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SU‐G‐JeP2‐04: Comparison Between Fricke‐Type 3D Radiochromic Dosimeters for Real‐Time Dose Distribution Measurements in MR‐Guided Radiation Therapy
Author(s) -
Lee H,
Alqathami M,
Kadbi M,
Wang J,
Blencowe A,
Ibbott G
Publication year - 2016
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4957024
Subject(s) - dosimeter , irradiation , nuclear medicine , dosimetry , materials science , linear particle accelerator , radiochemistry , chemistry , medicine , optics , physics , nuclear physics , beam (structure)
Purpose: To assess MR signal contrast for different ferrous ion compounds used in Fricke‐type gel dosimeters for real‐time dose measurements for MR‐guided radiation therapy applications. Methods: Fricke‐type gel dosimeters were prepared in 4% w/w gelatin prior to irradiation in an integrated 1.5 T MRI and 7 MV linear accelerator system (MR‐Linac). 4 different ferrous ion (Fe2?) compounds (referred to as A, B, C, and D) were investigated for this study. Dosimeter D consisted of ferrous ammonium sulfate (FAS), which is conventionally used for Fricke dosimeters. Approximately half of each cylindrical dosimeter (45 mm diameter, 80 mm length) was irradiated to ∼17 Gy. MR imaging during irradiation was performed with the MR‐Linac using a balanced‐FFE sequence of TR/TE = 5/2.4 ms. An approximate uncertainty of 5% in our dose delivery was anticipated since the MR‐Linac had not yet been fully commissioned. Results: The signal intensities (SI) increased between the un‐irradiated and irradiated regions by approximately 8.6%, 4.4%, 3.2%, and 4.3% after delivery of ∼2.8 Gy for dosimeters A, B, C, and D, respectively. After delivery of ∼17 Gy, the SI had increased by 24.4%, 21.0%, 3.1%, and 22.2% compared to the un‐irradiated regions. The increase in SI with respect to dose was linear for dosimeters A, B, and D with slopes of 0.0164, 0.0251, and 0.0236 Gy −1 (R 2 = 0.92, 0.97, and 0.96), respectively. Visually, dosimeter A had the greatest optical contrast from yellow to purple in the irradiated region. Conclusion: This study demonstrated the feasibility of using Fricke‐type dosimeters for real‐time dose measurements with the greatest optical and MR contrast for dosimeter A. We also demonstrated the need to investigate Fe 2+ compounds beyond the conventionally utilized FAS compound in order to improve the MR signal contrast in 3D dosimeters used for MR‐guided radiation therapy. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship Program under Grant No. LH‐ 102SPS.