Abstract Body (Do not enter title and authors here): Introduction
The number of patients with cardiac implantable devices (CIED) who undergo radiation therapy (RT) is increasing. Previous studies have shown that the adverse effects to the CIED in patients undergoing RT is ~5%. Those studies were done on older generation devices, included high energy (>10 MV) RT with high doses, and were not done in the US. There have been no studies evaluating the safety of Photon RT at lower energy (<10 MV).

Hypothesis
Photon RT at <10 MV is safe in patients with CIED and is not associated with adverse effects.

Methods
Electronic records of patients with CIED who underwent Photon RT at our institution in the last 5 years (2019-2023) were analyzed. All patients with CIED were evaluated in the device clinic by device nurses prior to initiation of RT, weekly during RT, and at the end of RT. No changes were made to the device settings during RT.

Results
A total of 138 patients with CIED underwent RT. Eleven patients were excluded from the analysis due to lack of clinical information or if they had a nontraditional device. One hundred and twenty-seven patients were included in the final analysis. All patients received either 6 MV or 10 MV photon energy. Baseline characteristics, device information, and details of RT are shown in the table. No serious adverse effects such as factory reset, inappropriate sensing, or changes in lead parameters were noted. One patient had a drop in battery life by 1.3 years, while another had a drop in battery life by 9 months. Twelve patients had a change in battery life by approximately 6 months.

Conclusions
Photon RT in patients with CIED is extremely safe and is associated with even fewer side effects than previously reported in the literature with current generation devices and with energy levels <10 MV. In addition, given the shortage of electrophysiology, a device nurse driving protocol for monitoring CIED during RT is beneficial in the early identification of the few drops in battery life that might occur. Large-scale studies involving multiple centers are needed to validate our findings before being widely applied to clinical practice.