Radiation: The Difficulty of Monitoring the Invisible – Post 1 of 2

Lately, I have noticed a plethora of stories on human factors mistakes with medical equipment that delivers radiation. I have collected them here for those who are interested in this problem. At times a computer bug was at fault, but often radiation overdoses came from:

  • inadequate training (and perhaps a poor display, but those are not available for me to examine)
  • non-transferrable mental models between pieces of equipment
  • team communication issues
  • trust in automation

I provide excerpts from each article calling out the HF-related errors.

A Pinpoint Beam Strays Invisibly, Harming Instead of Healing

In Missouri, for example, 76 patients were overradiated because a medical physicist did not realize that the smaller radiation beam used in radiosurgery had to be calibrated differently than the larger beam used for more traditional radiation therapy.

Linear accelerators can be adapted to perform stereotactic radiosurgery in two ways: with small computer-controlled metal leaves that shape the beam, or with a cone attached to the machine’s opening through which radiation is delivered. That opening is made smaller or larger by moving four heavy metal “jaws” that shape the beam into a square. When a cone attachment is used, the square beam must fit entirely within the circumference of the cone. If the square is slightly larger than the cone, radiation will leak out through the four corners of the jaws and irradiate healthy tissue. In the Evanston accidents, records show, the beam was four times too large. Operators could not see this incorrect setting directly because a metal tray on which the cone is mounted hides the jaws, though the settings should have been displayed on a computer screen, according to people who have worked with this device.

That system is supposed to work this way: A treatment plan is developed on one computer, then transferred into another software system that, among other things, verifies that the treatment plan matches the doctor’s prescription. The data is then sent to a third computer that controls the linear accelerator. Several months after the Evanston accidents, Brainlab reminded customers to verify the correct jaw setting, specifically citing the possibility that treatment information could be altered as it passed “through a chain of devices.”

Evanston Hospital had earlier encountered its own communication glitches after upgrading Varian software in December 2008. As a result, medical personnel had to load patient information onto a USB flash drive and walk it from one computer to another. Then, three months ago, concerned that radiation might leak outside the cone, Varian warned customers that its software did not recognize cone attachments on the type of linear accelerator involved in the Evanston accidents. To work around that problem hospitals needed to, as one medical physicist put it, essentially trick the machine into thinking it was using a different attachment, which it did recognize. To do that, users had to enter additional data into the SRS system.

After Stroke Scans, Patients Face Serious Health Risks

While in some cases technicians did not know how to properly administer the test, interviews with hospital officials and a review of public records raise new questions about the role of manufacturers, including how well they design their software and equipment and train those who use them… While in some cases technicians did not know how to properly administer the test, interviews with hospital officials and a review of public records raise new questions about the role of manufacturers, including how well they design their software and equipment and train those who use them.

…a feature that technicians thought would lower radiation levels actually raised them. Cedars-Sinai gave a similar explanation. “There was a lot of trust in the manufacturers and trust in the technology that this type of equipment in this day and age would not allow you to get more radiation than was absolutely necessary,” said Robert Marchuck, the Glendale hospital’s vice president of ancillary services.

At Cedars-Sinai and Glendale Adventist, technicians used the automatic feature — rather than a fixed, predetermined radiation level — for their brain perfusion scans. But a surprise awaited them: when used with certain machine settings that govern image clarity, the automatic feature did not reduce the dose — it raised it. … GE says the hospitals should have known how to safely use the automatic feature… GE further faulted hospital technologists for failing to notice dosing levels on their treatment screens.

Of course, this isn’t the first time we have posted on this issue at The Human Factors Blog, and I don’t imagine it will be the last.
Previous posts:
Error Leads to Radiation Overdose
“Set Phasers on Stun” still relevant in healthcare industry

 

Photo credit microwavedboy on Flickr