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Abstract NIPAM polymer gel dosimeter has low toxicity and its response does not particularly depend on dose rate and beam energy. However, a chief drawback of the NPAM gel dosimeter is its relatively low sensitivity. In the current study, the sensitivity of the NIPAM gel dosimeter was improved by adding urea which this new formula gel dosimeter was called U-NIPAM (Urea and NIPAM) and optimal amount of urea for this new formula was evaluated. For this purpose, various concentrations of the urea (1%, 2%, 3% and 4% (w/w)) were tested. The samples were irradiated using 1.25 MeV and 6 MV photon energies and imaged by a 1.5 T MRI scanner. Then, the MRI response (R 2) and the sensitivity of the conventional NIPAM and U-NIPAM gel dosimeters with different percentages of urea were analyzed at a 0–6 Gy dose range, different post irradiation time, and temperature during scanning. The radiological properties of U-NIPAM polymer gel dosimeter reveal that this substance can be considered as a water/soft tissue equivalent material. With analyzing the findings, it was found that the optimal amount of urea is 3%, because after this concentration, the R 2 -dose sensitivity of U-NIPAM gel dosimeter does not significantly changed (P > 0.05). Furthermore, the results showed that using 3% urea in conventional NIPAM gel formulation leads to a sensitivity increase of around 37% (0.242 vs. 0.177 s−1 Gy−1). In addition, other results for optimized U-NIPAM gel dosimeter include: a) an excellent linear R 2 -dose response in 0–6 Gy dose range, and b) stability in the R 2 value and the sensitivity for 18–21 °C temperatures. Highlights • Sensitivity of the NIPAM gel dosimeter was improved by adding urea. • The optimal amount of urea was determined 3%. • New formulation was named U-NIPAM. • Radiological properties of the U-NIPAM are equivalent to those of water and soft tissue. • Optimized U-NIPAM gel shows a sensitivity increase of about 37%. [ABSTRACT FROM AUTHOR]

One of the main drawbacks of NPAM gel dosimeter is its relatively low R 2-dose sensitivity. Recently, the sensitivity of NIPAM gel dosimeter has been improved by adding urea and this new formula gel dosimeter was named U-NIPAM (Urea and NIPAM). In the current project, photon energy and dose rate dependence of optimized U-NIPAM gel dosimeter (with 3% urea) was assessed by MRI technique. The gel samples were fabricated under normal atmospheric conditions and after 1 day, they were exposed to photon energies of 6 and 15 MV and dose rates of 300, 400, and 500 cGy/min. Then, MRI responses (R 2) of the U-NIPAM gel samples were analyzed at 12, 36, 72, 168 h after the irradiation process. The dosimetric evaluation of optimized U-NIPAM gel dosimeter characteristics at 12 h after the irradiation process resulted to following findings: 1) different photon energies (6 and 15 MV) have significant effect on the R 2 -dose sensitivity of gel dosimeter in 0–7 Gy dose range (P < 0.05), 2) the R 2 -dose sensitivity of gel dosimeter does not significantly change with different dose rate (300–500 cGy/min) in 0–7 Gy dose range (P ˃0.05), 3) the obtained dose resolution for evaluated various photon energies and dose rates ranges from 0.06 Gy to 0.20 Gy. Moreover, it was found that the R 2 -dose sensitivity dependence of gel dosimeter on photon energy can vary over post irradiation; nevertheless, the R 2 -dose sensitivity dependence of dosimeter on dose rate dose not vary over post irradiation time. • Photon energy and dose rate dependence of U-NIPAM gel dosimeter was assessed. • Sensitivity of U-NIPAM gel dosimeter is photon energy dependent. • Sensitivity of U-NIPAM gel dosimeter is independent of dose rate. [ABSTRACT FROM AUTHOR]

Abstract Radiotherapy has rapidly improved because of the use of new equipment and techniques. Hence, the appeal for a feasible and accurate three-dimensional (3D) dosimetry system has increased. In this regard, gel dosimetry systems are accurate 3D dosimeters with high resolution. This systematic review evaluates the clinical applications of polymer gel dosimeters in radiotherapy. To find the clinical applications of polymer gel dosimeters in radiotherapy, a full systematic literature search was performed on the basis of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines in electronic databases up to January 31, 2017, with use of search-related terms in the titles and abstracts of articles. A total of 765 articles were screened in accordance with our inclusion and exclusion criteria. Eventually, 53 articles were included in the study. The findings show that most clinical applications of polymer gel dosimeters relate to external radiotherapy. Most of the gel dosimeters studied have acceptable dose accuracy as a 3D dosimeter with high resolution. It is difficult to judge which is the best polymer gel dosimeter to use in a clinical setting, because each gel dosimeter has advantages and limitations. For example, methacrylic acid–based gel dosimeters have high dose sensitivity and low toxicity, while their dose response is beam energy dependent; in contrast, N -isopropylacrylamide gel dosimeters have low dose resolution, but their sensitivity is lower and they are relatively toxic. Highlights • Most polymer gel dosimeters have acceptable dose accuracy. • Acrylamide-based gel dosimeters are highly toxic. • The dose response of methacrylic acid–based gel dosimeters is beam energy dependent. • The sensitivity of N -isopropylacrylamide gel dosimeters is lower. • It is difficult to judge which is the best polymer gel dosimeter to use in the clinic. [ABSTRACT FROM AUTHOR]