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TH‐CD‐BRA‐08: Novel Iron‐Based Radiation Reporting Systems as 4D Dosimeters for 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 - 10.1118/1.4958151
Subject(s) - dosimeter , irradiation , absorbance , dosimetry , radiochemistry , ferric ion , nuclear medicine , linear particle accelerator , materials science , radiation therapy , radiation , ion , chemistry , nuclear magnetic resonance , medicine , optics , physics , radiology , nuclear physics , beam (structure) , organic chemistry , chromatography
Purpose: To compare novel radiation reporting systems utilizing ferric ion (Fe 3+ ) reduction versus ferrous ion (Fe 2+ ) oxidation in gelatin matrixes for 3D and 4D (3D+time) MR‐guided radiation therapy dosimetry. Methods: Dosimeters were irradiated using an integrated 1.5T MRI and 7MV linear accelerator (MR‐Linac). Dosimeters were read‐out with both a spectrophotometer and the MRI component of the MR‐Linac immediately after irradiation. Changes in optical density (OD) were measured using a spectrophotometer; changes in MR signal intensity due to the paramagnetic differences in the iron ions were measured using the MR‐Linac in real‐time during irradiation (balanced‐FFE sequences) and immediately after irradiation (T 1 ‐weighted and inversion recovery sequences). Results: Irradiation of Fe 3+ reduction dosimeters resulted in a stable red color with an absorbance peak at 512 nm. The change in OD relative to dose exhibited a linear response up to 100 Gy (R 2 =1.00). T 1 ‐weighted‐MR signal intensity (SI) changed minimally after irradiation with increases of 8.0% for 17 Gy and 9.7% after escalation to 35 Gy compared to the un‐irradiated region. Irradiation of Fe 2+ oxidation dosimeters resulted in a stable purple color with absorbance peaks at 440 and 585 nm. The changes in OD, T 1 ‐weighted‐MR SI, and R 1 relative to dose exhibited a linear response up to at least 8 Gy (R 2 =1.00, 0.98, and 0.99) with OD saturation above 40 Gy. The T 1 ‐weighted‐MR SI increased 50.3% for 17 Gy compared to the un‐irradiated region. The change in SI was observed in both 2D+time and 4D (3D+time) acquisitions post‐irradiation and in real‐time during irradiation with a linear increase with respect to dose (R 2 >0.93). Conclusion: The Fe 2+ oxidation‐based system was superior as 4D dosimeters for MR‐guided radiation therapy due to its higher sensitivity in both optical and MR signal readout and feasibility for real‐time 4D dose readout. The Fe 3+ reduction system is recommended for high dose applications. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship Program under Grant No. LH‐102SPS.