High incidence of implantable cardioverter defibrillator malfunctions during radiation therapy: neutrons as a probable cause of soft errors

To investigate the behaviour of the implantable cardioverter defibrillator (ICD) function during actual radiotherapy sessions. Fifteen patients with an ICD underwent 17 radiation treatments for cancer [cumulative dose to the tumour was between 16 Gray (Gy) and 70 Gy; photon beams with maximum energies between 6 megaelectronvolt (MeV) and 18 MeV were employed]. During every session, the ICD was programmed to a monitoring mode to prevent inappropriate therapy delivery. Afterwards, the ICDs were interrogated to ensure proper function. Calculated radiation dose at the ICD site was 1 Gy in all patients. In 5 out of 17 radiation treatments (29) the ICDs showed 6 malfunctions (35). We noticed four disturbances in the memory data or device resets during radiation treatment and one case of inappropriate ventricular fibrillation detection due to external noise. In one case a late device data error was observed. All malfunctions occurred at 10 and 18 MeV beam energies. Despite the fact that all recommended precautions were taken to minimize the damage to the ICDs during radiotherapy and the calculated dose to the ICDs was 1 Gy, in 29 of the treatments a malfunction occurred. We observed a possible correlation between the beam energy and the malfunctions. This correlation may be due to an interaction between neutrons produced in the head of the linear accelerator at beam energies epsilon 10 MeV, and boron-10 which is present in the integrated circuit.