FOUR-DIMENSIONAL MRI FOR IMAGE-GUIDED RADIATION THERAPY FOR PANCREATIC CANCER

Mayo Clinic Arizona, Scottsdale AZ

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Abstract

DESCRIPTION (provided by applicant): Pancreatic cancer ranks fourth in cancer related deaths in the United States. It has very poor prognosis. The five year survival rate is only 6%. Approximately 30% of pancreatic cancer patients die with locally destructive pancreatic cancer. For locally advanced pancreatic cancer, chemoradiotherapy can be used to provide locoregional control. However, it is often accompanied by gastrointestinal (GI) toxicity. Reducing GI toxicity for pancreatic cancer patients can be very challenging, mainly because none of the current imaging techniques have the capability to track the respiration induced motion of the pancreatic tumor itself. Although four dimensional (4D) computed tomography (CT) can be used to assess organ motion, poor soft tissue contrast makes it of limited value for the pancreas. Magnetic resonance imaging (MRI) has excellent soft tissue contrast and is ideal for imaging tissues within the abdomen. But current 4DMRI techniques are only compatible with Steady-State Free Precession (SSFP) sequences (balanced or spoiled). Those sequences have low tumor/tissue contrast and are not ideal for pancreatic cancer either. Without 4D imaging, the uncertainty of tumor location and motion is substantial. To ensure that the tumor is not missed, large treatment margins are typically employed. This practice makes the high-dose region larger than the original tumor and irradiates the surrounding normal anatomy to tomoricidal doses. To address this challenge, we propose to develop a respiration- amplitude-triggered 4DMRI technique that will quantify breathing motion. Our innovative 4DMRI technique will use triggers at selected respiratory amplitudes to drive image acquisition. For a given two dimensional (2D) slice, images at different respiratory amplitudes will no longer have to be acquired within a single respiratory cycle. Using the proposed technique, the acquisition process will be able to span over multiple breathing cycles, which will make the proposed 4DMRI technique more flexible in the selection of MRI sequences and also make possible the utilization of multi-shot data acquisition techniques. The efficiency of image acquisition can be kept comparable to standard MRI sequences by acquiring data for multiple slices during each respiratory cycle. The proposed 4DMRI technique will be superior 4DCT and previous 4DMRI techniques in that it can 1) accommodate a variety of image contrast mechanisms such as T2 weighting and diffusion weighting to enhance the contrast between the pancreatic tumor and surrounding tissues, and 2) achieve excellent spatial and temporal resolutions for motion tracking and radiation therapy treatment planning. If our method proves to be effective, we will be able to accurately track the movement of the pancreatic tumor, enabling more quantitative and accurate treatment planning, including the design of internal target volumes or gating techniques.