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Experimental Validation of the Dosimetric Impact of a Gadolinium-Based Contrast Agent On a Photon Beam in the Presence of 1.5 T Magnetic Field

K Hall1*, L Kim1, G Ibbott2, F Riaz4, M Reyhan3,4, (1) MD Anderson Cancer Center at Cooper, Camden, NJ, (2) The American Board of Radiology, Tucson, AZ, (3) Robert Wood Johnson University Hospital, Hamilton, NJ,(4) Rutgers Cancer Institute of New Jersey, New Brunswick, NJ

Presentations

MO-E115-IePD-F6-1 (Monday, 7/11/2022) 1:15 PM - 1:45 PM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 6

Purpose: The purpose of this study is to experimentally validate a previously published Monte Carlo (MC) simulation of the impact of Gadolinium-based contrast agents on the dose distribution produced by a 1.5 T MR-Linac.

Methods: Two custom 3D slab dosimeters composed of water equivalent radiochromic plastic approximately 10 cm x 10 cm x 1 cm were fabricated. Both dosimeters were designed with a centrally located 1 x 1 cm³ cavity for the addition of Gadavist (Gad) (Bayer Healthcare). Additionally, Gafchromic film (EBT3) was placed between the 2 slab dosimeters. The 3D dosimeters and film were irradiated with a 7X FFF 10x10 cm2 open field on the Elekta Unity MR-Linac (1.5T). A percent depth dose (PDD) curve was measured in film across the interfaces of the different media and compared to a baseline PDD created in the clinical treatment planning system in a homogeneous water phantom.

Results: In the proximal Gad region, the dose increased by an average of 2.1% compared to the TPS water phantom. For comparison, a previously published MC simulation using EGSnrc reported a 2.4% average dose increase in this region, which is in good agreement with our experimental results. Across the entire Gad region, the average difference was 0.5% (range: -3.5 to 2.7%.) The average difference in a region 0.6 cm upstream from the Gad was -0.3% (range: -2.3% to 1.8%).

Conclusion: This work experimentally validates that Gad in the presence of a 1.5T magnetic field has a minimal impact on a dose distribution. In addition, the PDD was affected < 4% by the presence of Gadavist contrast agent, suggesting the feasibility of using contrast agents during treatment on the Unity MR-Linac.

Keywords

MRI, Contrast Agent, Image-guided Therapy

Taxonomy

IM/TH- MRI in Radiation Therapy: MRI/Linear accelerator combined (general)

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