A framework for real-time target tracking in IGRT using three-dimensional ultrasound

Motion compensation is a well-known practice for radiation therapy [1, 2]. As the target is usually not directly measurable or the sampling rate is limited, surrogate signals are sampled with higher rates and correlated to the internal target movement [3]. This method works well for regular, periodic target motion and surrogate signals, which reflect a high amount of this internal motion. For irregular or changing motion patterns the results of this method are limited. Especially in areas, where multiple motion sources overlap into one target movement, e.g. in proximity of the heart or blood vessels, correlation is nearly impossible or requires a high sampling rate of the target region. We concentrate on using three-dimensional ultrasound as tracking modality for target localization. This method offers the possibility to directly monitor the target movement inside an ultrasound volume or to track surrogate signals in close proximity to the target, which are supposed to contain a maximum of target movement information. In this way the target movement can be measured with high temporal resolution and best accuracy, even in difficult areas.