Effect of X-ray dose rates higher than 8 Gy/min on the functioning of cardiac implantable electronic devices

What do national radiotherapy guidelines for patients with cardiac devices teach us?

The incidence of cardiac implantable electronic device (CIED) malfunctions caused by radiotherapy (RT) is approximately 5%. Although individual national guidelines and expert consensus documents exist, the increased use of RT to treat various cancers points out the need for a standardized document to guide risk assessment and management of CIEDs during RT. We describe potential adverse RT-related events on CIEDs as well as the proposed mechanism of dysfunction. We review the main current guidelines and recommendations, emphasizing similarities and differences.

A Systematic Review and Meta-analysis of the Prevalence and Risk Factors in Cardiac Implantable Electronic Device Malfunction

Introduction

Cardiac implantable electronic devices (CIED) include permanent pacemakers (PPMs), implantable cardioverter defibrillators (ICDs), and cardiac resynchronization therapy (CRT) devices. They treat several cardiac issues and are dependent on batteries; however, similar to any medical equipment, they can fail. The prevalence and risk factors for CIED malfunction must be understood for earlier detection and better patient outcomes.

Material and methods

A comprehensive search was conducted through electronic bibliographic sources (PubMed and Cochrane) until January 2023 in order to identify reviews, cohort studies and case reports pertaining to CIED. The primary outcome is the probability of CIED malfunction. The secondary outcome concerned significant risk factors. Two authors independently extracted articles by utilizing pre-established data fields. Using a random-effects model, the aggregated prevalence and 95 % confidence intervals (CIs) were computed.

Results

The meta-analysis comprised eight review articles, twenty-two retrospective studies, and thirty-seven case reports from the systematic review. The eight review articles contained a CIED malfunction of 4.03 % (random-effects model). The pooled prevalence of CIED malfunction in the meta-analysis of 22 retrospective studies was 0.41 percent (using a fixed-effects model) and 8.01 percent (using a random-effects model). Moreover, age, pre-existing cardiac conditions, CIED type, lead placement, and medical device interactions all contributed to an increase in the heterogeneity (I2 = 98.90 %) of the risk of CIED malfunction.

Conclusion

CIED malfunction is common and more likely to occur in elderly individuals and in certain types of CIED. Clinicians should focus on risk factors and closely monitor the patients with higher probability for CIED malfunction with short intervals.

PLA Renewable Bio Polymer Based Solid-State Gamma Radiation Detector-Dosimeter for Biomedical and Nuclear Industry Applications

Polylactic acid (PLA) as a "green," renewable corn-soy based polymer resin was assessed as a novel solid-state detector for rapid-turnaround gamma radiation dosimetry in the 1-100 kGy range-of significant interest in biomedical and general nuclear industry applications. Co-60 was used as the source of gamma photons. It was found that PLA resin responds well in terms of rheology and porosity metrics with an absorbed gamma dose (Dg). In this work, rheological changes were ascertained via measuring the differential mass loss ratio (MLR) of irradiated PLA placed within PTFE-framed (40 mm × 20 mm × 0.77 mm) cavities bearing ~0.9 g of PLA resin and pressed for 12-16 min in a controlled force hot press under ~6.6 kN loading and platens heated to 227 °C for the low Dg range: 0-11 kGy; and to 193 °C for the extended Dg range: 11-120 kGy. MLR varied quadratically from 0.05 to ~0.2 (1σ ~ 0.007) in the 0-11 kGy experiments, and from 0.05 to ~0.5 (1σ ~0.01) in the 0-120 kGy experiments. Rheological changes from gamma irradiation were modeled and simultaneously correlated with void-pocket formations, which increase with Dg. A single PLA resin bead (~0.04 g) was compressed 5 min at 216 °C in 0-16 kGy experiments, and compressed 2 min at 232 °C in the 16-110 kGy experiments, to form sturdy ~100 µm thick wafers in the same press. Aggregate coupon porosity was then readily measurable with conventional optical microscope imaging and analyzed with standard image processing; this provided complementary data to MLR. Average porosity vs. dose varied quadratically from ~0 to ~15% in the 0-16 kGy range and from ~0 to ~18% over the 16-114 kGy range. These results provide evidence for utilizing "green"/renewable (under $0.01) PLA resin beads for rapid and accurate (+/-5-10%) gamma dosimetry over a wide 0-120 kGy range, using simple to deploy mass and void measuring techniques using common laboratory equipment.

Local dose rate effects in implantable cardioverter-defibrillators with flattening filter free and flattened photon radiation

Purpose

In the beam penumbra of stereotactic body radiotherapy volumes, dose rate effects in implantable cardioverter–defibrillators (ICDs) may be the predominant cause for failures in the absence of neutron-generating photon energies. We investigate such dose rate effects in ICDs and provide evidence for safe use of lung tumor stereotactic radioablation with flattening filter free (FFF) and flattened 6 Megavolt (MV) beams in ICD-bearing patients.

Methods

Sixty-two ICDs were subjected to scatter radiation in 1.0, 2.5, and 7.0 cm distance to 100 Gy within a 5 × 5 cm² radiation field. Radiation was applied with 6 MV FFF beams (constant dose rate of 1400 cGy/min) and flattened (FLAT) 6 MV beams (430 cGy/min). Local dose rates (LDR) at the position of all ICDs were measured. All ICDs were monitored continuously.

Results

With 6 MV FFF beams, ICD errors occurred at distances of 1.0 cm (LDR 46.8 cGy/min; maximum ICD dose 3.4 Gy) and 2.5 cm (LDR 15.6 cGy/min; 1.1 Gy). With 6 MV FLAT beams, ICD errors occurred only at 1 cm distance (LDR 16.8 cGy/min; 3.9 Gy). No errors occurred at an LDR below 7 cGy/min, translating to a safe distance of 2.5 cm (1.5 Gy) in flattened and 7 cm (0.4 Gy) in 6 MV FFF beams.

Conclusion

A LDR in ICDs larger than 7 cGy/min may cause ICD malfunction. At identical LDR, differences between 6 MV FFF and 6 MV FLAT beams do not yield different rates of malfunction. The dominant reason for ICD failures could be the LDR and not the total dose to the ICD. For most stereotactic treatments, it is recommended to generate a planning risk volume around the ICD in which LDR larger than 7 cGy/min are avoided.

A new DOSXYZnrc method for Monte Carlo simulations of 4D dose distributions

The purpose of this study is to present a novel method for generating Monte Carlo 4D dose distributions in a single DOSXYZnrc simulation. During a standard simulation, individual energy deposition events are summed up to generate a 3D dose distribution and their associated temporal information is discarded. This means that in order to determine dose distributions as a function of time, separate simulations would have to be run for each interval of interest. Consequently, it has not been clinically feasible until now to routinely perform Monte Carlo simulations of dose rate, time-resolved dose accumulation, or electronic portal imaging devices (EPID) cine-mode images for volumetric modulated arc therapy (VMAT) plans. To overcome this limitation, we modified DOSXYZnrc and defined new input and output variables that allow a time-like parameter associated with each particle history to be binned in a user-defined manner. Under the new code version, computation times are the same as for a standard simulation, and the time-integrated 4D dose is identical to the standard 3D dose. We present a comparison of scintillator measurements and Monte Carlo simulations for dose rate during a VMAT beam delivery, a study of dose rate in a VMAT total body irradiation plan, and simulations of transit (through-patient) EPID cine-mode images.

Study of feasible and safe condition for total body irradiation using cardiac implantable electronic devices

Cardiac implantable electronic devices (CIEDs) were believed to have a tolerance dose and that direct irradiation has to be avoided. Thus, no clinical guidelines have mentioned the feasibility of total body irradiation (TBI) with a CIED directly. The purpose of this work was to study a feasible and safe condition for TBI using a CIED. Eighteen CIEDs were directly irradiated by a 6-MV X-ray beam, where a non-neutron producible beam was employed for the removal of any neutron contribution to CIED malfunction. Irradiation up to 10 Gy in accumulated dose was conducted with a 100-cGy/min dose rate, followed by up to 20 Gy at 200 cGy/min. An irradiation test of whether inappropriate ventricular shock therapy was triggered or not was also performed by using a 6-MV beam of 5, 10, 20 and 40 cGy/min to two CIEDs. No malfunction was observed during irradiation up to 20 Gy at 100 and 200 cGy/min without activation of shock therapy. These results were compared with typical TBI, suggesting that a CIED in TBI will not encounter malfunction because the prescribed dose and the dose rate required for TBI are much safer than those used in this experiment. Several inappropriate shock therapies were, however, observed even at 10 cGy/min if activated. The present result suggested that TBI was feasible and safe if a non-neutron producible beam was employed at low dose-rate without activation of shock therapy, where it was not inconsistent with clinical and non-clinical data in the literature. The feasibility of TBI while using a CIED was discussed for the first time.

A Review and Analysis of Managing Commonly Seen Implanted Devices for Patients Undergoing Radiation Therapy

Purpose

This review article aims to consolidate information regarding existing and emerging implanted devices used in patients undergoing radiation therapy and to categorize levels of attention needed for each device, including which devices require monitoring throughout treatment.

Methods and Materials

Based on the collective information from scholar searches, manufacturers' technical reports, and institutional experiences in the past years, commonly present devices in patients with cancer are compiled. This work summarizes cardiac pacemaker, implanted cardiac defibrillator, hepatic pump, intrathecal pain pump, neurostimulator, shunt, loop recorder, and mediport. Three different classifications of implanted devices can be made based on the potential effect of radiation: life-dependent, nonlife-dependent but with adverse effects if overdosed, and devices without electronic circuits. Implanted devices that contain electronic circuits that would be life-dependent or have adverse effects if overdosed, include cardiac pacemakers, implanted cardiac defibrillators, programmable hepatic pumps, pain pumps, neurostimulators, and loop recorders.

Results

Dose exposure to these devices need to be calculated or measured in vivo, especially for cardiac implanted devices, and they should be minimized to assure continued healthy functioning. Treatment planning techniques should be chosen to reduce entry, exit and internal scatter dose. Lower energy photon beams should be used to decrease potential neutron contamination. Implanted devices without electronic circuits are less of a concern. If a patient is life-dependent on the implanted device, it is not recommended to treat the patient with proton therapy.

Conclusions

This study reviewed the management of patients with commonly seen implanted devices and summarized a workflow for identifying and planning when a patient has implanted devices. Classifications of implanted devices could help clinicians make proper decisions in regard to patients with specific implanted devices. Lastly, the management of such devices in the era of the pandemic is also discussed in this review article.

Photoneutron-induced damage reduction for cardiac implantable electronic devices using neutron-shielding sheets in high-energy X-ray radiotherapy: A phantom study

PURPOSE

To evaluate damage reduction in cardiac implantable electronic devices (CIEDs) caused by photoneutrons in high-energy X-ray radiotherapy using a neutron-shielding sheet (NSS).

METHODS

The NSS consists of a bolus with a thickness of 1 or 2 cm (Bls1 or Bls2) as a moderator and several absorbers (20%, 50%, or 80% B₄C silicone sheet [B₄C20, B₄C50, or B₄C80] or a 40% LiF silicone sheet [LiF40]). First, a linear accelerator (LINAC) with a water-equivalent phantom was modeled in the simulation and measured experimentally. Several NSSs were placed on the phantom, a Eu:LiCaAlF₆ scintillator was placed between the phantom and the NSS, and X-rays were irradiated. The relative counts (Cr = counts when placing the NSS or Bls2) were compared between the experiment and simulation. Second, CIED damage was evaluated in the simulation. The relative damage (Dr = damage when placing or not placing the NSS) was compared among all the NSSs. In addition, the γ-ray and leaking X-ray dose from B₄C was measured using a dosimetric film. After determining the optimal NSS combination, Dr value analysis was performed by changing the length of one side and the thickness.

RESULTS

The Cr values of the simulation and experiment agreed within a 30% percentage difference, except for Bare or LiF40-only. The Dr value was reduced by 43% when Bls2 + B₄C80 was applied. The photon dose was less than 5 cGy/1500 MU. The Dr values were smaller for the smaller lengths of one side of B₄C80 and decreased as the M-layer thickness increased.

CONCLUSIONS

The CIED damage induced by photoneutrons generated by a LINAC was effectively reduced by applying the optimal NSS.

Implantable cardiac pacemaker failure by cumulative dose effects of flattening filter free beams

Cumulative dose effects, which are one of the main causes of errors that occur when an implantable cardiac pacemaker (ICP) is irradiated with ionizing radiation, induce permanent failure in ICPs. Although flattening filter free (FFF) beams, which are often used in stereotactic radiotherapy, are known to have different characteristics from conventional (with flattening filter [WFF]) beams, the cumulative dose effects on ICPs with FFF beams have been under-investigated. This study investigates ICP failure induced by cumulative dose effects of FFF beams. When the ICP placed in the center of the irradiation field was irradiated with 10 MV-FFF at 24 Gy/min, the cumulative dose at which failure occurred was evaluated on the basis of the failure criteria associated with high cumulative dose as described in the American Association of Physicists in Medicine Task Group 203. The ICP failures such as a mild battery depletion at a cumulative dose of 10 Gy, pacing-output voltage change >25% at a cumulative dose of 122 Gy, and the loss of telemetry capability at cumulative dose 134 Gy were induced by cumulative dose effects. The cumulative doses by which the cumulative dose effects of FFF beams induced ICP failure were not very different from those reported in previous studies with WFF beams. Therefore, radiotherapy with FFF beams (and WFF beams) for patients with ICP requires appropriate management for minimizing the cumulative dose effects.

Impact of different radiation techniques and doses on cardiac implantable electronic devices

BACKGROUND AND OBJECTIVE

Purpose of this investigation was to get deeper insight into the impact of different radiation techniques and doses on cardiac implantable electric devices (CIEDs). We aimed to mimic a worst-case scenario with very high doses and external radiation being applied directly on the devices.

METHODS

Radiation was applied on 21 CIEDs as photon or electron therapy with maximum dose of 150Gy in fractions of 2 -20Gy. CIEDS were put directly into the beam. Brachytherapy was applied with doses of 6Gy to a maximum of 42Gy. Check-ups took place after every fraction and one week after radiation. We calculated the estimated potential risk for the health and survival of patients as well as the risk for CIEDs' loss of function.

RESULTS

28 life- or health-threatening errors occurred during photon therapy, 3/7 devices showed complete loss of function. During electron therapy, 31 potentially patient-threatening errors and 2 losses of function were detected. During brachytherapy, none of the devices showed loss of function but 8 patient-threatening errors occurred. Inadequate shock releases were mostly seen after photon and brachytherapy, random noises occurred more often during electron therapy. The earliest potentially serious error occurred during after 2Gy photon radiation and 6Gy brachytherapy. Losses of function occurred earliest at 80Gy.

CONCLUSION

The results underline the warning for precaution concerning CIED patients derived from recommendations in the literature. Our study offers new information especially about the impact of electron radiation and brachytherapy on CIEDs. Risk for the devices to for loss of telemetry or battery capacity might be negligible with normafractionated therapy.

JASTRO/JCS Guidelines for radiotherapy in patients with cardiac implantable electronic devices

This publication is an English version of the Japanese Society for Radiation Oncology (JASTRO) and The Japanese Circulation Society official guidelines for patients with cardiac implantable electronic devices (CIEDs). Several radiotherapy-associated malfunctions have been reported for CIEDs such as pacemakers and implantable cardioverter-defibrillators. Accordingly, guidelines for radiotherapy in patients with CIEDs have been issued by other countries and societies. In August 2010, JASTRO published the ‘Radiotherapy Guidelines for Patients with Pacemakers and Implantable Defibrillators’ (hereafter referred to as the former guidelines). Given new findings in this decade, a multidisciplinary working group of radiation oncologists, medical physicists, radiation therapists and cardiologists jointly reviewed and revised the former guidelines.