A novel method for increasing the sensitivity of NIPAM polymer gel dosimeter

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: 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 (R₂) 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 R₂-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 R₂-dose response in 0–6 Gy dose range, and b) stability in the R₂ value and the sensitivity for 18–21 °C temperatures.