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Khan M, Heilemann G, Lechner W, et al. Basic Properties of a New Polymer Gel for 3D-Dosimetry at High Dose-Rates Typical for FFF Irradiation Based on Dithiothreitol and Methacrylic Acid (MAGADIT): Sensitivity, Range, Reproducibility, Accuracy, Dose Rate Effect and Impact of Oxygen Scavenger. Polymers (Basel). 2019;11(10)doi: 10.3390/polym11101717.
Khan, M., Heilemann, G., Lechner, W., Georg, D., & Berg, A. G. (2019). Basic Properties of a New Polymer Gel for 3D-Dosimetry at High Dose-Rates Typical for FFF Irradiation Based on Dithiothreitol and Methacrylic Acid (MAGADIT): Sensitivity, Range, Reproducibility, Accuracy, Dose Rate Effect and Impact of Oxygen Scavenger. Polymers, 11(10), . https://doi.org/10.3390/polym11101717
Khan, Muzafar, et al. "Basic Properties of a New Polymer Gel for 3D-Dosimetry at High Dose-Rates Typical for FFF Irradiation Based on Dithiothreitol and Methacrylic Acid (MAGADIT): Sensitivity, Range, Reproducibility, Accuracy, Dose Rate Effect and Impact of Oxygen Scavenger." Polymers vol. 11,10 (2019). doi: https://doi.org/10.3390/polym11101717
Khan M, Heilemann G, Lechner W, Georg D, Berg AG. Basic Properties of a New Polymer Gel for 3D-Dosimetry at High Dose-Rates Typical for FFF Irradiation Based on Dithiothreitol and Methacrylic Acid (MAGADIT): Sensitivity, Range, Reproducibility, Accuracy, Dose Rate Effect and Impact of Oxygen Scavenger. Polymers (Basel). 2019 Oct 19;11(10). doi: 10.3390/polym11101717. PMID: 31635117; PMCID: PMC6835276.
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Polymers (Basel). 2019 Oct 19;11(10). doi: 10.3390/polym11101717.

Basic Properties of a New Polymer Gel for 3D-Dosimetry at High Dose-Rates Typical for FFF Irradiation Based on Dithiothreitol and Methacrylic Acid (MAGADIT): Sensitivity, Range, Reproducibility, Accuracy, Dose Rate Effect and Impact of Oxygen Scavenger.

Polymers

Muzafar Khan, Gerd Heilemann, Wolfgang Lechner, Dietmar Georg, Andreas Georg Berg

Affiliations

  1. Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Waehringer Guertel 18-23, A-1090 Vienna, Austria. [email protected].
  2. High-Field MR-Center (MRCE), Medical University of Vienna; Lazarettg 14, A-1090 Vienna, Austria. [email protected].
  3. Nuclear Medicine, Oncology and Radiotherapy Institute (NORI), G-8/3 Islamabad 44000, Pakistan. [email protected].
  4. Department of Radiation Oncology, Medical University of Vienna/AKH Vienna, Waehringer Guertel 18-20, 1090 Vienna, Austria. [email protected].
  5. Department of Radiation Oncology, Medical University of Vienna/AKH Vienna, Waehringer Guertel 18-20, 1090 Vienna, Austria. [email protected].
  6. Department of Radiation Oncology, Medical University of Vienna/AKH Vienna, Waehringer Guertel 18-20, 1090 Vienna, Austria. [email protected].
  7. Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Waehringer Guertel 18-23, A-1090 Vienna, Austria. [email protected].
  8. High-Field MR-Center (MRCE), Medical University of Vienna; Lazarettg 14, A-1090 Vienna, Austria. [email protected].

PMID: 31635117 PMCID: PMC6835276 DOI: 10.3390/polym11101717

Abstract

The photon induced radical-initiated polymerization in polymer gels can be used for high-resolution tissue equivalent dosimeters in quality control of radiation therapy. The dose (D) distribution in radiation therapy can be measured as a change of the physical measurement parameter T2 using T2-weighted magnetic resonance imaging. The detection by T2 is relying on the local change of the molecular mobility due to local polymerization initiated by radicals generated by the ionizing radiation. The dosimetric signals R2 = 1/T2 of many of the current polymer gels are dose-rate dependent, which reduces the reliability of the gel for clinical use. A novel gel dosimeter, based on methacrylic acid, gelatin and the newly added dithiothreitol (MAGADIT) as an oxygen-scavenger was analyzed for basic properties, such as sensitivity, reproducibility, accuracy and dose-rate dependence. Dithiothreitol features no toxic classification with a difference to THPC and offers a stronger negative redox-potential than ascorbic acid. Polymer gels with three different concentration levels of dithiothreitol were irradiated with a preclinical research X-ray unit and MR-scanned (T2) for quantitative dosimetry after calibration. The polymer gel with the lowest concentration of the oxygen scavenger was about factor 3 more sensitive to dose as compared to the gel with the highest concentration. The dose sensitivity (α = ∆R2/∆D) of MAGADIT gels was significantly dependent on the applied dose rate D ˙ (≈48% reduction between D ˙ = 0.6 Gy/min and D ˙ = 4 Gy/min). However, this undesirable dose-rate effect reduced between 4-8 Gy/min (≈23%) and almost disappeared in the high dose-rate range (8 ≤   D ˙ ≤   12 Gy/min) used in flattening-filter-free (FFF) irradiations. The dose response varied for different samples within one manufacturing batch within 3%-6% (reproducibility). The accuracy ranged between 3.5% and 7.9%. The impact of the dose rate on the spatial integrity is demonstrated in the example of a linear accelerator (LINAC) small sized 5 × 10 mm

Keywords: 3D; FFF; dose rate; dosimetry; flattening filter free; gel; magnetic resonance; oxygen scavenger; polymer; precision; radiation therapy; responsive gels in biomedical and diagnostic applications

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