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Evaluation of Contrast Induced CT Artifact for Intracavitary Brachytherapy

B Libby

B Libby*, L Handsfield, K Reardon, T Showalter, University of Virginia, Charlottesville, VA

SU-E-T-567 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Use of heterogeneity correction has only recently been applied in brachytherapy. Vaginal packing with gauze is used in gynecological brachytherapy to physically move the bladder and rectum farther from the applicator, reducing dose to these structures. The Alatus balloon packing system accomplishes the same task, but use of contrast in the balloon can also obscure these structures on CT images. This work was designed, and conducted using a prostate phantom, to determine the optimal contrast concentration in terms of streak artifact and noise and whether patient anatomy would be obscured by high contrast concentration.

A 60 cc syringe was filled with Omnipaque contrast liquid (350 mg I/ml) of varying concentrations (100% contrast to pure water as well as air) and placed in the phantom rectum in a CIRS prostate phantom (used to permit consistent measurement CT scan was then acquired. The mean CT number of a region of interest inside the prostate was determined, along with the percent noise. Additionally, the distance between the rectum and prostate was determined to see if resolution near the high density material was lost.

The mean CT number of the region of interest did not change from air or water in the syringe through the 100% contrast scan, but the noise increased from 12% to 33%. In all scans the 2 mm distance from the edge of the rectum to the prostate was readily seen.

Previous work has shown that overriding the density in the Alatus balloon packing system for gynecological brachytherapy can lead to additionally radioprotection of the bladder and rectum. This study shows that use of undiluted contrast does not lead to unacceptable streak artifacts that would obscure anatomy, and can be clinically implemented.

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