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ASTRO: IMRT can interfere with pacemakers

by Brendon Nafziger, DOTmed News Associate Editor | October 06, 2011
From the November 2011 issue of HealthCare Business News magazine

Radiation from newer radiation therapy equipment can erase the memory of implanted cardiac devices during prostate cancer treatment, according to a new study presented Wednesday at the America Society for Radiation Oncology's annual meeting in Miami.

In the study, almost a quarter of men with the implants undergoing radiation therapy had their devices reset. At least two patients' devices were not reprogrammable, and they needed to be replaced, the researchers said.

While past studies had shown little risk, especially when treatment wasn't near the chest, newer, more powerful equipment and more sensitive implantable devices might have made radiation-induced resets more likely, according to the researchers.

"It's new data that everyone should be aware of," Dr. Steven DiBiase, the lead investigator and a radiation oncologist at the Robert Wood Johnson School of Medicine in Camden, N.J., told DOTmed News by phone.

In the study, DiBiase and colleagues examined a group of 505 men before and after they underwent treatment for prostate cancer using intensity modulated radiation therapy, or IMRT. Introduced about a decade ago, this technology enables radiation oncologists to deliver more precise doses and spare more healthy tissue. It has since taken off and become one of the dominant forms of radiation therapy. A community poll, taken at ASTRO, found nearly 80 percent of radiation oncologists in the audience now use IMRT, DiBiase said.

Of these 505 men, about 5 percent, or 24 patients, had an implantable cardiac device, a pacemaker or defibrillator. And DiBiase said six men, or 25 percent of those with the implants, had their devices affected.

"The memory was erased," DiBiase said. "What happens is, the devices go back to factory settings. The devices still work, but the specifics the cardiologist wanted" are lost.

While four patients could have their devices reprogrammed, two devices had their memory so scrambled they had to be replaced, DiBiase said.

Blame it on the neutrons?

It's not clear why a higher risk was found than in past studies. It's possible that the study parameters were just better set up to capture evidence of an interaction, as it looked at a relatively homogeneous population -- older men with prostate cancer receiving IMRT, DiBiase said.

But DiBiase also noted that newer cardiac devices are likely more sensitive to radiation, especially defibrillators. Of the six patients affected, five had defibrillators, DiBiase said. Also, IMRT generates more radiation than older radiation therapy models.

"Ten years ago, the amount of radiation being generated wasn't as high as with IMRT treatments," DiBiase said. And this higher output of energy -- measured in monitor units -- might produce a new phenomenon that interferes with the devices.

For now, it's just speculation, and DiBiase said he and his team have to go back and study the problem. But the idea is that the a neutron particle beam might be created with IMRT. "Neutrons are produced when there's a lot more monitor units being produced," he said. And they might not have been created to such a degree during treatment with 3-D conformal therapy, an earlier radiation therapy technique.

"Clearly there's something else going on than we had previously thought about," he said.

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