Key Points

  • IMRT for prostate cancer caused 25% of implanted cardiac devices to malfunction.
  • Closer monitoring of cardiac devices in patients undergoing IMRT may be necessary.
  • Researchers speculate that cardiac devices today are more sensitive to radiation than in the past.

MIAMI BEACH, Fla.—Intensity modulated radiation therapy (IMRT) may cause implanted cardiac devices to malfunction, according to a new study of men undergoing IMRT for prostate cancer (PCa).

The new finding is in contrast to previous reports suggesting that unsafe interactions with cardiac pacemakers and cardiac defibrillators and IMRT therapy are rare. In fact, the researchers who conducted the new study were surprised that such a high number of cardiac devices may malfunction during IMRT.

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Study investigator Steven DiBiase, MD, a radiation oncologist at the Robert Wood Johnson School of Medicine in Camden, N.J., said it is possible that pacemakers and defibrillators today may be more sensitive than in the past.

“This cardiac device interaction is not fully understood,” Dr. DiBiase told Renal & Urology News. “It is not clear whether this cardiac device interaction is unique to IMRT treatments or related to more sensitive cardiac devices to ionizing radiation in recent years. The study results will hopefully encourage closer monitoring of cardiac devices. Such close monitoring could provide rapid intervention to prevent any clinical cardiac problems when IMRT is administered.”

Dr. DiBiase and his colleagues conducted a retrospective study with PCa patients undergoing IMRT because many of them have cardiac pacemakers and defibrillators. The study focused on 24 patients with implanted medical devices who underwent IMRT for localized PCa. These patients were closely monitored before and after treatment for any interaction between IMRT and their cardiac device. 

Six (25%) of the 24 patients experienced a mechanical malfunction as a result of their IMRT treatments, causing the device to reset to the manufacturer’s designated default settings. Of these six patients, one was dependent on his pacemaker and five were not. “That means in some patients the function of their heart is dependent on the function of the pacemaker. If they are ‘not dependent’ it means if their pacemaker malfunctioned they would still be relatively fine. If they were ‘dependent’ they would be more directly affected,” Dr. DiBiase said.

None of the patients developed clinical cardiac problems, yet two men required pacemaker replacements. In these two men, the pacemaker could not maintain the designated settings and continued to return to the default setting. “It is like your computer losing its memory. With pacemakers and defibrillators, they may be reset to the manufacturer designated default settings.  We saw in six of these patients that the memory was erased and the devices returned to the default settings introduced back at the factory,” Dr. DiBiase explained.