Optical and NMR dose response of N-isopropylacrylamide normoxic polymer gel for radiation therapy dosimetry

BackgroundApplication of less toxic normoxic polymer gel of N-isopropyl acrylamide (NIPAM) for radiation therapy has been studied in recent years.AimIn the current study the optical and NMR properties of NIPAM were studied for radiation therapy dosimetry application.Materials and methodsNIPAM normoxic polymer gel was prepared and irradiated by 9 MV photon beam of a medical linac. The optical absorbance was measured using a conventional laboratory spectrophotometer in different wavelengths ranging from 390 to 860 nm. R2 measurements of NIPAM gels were performed using a 1.5 T scanner and R2–dose curve was obtained.ResultsOur results showed R2 dose sensitivity of 0.193 ± 0.01 s−1 Gy−1 for NIPAM gel. Both R2 and optical absorbance showed a linear relationship with dose from 1.5 to 11 Gy for NIPAM gel dosimeter. Moreover, absorbance–dose response varied considerably with light wavelength and highest sensitivity was seen for the blue part of the spectrum.ConclusionOur results showed that both optical and NMR approaches have acceptable sensitivity and accuracy for dose determination with NIPAM gel. However, for optical reading of the gel, utilization of an optimum optical wavelength is recommended.