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

Abstract

Background

Application of less toxic normoxic polymer gel of N-isopropyl acrylamide (NIPAM) for radiation therapy has been studied in recent years.

Aim

In the current study the optical and NMR properties of NIPAM were studied for radiation therapy dosimetry application.

Materials and methods

NIPAM normoxic polymer gel was prepared and irradiated by 9[[ce:hsp sp="0.25"/]]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[[ce:hsp sp="0.25"/]]nm. R₂ measurements of NIPAM gels were performed using a 1.5[[ce:hsp sp="0.25"/]]T scanner and R₂–dose curve was obtained.

Results

Our results showed R₂ dose sensitivity of 0.193[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]0.01[[ce:hsp sp="0.25"/]]s⁻¹[[ce:hsp sp="0.25"/]]Gy⁻¹ for NIPAM gel. Both R₂ and optical absorbance showed a linear relationship with dose from 1.5 to 11[[ce:hsp sp="0.25"/]]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.

Conclusion

Our 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.