Sensitivity Optimization for a New Radio-Chromic Dosimeter (PRESAGE)

Document Type: Original Paper

Authors

1 M.Sc. of Radiation Medicine Dept., Shahid Beheshti University, Tehran, Iran.

2 Assistant Professor, Nuclear Engineering Dept., Shahid Beheshti University, Tehran, Iran

3 Associate Professor, Shahid Beheshti University, Evin, Tehran, Iran

4 M.Sc. in Medical Physics, Shahid Beheshti University, Tehran, Iran

Abstract

Introduction: Different dosimetric modalities (e.g., ionization chambers, semiconductors, TLDs, radiographic films) often have some problems determining isodose curves and percentage depth doses in high dose gradient regions. Research has been ongoing to develop portable high resolution dosimetry devices with accurate absolute dosimetry capabilities and easy data analysis. The ‘PRESAGE’ dosimeter is a type of polymer dosimeters with improved characteristics in comparison with older polymer dosimeters. It is solid, insensitive to oxygen, and can be made in different shapes. This work presents the fabrication process for a PRESAGE dosimeter and optimization of its radiation sensitivity.
Material and Methods: The PRESAGE gel was formed in two steps. In the first step, Leuco Malachite Green was dissolved in a free radical initiator (carbon tetrachloride; CCl4) and a polyol, referred to as ‘Part B’ was added to the solution. The second step consisted of mixing the Leuco dye, a free radical initiator, and a catalyst with ‘Part B’ (a commercially available polyol), then blending them with Part A in equal proportions, placing the blended materials in an appropriate mold, and incubating at an optimal temperature under a pressure of 60 psi for 18 to 24 hours. After this period, the solution turned solid and was subsequently exposed using a cobalt-60 unit. Finally, the PRESAGE gel was read using a spectrophotometer.
Results: The results showed that by changing the percentage of both Leuco dye and CCl4 to 4%, an optimum sensitivity of 0.0144 units/Gy can be reached.
Discussion and Conclusion: Our results showed that the response function of the PRESAGE dosimeter is linear between 2.5 to 55 Gy. Using different material percentages to make the PRESAGE gel can result in a sensitivity variation ranging from 0.0099 to 0.0144 units/Gy.

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