Real Time Prostate Motion Tracking Using the Portal Imaging Device in Radiation Therapy
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Intrafractional motion management is the key step in image-guided radiation therapy. Prostate location can change vastly during treatment. This work is to provide a way to implement and facilitate real-time MV tumor surrogate tracking of the fiducial marker implanted for prostate cancer treatment. An in-house program was developed to automatically extract fiducial marker locations based on patient planning CT images. The corresponding location coordinates were used to determine the possibility of true marker presence at that location with the approved radiation treatment plan. Various ways and inter-fiducial-marker distance of implanted markers were investigated to pinpoint the optimal combination for better tracking the fiducial markers using the MV imager. An optimal pattern and corresponding location range for better tracking the fiducial markers were recommended based on the calculation results. Experimental verification was performed with a homogenous bolus phantom. Three different MLC modulated arc therapy plans were randomly selected to verify the predicted and measured detectability score for five fiducial marker patterns (from all four pattern categories). All the MV-cine images were recorded and analyzed. The results of predicted and measured detectability score matched well with each other, confirming the suggested pattern and location range proposed in this study. Lastly, a dose perturbation algorithm was examined. Different types of errors were introduced to radiation therapy plans. The modified plans were measured by ArcCHECK QA device to evaluate the dosimetry impact of the induced error.