SU‐E‐T‐217: Characterization of the Respisens™ Motion Sensor Device for Intra‐Fraction Patient Tracking

Purpose: To assess the accuracy and response characteristics of the novel Respisens™ intra‐fraction motion monitoring device. Methods: The Respisens™ (CIVCO, Orange City IA) device is a highly sensitive, real time (20Hz sampling frequency) magnetic distance sensor used for patient motion tracking during radiotherapy—i.e. intra‐fraction motion monitoring. The device consists of both a miniaturized magnetic transmitter and receiver which measure the coplanar distance between the two probes real‐time. The device was evaluated for five different characteristic prior to clinical implementation: (1) Distance accuracy, (2) Distance range, (3) Off‐plane (non‐coplanar) response, (4) Angular response, and (5) Displacement detection accuracy. Results: The Respisens™ showed a distance tracking range from 7.5 to 23.5cm. The distance accuracy was <1.0mm for distances 7.5 to 16.0cm—above 16.0cm deviations were 2.0mm. The off‐plane (non‐coplanar) response was highly dependent on displacement due to the shape of the magnetic field. Overall, the off‐plane response was minimized with small off‐plane displacements (<1.0cm) and increased distance. The distance reading was also sensitive to angular displacement of the receiver relative to the transmitter. Relative to baseline—receiver perpendicular to transmitter, an over‐response of <10.0% was noted with angular deviations of up to 40°. Above 40°, the over‐response increases exponentially to 200% (89°). With regards to displacement detection accuracy based on initial position, the Respisens™ showed accurate response (<0.6%) for a 5.0cm displacement when the initial position was <16.5cm. When the initial position was >16.5cm, a varying response of up to 2.0% was noted. Conclusions: Based on the preliminary findings, the Respisens™ intra‐fraction motion monitoring device can be used to accurately measure patient motion realtime. Precaution must be taken to ensure that the probes are coplanar and not rotated relative to one another.