Methods and systems to determine respiratory phase and motion state during guided radiation therapy

Abstract

Methods and systems using magnetic resonance and ultrasound for tracking anatomical targets for radiation therapy guidance are provided. One system includes a patient transport configured to move a patient between and into a magnetic resonance (MR) system and a radiation therapy (RT) system. An ultrasound transducer is also provided that is hands-free and electronically steerable, securely attached to the patient, such that the ultrasound transducer is configured to acquire four-dimensional (4D) ultrasound images concurrently with one of an MR acquisition or an RT radiation therapy session. The system also includes a controller having a processor configured to use the 4D ultrasound images and MR images from the MR system to control at least one of a photon beam spatial distribution or intensity modulation generated by the RT system. The system determines the previously-acquired correct MR images that represent a specific motion state at some time, t, by a plurality of transformations that allow the representation of the position of fiducial markers in the corresponding ultrasound images to match that of a prior ultrasound acquisition.