Purpose: Motion management is important while delivering high-dose radiation therapy. Image-based systems are often considered the gold standard; however some frame-based radiosurgery platforms lack the ability to perform imaging. This work assesses the ability of time-of-flight (ToF) distance sensors to monitor and detect gross patient motion in the absence of an image-based patient position verification system.
Methods: Two low-cost distance sensors were assessed – VL53L1X and the TF MiniPlus. Both sensors operate on the time-of-flight (ToF) principle by emitting a laser beam and measuring its travel time to measure distance. Accuracy and precision were measured from 20cm to 90cm in 10cm increments. Fifteen readings were obtained at each position. The sensors were controlled by a microcontroller (Arduino Uno) and the readings were transferred to a computer through a serial port for further analysis. Additionally, both sensors were utilized in conjunction with a head phantom to assess stability over a 200s period and the ability to detect arbitrary movement induced by the operator.
Results: The VL53L1X sensor produced more accurate results over the range of measurements performed while the TF MiniPlus produced more precise results. Over the measured range of distances, the TF MiniPlus sensor accuracy varied from 3% to 6% and the precision varied from 0.03% to 0.21%. The VL53L1x sensor accuracy varied by ± 2% and the precision varied from 0.57% to 0.16%. When utilized with the head phantom, the sensors were able to detect an arbitrary induced movement of 5mm.
Conclusion: These devices provide a mean to assess gross (> 4 mm) intrafraction patient motion in situations where image guidance or clear visual line of sight challenges may exist. This work serves as a proof of concept for industrial-grade sensors and/or multiple sensors which can be utilized to further reduce uncertainty and improve motion detection.