Author: Angela Gearhardt, Stephen F. Kry, Christopher Ryan Peeler, Julianne M. Pollard-Larkin 👨🔬
Affiliation: The University of Texas MD Anderson Cancer Center UTHealth Houston Graduate School of Biomedical Sciences; The University of Texas MD Anderson Cancer Center, The University of Texas MD Anderson Cancer Center 🌍
Purpose: A growing number of radiation therapy (RT) patients have cardiovascular implantable electronic devices (CIEDs). Patients with CIEDs must be carefully managed because the devices are susceptible to malfunction, which can be life-threatening if not identified within sufficient time. The risk of CIED malfunction increases with exposure to neutrons. This study aims to characterize the risk of CIED malfunction from secondary neutron exposure.
Methods: This study included 110 patients with CIEDs who received neutron-producing photon therapy at a large academic cancer center from December 2014 to April 2023. The patients represented a variety of treatment sites including thoracic, adominal, pelvic, head and neck, and extrimites. An analytical model was used to calculate secondary neutron Ambient Dose Equivalent, Dose Equivalent, total Fluence, thermal Fluence (< 1 eV), epithermal Fluence (1 eV – 1 keV), and fast Fluence (> 1 keV) to each CIED, considering all boosts and reirradiations. The analytical model was developed from previously published measured data taken with a Varian LINAC. The model considered particle type (photon or electron), energy, MU, and depth of the CIED.
Results: Of the 110 patients who received neutron-generating photon RT, 4 experienced malfunction (3%, 95% CI: [1%, 10%]). The mean Ambient Dose Equivalents for CIEDs with and without resets were 33 mSv (range: 21, 57) and 21 mSv (range: 0.01, 145), respectively; there was no statistically significant difference between these values. Similarly, physical dose and fluence were not observed to be significantly predictive of CIED reset.
Conclusion: Neutrons induce CIED resets in the clinical setting; therefore, CIED patients must be carefully managed when receiving neutron-generating RT. Unfortunately, none of the metrics of neutron exposure examined were significantly predictive of CIED reset. Best clinical practice therefore remains to broadly minimize use of high-energy photon beams for CIED patients.