In 1970, the Energy Research and Development Administration’s (now DOE) Intercalibration Committee for Low-Energy Photon Measurements established a forum to compare data and methods of plutonium whole-body counting – the methods for the measurement of radioactivity within the human body. For a variety of reasons, actinides, like plutonium 239, had proven especially difficult for health physicists to detect and quantify. In 1974, after an international, multilaboratory study, the committee concluded that the calibration phantoms (manikins) in use at the time were mostly inadequate and not designed to detect X-ray emitters in the human lung. As such, the need for a new phantom was warranted, and Livermore’s Hazards Control Department was selected to construct three realistic torso-only manikins, molded from human cadavers.
Livermore researchers began by gathering data (height, weight, and chest circumference) from more than 500 male employees at the Livermore and Los Alamos laboratories, to build a physical profile for the “average” male radiation worker. Based on the data, Lab researchers selected a cadaver of like dimensions from the University of California, San Francisco (UCSF) Anatomy Department from which molds of the torso and organ cavity were made.
After the molds were completed, the rib cage was extracted from the cadaver and cleaned. The remaining soft tissue was removed using a colony of dermestid beetles from the University of California, Berkeley. Lab researchers next affixed the rib cage to a dissolvable cast of the organ cavity to form an inner mold. This rib cage-affixed inner-mold was suspended in position inside of a hollow silicone mold, made from the model of the torso, and the space between was filled with tissue-equivalent (TE) plastic. The organ cavity mold was then dissolved, leaving the rib cage imbedded in the torso casting, surrounding the organ cavity.
Once the polyurethane torso shell with imbedded rib cage was completed, the simulated organs, molded from the cadaver’s organs, were inserted into the cavity, and a series of removable chest plates of TE material were fabricated to simulate a wide range of sizes. Two additional rib cages were obtained from the UCSF Anatomy Department and prepared in a similar manner to construct the second and third phantoms.
Upon completion, Livermore sent its three fabricated phantoms to laboratories in the United States, Europe, and Canada as part of an intercomparison program to compile and exchange data necessary to upgrade calibration and whole-body counting techniques. As the program proceeded, it became clear that each of the laboratories involved required use of the phantoms for longer periods of time than allotted. In addition, several facilities expressed interest in acquiring phantoms as permanent parts of their calibration programs. As such, Livermore agreed to fabricate a second set of torso manikins, and 16 second-generation phantoms were made. The new phantoms were nearly identical to the first three, except that a simulated rib cage replaced the real bone used in the original phantoms.
Following the development of the first and second-generation phantoms, and their subsequent commercial production, the validity of the Livermore phantom was tested in various international intercomparison studies. The tests conducted validated the Lab’s phantom as a highly realistic calibration tool.
The Livermore realistic torso phantom technology was transferred to the public sector in the early 1980s and is still commercially sold.
Pictured: Rib cage attached to the soluble organ cavity mold and positioned inside the hollow torso silicone mold.