Timing considerations for preclinical MRgRT: effects of ion diffusion, SNR and imaging times on FXG gel calibration

8th International Conference on 3D Radiation Dosimetry

Welch, M.^1 ; Foltz, W.D.^2,3 ; Jaffray, D.A.^1,2,3,4

Department of Medical Biophysics, University of Toronto, Toronto

ON, Canada^1

Radiation Medicine Program, Princess Margaret Hospital, Toronto

ON, Canada^2

Department of Radiation Oncology, University of Toronto, Toronto

ON, Canada^3

TECHNA Institute for the Advancement of Technology for Health, Toronto

ON, Canada^4

关键词: Calibration curves;    Depth-dose data;    Fick's second law;    High resolution;    Postirradiation;    Relaxation rates;    Sub-millimeter resolutions;    Xylenol Orange;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/573/1/012045/pdf
DOI  :  10.1088/1742-6596/573/1/012045

来源: IOP

【 摘 要 】

Sub-millimeter resolution images are required for gel dosimeters to be used in preclinical research, which is challenging for MR probed ferrous xylenol-orange (FXG) dosimeters due to ion diffusion and inadequate SNR. A preclinical 7 T MR, small animal irradiator and FXG dosimeters were used in all experiments. Ion diffusion was analyzed using high resolution (0.2 mm/pixel) T1MR images collected every 5 minutes, post-irradiation, for an hour. Using Fick's second law, ion diffusion was approximated for the first hour post-irradiation. SNR, T1 map precision and calibration fit were determined for two MR protocols: (1) 10 minute acquisition, 0.35mm/pixel and 3mm slices, (2) 45 minute acquisition, 0. 25 mm/pixel and 2 mm slices. SNR and T1 map precision were calculated using a Monte Carlo simulation. Calibration curves were determined by plotting R1 relaxation rates versus depth dose data, and fitting a linear trend line. Ion diffusion was estimated as 0.003mm2in the first hour post-irradiation. For protocols (1) and (2) respectively, Monte Carlo simulation predicted T1 precisions of 3% and 5% within individual voxels using experimental SNRs; the corresponding measured T1 precisions were 8% and 12%. The linear trend lines reported slopes of 27 ± 3 Gy∗s (R2: 0.80 ± 0.04) and 27 ± 4 Gy∗s (R2: 0.90 ± 0.04). Ion diffusion is negligible within the first hour post-irradiation, and an accurate and reproducible calibration can be achieved in a preclinical setting with sub-millimeter resolution.