Korean J Med Phys.  2012 Jun;23(2):71-80.

A Study of Optimized MRI Parameters for Polymer Gel Dosimetry

Affiliations
  • 1Department of Radiological Science, Eulji University College of Health Science, Seongnam, Korea.
  • 2Department of Medical Physics, Kyonggi University, Suwon, Korea. sikwon@kyonggi.ac.kr
  • 3Department of Radiation Oncology, Cheil General Hospital & Women's Healthcare Center, Kwandong University College of Medicine, Seoul, Korea.
  • 4Department of Radiation Oncology, Inha University Hospital, Incheon, Korea.
  • 5Department of Radiation Oncology, Gachon University Gil Hospital, Incheon, Korea.
  • 6Department of Radiation Oncology, College of Medicine, Eulji University, Seoul, Korea.

Abstract

In order to verify exact dose distributions in the state-of-the-art radiation techniques, a newly designed three-dimensional dosimeter and technique has been took strongly into consideration. The main purpose of our study is to verify the optimized parameters of polymer gel as a real volumetric dosimeter in terms of the various study of MRI. We prepared a gel dosimeter by combing 8% of gelatin, 8% of MAA, and 10 mM of THPC. We used a Co-60 gamma-ray teletherapy unit and delivered doses of 0, 2, 4, 6, 8, 10, 12, and 14 Gy to each polymer gel with a solid phantom. We used a fast spin-echo pulse to acquire the characterized T2 time of MRI. The signal noise ratio (SNR) of the head & neck coil was a relatively lower sensitivity than the body coil; therefore the dose uncertainty of head & neck coil would be lower than body coil's. But the dose uncertainty and resolution of the head & neck coil were superior to the body coil in this study. The TR time between 1,500 ms and 2,000 ms showed no significant difference in the dose resolution, but TR of 1,500 ms showed less dose uncertainty. For the slice thickness of 2.5 mm, less dose uncertainty of TE times was at 4 Gy, as well, it was the lowest result over 4 Gy at TE of 12 ms. The dose uncertainty was not critical up to 6 Gy, but the best dose resolution was obtained at 20 ms up to 8 Gy. The dose resolution shows the lowest value was over 20 ms and was an excellent result in the number of excitation (NEX) of three. The NEX of two was the highest dose resolution. We concluded that the better result of slice thickness versus NEX was related to the NEX increment and thin slice thickness.

Keyword

Polymer gel dosimeter; Optimized parameters; Dose resolution; MRI

MeSH Terms

Gelatin
Head
Neck
Noise
Organophosphorus Compounds
Polymers
Uncertainty
Gelatin
Organophosphorus Compounds
Polymers
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