In-vitro effects of modern radiotherapy regimes on cardiac implanted electrical devices

Background and purpose: External Beam Radiotherapy (EBRT) of patients with Cardiac Implanted Electrical Devices (CIEDs) have guidelines developed over many decades, during which both technologies have advanced. Consequently, guidelines may not reflect modern device interactions. Asynchronous modes, with pace sensing and shocks turned off whilst regulating pacing output, is used routinely for MRI scanning and could reduce risks for pace sensing errors in radiotherapy. Evidence is limited on modern radiotherapy using high dose, high doserate beams, with CIEDs in asynchronous mode. We present the effects of irradiating modern CIEDs using contemporary radiotherapy regimes. Materials and methods: One hundred and sixty explanted CIEDs were irradiated, to corroborate historical findings for modern devices in normal operational modes, and explore effects when in asynchronous mode. Regimes knowingly detrimental to CIEDs; 48 Gy single fraction, neutron producing, alongside clinically relevant regimes of 60 Gy in 5 fractions using 10 MV flattening filter free [FFF] beams at clinical, and maximal dose rates. Results: No significant changes occurred to pacing voltages from 60 Gy in 5 fractions 10 MV FFF deliveries in asynchronous mode.No evidence supported restricting 6 MV flattened beams for CIED patients, including defibrillation capable devices. Conclusions: This study demonstrates asynchronous mode can reduce the frequency of CIED malfunctions during EBRT. However, clinical context, risks and benefit must be evaluated per patient. While some current guidelines potentially compromise plan quality to reduce dose to the CIED, the use of asynchronous mode may provide planning options, which more closely align to non-CIED cases.