Machine Overused

 
 
By John McCormick  |  Posted 2004-03-08 Email Print this article Print
 
 
 
 
 
 
 


In the report, the staff claimed the hospital was understaffed and poorly equipped, and they asked for more frequent maintenance on the Cobalt-60 teletherapy machine. The contention: the machine was being used 3,780 hours per year, nearly twice what the maintenance program recommended.

The staff also asked the hospital to have Multidata do "preventive maintenance" on the software. But the software was never maintained, and by 2000, the hospital was using just the one Cobalt-60 machine to treat all patients, according to Saldaña. A second, older machine was retired.

By then, two of the hospitals five radiation physicists had quit. Saldaña says the remaining three did the work of five, which sometimes required 16-hour days.

Victor Garcia remembers waiting five to six hours for every treatment. And after each of those six treatments, he felt sicker. As his intestines struggled to slough off cells killed by the radiation, he developed diarrhea. Burns seared through the flesh on his back. He lost 30 pounds. Hospital doctors told him the symptoms were normal. One reason it took hospital staff seven months to discover the overdoses, according to hospital director Juan Pablo Bares, is that patients with pelvic cancers often show symptoms of radiation toxicity, and the number of patients overdosed was small compared to the number being treated.

But another reason was the complexity of the software. The glitch involving Multidata was activated only under very specific circumstances-when the dimensions of the blocks that defined the patients treatment area were entered in a particular way. If the blocks were treated as a single, composite shape, and the descriptions of their dimensions were entered so that the "loops" that defined the inner and outer perimeters of that shape crossed, the software would increase patients treatment time, the IAEA report said.

As patients began to sicken and then die, the staff hunted for the cause. Saldaña remembers that by March 2001, she was thinking the problem had to be the software. But even then she discovered it by accident: On the morning of March 2, according to a statement she gave to the prosecutors office, she was calculating dosages for two patients with equivalent treatment areas and treatment depths and suddenly realized that the treatment times that came out of the software werent even close.

And so began the hospitals effort to unearth the causes of the overdoses.

Radiotherapy expert J. Francisco Aguirre, who investigated the overdoses for the Panamanian government as part of a team from the M.D. Anderson Cancer Center in Houston, says the calculation error was a problem that occurred with algorithms in older software used to plan treatments, a linkage that Multidata president Arne Roestel denies. Aguirre says the error was so obscure he wouldnt have thought to look for it-except that while he was in Panama, he remembered seeing a physicist in the U.S. cause a similar error 10 years before.

"The trick is how to tell the computer what are [empty] holes and what is solid," Aguirre says. "If the lines you are digitizing cross along the way, you fool the computer."

Indeed, during the IAEAs May 2001 investigation, the agency found ways to get the software to miscalculate treatment times that the hospital staff hadnt tried. Investigators were able to enter the dimensions for one block, two blocks or four blocks of varying shapes, and every time they treated them as a single block and entered the coordinates so that the perimeter loops crossed, the software always increased the treatment times.

Both the M.D. Anderson and IAEA investigating teams found Multidatas manual hard to understand. "It does not describe precisely how to digitize co-ordinates of shielding blocks and there are not enough relevant illustrations," the IAEA report said. "In addition, it does not provide specific warning against data entry approaches that are different from the one described."

The Houston teams report said: "The manufacturers manual of instructions was reviewed, and no indication was found in the instructions on how to digitize the blocks, or procedures to avoid, that could result in bad calculations."

On Aug. 10, 2001, in an "urgent notice" to users, Multidata used a series of diagrams to describe how the "crossing-loop" problem-which the company described as a "data entry sequence that creates a self-intersecting shape outline"-would not be acceptable to its program and would cause miscalculations. And it appeared to specifically absolve those users who, like Saldaña, had tried to get the software to give results when five shields were being placed on patients instead of four.

"Digitizing direction and exceeding the number of blocks, numbers of points per block or the block shape have no unexpected effect on the dose calculation," the notice said.

Next Page: The investigations.



 
 
 
 
 
 
 
 
 
 
 

Submit a Comment

Loading Comments...
 
Manage your Newsletters: Login   Register My Newsletters























 
 
 
 
 
 
 
 
 
 
 
Thanks for your registration, follow us on our social networks to keep up-to-date
Rocket Fuel