High energy radiation treatment could affect the function of an implanted cardiac pacemaker or defibrillator. Radiation treatment for cancer with energy levels above 10 MV could interact with the material in the head of the linear accelerator and release neutrons. Such high energy radiation is more likely to be used for treatment of cancers in the chest or abdomen. A recent study published online in JAMA Oncology (free access to this article from publisher) has shown interference in the function of implanted devices for the heart in up to one fifth of the cases. The interference was lower, about one in ten for pacemakers while it was about one third for implanted defibrillators (devices used to shock the heart back into action when it stops functioning due to an abnormal rhythm).
The positive news in the study is that when lower energy radiation treatment which would not cause the release of neutrons (energy less than 10 MV) in the body was used, there was zero chance for impairment of device function. Another positive point in the study was that no delayed effects on device function was noted, meaning that whatever effect occurs, will be recognizable soon after the radiation treatment. It is also heartening to note that no deaths were reported due to device malfunction, though there were episodes of slow / fast heart beating and fall in blood pressure during the device malfunction. It may be noted that only 7 percent of the 249 courses of radiation treatment in those with cardiac implantable electronic devices (CIED) had device malfunction, possibly indicating that only a fraction of them needed really high energy treatment capable of releasing neutrons within the body.
Another curious observation in the study was that the proximity of part which was being treated by radiation did not predict the chance of device malfunction. This would suggest that there may be no role in changing the position of the device by surgical procedures prior to initiation of radiation treatment. But this aspect may need verification in further studies.
The proposed mechanism of interference is the effect neutrons on boron which is used as a dielectric in the integrated circuits of the CMOS (complementary metal oxide semiconductor) components of the cardiac implantable electronic device. In two instances, malfunction due to radiation treatment needed replacement of the device.