Clinical Implementation of TG-203 in a High Risk CIED Patient

Purpose: Cardiovascular implantable electronic devices (CIEDs), including pacemakers and defibrillators, are sensitive to the effects of radiation and can potentially fail at high doses (or even at unpredictable doses). When planning radiation treatment in patients with CIEDs, several factors must be taken into account, including proximity of the CIED to the radiation field, dose, and beam energy. The American Association of Physicists in Medicine (AAPM) published TG-203 guidelines in 2019 to facilitate management of patients with CIEDs receiving radiation therapy. No evaluation of TG-203 implementation in a high risk patient has been reported, though one abstract describes a single institution’s review of low risk patients.

Methodology: A head and neck cancer radiation treatment patient with a CIED in close proximity to the radiation field was identified. Using this treatment planning dataset, we calculated scatter dose at various distances from the 50% isodose line of the VMAT plan, including at the CIED, and compared those calculations to TLD measurements obtained during a single fraction of treatment.

Results: Interest point scatter dose calculations showed a nice exponential decrease in dose the further away from the 50% isodose line we calculated. However, TLD measurements on the CIED did not correlate well with predicted scatter dose. Placement of TLDs on/around CIEDs is not a simple or easily reproducible process, given the shape of the CIED, the need for bolus, and in this patient’s case, the recommendation to place a magnet over the CIED as well.

Conclusions: TG-203 recommends that CIEDs within a certain distance of the field edge or 50% isodose line be consider high risk, and that those with predicted scatter dose >500 cGy be monitored more closely. We would add that confirmational measurement of scatter in the clinical setting is difficult and unreliable, and it should not be done with the intent not to monitor the patient closely, if indicated. When dealing with potential failure of a life-sustaining device, err on the side of caution.

References: Influence of radiotherapy on the latest generation of implantable cardioverter-defibrillators https://doi.org/10.1016/j.ijrobp.2005.04.047

Management of radiotherapy patients with implanted cardiac pacemakers and defibrillators: A Report of the AAPM TG-203 https://doi.org/10.1002/mp.13838

Clinical Implementation of TG-203 for Patients With Implanted Cardiac Devices at One Institution https://doi.org/10.1016/j.ijrobp.2020.07.2346