Assessment of photon energy and dose rate dependence of U-NIPAM polymer gel dosimeter

摘要

One of the main drawbacks of NPAM gel dosimeter is its relatively low R2-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.