Abstract Funding Acknowledgements Type of funding sources: None. Background An increasing number of patients need cardiac implantable electronic devices (CIED) for bradycardia or to prevent sudden cardiac death. At the same time many patients require radiotherapy for oncologic reasons. Interaction between CIEDs and ionizing radiations may cause several dysfunctions: electromagnetic interferences due to oversensing, CIED reset, drainage of the battery, hardware damage to the pulse generator and to the lead-tissue interface. Purpose An adequate planning is expected to guarantee the safety of CIED patients, reducing the potential complications. We describe our protocol in use and its application. Methods In 2016 an internal protocol was written to standardize the approach to CIED patients undergoing radiotherapy. Cardiology Department, Radiotherapy Unit and Medical Physics were involved in the draft. We stratified patients in high and low risk groups according to the CIED characteristics (ICD vs pacemaker), electro-dependency (yes vs no), and the estimated radiation dose (< 2 Gy: 2-10 Gy, > 10 Gy). Low risk group: - Non pacemaker (PM) dependent patients, estimated dose < 10 Gy - PM dependent patients, estimated dose < 2 Gy High risk group: - PM dependent patients, estimated dose > 2 Gy - Non-PM dependent patients estimated dose >10 Gy - ICD patients Two EHRA certificated nurses followed up the patients before, during and after the radiotherapy. Low risk patients received weekly in office evaluation during radiotherapy course. High risk patients were scheduled for daily in office check plus monitoring during each radiotherapy session, ICD therapy was temporarily switched off during each radiotherapy session. An in office evaluation was planned 1, 3, 6 and 12 months after the end of radiotherapy course until 2019, since 2020 all patients were given remote monitoring for accurate follow up. Results Between 2016 and November 2022 101 patients with CIED underwent radiotherapy in our facility. Clinical characteristics of the patients are described in Table 1. EHRA certificated nurses managed 1282 radiotherapy sessions without any complication. A transient underestimation of ICD longevity was the only software error occurred. Conclusions The reported protocol assured a safe radiotherapy course for all our CIED patients. Given the limited data available about the interaction between the newest CIEDs and radiotherapy, we opted for a high safety profile. The EHRA certified nurse’s involvement allowed to optimize personnel resources.

Abstract Funding Acknowledgements None Background Direct photon exposure of implantable cardioverter-defibrillators (ICDs) during radiotherapy is still considered not recommended, or even unsafe, by manufacturers and guidelines. The effects of photon beams on ICDs are unpredictable, depending on multiple factors, and electromagnetic interferences (EMIs) may present during exposure. Purpose To evaluate transient ICD malfunctions by direct exposure to doses up to 10 Gy during low-energy radiotherapy, 36 contemporary wireless-enabled ICDs, with at least 4 months to elective replacement indicator (E.R.I.) were evaluated in a realtime in-vitro session. Methods All ICDs had baseline interrogation. Single chamber devices were programmed in the VVI/40 mode and dual or triple chamber devices were programmed in the DDD/40 mode. Rate response function and antitachycardia therapies were disabled, with the ventricular tachycardia (VT)/ventricular fibrillation (VF) detection windows still working. A centering computed tomography was performed to build the corresponding treatment plan and the ICDs were blinded randomized to receive either 2, 5 or 10 Gy exposure by a low photon-energy linear accelerator (6MV) in a homemade water phantom (600 MU/min). The effective dose received by the ICDs was randomly assessed by an in-vivo dosimetry. During radiotherapy course, the devices were observed in a real-time session using manufacturer specific programmer, and ICD function (pacing, sensing, programmed parameters, detection) was recorder by the video camera in the bunker throughout the entire photon exposure. All ICDs had an interrogation session immediately after exposure. Results During radiotherapy course, almost all ICDs (90.9%) recorded major or minor transient EMIs. On detail, 16 ICDs (44.4%) reported EMI-related atrial and/or ventricular oversensing, with base-rate-pacing inhibition and VT/VF detection. 16 ICDs (44.4%) recorded not clinically relevant minor EMIs, and no detections were observed. Only 4 ICDs (11.2%) reported neither transient malfunction nor minor EMIs, withstanding direct radiation exposure. At immediate post-exposure interrogation, the ICDs that recorded major real-time malfunctions had VT/VF detections stored in the device memory. In none of the ICDs spontaneous changes in parameter settings were reported. EMI-related malfunctions occurred regardless of either 2, 5 or 10 Gy photon beam exposure. Conclusions Transient EMIs were observed in most of the contemporary ICDs. To avoid potentially life-threatening ICD malfunctions such as pacing inhibition or inappropriate shock delivery, magnet application on the pocket site or reprogramming in the asynchronous mode are still suggested in ICD patients ongoing even low energy radiotherapy exposure.

Abstract Background Direct photon exposure of pacemakers (PMs) or implantable cardioverter-defibrillators (ICDs) during oncologic radiotherapy may transiently or permanently affect normal device function. To evaluate potential malfunctions by direct exposure to doses up to 10 Gy in 6-MV oncologic radiotherapy, commonly considered unsafe or even not recommended, 145 PMs and 65 ICDs were observed in three different centres. Methods All devices had a baseline interrogation and reprogramming to VVI/40 or to DDD/40 mode, depending on type and model. Rate-adaptive function was disabled in all the devices, whereas in ICDs, even antitachycardia therapies were disabled with the ventricular tachycardia/fibrillation (VT/VF) windows left enabled. To build the corresponding treatment plan, a centring computed tomography was performed with different Treatment Plan Systems among the centres. The devices were blinded randomized to receive either 2-, 5- or 10-Gy direct exposure by a 6-MV linear accelerator (different among the three centres) in a water phantom (600 MU/min). The effective dose received was assessed by a random in-vivo dosimetry. All devices had a telemetry interrogation immediately after exposure and once monthly during a six-month follow-up. Results Immediately after photon exposure, no changes in device parameters or software errors were observed in 209 devices (99.5%). A non-reprogrammable reset to emergency back-up mode (VVI/65) occurred in a PM (0.5% overall; 0.7% among PMs). Seven PMs reached the Elective Replacement Indicator immediately after exposure (3.3% overall; 4.8% among PMs). Sixteen ICDs (7.6% overall; 24.6% among ICDs) had multiple VT/VF detections stored in the device memory. Two PMs (1% overall; 1.4% among PMs) reported atrial fibrillation detections. During a six-month follow-up, a non-reprogrammable software reset (back-up to VVI/65 mode) was reported in one PM three months after a single exposure of 2 Gy (0.5% overall; 0.7% among PMs). Abnormal battery drain was observed in thirteen PMs (6.2% overall; 9% among PMs), and in one ICD (0.5% overall; 1.5% among ICDs). All events presented regardless of exposure dose of either 2, 5, or 10 Gy. Conclusions Last-generation devices, both PMs and ICDs, withstood direct 6-MV photon exposure up to 10 Gy, commonly considered not recommended or even unsafe by manufacturer statements and clinical guidelines. The most common failures were referred to battery issues. Malfunctions occurred solely in less recent devices, regardless of photon dose. Funding Acknowledgement Type of funding source: None

Abstract Funding Acknowledgements None Background The effects of high dose oncologic radiotherapy (RT) on cardiac pacemakers (PMs), at even less than 6 MV power, are unpredictable, depending on multiple factors. Normal PM function may be impaired during direct exposure, due to electromagnetic interferences (EMIs). Potentially life-threatening malfunctions may occur, expecially in PM-dependent patients, and both manufacturers and guidelines discourage direct exposure. Purpose To evaluate transient EMI-related PM malfunctions during direct exposure to doses up to 10 Gy during radiotherapy course, 17 wireless-telemetry-enabled PMs with sufficient residual battery charge for the purpose of the study (at least 4 months to elective replacement indicator, E.R.I.) were evaluated in three different centres. Methods All PMs underwent baseline interrogation. Single chamber devices were programmed in the VVI/40 mode while dual or triple chamber devices were programmed in the DDD/40 mode. To avoid the "run-away" phenomenon during exposure rate-adaptive function was disabled. A centering computed tomography was performed to build the corresponding treatment plan and the PMs were blinded randomized to receive either 2, 5 or 10 Gy exposure by a 6 MV linear accelerator in a homemade water phantom (600 Um/min). The effective dose received by the PMs was randomly assessed by an in-vivo dosimetry. During RT course, the devices were observed in a real-time session using manufacturer specific equipment, and PM function (pacing and sensing, programmed parameters) was recorder by a video camera in the bunker throughout the entire radiation exposure. Results During RT course, 13 PMs (76.5%) recorded not clinically relevant minor transient EMIs, and no atrial and/or ventricular oversensing nor base-rate-pacing inhibition were observed. Only 4 PMs (23.5%) reported neither transient malfunction nor minor EMIs, withstanding direct radiation exposure. Transient EMI-related malfunctions were observed regardless of either 2, 5 or 10 Gy exposure. Conclusions Minor, not clinically relevant EMI-related interferences were observed in most of the PMs during direct exposure. Nevertheless, to avoid potentially life-threatening PM malfunctions, magnet application on the PM pocket site or reprogramming are still suggested in PM-dependent (high risk) patients ongoing even low energy RT exposure.

Abstract Funding Acknowledgements None Backgroung. Direct photon exposure of cardiac implantable devices (CIEDs), both pacemakers (PMs) or implantable cardioverter defibrillators (ICDs), during oncologic radiotherapy (RT) courses may transiently or permanently affect normal device function. Purpose To evaluate CIED damage by direct exposure to doses up to 10 Gy in oncologic RT, commonly considered unsafe or even potentially harmful, 206 CIEDs (143 PMs and 63 ICDs) from three different centres, with at least 4 months to Elective Replacement Indicator (E.R.I.) were observed. Methods. All CIEDs had a baseline telemetry interrogation. Single chamber devices were programmed in the VVI/40 mode and dual or triple chamber ones were programmed in the DDD/40 mode. Rate adaptive function was disabled. In ICDs, antitachycardia therapies were disabled with the ventricular tachycardia/fibrillation window left enabled. A centering Computed Tomography was performed to build the corresponding treatment plan and CIEDs were blinded randomized to receive either 2, 5 or 10 Gy (direct exposure) by a 6 MV linear accelerator in a home-made water phantom. An in-vivo dosimetry randomly assessed the effective dose received by the CIEDs. All CIEDs were interrogated immediately after exposure and monthly during a three-month follow-up. Results. Immediately after photon exposure, no changes in device setting or software errors were observed in 205 CIEDs (99·5%). Reset to emergency back-up mode was observed in a PM (0·49% overall; 0·7% among PMs). Seven PMs reached the E.R.I immediately after exposure (3·4% overall; 4·9% among PMs). Sixteen ICDs (7·8% overall; 25·4% among ICDs) reported multiple ventricular tachycardia/fibrillation detections stored in the device memory. During follow-up, a non-reprogrammable software reset (emergency backup VVI/65 mode) was observed in one PM after a single dose of 2 Gy (0·49% overall; 0.7% among PMs), whereas an abnormal battery drain was observed in 6 PMs (2.9% overall; 4.2% among PMs). No battery issues were observed in ICDs. All reported events occurred regardless of either 2, 5, or 10 Gy direct exposure. Malfunctions were observed in only older CIEDs. Conclusions. Recent CIEDs have shown to be safe during oncologic RT, withstanding direct exposure up to 10 Gy, commonly considered not recommended or even unsafe by manufacturers statements and clinical guidelines. Malfunctions occurred solely in older devices.

Abstract Background Direct exposure of implantable cardioverter-defibrillators (ICDs) during radiotherapy is still considered potentially harmful, or even unsafe, by manufacturers and current recommendations. The effects of photon beams on ICDs are unpredictable, depending on multiple factors, and malfunctions may present during exposure. Purpose To evaluate transient ICD malfunctions by direct exposure to doses up to 10 Gy during low-energy RT, forty-three contemporary wireless-enabled ICDs, with at least 4 months to elective replacement indicator (ERI) were evaluated in a real-time in-vitro session in three different centres. Methods All ICDs had baseline interrogation. Single chamber devices were programmed to the VVI/40 mode and dual or triple chamber devices were programmed to the DDD/40 mode. Rate response function and antitachycardia therapies were disabled, with the ventricular tachycardia (VT)/ventricular fibrillation (VF) detection windows still active. A centring computed tomography was performed to build the corresponding treatment plan and the ICDs were blinded randomized to receive either 2-, 5- or 10-Gy exposure by a low photon-energy linear accelerator (6MV) in a homemade water phantom (600 MU/min). The effective dose received by the ICDs was randomly assessed by an in-vivo dosimetry. During radiotherapy, the ICDs were observed in a real-time session using manufacturer specific programmer, and device function (pacing, sensing, programmed parameters, arrhythmia detections) was recorder by the video camera in the bunker throughout the entire photon exposure. All ICDs had an interrogation session immediately after exposure. Results During radiotherapy course, almost all ICDs (93%) recorded major or minor transient electromagnetic interferences. On detail, sixteen ICDs (37.2%) reported atrial and/or ventricular oversensing, with base-rate-pacing inhibition and VT/VF detection. Twenty-four ICDs (55.8%) recorded non clinically relevant noise, and no detections were observed. Only three ICDs (7%) reported neither transient malfunction nor minor noise, withstanding direct radiation exposure. At immediate post-exposure interrogation, the ICDs that recorded major real-time malfunctions had VT/VF detections stored in the device memory. In none of the ICDs spontaneous changes in parameter settings were reported. Malfunctions occurred regardless of either 2-, 5- or 10-Gy photon beam exposure. Conclusions Transient electromagnetic interferences were observed in most of the contemporary ICDs during radiotherapy course, regardless of photon dose. To avoid potentially life-threatening ICD malfunctions such as pacing inhibition or inappropriate shock delivery, magnet application on the pocket site or ICD reprogramming to the asynchronous mode are still suggested in ICD patients ongoing even low energy radiotherapy exposure. Funding Acknowledgement Type of funding source: None

Abstract Background Direct exposure of implantable cardioverter-defibrillators (ICDs) during radiotherapy is still considered not recommended, or even unsafe, by manufacturers and guidelines. The effects of photon beams on ICDs are unpredictable, depending on multiple factors, and malfunctions may occur during exposure. Purpose To evaluate transient ICD malfunctions by direct exposure to doses up to 10 Gy during low-energy radiotherapy, 33 contemporary wireless-enabled ICDs, with at least 4 months to elective replacement indicator (E.R.I.) were evaluated in a realtime in-vitro session. Methods All ICDs had baseline interrogation. Single chamber ICDs were programmed in the VVI/40 mode and dual or triple chamber ICDs were programmed in the DDD/40 mode. Rate response function and antitachycardia therapies were disabled, with the ventricular tachycardia (VT)/ventricular fibrillation (VF) detection windows still active. A centering computed tomography was performed to build the corresponding treatment plan and the ICDs were blinded randomized to receive either 2, 5 or 10 Gy exposure by a low photon-energy linear accelerator (6MV) in a homemade water phantom (600 MU/min). The effective dose received by the ICDs was assessed by an in-vivo dosimetry. During radiotherapy, the devices were observed in a real-time session using manufacturer specific programmer, and ICD function (pacing, sensing, programmed parameters, detection) was recorder by the video camera in the bunker throughout the entire photon exposure. All ICDs had an interrogation session immediately after exposure. Results During radiotherapy course, almost all ICDs (90.9%) recorded major or minor transient electromagnetic interferences. On detail, 13 ICDs (39.4%) reported atrial and/or ventricular oversensing, with base-rate-pacing inhibition and VT/VF detection. 16 ICDs (48.5%) recorded non clinically relevant noise, and no detections were observed. Only 4 ICDs (12.1%) reported neither transient malfunction nor minor noise, withstanding direct radiation exposure. At immediate post-exposure interrogation, the ICDs that recorded major real-time malfunctions had VT/VF detections stored in the device memory. In none of the ICDs spontaneous changes in parameter settings were reported. Malfunctions occurred regardless of either 2, 5 or 10 Gy photon beam exposure. Conclusions Transient electromagnetic interferences were observed in most of the contemporary ICDs during radiotherapy course, regardeless of photon dose. To avoid potentially life-threatening ICD malfunctions such as pacing inhibition or inappropriate shock delivery, magnet application on the pocket site or reprogramming devices in the asynchronous mode are still suggested in ICD patients ongoing even low energy radiotherapy exposure. Acknowledgement/Funding None

Abstract Background The effects of high dose oncologic radiotherapy on cardiac pacemakers (PMs), at even less than 6MV power, are unpredictable, depending on multiple factors. Normal PM function may be impaired during photon exposure, with potentially life-threatening consequences in PM-dependent patients, and, unlike in magnetic resonance imaging setting, both manufacturer statements and guidelines discourage direct exposure. Purpose To evaluate transient PM malfunctions by direct exposure to doses up to 10 Gy during radiotherapy course, actually not recommended or considered even unsafe, 17 wireless-telemetry-enabled PMs obtained after upgrade or extraction of the system, with sufficient residual battery charge for the purpose of the study (at least 1 year to elective replacement indicator, E.R.I.) were evaluated in a real-time in-vitro session. Methods All PMs underwent baseline interrogation. Single chamber devices were programmed in VVI/40 mode while dual or triple chamber devices were programmed in DDD/40 mode. Rate adaptive function was disabled to avoid the “run-away” phenomenon during exposure. A centering computed tomography was performed to build the corresponding treatment plan and the PMs were blinded randomized to receive either 2, 5 or 10 Gy exposure by a low photon-energy linear accelerator (6MV) in a homemade water phantom (600 MU/min). The effective dose received by the PMs was assessed by an in-vivo dosimetry. During radiotherapy course, the devices were observed in a real-time session using manufacturer specific equipment, and PM function (pacing and sensing, programmed parameters) was recorder by a videocamera in the bunker before (5 minutes), throughout, and after (5 minutes) the entire radiation exposure. Results During radiotherapy course, non of the PMs reported spontaneous changes in parameter settings. 13 PMs (76.5%) recorded non clinically relevant minor transient electromagnetic sensing interferences. No atrial and/or ventricular oversensing nor base-rate-pacing inhibition were observed. Only 4 PMs (23.5%) reported neither transient malfunction nor minor noise, withstanding direct radiation exposure. Transient oversensing-related malfunctions were observed regardless of either 2, 5 or 10 Gy exposure. Conclusions Minor, non clinically relevant electromagnetic sensing interferences were observed in most of the PMs during direct exposure. Nevertheless, to avoid potentially life-threatening PM malfunctions, magnet application on the PM pocket site or reprogramming in the asynchronous mode are still suggested in PM-dependent patients ongoing even low energy radiotherapy exposure. Acknowledgement/Funding None