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.
MRI, Contrast Agent, Image-guided Therapy
IM/TH- MRI in Radiation Therapy: MRI/Linear accelerator combined (general)