CIED relocation may be considered in situations where the location of the CIED interferes with the ability to adequately treat the patient, for example, the device is located in the path of the beam.
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. Discussions regarding the risks and benefits of CIED relocation should occur with the cardiologist, CIED technician, radiation oncologist and patient.
CT simulation and treatment verification imaging
The likelihood of CIED malfunction during CT scanning is extremely low and the presence of a CIED should not stop the acquisition of a scan that is clinically indicated.rrr
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 doser
- 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 beamrr
- avoiding unnecessary imaging including unnecessary 4D CT or 4D CBCTrr
- where possible, exclude the device from imaging fields. r
It is reasonable to monitor CIED function during the imaging procedure if a CIED will undergo prolonged uninterrupted exposure to the primary x-ray beam of the CT (e.g. >30 seconds) and the patient is either pacing dependent or has an ICD.r
MRI simulation for radiation therapy planning
CIEDs are generally contra-indicated for MRI, although some MRI conditional CIEDs exist.r MRI scanning of MRI conditional devices should comply with the stated conditions for that device model and may require device monitoring and adjustment for the scan by a CIED technologist or cardiologist.r Any device with an unknown MRI safety status should be assumed to be MRI unsafe.r
Safe scanning of non-MRI conditional devices may be possible, but require special precautions and discussions with the cardiologist, MRI unit director, radiation oncologist and patient regarding the risks and benefits of the procedure.r
Radiation therapy treatment planning considerations
Evidence to provide a safe range of acceptable radiation doses to the CIED is limited and the majority of RT-related CIED malfunctions are associated with neutron producing beams.r
To reduce the risk of CIED malfunction the following should be considered during radiation therapy treatment planning:
- use of non-neutron producing beam energies
- minimise dose to the CIED
- avoid the CIED being in the PTV or path of a planned radiation beam
- consider dose/repetition rate (MU/min) and pulse repetition frequency (Hz).rrrr
Neutron producing beam energies
The use of neutron producing radiation therapy beam energies is the strongest predictor of CIED malfunction and should be avoided where possible.r This risk has been reported to be independent of proximity to beam edges, body region receiving treatment, or cumulative dose.rrr See table 2 for neutron producing characteristics.
Table 2 - Neutron producing characteristics of radiation beams. Adapted from Indik et al. 2017r
||No relevant neutron production
||Marginal neutron production
||Clinically significant neutron production
||All clinically used energies.
|Radioactive isotopes (brachytherapy)
||All clinically used modalities.
* 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
Where possible, avoid use of physical wedges 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
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.
Planned dose to CIED
The planned cumulative dose to the CIED should be estimated and kept as low as reasonably acceptable in the radiation therapy treatment plan. Whilst changes to CIED function have been associated with doses of 2 Gy and CIED failure with doses of 10 Gy,r it is important to note that:
- the use of neutron producing energies in some early studies may have overestimated the dose sensitivity of CIEDsr
- the majority of reported CIED malfunctions with device doses <5 Gy are likely due to neutron exposure rather than dose receivedr
- the risk of failure with doses <10 Gy remains relatively low.r
Where the planned dose to the CIED is considered to be too high, additional CIED evaluation may be needed.r It may also be appropriate to consider device relocation, taking into account the risk and benefit to the individual patient.
Additional dosimetric considerations
If the location of the CIED is in the path of a planned radiation beam it 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.
Where possible, a radiation therapy treatment beam (including non-coplanar treatment fields) should not enter or exit through the CIED. When this is not possible, consideration should be given to the relocation of the device.
Alteration of CIED function
To avoid malfunction during radiation therapy treatment, some patients may require temporary alteration of CIED function through the application of clinical magnets or alteration of device programming.r
The cardiologist or CIED technician should identify:
- if the patient requires CIED function alteration
- what function changes are required (e.g. asynchronous pacing mode, disabling tachy 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 pre, during and post function alteration.
The length of time a device’s function is altered prior to each treatment/procedure should be kept as short as reasonably possible and function returned to normal immediately following treatment/procedure completion.