Assessment of Two Treatment Planning Methods for Accounting CT Metal-Artifacts in Breast Tissue Expanders
J Ramos-Mendez1*, A Villa1, X Li2, A Melancon3, M Sharma1, (1) University of California San Francisco, San Francisco, CA, (2) University of California, Berkeley, (3) University of Texas MD Anderson Cancer Center, Houston, TX
Presentations
MO-E115-IePD-F7-2 (Monday, 7/11/2022) 1:15 PM - 1:45 PM [Eastern Time (GMT-4)]
Exhibit Hall | Forum 7
Purpose: To assess two treatment planning strategies for accounting metal-artifacts introduced by the magnet contained in three breast tissue expander devices subject to MV x-ray irradiation.
Methods: The CT metal-artifacts caused by the metal-ports can be managed using two density override strategies as follows. 1) Identify the metal by the image window-level adjustment and subsequently, delineate a contour enclosing the artifact and set the surrounding voxels density to unity (RS-1). 2) Overlapping a geometry template with dimensions, materials, and densities from the corresponding metal-ports (RS-2). Both strategies were compared using Collapsed Cone Convolution (CCC) in RayStation, TOPAS Monte Carlo simulations (MC) using the actual geometry and film measurements. For that, three customized wax-phantoms (30x30x1.7 cm3) were created with metallic sleeves of DermaSpan, AlloX2 and AlloX2Pro tissue-expanders. The phantoms, stacked with plastic water slabs, were scanned with iMAR artifact reduction on a Siemens CT-scanner and imported to RayStation TPS to calculate the dose distribution using RS-1 and RS-2. The Varian TrueBeam Linac was used to deliver 500 MUs, 6 MV AP beam (15x10 cm2).
Results: MC agreed with film measurements within 2%, 1 standard deviation, for the three metal-port devices. For DermaSpan and AlloX2 ports, RS-1 and RS-2 produced equivalent depth-dose curves which agreed with MC and film within 2%. For AlloX2Pro, CCC underestimated the measured results by 8%-13% for RS-2 and RS-1, respectively. From MC simulations, the underdosage caused by the magnets were (6.4±0.4)%, (4.9±0.7)% and (2.0±0.9)% for DermaSpan, Allox2 and Allox2Pro, respectively.
Conclusion: Two strategies for accounting CT metal-artifacts from three breast tissue-expanders were assessed using CCC, MC and film measurements. Both strategies are equivalent for DermaSpan and AlloX2 devices. However, CCC could not model AlloX2Pro accurately. Guidelines to correctly account the presence of the metal magnet for AlloX2Pro are undergoing by our research group.
Funding Support, Disclosures, and Conflict of Interest: Funding support from Sientra Inc
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