2012 AAPM Annual Meeting
Parag Parikh, St. Louis, MO, , United States
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4D-CT has been widely used in radiotherapy for imaging moving tumors, especially in the thoracic regions. In other body sites such as the abdominal, 4D-CT is limited due to its low soft-tissue contrast. Additional concern for 4D-CT includes increased radiation dose to the patient. On the other hand, MRI has no known radiation hazard and has excellent soft-tissue contrast. It is desirable to develop 4D-MRI techniques to address the problems associated with 4D-CT.
There are different methods of 4D-MRI imaging. One is to use sophisticated MR pulse sequence and/or use advanced software and hardware. Another method is to retrospectively sort slice MR images acquired continuously throughout the volume based on respiratory phases. The first method typically results in a temporal resolution of ~0.7 frame/s and a spatial resolution of 3-4 mm. The second method requires simultaneously acquired respiratory signals, either by using external surrogate or internal/image-based surrogate. The temporal resolution is ~ 3 frames/s, the in-plane spatial resolution is ~1.5-2 mm, and the slice thickness is ~ 3-5 mm. Both methods are doable using commercially available MR sequences. 4D-MRI can be used to improve the determination of patient specific tumor motion margin for radiation therapy, especially for the tumors in the abdominal regions where 4D-CT has limitations.
We presented this topic as a joint imaging/therapy scientific symposium in 2011 AAPM annual meeting. This proposal aims to provide a follow up education on this topic and present technical details on how to establish the 4D-MRI program in the clinic.
1. Discuss the need of 4D-MRI technique for improving patient care in radiation therapy
2. Understand technical aspects of different 4D-MRI imaging techniques
3. Discuss the procedures to establish 4D-MRI program in a radiation oncology clinic