmortem along the sagittal plane. The left side of the skeleton was radiochemically analyzed (McInroy et al, 1985) while the right side was used to build anthropomorphic phantoms from skull, torso, arm and leg for in vivo counting systems (Hickman and Cohen, 1988). The USTUR phantoms are unique since they contain a real human skeleton with a natural metabolic 241 Am activity incorporation into the bone matrix.…”

“…The USTUR Case 0102 skull phantom consists of one-half (bilateral slice) with 241 Am contaminated bones from the exposed individual on the right side, and non-contaminated bones on the left side. The phantom is filled and covered with tissue equivalent material (Hickman and Cohen, 1988). A recent re-evaluation of the activity content indicates that this skull phantom contains 287.2 ± 3.7 Bq of 241 Am at the reference date January 1, 2012 (Tolmachev, 2012).…”

“…Figure 6 also shows a significant variation of the detection efficiency with measurement position. The reason for this is that a) only half of the skull bone is active in this phantom, b) a different thickness of the soft tissue material is used at different positions, and c) the 241 Am activity distribution pattern present in the USTUR skull phantom is inhomogeneous (Hickman and Cohen, 1988). Figure 6: Results of Task 1 -59.54 keV detection efficiency for various positions on the USTUR skull phantom, as a function of PBC detector diameter.…”

EURADOS intercomparison exercise on MC modelling for the in-vivo monitoring of AM-241 in skull phantoms (Part II and III).

“…The active half of the skull was matched with a non-active skull from other human subject. The combined skull halves were filled and wrapped with a tissue equivalent material simulating skeletal muscle (Hickman and Cohen, 1988).…”