An integrated ultrasound imaging and abdominal compression device for respiratory motion management in radiation therapy.

Abstract

Radiotherapy to tumors in the abdomen is challenging because of the significant organ movement and tissue deformation caused by respiration. A motion management strategy that integrated ultrasound (US) imaging with abdominal compression was developed and evaluated, where US was used to real-time monitor organ motion after abdominal compression. A device that combined a US imaging system and an abdominal compression plate (ACP) was developed. Twenty-one healthy volunteers were involved to evaluate the motion management efficacy. Each volunteer was immobilized on a flat bench by the device. Abdominal US data were successively collected with and without ACP compression, and experiments were repeated three times to verify the imaging reproducibility. A template matching algorithm based on normalized cross-correlation was implemented to track the targets (vessels in the liver, pancreas, and stomach) automatically. The matching algorithm was validated by comparing with the manual references. Automatic tracking was judged as failed if the center-of-mass difference from manual tracking was beyond a failure threshold. Based on the locations obtained through the template matching algorithm, the motion correlation between liver and pancreas/stomach was investigated using the Pearson correlation test. Paired Student's t-test was used to analyze the difference between the results without and with ACP compression. The liver motion amplitude over all 21 volunteers was significantly (p<0.001) reduced from 14.9±5.5/3.4±1.8mm in superior-inferior (SI)/anterior-posterior (AP) direction before ACP compression to 7.3±1.5/1.6±0.7mm after ACP compression. The mean liver motion standard deviation before compression was on average 2.8/1.4mm in SI/AP direction and was significantly (p<0.001) reduced to 0.9/0.4mm after compression. The failure rates of automatic tracking for liver, pancreas, and stomach were reduced for failure thresholds of 1-5mm after applying ACP. The Pearson correlation coefficients between liver and pancreas/stomach were 0.98/0.97 without ACP and 0.96/0.94 with ACP in the SI direction and were 0.68/0.68 and 0.43/0.42 in the AP direction. The motion prediction errors for pancreas/stomach with ACP have significantly (p<0.001) reduced to 0.45±0.36/0.52±0.43mm from 0.69±0.56/0.71±0.66mm without ACP in the SI direction, and to 0.38±0.33/0.39±0.27mm from 0.44±0.35/0.61±0.59mm in the AP direction. The proposed strategy that combines real-time US imaging and abdominal compression has the potential to reduce the abdominal organ motion while improving both target tracking reliability and motion reproducibility. Furthermore, the observed correlation between liver and pancreas/stomach motion indicates the possibility of indirect pancreas/stomach tracking using liver markers as tracking surrogates. The strategy is expected to provide an alternative for respiratory motion management in the radiation treatment of abdominal tumors.