The effect of radiotherapy beam energy on modern cardiac devices: an in vitro study

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Abstract
Radiotherapy (RT) for malignancies can harm pacemakers (PMs) and implantable cardioverter-defibrillators (ICDs). There is some evidence that, besides cumulative dose, the damaging radiation effects increase with beam energy. The aim of this study was to determine whether modern PMs and ICDs are more sensitive to high-energy than to low-energy photon beams. Two groups of unused PMs and explanted ICDs (five PMs and one ICD in each) were subjected to irradiations in a phantom with 6 and 18 megavolt (MV) photons, respectively. The devices were exposed to radiation at doses of 2 gray (Gy) daily to simulate two clinical scenarios with the PM/ICD in the RT field. A cumulative dose of 150 Gy was given to each device, corresponding to approximately twice the therapeutic dose. In the 6 MV group, one episode of PM malfunction was detected after reaching 150 Gy. In the 18 MV group, a total of 14 episodes of malfunction were detected starting at 30 Gy in all five PMs. No episodes appeared in the ICD, at the respective treatment groups. This corresponded to a hazard ratio of 9.11 [∼95% confidence interval (CI): 1.04–79.69] by Cox regression analysis between the two groups. In a repeated measures logistic regression model comparing the incidence rate of malfunctions, the odds ratio was 18.29 (∼95% CI: 1.52–219.41). Photon beam energy plays a considerable role in inducing implantable cardiac device malfunctions. Low-energy RT may be safer in PM/ICD patients despite relatively high radiation dose to the device.

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