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The Effects of Pencil Beam Scanning Proton Radiation Therapy on a Left Ventricular Assist Device: Implications for Patient Safety

      Purpose/Objective(s)

      Heart failure remains a major source of morbidity and mortality worldwide. Left ventricular assist devices (LVADs) provide mechanical circulatory support and offer superior outcomes to medical therapy in patients with end-stage heart failure. LVADs can be used as a bridge to cardiac transplantation but are now more commonly used as destination therapy. While the safety of photon beam and older proton beam therapy (PBT) techniques have been established in patients with LVADs, data evaluating the safety of pencil beam scanning (PBS) PBT techniques are lacking. In this study, we evaluated the dose tolerance of an LVAD to PBS proton irradiation. We hypothesized that proton irradiation would affect the function of the LVAD.

      Materials/Methods

      We conducted three experiments in which we exposed elements of separate LVADs to a proton beam whose Spread Out Bragg Peak (SOBP) had a range of 100 mm and a width of 60 mm. The LVAD was placed in a water-based phantom with a wall of water-equivalent thickness of 11.59 mm at a depth of 5 cm. In the first experiment, we delivered escalating doses of proton beam radiation to the device pump, starting at 5 GyE and increasing in increments of 5 GyE up to 70 GyE. In replicative second and third experiments, we delivered proton beam radiation continuously to a dose of 70 GyE (prescribed to the middle of the SOBP) to the pump and driveline, respectively. Optical stimulated luminescent dosimeters (OSLDs) were utilized to monitor dose to the battery and controller, which were located outside of the field of radiation. Our institutional review board deemed this study exempt.

      Results

      The pump showed no significant operational changes after irradiation in the first and second experiments. However, during continuous irradiation of the driveline in the third experiment, communication between the pump and monitor was lost at 30 GyE (confirmed on the device's log files). While the pump continued to run during this time, the monitor displayed a low flow alarm. OSLD measurements were 0.02 cGy for the monitor and 0.069 cGy for the battery after the completion of the third experiment. No mechanical damage was noted to the components of the LVAD after any of the three experiments.

      Conclusion

      The pump and driveline of the LVAD exhibited no structural damage after direct irradiation by a proton beam. The pump tolerated escalating doses of up to 70 GyE, which is consistent with prior published data. However, when the driveline was irradiated continuously, the controller and pump lost connection at 30 GyE, and a low flow alarm was generated. These results suggest that while the LVAD pump can tolerate clinically significant doses of PBS PBT, further study is necessary to assess the resilience of the driveline to fractionated PBT.
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