Room: Exhibit Hall | Forum 6
Purpose: Radiation dose delivered to a target located near the upper abdomen or thorax are significantly affected by respiratory-motion stemming from the expansion and contraction of diaphragmatic and intercoastal muscles. Relatively large margins are commonly added to the Clinical Target Volume to compensate for this motion -limiting dose escalation capability. Currently, normal-tissue sparing can be improved by using real-time position management (RPM) systems. Unfortunately, most of these systems are sophisticated, involving advanced and expensive optical or stress-gauge equipment, which could impede the widespread use in locations where staff and resources are limited (Keall et al, Med. Phys., 2008). We developed and evaluated a novel real-time position management system that uses an accelerometer (RPM(Acc)) as a simple-to-use, easy-to-implement and low-cost alternative to commercially available products.
Methods: The RPM(Acc) system consists of an integrated 6-axis motion-tracking-device (3-axis-gyroscope+3-axis-accelerometer) MPU-6050 unit (InvenSense Inc, Sunnyvale, CA) connected to an Arduino Uno-Rev3 microcontroller-board (http://arduino.cc). Direct comparison between RPM(Acc) and Varianâ€™s Real-time-Position-Management (RPM(Varian)) camera system (Varian Medical Systems, Palo Alto, CA) was performed using a respiratory-motion phantom. The RPM(Acc) system and RPM(Varian) camera tracking marker were placed on the phantom allowing for simultaneous data acquisition on a Varian Clinac 21X (Varian Medical Systems). The RPM(Acc) surrogate measurement of displacement was compared to the signal-trace acquired using the RPM(Varian) with univariate-regression analysis (Pearson-correlation-coefficient [r]).
Results: The RPM(Acc) provided real-time measurement of angular displacement in 3-axis clearly showing full phantom motion. Comparison of RPM(Varian) and RPM(Acc) systems show very similar signal-traces that were significantly related (r=.97,p=<.0001).
Conclusion: We demonstrated the feasibility of a low-cost (<$30.00USD) alternative to a commercially available RPM-system to monitor respiratory-motion. Future work will focus on comprehensively evaluating of RPM(Acc), such as subjecting the device to irregular breathing patterns, in an effort to translate this technology to centres that currently do not have access to respiratory-motion-management.