Effective polymer gel dosimetry and dose enhancement for photon radiotherapy using ZnO and Bi2O3 nanoparticles

Abstract In radiotherapy, the deposition of a specific dose to the target volume with the lowest dose to the surrounding healthy tissue is an important aspect. Therefore, the current study was performed to analyze the dose enhancement effect of ZnO and Bi 2 O 3 nanoparticles (NPs) in the N-iso propylacrylamide-N,N'-methylene-bisacrylamide (NIPAM-Bis) gel dosimeter. The accuracy of nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) techniques for dose verification with the assistance of gel dosimeters was also studied. Morphological structures of ZnO and Bi 2 O 3 NPs were determined using scanning and transmission electron microscopes. The stability of the nanoparticles suspensions was verified by measuring the zeta potential. For dose enhancement measurements, 0.1 mg/ml ZnO or Bi 2 O 3 NPs doped gel were irradiated with 3, 7 and 10 Gy doses with 6 MeV photons. Unirradiated and irradiated gel samples (doped and pure) absorbance spectra were measured by UV–Vis spectrometry for estimation of dose response. The results of the t test analysis of the dose measured by NMR and MRI show that there is no significant difference between the dose values for both techniques. The measured moderate value of zeta potential (23.90 and − 23.71 mV for ZnO and Bi 2 O 3 NPs, respectively) confirmed the stability of nanoparticle suspension. The dose response of gel dosimeters doped with ZnO as well as Bi 2 O 3 and irradiated with different doses showed sensitivity enhancements of approximately 2.2 and 2.8 times, respectively, compared to the pure gel with good linearity in dose range studied. The corresponding dose enhancement factors (DEF) were 1.55 for ZnO and 2.06 for Bi 2 O 3 . These high DEF values can be explained by several factors, including the high electron density of the NPs used, the relatively high values of the mass attenuation coefficients (Compton and pair production), and the softening effect of the 6 MeV photons in the volumetric polymer gel doped with NPs, which increases the photoelectric effect. Choosing an appropriate concentration of nanoparticles that maintains the transparency of the gel, and the type of polymer used, are also among the reasons that contribute to high DEF values.