Patients with gynecologic cancers localized to the pelvis may be curatively treated with radiation. The use of brachytherapy, the placement of radioactive seeds directly into the center of the tumor, after external beam radiation, permits dose escalation to the tumor, resulting in successful regression and eradication of the tumor. However, adjacent to the tumor, critical normal tissue structures including the small bowel, sigmoid, rectum, and bladder may rest in regions that can receive high doses of radiation. In most centers in the U.S., simple imaging (X-ray or CT) with doses prescribed to a single point are the standard of care. Normal tissues are not defined by their actual dimensions, rather by points that approximate their location. In order to successfully determine the location of the tumor and its relationship to the normal tissues structures in order to minimize the dose to them, it is necessary to image the pelvis during brachytherapy applicator placement. MRI delineate tumor and OAR in the pelvis with much more precision than other imaging modalities. In this clinical trial, the utility of 3T T2- weighted MRI imaging, in addition to DWI MRI, and how the images correlate with biopsy-confirmed presence of cancer will be studied.
The long term goal of this work is to reduce toxicity due to gynecologic brachytherapy. We will confirm the relationship of MR-detected tumor and biopsy confirmed tumor. This information will guide development of a trial of dose escalation in patients with residual disease based on MR-identified residual tumor and de-escalation with a complete response. Should this trial demonstrate a clearly defined tumor from 3T MR that results in a reduced dose to the normal tissues compared to historical controls, this will result in MR image-guided brachytherapy becoming the standard at the BWH, and in the U.S. We will ultimately develop an imaging-based protocol to determine which patients may benefit the most from MR-based planning. Future studies will explore changes in radiation dose to the tumor and the cervix in order to more determine the minimum required dose to the cervix for curative management.
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