Cardiac implantable electronic device management during radiation therapy

• Exposure to ionising radiation may lead to the malfunction of cardiac implantable electronic devices (CIEDs).
• The risk of CIED malfunction from ionising radiation is serious but rare.
• When applying the CIED assessment and management strategies in this resource it is important to consider the potential impact on treatment quality or delays in commencing treatment and the subsequent risk and benefit to each individual patient and clinical scenario.
• CIED function assessment provides patient specific CIED information including recommendations for:
  • daily monitoring of vital signs
  • daily device function alteration
  • additional CIED function assessment.
• Cardiologist and/or CIED technician involvement may be required to determine individual patient management strategies.
• All patients with a CIED should have a CIED function assessment within the last 12 months prior to the commencement, and at the conclusion, of a course of radiation therapy. Some patients may require ongoing weekly CIED function assessment.
• The use of neutron-producing beam energies is the strongest predictor of CIED malfunction.
• Published studies and guidelines recommend doses be kept under 2-5 Gy and there is generally consensus that doses >10 Gy should be avoided.^rr
• Key treatment planning strategies to reduce the risk of CIED malfunction include:
  • avoiding neutron-producing beam energies
  • minimising dose to the CIED
  • avoiding the path of the planned radiation beam passing through the CIED.

Definitions

Table 1.0 Definitions of key terms

Risk vs benefit of CIED assessment and monitoring

In cases where delays to commencing treatment may negatively impact on a patient’s clinical outcome, the risks and benefits of omitting or delaying the listed assessment and management strategies should be carefully considered.

Assessment and monitoring summary table

When deciding on the need for any of the actions listed in the summary table (table 2.0), it is important to consider the patient’s performance, treatment time, and cardiologist advice.

Precautions should not be limited based on the region of the body receiving radiation therapy, as the risk of CIED malfunction is not limited to patients receiving treatment to body regions close to the device.^r

Table 2.0 Assessment and monitoring summary table

^*Pre-treatment CIED function assessment to be done within last 12 months, if patient has symptoms of CIED malfunction or if patient is considered high risk after discussion with cardiologist

^{^}Monitoring for cardio-respiratory symptoms may include ECG and pulse oximetry. In some cases, patient-specific parameters and acceptable variance during monitoring may be provided e.g. programmed pacing rates and asynchronous pacing rate. Consider patient’s performance, treatment time, and cardiologist advice which may be relevant in decision making regarding daily vital signs monitoring.

^∞If CIED function has been altered, vital signs should be monitored until the device function is returned to normal.

Table 2.1 Assessment and monitoring intervention level definitions

This information is also available as flowchart.

Other types of implantable devices

Recommendations on other implantable medical devices are beyond the scope of this resource, the AAPM TG-203 report provides some information (section 9).^r

Purpose of CIED function assessment

The main purpose of a CIED function assessment is to collect information on the risk to, and management of, the individual patient including:

• any relevant device factors such as battery status, impedance thresholds, pacing, tracking and sensor rates
• the need for additional weekly CIED function assessments
• recommendations on:
  • surgical relocation
  • device alteration and the appropriate procedure and precautions required (including alteration of CIED programming to a fail-safe mode or the use of magnets to inhibit the CIEDs function)
  • appropriate levels of observation and monitoring of vital signs during radiation therapy.

Definition of CIED function assessment

A CIED function assessment is where a patient with a CIED has an individual assessment to determine the management they require pre-, during, and post-radiation therapy treatment.

This usually involves completing an interrogation of the CIED device in conjunction with completing a CIED function assessment form.

CIED function assessment form

The CIED function assessment form includes information on:

• CIED features
• Pacing system and function parameters
• Radiation therapy treatment plan information
• Recommendations to manage the risk to CIEDs including the need to alter device function, patient monitoring during treatment and additional function assessment during treatment.

The information entered in the assessment form may come from a variety of sources and involve multidisciplinary input e.g. device interrogation information, radiation therapy plan and cardiologist advice.

Examples of CIED function assessment forms are:

• eviQ CIED function assessment form.
• Table 6 in the 2017 HRS expert consensus statement (table 6).

CIED device interrogation

Interrogation of the CIED device may be done via an in-person appointment with a qualified cardiac technician or cardiologist, or via a remote interrogation device used by a suitably trained person.

Important considerations when using a remote interrogation device (figure 1.0) for CIED function assessment:

• Remote interrogation should only be performed by a suitably trained person, as per manufacturer instructions and local institution guidelines and policies.
• Ensure that all relevant parameters required for the function assessment are included in the interrogation.
• A cardiologist or CIED technician should interpret the report and be consulted to provide the appropriate advice on risk and management of these patients.

Figure 1.0. Example of a remote interrogation device

Image used with permission

When is a CIED function assessment required?

Patients with a CIED should be identified prior to any exposure to ionising radiation e.g. during the initial radiation oncology consultation or prior to simulation.

Patients with symptoms of pacemaker malfunction, or those who are considered high-risk of pacemaker malfunction (after consultation with their cardiologist), should have a CIED function assessment completed prior to commencing treatment.

All other patients should have a CIED function assessment within 12 months prior to commencing treatment. If the most recent CIED function assessment was completed >12 months prior or the assessment doesn’t provide adequate information to determine the risk and management of the patient’s CIED, a new CIED function assessment should be completed.

The time points for CIED function assessment are outlined in this table.

CIED components

CIEDs consist of two main components: the device generator and the leads. There is insufficient evidence to suggest that the leads are sensitive to radiation, therefore the effects on CIED function in this document refer to the device generator.

Planning considerations

To reduce the risk of CIED malfunction consider:

• using non-neutron producing beam energies and avoid using neutron producing equipment e.g. physical wedges
• minimising dose to the CIED
• avoiding the CIED being included in the planning target volume (PTV) or planned beam path
• the dose/repetition rate (MU/min) and pulse repetition frequency (Hz) i.e. where possible, when treating near the CIED, use lower dose rates and lower energy treatment beams.^rrrr

Neutron producing beam energies and equipment

Evidence to provide a safe range of acceptable radiation doses to the CIED is limited and the majority of radiation therapy-related CIED malfunctions are associated with neutron producing beams.^r This risk has been reported to be independent of proximity to beam edges, body region receiving treatment, or cumulative dose.^rrr See table 3.0 for neutron producing characteristics of radiation beams.

• The use of neutron producing radiation therapy beam energies is the strongest predictor of CIED malfunction and should be avoided where possible.^r
• The use of physical wedges should also be avoided due to an increase in neutron production.^r
• High z-value shielding materials, including lead shielding on skin, do not provide protection against neutrons or internal scatter.^r

Table 3.0 Neutron producing characteristics of radiation beams. Adapted from Indik et al. 2017^r

* Neutron production in 10 MV photon beams is approximately 20-fold less compared to 18 MV beams.
NB: heavy ion particles have a similar net neutron production to protons.^r

Planned cumulative dose to CIED

Whilst the strongest association of CIED malfunction is with neutron producing beams, there is still evidence for increased risk of CIED malfunction with increased cumulative doses to the CIED.

The planned cumulative dose to the CIED should be estimated and kept as low as reasonably acceptable in the radiation therapy treatment plan.

Published studies and guidelines recommend doses be kept under 2-5 Gy and there is generally consensus that doses >10 Gy should be avoided.^rr Doses >5 Gy have been reported to result in CIED malfunction.^r

Where the planned dose to the CIED is too high, consider:

• additional CIED evaluation/assessment e.g. on treatment monitoring may be recommended.^r
• device relocation. When a device is planned to receive a maximum cumulative dose of ≤5 Gy, CIED relocation is not recommended.^r There is insufficient evidence to guide recommendations for relocation when the dose exceeds 5 Gy.

Radiation beam path and CIED location

Where possible, a radiation therapy treatment beam (including non-coplanar treatment fields) should not enter or exit through the CIED. CIEDs in the direct path of a planned radiation beam can result in:

• dosimetric uncertainties in the radiation therapy treatment plan of up to 20%^rr
• limited ability to deliver adequate radiation doses to the target.

If the device cannot be avoided, CIED relocation may be considered in the context of the risks and benefits for the individual patient.

Considerations for non-MV treatments

Orthovoltage and superficial beam energies

Although there is no published literature regarding the effect on CIEDs from low energy radiation therapy beams used in orthovoltage and superficial radiation therapy, monitoring and interventions for patients undergoing these treatments should be determined in consultation with the CIED technician or cardiologist, and clinical medical physics specialist. Where possible, beam paths should avoid entry and exit through the CIED.

Brachytherapy

In general, pelvic brachytherapy would be of low risk of CIED malfunction. However, if brachytherapy is performed close to the CIED in vivo dosimetry may be required.^r A dose assessment from radiation oncology medical physics should be completed and documented.

Although the risk of CIED malfunction from treatment verification imaging is low, the benefits and risks of imaging (e.g. 4D CBCT) should be carefully considered.^rr Interference with the CIED can be completely avoided by ensuring the device is not in the primary x-ray beam of the kV imaging device.^r In this case, there is no need for additional device assessment, programming or monitoring.^r

When it is necessary for the device to be in the primary x-ray beam of the kV imaging device, the likelihood of interference can be lowered by:

• reducing the radiation dose^r
• reducing the dose rate (either by lowering the pitch value or increasing the rotation time)^r 
• reducing the time the device is in the direct primary beam^rr
• where possible, excluding the device from imaging fields or field of view (FOV).^r

Purpose of daily CIED function alteration

• To avoid malfunction during treatment, some patients may require temporary alteration of CIED function using clinical magnets or alteration of device programming.^r
• Prior to commencing treatment, the need to alter CIED function should be identified during the CIED function assessment e.g. if the patient has an ICD and is at risk of inappropriate shock from the device.
• The potential risks and benefits of modifying CIED function, in particular defibrillators, should be considered and discussed with the patient’s cardiologist.

How is CIED function altered?

The cardiac technician or cardiologist should provide guidance on:

• what device function alteration is required (e.g. asynchronous pacing mode, disabling tachycardia therapies)
• the method to apply these function changes for each treatment (e.g. use of a magnet or alteration of programming)
• what monitoring of the patient is required before, during and after device function alteration.

When is the CIED function altered?

• The CIED function should be altered immediately prior to each treatment fraction delivery.
• The length of time a device’s function is altered should be kept as short as possible.
• Function should be returned to normal immediately following treatment.

Purpose of daily cardiovascular function monitoring

Some patients require daily cardiovascular monitoring during treatment delivery. This is to identify any CIED device malfunctions or cardiovascular events.

Who requires daily cardiovascular function monitoring?

The need to monitor a patient's cardiovascular vital signs should be determined during the CIED function and assessment.

Daily monitoring is generally indicated for patients that are:

• pacemaker dependent
• receiving treatment with a neutron producing beam energy (>10 MV)
• receiving a cumulative dose ≥2 Gy to CIED.
• have the CIED function altered for treatment.

Generally, daily monitoring is not indicated for patients that are pacemaker non-dependent AND receiving treatment with non-neutron producing beam (≤10 MV) AND a cumulative dose <2 Gy to the CIED.

Daily monitoring may be indicated in patients where the CIED function assessment identifies a need for monitoring or based on individual patient factors and should be discussed with the cardiologist and cardiac technician.

Patients who have their CIED function altered should be monitored from when the CIED function is altered to when it is returned to normal function.^r

Cardiovascular function monitoring equipment

• Equipment to monitor cardiovascular vital signs may include an ECG monitor and/or pulse oximeter.
• An emergency trolley should be readily available in case of an emergency caused by a CIED malfunction (as per local institution policy and guidelines).

Cardiovascular function monitoring staff

• Monitoring should be performed by a suitably trained staff member (e.g. nurse trained to read ECGs).
• In case of an emergency caused by a CIED malfunction, suitably trained staff should be readily available (as per local institution policy and guidelines).

Cardiovascular function monitoring procedure

During treatment delivery, continuously monitor the patient's cardiovascular function for signs and symptoms of a CIED malfunction.

Cardiovascular function monitoring may include:

• continuous visual observation and audio contact
• observation of vital signs for cardio-respiratory symptoms using relevant equipment (e.g. ECG monitor and/or pulse oximeter).
• the cardiologist or CIED technician may provide patient-specific parameters and acceptable variance during monitoring e.g. programmed pacing rates and asynchronous pacing rate.

Signs and symptoms of a CIED malfunction include: 

• dizziness shortness of breath
• loss of consciousness
• palpitations (rapid, fluttering or pounding heart)
• bradycardia (slower than normal heart rate)
• receiving a shock from their ICD.

Resolving CIED malfunctions

• In an emergency follow local institutional policy and guidelines.
• The majority of CIED malfunctions are due to software errors and electronic resets, which programming can correct.^r
• If device malfunction is suspected, due to ECG observations or patient signs and symptoms, additional discussion, investigations, and consultation with the cardiologist should be considered.

Documentation

• Record all observations as per local institution policy and guidelines.

A weekly CIED function assessment during treatment may be required to identify any CIED malfunctions in patients including those:

• who are pacemaker dependent
• requiring CIED function alteration
• receiving neutron producing treatment
• receiving non-neutron producing treatment and >5 Gy dose to CIED.

The cardiologist or cardiac technician may identify other patients requiring weekly CIED function assessments.

Treatment course completion

A CIED function assessment should be done after delivering final fraction to assess CIED functionality and any radiation induced impact on CIED.

Assessment follow-up

A patient's CIED should be routinely checked by the cardiologist at follow up appointments. It is advisable that documentation of radiation treatment and dose received to the CIED (if any) is provided to cardiologist at completion of treatment.

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