Clinical physics
Influence of radiotherapy on the latest generation of pacemakers

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Abstract

The influence of radiotherapy on 19 new, modern pacemakers has been determined. Seven pacemakers lost output at 120 Gy. Eight pacemakers showed inhibitions during irradiation in the direct beam. Five pacemakers did not show any malfunction at all. Most malfunctions were observed at dose levels exceeding 20 Gy. Although the newest generation of pacemakers exhibit a variety of defects, AAPM taskgroup 34 guidelines still seem to be valid.

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Methods and materials

Nineteen pacemakers from 4 different manufacturers (Medtronic, Vitatron, Guidant and St Jude Medical) were tested in this study. All devices were new, i.e.; no used pacemakers were included as these might have a history of use, which could influence the results. All pacemakers were programmed to a maximum and minimum frequency of 120 beats per minute (bpm) and 60 bpm, respectively. A pulse duration of 0.5 ms and a pulse amplitude of 2.5 V were used. The sense threshold was programmed at most

Pacing pulse. A. All amplitude deviations of more than 25%

Amplitude deviations of more than 25% were only observed just after the last irradiation for three out of 19 pacemakers. These pacemakers all received a cumulative dose of 120 Gy. Devices 6 and 19 suffered amplitude changes at both the atrial and ventricular channel, during the post 120 Gy and the final measurement. The amplitude deviation was only observed at the atrial channel of pacemaker 18 during the post 120 Gy measurement.

Normal amplitude measurements were not possible for device 3,

Discussion

In our study, the devices were placed in the direct beam, in order to limit the total actual irradiation time needed in our study to 11 h per device. With the extensive measurements performed before, during and after each irradiation, this resulted in a total of 440 man-hours needed for data acquisition only. In clinical practice, pacemakers and ICDs should be placed outside of the unshielded beam, as recommended in the AAPM taskgroup report 34 [5]. Such test geometry would have led to an

Conclusion

Pacemakers show a large variation in thier sensitivity to radiation. Except one device, which showed its point of failure at 20 Gy, all other devices could withstand a dose of 90 Gy or more before it reached a point of failure. Five devices did not show any error at all. The most commonly observed point of failure was loss of output. Five out of 19 devices showed a battery replacement warning, a short period after the last irradiation. Since all devices in this study were new, this error could

Acknowledgements

We wish to thank Gijs de Ruiter, cardiologist at the OLVG for useful comments and discussions. Gert Meijer, clinical physicist at the Catharina Hospital, is greatly acknowledged for his critically comments and suggestions. The donation of the pacemakers by the pacemaker manufacturers and the valuable discussions with the manufacturers are greatly appreciated.

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