Evaluation of a ventricular assist device: stability under x-rays and therapeutic beam attenuation

Case study with dosimetric analysis: Total body irradiation to a patient with a left ventricular assist device

Key Clinical Message

A patient presented with cardiogenic shock, requiring the implantation of a left ventricular assist device (LVAD), and acute myeloblastic leukemia. This necessitated total body irradiation (TBI) while balancing dose reduction to the LVAD components to avoid potential radiation damage. Here we outline our treatment approach and dose estimates to the LVAD.

Abstract

This case report discusses the delivery of TBI to a patient with an LVAD. This treatment required radiation-dose determinations and consequential reductions for the heart, LVAD, and an external controller connected to the LVAD. The patient was treated using a traditional 16MV anterior posterior (AP)/posterior anterior (PA) technique at a source-to-surface-distance of 515 cm for 400 cGy in two fractions. A 3 cm thick Cerrobend block was placed on the beam spoiler to reduce dose to the heart and LVAD to 150 cGy. The external controller was placed in a 1 cm thick acrylic box to reduce neutron dose and positioned as far from the treatment fields as achievable. In vivo measurements were made using optically stimulated luminescence dosimeters (OSLDs) placed inside the box at distances of 2 cm, 8.5 cm, and 14 cm from the field edge, and on the patient along the central axis and centered behind the LVAD block. Further ion chamber measurements were made using a solid water phantom to more accurately estimate the dose delivered to the LVAD. Neutron dose measurements were also conducted. The total estimated dose to the controller ranged from 135.3 cGy to 91.5 cGy. The LVAD block reduced the surface dose to the patient to 271.6 cGy (68.1%). The block transmission factors of the 3 cm Cerrobend block measured in the phantom were 45% at 1 cm depth and decreased asymptotically to around 30% at 3 cm depth. Applying these transmission factors to the in vivo measurements yielded a dose of 120 cGy to the implanted device. The neutron dose the LVAD region is estimated around 0.46 cGy. Physical limitations of the controller made it impossible to completely avoid dose. Shielding is recommended. The block had limited dose reduction to the surface, due to secondary particles, but appropriately reduced the dose at 3 cm and beyond. More research on LVADs dose limits would be beneficial.

Cardiac stereotactic radiation therapy for refractory ventricular arrhythmias in patients with left ventricular assist devices

Left ventricular assist device (LVAD) implantation is an established treatment for patients with advanced heart failure refractory to medical therapy. However, the incidence of ventricular arrhythmias (VAs) is high in this population, both in the acute and delayed phases after implantation. About one-third of patients implanted with an LVAD will experience sustained VAs, predisposing these patients to worse outcomes and complicating patient management. The combination of pre-existing myocardial substrate and complex electrical remodeling after LVAD implantation account for the high incidence of VAs observed in this population. LVAD patients presenting VAs refractory to antiarrhythmic therapy and catheter ablation procedures are not rare. In such patients, treatment options are extremely limited. Stereotactic body radiation therapy (SBRT) is a technique that delivers precise and high doses of radiation to highly defined targets, reducing exposure to adjacent normal tissue. Cardiac SBRT has recently emerged as a promising alternative with a growing number of case series reporting the effectiveness of the technique in reducing the VA burden in patients with arrhythmias refractory to conventional therapies. The safety profile of cardiac SBRT also appears favorable, even though the current clinical experience remains limited. The use of cardiac SBRT for the treatment of refractory VAs in patients implanted with an LVAD are even more scarce. This review summarizes the clinical experience of cardiac SBRT in LVAD patients and describes technical considerations related to the implementation of the SBRT procedure in the presence of an LVAD.

Feasibility of Mediastinal Radiation Use in HeartMate 3 LVAD Recipients with Cancer

The HeartMate 3 left ventricular assist device possesses the unique feature of having its electronics and software located within the housing of the pump, which may predispose it to malfunction from radiation exposure during cancer treatment. We investigated this association in a case series of two patients at our institution.

Stereotactic Arrhythmia Radioablation as a Novel Treatment Approach for Cardiac Arrhythmias: Facts and Limitations

Stereotactic ablative radiotherapy (SABR) is highly focused radiation therapy that targets well-demarcated, limited-volume malignant or benign tumors with high accuracy and precision using image guidance. Stereotactic arrhythmia radioablation (STAR) applies SABR to treat cardiac arrhythmias, including ventricular tachycardia (VT) and atrial fibrillation (AF), and has recently been a focus in research. Clinical studies have demonstrated electrophysiologic conduction blockade and histologic fibrosis after STAR, which provides a proof of principle for its potential for treating arrhythmias. This review will present the basic STAR principles, available clinical study outcomes, and how the technique has evolved since the first pre-clinical study. In addition to the clinical workflow, focus will be given on the process for stereotactic radiotherapy Quality Assurance (QA) tests, as well as the need for establishing a standardized QA protocol. Future implications and potential courses of research will also be discussed.

Development of malignancies and their outcomes in patients supported on continuous-flow left ventricular assist devices-a systematic review

Background

With increased use of continuous-flow left ventricular assist devices (CF-LVAD), development of malignant tumors in this population is not uncommon. We sought to evaluate malignancies in CF-LVAD patients and evaluate the outcomes of treatment strategies.

Methods

Overall, 18 articles consisting of 28 patients were identified who developed malignancies after CF-LVAD placement. Patient-level data were extracted for systematic review.

Results

Median patient age was 60 years [59-67] and 85.7% (24/28) were male. CF-LVAD was placed as bridge-to-transplant (BTT) in 60.9% (14/23) of patients. The three most common malignancy types were GI in 35.7% (10/28) of patients, lung in 21.4% (6/28) and skin in 10.7% (3/28). Median time from CF-LVAD implant to malignancy diagnosis was 6.9 [2.5-12.8] months. Metastatic disease occurred in 17.9% (5/28) over a median time of 5.0 [1.0-82.0] months from the diagnosis. Surgical resection of the malignancy was performed in 57.1% (16/28) of patients. Our results showed that while there was a significantly higher probability of survival among patients who underwent surgery versus those who did not, when only stage I and II patients were included in the analysis, this difference was no longer statistically significant. Three patients were relisted for heart transplant after surgical treatment, and two received the transplant.

Conclusions

Surgical management of malignancies in patients on CF-LVADs may improve survival and transplant eligibility status, therefore, a CF-LVAD should not always preclude surgical treatment.

Effects of high-energy photon beam radiation therapy on Jarvik 2000 LVAD: in vitro evaluation

PURPOSE

Left ventricular assist device (LVAD) is considered a standard care for patients with advanced heart failure. The aim of this work was to study in vitro the effects of direct exposure of the Jarvik 2000 LVAD to 10-MV photon beams.

METHODS

Jarvik 2000 pump was immersed in a siliconized box filled with deionized water. A 30 × 30 × 15 cm RW3 slabs were added forth and back to the box. A treatment plan consisting of a single direct 10 × 10 cm² field size beam was used to deliver 1000 MU at the center of the pump. During irradiation, the external Flow Maker controller and the lithium battery were positioned away from the beam. Pump parameter data (included voltage, current and frequency) were measured, recorded and analyzed for changes in pump function among baseline, pre-irradiation, during irradiation, post-irradiation and after 6 months. The whole session lasted 6 months. The Mann-Whitney U test was used to compare the repeated measurements. X-ray radiation attenuation was also studied.

RESULTS

The parameters investigated remained stable over the 6 months; that is, no pump stops, alarms, events, operational changes or abnormalities during the discharge rate of the connected power sources, were encountered, confirmed by the Mann-Whitney U test applied to all sessions (p > 0.1). The measured X-ray attenuation differed from the calculated one by TPS by 34%.

CONCLUSION

The Jarvik 2000 resulted stable under direct X-ray beam of 10-MV energy. Its strong attenuation, however, can affect dose deposition in the pump in TPS, and it must be taken into account.

Is it safe to irradiate the newest generation of ventricular assist devices? A case report and systematic literature review

An increasing number of mechanical assist devices, especially left ventricular assist devices (VADs), are being implanted for prolonged periods and as destination therapy. Some VAD patients require radiotherapy due to concomitant oncologic morbidities, including thoracic malignancies. This raises the potential of VAD malfunction via radiation-induced damage. So far, only case reports and small case series on radiotherapy have been published, most of them on HeartMate II (HMII, Abbott, North Chicago, IL, USA). Significantly, the effects of irradiation on the HeartMate 3 (HM3, Abbott) remain undefined, despite the presence of controller components engineered within the pump itself. We report the first case of a patient with a HM3 who successfully underwent stereotactic hypofractionated radiotherapy due to an early-stage non-small-cell lung cancer. The patient did not suffer from any complications, including toxicity or VAD malfunction. Based on this case report and on published literature, we think that performing radiotherapy after VAD implantation with the aid of a multidisciplinary team could be performed, but more in vitro studies and cases series are needed to reinforce this statement.

Safe delivery of lung stereotactic body radiation therapy in a patient with a left ventricular assist device and implantable cardioverter defibrillator

This is the first case to discuss the safe delivery of stereotactic body radiation therapy to a left lower lobe lung nodule in a patient with a third generation left ventricular assist device (Heartware®) and implantable cardioverter defibrillator.

In Vitro PET Imaging of a Miniature Ventricular Assist Device

Interactions between the life-sustaining ventricular assist devices and diagnostic therapies must be carefully considered to decrease the risk of inaccurate diagnostic imaging or pump failure.

METHODS

The MVAD(®) pump, currently under investigational use, was tested for interaction with radiotracers in an in vitro flow-loop study. The radiotracers (18)F-sodium fluoride and (18)F-FDG were injected into a closed loop to determine the feasibility of direct imaging of the MVAD(®) pump in a PET scanner.

RESULTS

No real-time changes were observed in pump operation, and there were no statistical differences in pump parameters (power consumption, speed, and estimated flow rate) between the baseline and circulation conditions. In addition, no effect was observed on any external components, including the permissive-action-link controller and the batteries powering the device. Imaging of the internal pump components was possible, with obscuration observed only in the portion of the pump where the spinning impeller is located. Retention of radiotracer in the pump components after circulation was minimal (<1%).

CONCLUSION

PET imaging is an attractive diagnostic tool for patients with a ventricular assist device and may have additional utility outside its current use, detection of infection.

Radiation Testing of the GERD Stimulation Therapy System Using a Particle Accelerator

OBJECTIVE

This testing was conducted to determine if exposure from a particle accelerator used to treat cancer patients would alter the performance of the EndoStim® neurostimulator when programmed either passively or actively and while being irradiated.

METHODS

A total of 12 EndoStim Lower Esophageal Sphincter (LES) Stimulation System implantable neurostimulators were investigated in this research. Included were six each of the EndoStim I and EndoStim II. Half were used for passive testing, with the remaining half for active testing. Bremsstrahlung x-rays were delivered having a nominal energy of 18 MV at a rate of 6 Gy/min. A total dose of 80 Gy was achieved in testing minimally.

RESULTS

Monitoring of stimulation frequency, amplitude, pulse width, stimulation time, and voltage was conducted using software developed by EndoStim along with an oscilloscope. No observed changes to the intended stimulation were noted and all scheduled parameter magnitudes were achieved with device operation. All functional parameter changes were within ±10% from baseline.

CONCLUSIONS

EndoStim I and EndoStim II implant pulse generators appear to be immune to x-ray radiation from the particle accelerator at energies up to 18 MV, at dose rates of up to 6 Gy/min, and up to cumulative doses of minimally 80 Gy. As there were no observable effects on neurostimulation requirements, the EndoStim LES Stimulation System implantable neurostimulators are capable of withstanding direct radiation. The recommendations of the manufacturer should be followed further regarding the labeling requirements for insured safety to patients.