fda.gov/cdrh/ocd/panamaradexp.html, July 6, 2001). When investigated, the
cause turned out to be an erroneous software algorithm in the Multidata software controlling the Theratronics
Cobalt-60 machine.
The Multidata software provided a way for operators to digitize representations of metal shields called
blocks, which are used to protect healthy, delicate tissue from exposure to x-rays. The doctors prescribed the
use of various blocks for individual patients. The machine operators entered descriptions of the blocks into the
software, and the Multidata software then calculated the amount of radiation to deliver.
When investigating the cause of the radiation overexposures, investigators found that operators could
enter data about the blocks in such a way that the software would ???misunderstand??? the digitized representation,
mistaking holes in the pattern of blocks for the block itself. Multidata later recognized the problem as the
CHAP. 9] SOCIAL ISSUES 177
???self-intersecting shape outline??? problem. In that circumstance, the software calculated radiation doses that
were too high by margins of 20 percent to 100 percent.
Because the problem only manifested itself with certain combinations of blocks, and with certain data input
practices of individual operators, the cause of the few overexposures (the hospital treated about 100 people per day)
was difficult to determine.
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