Dosimetric review of cardiac implantable electronic device patients receiving radiotherapy

Safety Review of Radiotherapy for Tumor Patients with Implantable Cardiac Pacemaker

Permanent pacemaker implantation is one of the most effective treatments for chronic arrhythmia. However, there is a certain risk associated with radiation therapy in cancer patients with implantable cardiac pacemakers. To prevent radiotherapy-induced pacemaker failure, there are established medical guidelines for the use of pacemakers in patients undergoing radiotherapy. With advancements in science and technology, the variety of available pacemakers has considerably increased, and radiotherapy equipment has also been updated. Given the variations in irradiation methods and the types of radiation used in clinical practice, there is a pressing need for international consensus on the regulations governing the use of cardiac pacemakers in cancer patients. Currently, many countries lack clinical guidelines for radiotherapy in cancer patients with cardiac pacemakers. This review summarizes recent reports and studies from PubMed (National Center for Biotechnology Information) regarding the safety of radiotherapy in cancer patients with implanted cardiac pacemakers, and provides valuable insights for clinical practice.

Impact of Radiotherapy on Malfunctions and Battery Life of Cardiac Implantable Electronic Devices in Cancer Patients

PURPOSE

This study analyses a large number of cancer patients with CIEDs for device malfunction and premature battery depletion by device interrogation after each radiotherapy fraction and compares different guidelines in regard to patient safety.

METHODS

From 2007 to 2022, a cohort of 255 patients was analyzed for CIED malfunctions via immediate device interrogation after every RT fraction.

RESULTS

Out of 324 series of radiotherapy treatments, with a total number of 5742 CIED interrogations, nine device malfunctions (2.8%) occurred. Switching into back-up/safety mode and software errors occurred four times each. Once, automatic read-out could not be performed. The median prescribed cumulative dose at planning target volume (PTV) associated with CIED malfunction was 45.0 Gy (IQR 36.0-64.0 Gy), with a median dose per fraction of 2.31 Gy (IQR 2.0-3.0 Gy). The median maximum dose at the CIED at time of malfunction was 0.3 Gy (IQR 0.0-1.3 Gy). No correlation between CIED malfunction and maximum photon energy (p = 0.07), maximum dose at the CIED (p = 0.59) nor treatment localization (p = 0.41) could be detected. After excluding the nine malfunctions, premature battery depletion was only observed three times (1.2%). Depending on the national guidelines, 1-9 CIED malfunctions in this study would have been detected on the day of occurrence and in none of the cases would patient safety have been compromised.

CONCLUSION

Radiation-induced malfunctions of CIEDs and premature battery depletion are rare. If recommendations of national safety guidelines are followed, only a portion of the malfunctions would be detected directly after occurrence. Nevertheless, patient safety would not be compromised.

Management of radiotherapy patients with implanted cardiac pacemakers and defibrillators: A Report of the AAPM TG-203†

Managing radiotherapy patients with implanted cardiac devices (implantable cardiac pacemakers and implantable cardioverter-defibrillators) has been a great practical and procedural challenge in radiation oncology practice. Since the publication of the AAPM TG-34 in 1994, large bodies of literature and case reports have been published about different kinds of radiation effects on modern technology implantable cardiac devices and patient management before, during, and after radiotherapy. This task group report provides the framework that analyzes the potential failure modes of these devices and lays out the methodology for patient management in a comprehensive and concise way, in every step of the entire radiotherapy process.

A multicenter dosimetry study to evaluate the imaging dose from Elekta XVI and Varian OBI kV-CBCT systems to cardiovascular implantable electronic devices (CIEDs)

The increasing use of daily CBCT in radiotherapy has raised concerns about the additional dose delivered to the patient, and it can also become a concern issue for those patients with cardiovascular implantable electronic devices (CIEDs) (Pacemaker [PM] and Implantable Cardioverter Defibrillator [ICD]). Although guidelines highly recommend that the cumulative dose received by CIEDs should be kept as low as possible, and a safe threshold based on patient risk classification needs to be respected, this additional imaging dose is not usually considered. Four centers with different dosimetry systems and different CBCT imaging protocols participated in this multicenter study to investigate the imaging dose to the CIEDs from Elekta XVI and Varian OBI kV-CBCT systems. It was found that although imaging doses received by CIEDs outside the CBCT field are negligible, special attention should be paid to this value when CIEDs are inside the field because the daily use of CBCT can sometimes contribute considerably to the total dose received by a CIED.

On the use of bolus for pacemaker dose measurement and reduction in radiation therapy

Special attention is required in planning and administering radiation therapy to patients with cardiac implantable electronic devices (CIEDs), such as pacemaker and defibrillator. The range of dose to CIEDs that can induce malfunction is large among CIEDs. Clinically significant defects have been reported at dose as low as 0.15 Gy. Therefore, accurate estimation of dose to CIED and dose reduction are both important even if the dose is expected to be less than the often-used 2-Gy limit. We investigated the use of bolus in in vivo dosimetry for CIEDs. Solid water phantom measurements of out-of-field dose for a 6-MV beam were performed using parallel plate chamber with and without 1- to 2-cm bolus covering the chamber. In vivo dosimetry at skin surface above the CIED was performed with and without bolus covering the CIED for three patients with the CIED <5 cm from the field edge. Chamber measured dose at depth ~0.5-1.5 cm below the skin surface, where the CIED is normally located, was reduced by ~7-48% with bolus. The dose reduction became smaller at deeper depths and with smaller field size. In vivo dosimetry at skin surface also indicated ~20%-60% lower dose when using bolus for the three patients. The dose measured with bolus more accurately reflects the dose to CIED and is less affected by contaminant electrons and linac head scatter. In general, the treatment planning system (TPS) calculation underestimated the dose to CIED, but it predicts the CIED dose more accurately when bolus is used. We recommend the use of 1- to 2-cm bolus to cover the CIED during in vivo CIED dose measurements for more accurate CIED dose estimation. If the CIED is placed <2 cm in depth and its dose is mainly from anterior beams, we recommend using the bolus during the entire course of radiation delivery to reduce the dose to CIED.

A review of implantable cardioverter defibrillator failures during radiation therapy in three Sydney hospitals

INTRODUCTION

In recent years, using radiation energies greater than 10 MV in patients with implantable cardioverter defibrillators (ICDs) has been contra-indicated due to the risk of a power on reset (POR) occurring. The ICD is often greater than 30 cm from the treatment field and subject to scatter radiation only. The aim of this study was to use recent patient cases to verify published failure rates and treatment recommendations.

METHOD

Five patients with ICDs who experienced a device malfunction during radiation therapy treatments were identified in three Sydney hospitals between 2008 and 2012. The types of treatments delivered during these events were assessed. Further assessment of all ICD patients at one Sydney hospital during this time was carried out to assess the rate of ICD failure during high energy treatments using 18 MV.

RESULTS

All ICDs that suffered malfunctions were exposed to scatter radiation only. All were exposed to partial or exclusive irradiation using 18 MV photons. Accumulated doses to the ICDs were estimated to be well below accepted dose limits found in literature. One centre reported a 22.2% rate of POR during exposure to 18 MV radiation therapy during this time frame.

CONCLUSIONS

Where possible, radiation therapy using energies greater than 10 MV should be avoided for ICD patients. While the use of these energies carries a risk of failure, it must be weighed against potential benefit to the patient requiring treatment if no alternatives are available. Stringent monitoring of these patients, including regular cardiac device checks and ECG monitoring is recommended if treatment is to proceed with energies greater than 10 MV.

Revisiting fetal dose during radiation therapy: evaluating treatment techniques and a custom shield

To create a comprehensive dataset of peripheral dose (PD) measurements from a new generation of linear accelerators with and without the presence of a newly designed fetal shield, PD measurements were performed to evaluate the effects of depth, field size, distance from the field edge, collimator angle, and beam modi-fiers for common treatment protocols and modalities. A custom fetal lead shield was designed and made for our department that allows external beam treatments from multiple angles while minimizing the need to adjust the shield during patient treatments. PD measurements were acquired for a comprehensive series of static fields on a stack of Solid Water. Additionally, PDs from various clinically relevant treatment scenarios for pregnant patients were measured using an anthropomorphic phantom that was abutted to a stack of Solid Water. As expected, the PD decreased as the distance from the field edge increased and the field size decreased. On aver-age, a PD reduction was observed when a 90° collimator rotation was applied and/or when the tertiary MLCs and jaws defined the field aperture. However, the effect of the collimator rotation (90° versus 0°) in PD reduction was not found to be clini-cally significant when the tertiary MLCs were used to define the field aperture. In the presence of both the MLCs and the fetal shield, the PD was reduced by 58% at a distance of 10 cm from the field edge. The newly designed fetal shield may effectively reduce fetal dose and is relatively easy to setup. Due to its design, we are able to use a broad range of treatment techniques and beam angles. We believe the acquired comprehensive PD dataset collected with and without the fetal shield will be useful for treatment teams to estimate fetal dose and help guide decisions on treat-ment techniques without the need to perform pretreatment phantom measurements.

Experimental assessment of out-of-field dose components in high energy electron beams used in external beam radiotherapy

The purpose of this work was to experimentally investigate the out-of-field dose in a water phantom, with several high energy electron beams used in external beam radiotherapy (RT). The study was carried out for 6, 9, 12, and 18 MeV electron beams, on three different linear accelerators, each equipped with a specific applicator. Measurements were performed in a water phantom, at different depths, for different applicator sizes, and off-axis distances up to 70 cm from beam central axis (CAX). Thermoluminescent powder dosimeters (TLD-700) were used. For given cases, TLD measurements were compared to EBT3 films and parallel-plane ionization chamber measurements. Also, out-of-field doses at 10 cm depth, with and without applicator, were evaluated. With the Siemens applicators, a peak dose appears at about 12-15 cm out of the field edge, at 1 cm depth, for all field sizes and energies. For the Siemens Primus, with a 10 × 10 cm(²) applicator, this peak reaches 2.3%, 1%, 0.9% and 1.3% of the maximum central axis dose (Dmax) for 6, 9, 12 and 18 MeV electron beams, respectively. For the Siemens Oncor, with a 10 × 10 cm(²) applicator, this peak dose reaches 0.8%, 1%, 1.4%, and 1.6% of Dmax for 6, 9, 12, and 14 MeV, respectively, and these values increase with applicator size. For the Varian 2300C/D, the doses at 12.5 cm out of the field edge are 0.3%, 0.6%, 0.5%, and 1.1% of Dmax for 6, 9, 12, and 18 MeV, respectively, and increase with applicator size. No peak dose is evidenced for the Varian applicator for these energies. In summary, the out-of-field dose from electron beams increases with the beam energy and the applicator size, and decreases with the distance from the beam central axis and the depth in water. It also considerably depends on the applicator types. Our results can be of interest for the dose estimations delivered in healthy tissues outside the treatment field for the RT patient, as well as in studies exploring RT long-term effects.