Program Information
Developing and Characterizing MR/CT Compatible Materials Used in QA Phantoms for MRgRT Modalities
A Steinmann*, R Stafford , G Sawakuchi , Z Wen , L Court , C Fuller , D Followill , The University of Texas MD Anderson Cancer Center, Houston, TX
Presentations
MO-L-GePD-JT-5 (Monday, July 31, 2017) 1:15 PM - 1:45 PM Room: Joint Imaging-Therapy ePoster Theater
Purpose: Tissue equivalent (TE) materials currently used in IROC-Houston’s end-to-end QA phantoms are not visualized on MR. The purpose of this study is to characterize alternate TE materials that can be used in IROC’s QA phantoms for MR-guided-radiotherapy (MRgRT).
Methods: Over 80 materials’ MR, CT, and dosimetric TE properties were investigated for use in MRgRT QA phantoms. The materials tested included homogeneous and heterogeneous materials to simulate soft-tissue/tumor and lung tissues. Materials were scanned on a Siemens’ Magnetom Espree 1.5T using four sequences, to show the materials’ T1 and T2 weighted images visual contrast. Each material’s attenuation data were collected using GE’s CT Lightspeed. Dosimetric properties of the selected materials were examined in a 10x10x20 cm³ phantom made of the materials. An Elekta Versa 6 MV beam was used to irradiate each phantom with radiochromic film to measure the percent depth dose (PDD). Measured film PDD curves were compared to planning system calculations and conventional TE materials’ PDD curves.
Results: Most materials tested had comparable HUs to their simulated organ but, the majority of materials were not visible with MR. Silicone, hydrocarbon, synthetic gelatin and liquid PVC plastic based materials showed good MR image contrast. In-house lung equivalent materials made with silicone and hydrocarbon based materials had HUs ranging from -978 to -117 and -666 to -593, respectively. Plastic and gelatin based materials resembled soft-tissue/tumor equivalent materials with HUs ranging from -29 to 32 and -175 to -170, respectively. Chosen MR/CT compatible materials’ PDD curves were comparable to IROC-Houston’s conventional TE materials. The smallest field size showed the largest disagreements, where the average discrepancies between calculated and measured PDD curves were 1.8% and 5.9% for homogeneous and heterogeneous testing materials, respectively.
Conclusion: Gelatin, liquid plastic, and hydrocarbon based materials were determined as alternative TE substitutes for MRgRT QA phantoms.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by Public Health Service Grant No. CA180803 awarded by the National Cancer Institute, United States Department of Health and Human Services.
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