PO-632-06 REAL-TIME EX-VIVO RADIOTHERAPY IMPACTS ON PACEMAKER FUNCTION ARE MINIMAL

Abstract

There is a paucity of data regarding the safety of radiotherapy in patients with pacemakers and the impact of linear accelerator parameters is unclear. To assess the function of pacemakers when exposed to different linear accelerator parameters. Pacemakers (2 single, 1 dual chamber) were exposed to radiation at dose rates 0.2-11.8Gy/min. Dose rate was modulated by adjusting the distance from the beam edge, linear accelerator pulse repetition rate (rep rate) and distance from source. Noise amplitude, pacemaker output, and device behavior during irradiation were assessed in VVI or DDD modes. Each device was irradiated 28 times for 10 seconds. Noise amplitude on bipolar (Bi) channel increased with dose rate (r2=0.3611, p<0.0001, B) and on unipolar (Uni) channel decreased with rep rate (r2 = 0.09, p<0.01; C). On both channels noise amplitude decreased with distance from field edge (Bi r2 = 0.53, p<0.01; Uni r2 = 0.42, p<0.01; D). No over-sensed events occurred in response to radiation induced background noise. Low frequency signals on the Uni and Bi channels were observed with beam on and off (E), resulting in over-sensed events only when directly in the radiation beam and sensing Uni. When directly in the beam, oversensing of A pacing on the V sensing Uni channel was observed leading to pacing inhibition (F). Post-radiation exposure interrogation was unremarkable revealing no evidence of device malfunction. Pacemaker malfunctions when directly in photon radiation beam are related to oversensing and crosstalk phenomena preferentially affecting the unipolar sensing channel. There was no evidence of long-term device malfunction upon repeated interrogations despite multiple exposures.