Purpose: To determine if the ZioXT™ heart monitor can function normally after exposure to an accumulated radiation dose of less than 60cGy.
Methods: Patient being treated for head/neck cancer on a Tomotherapy Hi-Art treatment machine. The first day after the ZioXT was put in place on the patient's chest, imaging was performed to align the patient for treatment. After imaging, two nanoDots™ were placed on top of the patient's head/neck mask (instead of underneath to avoid patient discomfort) at the most superior portion of the Zio device. Per TG-203, 0.5cm thick bolus was placed over the ZioXT device to give the nanoDots a depth of 0.5cm. Since 6MV was being used, neutrons were not a concern. The treatment fraction was delivered to the patient, and the nanoDots were removed and sent to Landauer Special Service Dosimetry (LSSD) for analysis.
Results: The LSSD report indicated the highest radiation dose recorded by the nanoDots was 6.42cGy. The patient was to wear the ZioXT monitor for a total of 14 days which encompassed 8 radiation treatments. The 8 radiation treatments equate to a total estimated radiation dose to the ZioXT of approximately 51.4cGy. The Radixact treatment planning system (TPS) had predicted a total radiation dose to the ZioXT of approximately 30cGy, or almost half the estimated accumulated radiation dose based on measurement. The significantly lower estimated dose by the TPS is supported by TG-203. The ZioXT daily monitoring reports did not indicate any significant deviation on the performance of the ZioXT.
Conclusion: Based on the nanoDots' results and the ZioXT daily reports, the ZioXT did not suffer any noticeable physical damage or degradation in performance from receiving less than 60cGy from the patient's radiation treatments. More measurements need to be made to help ascertain a definitive radiation dose threshold for the ZioXT.