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Impact of Iterative Metal Artifact Reduction Algorithm On Scatter Contouring in Radiation Therapy Treatment Planning

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S Anderson

S Anderson*, D Brinkmann , Mayo Clinic, Rochester, MN


PO-BPC-Exhibit Hall-7 (Saturday, March 5, 2016)  Room: Exhibit Hall

Purpose: To investigate whether CT datasets reconstructed with an iterative metal artifact reduction (IMAR) algorithm can be used for radiation therapy planning without further corrections for scatter, thus eliminating the time-intensive need to contour metal artifacts.

Methods: We selected patient CT datasets with metal artifact in the beam path. We analyzed four cases with different sources of metal artifact: dental fillings, hip implants, spinal implants, and breast expanders. For each patient, a plan was first calculated on the original dataset, with scatter contoured and reassigned to an HU of 0. The plan, with same field geometry and MU, was then calculated on the IMAR-corrected images, without any contouring of artifacts. The dose statistics for target volumes and organs at risk were compared for the original and IMAR-corrected plans.

Results: Dose statistics for the planning structures agreed within 1.5Gy and 2.2cc, the largest differences being for small volumes on the order of a few cubic centimeters. The statistics for the IMAR-corrected images had higher values, in general, than the uncorrected images. A qualitative comparison of the dose distributions indicated that there were no major differences. A patient dataset without metal artifact was reconstructed with and without IMAR, and a plan calculated on both datasets resulted in identical dose statistics.

Conclusion: Plans calculated on the IMAR-corrected images resulted in similar dose statistics to those obtained under the current clinical practice of contouring metal artifact and reassigning HU values. The largest differences were for small volumes, where small absolute changes result in large relative differences. The fact that the dose statistics for the organs at risk with IMAR were in general higher than the current clinical practice lessens the risk of overdosing a critical structure using IMAR. The outlook for using IMAR to avoid the time-consuming process of contouring metal artifact is promising.

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