Contents lists available at ScienceDirect Physica Medica journal homepage: www.elsevier.com/locate/ejmp Original paper A new less toxic polymer gel dosimeter: Radiological characteristics and dosimetry properties Seyed Mohammad Mahdi Abtahi a, ⁎ , Mohammad Pourghanbari b a Physics Department, Imam Khomeini International University, Qazvin, Iran b Medical Imaging Center, Imam Reza Hospital, Kermanshah University of Medical Sciences, Kermanshah, Iran ARTICLE INFO Keywords: Polymer gel dosimeter PAMPSGAT MRI Radiological characteristics ABSTRACT Purpose: A new polymer gel dosimeter recipe was investigated that may be more suitable for widespread ap- plications than polyacrylamide gel dosimeters, since the extremely toxic acrylamide has been replaced with the less harmful monomer 2-Acrylamido 2-Methyl Propane Sulfonic acid (AMPS). Methods: The new formulation was named PAMPSGAT. The MRI response (R2) of the dosimeters was analyzed for conditions of varying dose, dose rate, and temperature during scanning. Radiological properties of the PAMPSGAT polymer gel dosimeter were investigated. Results: The dose-response (R2) of AMPS/Bis appears to be linear over a dose range 10–40 Gy. The percentage of difference between the R2 values for imaging at 15 °C and MRI room temperature is about 4.6% for vial with 40 Gy absorbed dose which decreased to less than 1% for imaging at 20 °C. The percentage difference of Zeff of PAMPSGAT gel and soft tissue was less than 1% in the practical energy range (100 KeV–100 MeV). The electron density of the PAMPSGAT polymer gel was 2.9% higher than that of muscle. Results showed that the sensitivity of PAMPSGAT polymer gel dosimeter irradiated by 60 Co (energy = 1.25 MeV) is about 27.7% higher than that of irradiated using a 6 MeV Linac system. Conclusions: Temperature during MRI scanning has a small effect on the R2 response of the PAMPSGAT polymer gel dosimeter. Results confirmed tissue equivalency of the PAMPSGAT polymer gel dosimeter in most practical energy range. The PAMPSGAT polymer gel dosimeter response depends on energy and dose rate. 1. Introduction The use of dosimetry gels has the potential to provide high-resolu- tion measurements of dose in modern radiotherapy technique to verify dose distributions. Furthermore, use of dosimetry gels minimizes the disadvantages of volume averaging, non-water equivalence or need for dose perturbation correction. Gore et al. [1] first applied ferrous sulfate chemical dosimeter to gel dosimetry, used in conjunction with nuclear magnetic resonance (NMR) imaging to obtain quantitative dose distributions. However, the use of radiation sensitive polymer gels for the purpose of radiation dosimetry, as currently used, is as a result of the work undertaken by Maryanski et al in 1993. They introduced polymer gel dosimetry as a useful tools in measuring three dimensional dose distributions by magnetic re- sonance imaging (MRI) [2]. Prior to 2001, gel dosimeters had to be prepared under hypoxic conditions. Fong et al. proposed a new for- mulation by addition of antioxidant to the gel composition which can be made under conditions of normal oxygenation [3]. Polymer gel dosimeters utilize the mechanism of radiation-induced polymerization of monomers, where radiolysis products join small monomer molecules together. The amount of polymer produced by radiation is proportional to the absorbed dose. To preserve spatial information of the absorbed dose, polymer structures hold in place using a gel matrix. Some MRI contrast parameters such as spin-spin relaxation rate are changed due to the irradiation. Hence, high spatial resolution 3D maps of dose have been obtained by MR scanning. In addition to the MRI [4], other imaging modality have been used for gel dosimeters read out including optical-computerized tomography (optical-CT) [5], x-ray CT [6] and ultrasound [7]. Numerous authors have investigated the applications of dosimetric gels for different treatment techniques such as Intensity Modulated Radiation Therapy (IMRT) [8], Brachytherapy [9] and Streotactic Radiosurgery (SRS) [10]. However, one major limitation of polymer gel dosimetry is the toxicity of its chemical compounds, which may en- danger an operator’s safety. Recently, a new less toxic polymer gel dosimeter has been proposed with striking performance characteristics https://doi.org/10.1016/j.ejmp.2018.08.018 Received 21 June 2017; Received in revised form 20 August 2018; Accepted 25 August 2018 ⁎ Corresponding author at: Imam Khomeini International University, Norouzian, P. O. Box 34149-16818, Qazvin, Iran. E-mail addresses: smabtahi2007@gmail.com, sm.abtahi@sci.ikiu.ac.ir (S.M.M. Abtahi). Physica Medica 53 (2018) 137–144 Available online 05 September 2018 1120-1797/ © 2018 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved. T