Local dose rate effects in implantable cardioverter–defibrillators with flattening filter free and flattened photon radiation

Abstract

Purpose In the beam penumbra of stereotactic body radiotherapy volumes, dose rate effects in implantable cardioverter–defibrillators (ICDs) may be the predominant cause for failures in the absence of neutron-generating photon energies. We investigate such dose rate effects in ICDs and provide evidence for safe use of lung tumor stereotactic radioablation with flattening filter free (FFF) and flattened 6 Megavolt (MV) beams in ICD-bearing patients. Methods Sixty-two ICDs were subjected to scatter radiation in 1.0, 2.5, and 7.0 cm distance to 100 Gy within a 5 × 5 cm2 radiation field. Radiation was applied with 6 MV FFF beams (constant dose rate of 1400 cGy/min) and flattened (FLAT) 6 MV beams (430 cGy/min). Local dose rates (LDR) at the position of all ICDs were measured. All ICDs were monitored continuously. Results With 6 MV FFF beams, ICD errors occurred at distances of 1.0 cm (LDR 46.8 cGy/min; maximum ICD dose 3.4 Gy) and 2.5 cm (LDR 15.6 cGy/min; 1.1 Gy). With 6 MV FLAT beams, ICD errors occurred only at 1 cm distance (LDR 16.8 cGy/min; 3.9 Gy). No errors occurred at an LDR below 7 cGy/min, translating to a safe distance of 2.5 cm (1.5 Gy) in flattened and 7 cm (0.4 Gy) in 6 MV FFF beams. Conclusion A LDR in ICDs larger than 7 cGy/min may cause ICD malfunction. At identical LDR, differences between 6 MV FFF and 6 MV FLAT beams do not yield different rates of malfunction. The dominant reason for ICD failures could be the LDR and not the total dose to the ICD. For most stereotactic treatments, it is recommended to generate a planning risk volume around the ICD in which LDR larger than 7 cGy/min are avoided.

A systematic review and meta‐analysis on oncological radiotherapy in patients with a cardiac implantable electronic device: Prevalence and predictors of device malfunction in 3121 patients

“…These data were confirmed by another even more recent study where, again with 6‐MV flattened and flattening‐filter‐free beams, CIED malfunctions were not related to total dose but seemed to be correlated with instantaneous local dose rate. 50 About the value of 2 Gy as a limit of the energy delivered to the CIED, an aforementioned European Heart Rhythm Association survey 44 reports that only 14% of centres involved in management of patients with CIED undergoing RT considered 2 Gy as risky limit, while 7% of respondent centres considered safe a limit of 5 Gy and another 7% did not take into account safety limits. It is noteworthy that, according to our meta‐analysis, the type of CIED and the use of neutron‐producing beam energies appear to be actually more important than these safety levels of RT dose.…”