Purpose: Radiotherapy to tumors in the abdomen is challenging because of the significant organ movement and deformation caused by respiration. We developed a motion management strategy using ultrasound (US) integrated with an abdominal compression plate (ACP), where the US was to monitor motion after the abdomen was compressed with the ACP.
Methods: Twenty-one volunteers were immobilized using an in-house developed device that integrated an US probe with an ACP. For each subject, abdominal US data was successively collected with and without an ACP. Experiments were repeated three experiments to verify the reproducibility. A template matching algorithm based on normalized cross correlation was implemented for motion tracking. And the failure rates of the liver, pancreas and stomach tracking were analyzed. On the basis of the obtained organ locations in the US, linear correlation models between liver and pancreas/stomach were established to predict the motion of pancreas/stomach using liver as a surrogate.
Results: The liver motion amplitudes for individual subjects with ACP compression were significantly reduced with ACP compression in both superior-inferior (SI) (p<0.0001) and anterior-posterior (AP) (p<0.0001) directions. The failure rates in liver, pancreas and stomach tracking were reduced from 1 %, 2.54% and 2.79 % to 0.03%, 0.73% and 1.07% after ACP compression respectively. The correlation coefficients between liver and pancreas/stomach were 0.98/0.97 without ACP and 0.96/0.94 with ACP in SI and were 0.68/0.68 and 0.43/0.42, respectively, in AP.
Conclusion: While slightly reducing the linear correlation between organs, ACP effectively inhibits the abdominal motion and improves the reliability of organ tracking in US. The US and ACP combined device can work as an effective motion management strategy in abdominal radiotherapy.