ABSTRACT
Tumor motion is typically classified as one of two types: interfractional motion refers to differences between planned and actual tumor position observed during patient setup for daily treatment delivery and intrafractional motion refers to differences between daily setup position and actual tumor position during therapy delivery. Intrafractional motion generally causes a blurring of the target dose distribution. In the current clinical standard of care intrafractional motion is, therefore, accounted for by irradiating an enlarged tissue volume encompassing all tumor positions expected to occur during treatment delivery. Tumor tracking can be used to verify and mitigate the negative effects of tumor motion on the delivered dose distribution while improving the necessary treatment margins. A general physical limit to real-time motion estimation from portal imagery is imposed by the information content encoded in the image. A multitude of tumor-localization methods utilizing the electronic portal imaging devices (EPID) have been developed over the past two decades.
