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Use of a MEMS Accelerometer to Detect Motion in Patients During Delivery of Radiotherapy


A Markovic

A Markovic1*, (1) Banner Health, Greeley, CO

SU-E-T-361 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:Patient movement during radiotherapy treatments can result in delivery of dose to unintended areas resulting in a poor prognosis. It is desirable to minimize intra-fraction (during treatment) motion since treatment times typically range from 5 to 30 minutes. A small MEMS (micro electromechanical systems) accelerometer can be placed on the patient's skin and be used to instantaneously detect slight motions exhibited by the patient. Information about patient motion can be displayed on the therapist's console and be used to interrupt the treatment or to coach the patient when a significant deflection occurs.

Methods:A 12-bit ST Microelectronics accelerometer (LIS3DH) of dimensions 3x3x1 mm on a 5x6 cm breadboard (Fig. 1) was used to measure deflections under simulated treatment conditions. The accelerometer can transfer data at rates ranging from 100 to 1600 Hz via either a USB cable or Bluetooth that relays acceleration data to a computer running a MATLAB program. This high-speed data rate allows for averaging which reduces random noise. The accelerometer provides a resolution of 9.8x10⁻³ m/sec². We are currently investigating the use of a new low-noise 16-bit accelerometer which will improve signal to noise response.

Results:Figs. 3 and 4 display data acquired at a rate of 100Hz while the accelerometer was attached to a subject's forehead. The data in Fig. 3 show the subject intentionally making two short, small movements. The data in Fig 4. show movement from the same subject intentionally turning their head slowly over a deflection of approximately 8 degrees.

Conclusion:A MEMS accelerometer was used in this pilot study to detect subject motion in real time involving quick as well as slow deflections of the head. Data rates of 100Hz allowed point averaging which resulted in smooth traces. Thresholds can be configured in the monitoring software to alert when a significant deflection occurs.

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