PURPOSE: Cardiac implantable electronic devices (CIED) are sensitive to scattered secondary neutrons from proton beam irradiation. This experimental in vitro study investigated risk of CIED errors during pencil beam proton therapy.
METHODS AND MATERIAL: We used 62 explanted CIEDs from four manufacturers; 49 CIEDs were subjected to a simulated clinical protocol with daily 2 Gy relative biological effectiveness (RBE) fractions prescribed to the phantom. Devices were located at three different lateral distances from the spread-out Bragg peak to investigate risk of permanent or temporary device errors. Additionally, 13 devices with leads connected, were monitored live during consecutive irradiations to investigate risk of noise, over- or under-sense, pace-inhibition and inappropriate shock-therapy.
RESULTS: We detected 61 reset errors in 1,728 fractions and all except one CIED were reprogrammed to normal function. All, except one reset, occurred in devices from the same manufacturer. These were successfully reprogrammed to normal function. The one remaining CIED was locked in permanent safety mode. Secondary neutron dose, as estimated by Monte Carlo simulations, was found to significantly increase the odds of CIED resets by 55% per mSv. Clinically significant battery depletion was observed in five devices. We observed no noise, over- or under-sense, pace-inhibition or inappropriate shock therapy during 362 fractions of live-monitoring.
CONCLUSION: Reprogrammable CIED reset was the most commonly observed malfunction during proton therapy and reset risk depended on secondary neutron exposure. The benefits of proton therapy are expected to outweigh the risk of CIED malfunctioning for most patients.