Management of Cardiac Implantable Electronic Devices for Patients Receiving MR-Guided Radiotherapy: 4-Year Single Institution Experience

Abstract

<h3>Purpose/Objective(s)</h3> Implanted metallic devices are a potential contraindication to MR-guided radiotherapy (MRgRT). The safety and feasibility of treating patients with a cardiac implantable electronic device (CIED), such as a pacemaker/defibrillator/loop recorder, is not well understood. We developed an institutional CIED MRgRT workflow for patient triage/evaluation and treatment on a 0.35 T MR Linac. <h3>Materials/Methods</h3> Patients (including pacemaker dependent) with MR-compatible CIEDs were prospectively evaluated according to an institutional MRgRT CIED workflow. This workflow includes prior to simulation: (1) MR patient screening form at consultation to identify CIED; (2) Medical necessity for MRgRT determined by clinician and approved by MRgRT director. If medical necessity not established, patient is triaged to non-MR RT; (3) Cardiologist to complete CIED programming orders; (4) Medical physicist to verify that MR-compatible CIED matches vendor's records; (5) Chest X-ray to be reviewed to ensure no extenders, adaptors, or abandoned leads and to confirm radiopaque CIED ID; (6) Patient to consent for off-label CIED according to risk assessment. The workflow for MRgRT treatment includes: (1) Crash cart, pulse oximetry, and electrocardiogram availability/use; (2) Cardiology present; (3) CIED pacemaker and defibrillator interrogated for lead impedance, battery voltage, and pacing threshold; (4) CIED programmed according to orders; (5) Vitals monitored during MRgRT using in-vault camera; (6) Post-treatment, CIED returned to normal pacing and interrogated. (7) All patients monitored for cardiac events throughout the course of treatment. <h3>Results</h3> Five different CIED models in 12 patients (9 pacemaker, 2 loop recorder, 1 defibrillator) were encountered in patients with cancers of the pancreas (5), kidney (2), lung (2), adrenal (1), bile duct (1), oligometastases (1). Patients received a median dose of 50 Gy (range 25-60 Gy) in 5 fractions (fx) (range 1-5); 80% of patients were adaptively replanned on-table. Maximum CIED dose was < 2 Gy for all patients. No intra- or interfraction CIED change was noted for lead impedance, pacing threshold voltage, and battery voltage. With median follow up of 5.2 months, no patient experienced a cardiac event or CIED malfunction. <h3>Conclusion</h3> We developed a thorough and efficient workflow for management of CIED in patients receiving MRgRT. Safety of consecutive use of MR imaging up to 6 sessions (i.e., simulation and treatment) was shown. Under controlled conditions and monitoring, low-field MRgRT, with cumulative device dose < 2 Gy, may be used without adverse events in patients with CIEDs, including high-risk patients. Ultra-hypofractionation (1-3 fxns) may be considered to further reduce patient risk and departmental resources.