Program Information
Novel Iron-Based Radiation Reporting Systems as 4D Dosimeters for MR-Guided Radiation Therapy
H Lee1*, M Alqathami1 , M Kadbi2 , J Wang1 , A Blencowe3 , G Ibbott1 , (1) UT MD Anderson Cancer Center, Houston, Texas, (2) MR Therapy, Philips healthTech, Cleveland, OH, (3) The University of South Australia, South Australia, SA
Presentations
TH-CD-BRA-8 (Thursday, August 4, 2016) 10:00 AM - 12:00 PM Room: Ballroom A
Purpose: To compare novel radiation reporting systems utilizing ferric ion (Fe³⁺) reduction versus ferrous ion (Fe²⁺) 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 (T₁-weighted and inversion recovery sequences).
Results: Irradiation of Fe³⁺ 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 (R²=1.00). T₁-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 Fe²⁺ oxidation dosimeters resulted in a stable purple color with absorbance peaks at 440 and 585 nm. The changes in OD, T₁-weighted-MR SI, and R₁ relative to dose exhibited a linear response up to at least 8 Gy (R²=1.00, 0.98, and 0.99) with OD saturation above 40 Gy. The T₁-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 (R²>0.93).
Conclusion: The Fe²⁺ 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 Fe³⁺ reduction system is recommended for high dose applications.
Funding Support, Disclosures, and Conflict of Interest: This material is based upon work supported by the National Science Foundation Graduate Research Fellowship Program under Grant No. LH-102SPS.
Contact Email: