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Dosimetric Results for Magnetic Resonance Guided Radiotherapy Using Hybrid Magnetic Resonance/Computed Tomography Compatible Phantom

M Kim1,2*, S Lee2, B Choe2, T Suh2, (1) Department of Radiation Oncology, Yonsei Cancer Center, Yonsei University College of Medicine, Yonsei University Health System, Seoul, KR, (2) Department of Biomedical Engineering, Research Institute of Biomedical Engineering, The Catholic University of Korea College of Medicine, Seoul, KR

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose:
Dosimetric evaluation was performed by applying image of hybrid MR/CT compatible phantom which contains tissue-equivalent materials for each MR and CT image.
Methods:
The hybrid MR/CT compatible phantom was developed from previous study, and through the previous study, the essential requirements necessary for the development of a hybrid MR/CT compatible phantom was determined and development process was described. A total of 12 different tissue-equivalent materials for each MR and CT image were developed from chemical components. The uniformity of each sample was calculated. The developed phantom was designed to use 14 plugs that contained various tissue-equivalent materials. Measurement using the developed phantom was performed using a 3.0-T scanner with 32 channels and a Somatom Sensation 64. Dose distribution from CT image was utilized as reference data and dosimetric results from converted MR image set, which imported to commercialized treatment planning system and converted to CT-like image. Dose calculation using collapsed cone algorithm in RayStation was performed by applying 500 cGy on isocenter of 6 MV photon for SSD (source to surface distance) 90 cm and 30 x 30 cm² fields with 0° of gantry angle and isocenter was the center coordinate of phantom external region of interest.
Results:
The maximum percentage difference of the SI value on MR images after adding K2CO3 was 3.31%. Additionally, the uniformity of each tissue was evaluated by calculating the %PIU of the MR image, which was 82.18% ±1.87 with 83% acceptance, and the average circular-shaped ROIs on CT images for all samples were within ±5 HU. Also, dosimetric evaluation was performed. The percentage differences of each tissue-equivalent sample for average dose was ranged from -0.76% to 0.21%.
Conclusion:
A hybrid MR/CT compatible phantom for MR and CT was investigated as the first trial in this field of radiation oncology and medical physics.

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Keywords

MRI, Dose, Phantoms

Taxonomy

IM/TH- MRI in Radiation Therapy: Development (new technology and techniques)

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