Therapeutic Radiation on SJM Confirm™

Effects of Therapeutic Radiation on SJM Confirm™ Implantable Cardiac Monitors

Background

Therapeutic radiation such as that used in cancer treatment can affect the operation of implantable cardiac monitors, including SJM Confirm.

Today’s implantable device technology uses complementary metal-oxide semiconductor (CMOS) integrated circuits. Low current consumption CMOS circuits are a breakthrough in the implantable device industry due to their inherent low current consumption, allowing for greater device longevity while keeping the size of devices small. However, these circuits can be more susceptible to therapeutic doses of radiation such as those used in cancer treatment. The damage can occur when cumulative doses of radiation affect the small silicon and silicon oxide insulators within the transistors.

While the risk of effects on device operation increases with increasing cumulative radiation exposure, no exact threshold for damage has been determined. It is important to note that the SJM Confirm™ provides no therapy to the patient and is a cardiac diagnostic monitor only. Permanent damage to devices is rare.

Sources of therapeutic radiation

Radiation therapy is frequently used as a treatment in many types of cancer. There are three typical ways this radiation may be administered—radioactive cobalt, linear accelerators, and betatrons. Note that linear accelerators and betatrons produce strong electromagnetic fields as well as radiation, which can also affect device operation.

Potential effects

The modes of interaction or failure as a result of exposure to radiation therapy are random. The effects can be temporary or permanent. A summary of potential effects is provided in the table below and is based on device testing at St. Jude Medical, clinical experience, and a review of the scientific literature.

Potential Effect Estimated Frequency
  Pacemakers ICDs
Permanent damage Rare Rare
Temporary loss of sensing Uncommon Uncommon
Device Uncommon Uncommon

Recommendations

St. Jude Medical recommends that ionizing radiation not be used in the vicinity of an implanted SJM Confirm. However, if it must be used in the vicinity of the implanted SJM Confirm, the following recommendations will help in patient management:

Patient management before therapy

Coning the radiation field to avoid the implantable cardiac monitor region helps reduce overall received dosage.

Patient management during therapy

It is recommended to monitor and record the cumulative radiation dosage to which a device has been exposed. While the risk of effects on device operation increases with increasing cumulative radiation exposure, no exact threshold for damage has been determined. Current devices have been tested to 70 gray (7,000 rads) without any adverse effects. This testing was performed using a low dose radiation source such as x-ray. No correlation testing to high dose sources presently used, such as linear accelerators or betatrons, has been performed. Cumulative dosage levels of 20 gray (2,000 rads) are seldom encountered by the implantable cardiac monitor when situated outside the irradiated field.

Patient evaluation following completion of radiation therapy

Following completion of the course of therapeutic radiation, the clinician may want to consider a detailed device evaluation. This should include device interrogation, evaluation of sensing function, and analysis of device diagnostics.

If you have any questions on this topic, please contact CRM Technical Services.

PDF Effects of Therapeutic Radiation on SJM Confirm™ Implantable Cardiac Monitors (84kb)
EMI TI16-101