Dosimetry study of diagnostic X-ray using doped iodide normoxic polymer gels

Radiation Dosimetry by Use of Radiosensitive Hydrogels and Polymers: Mechanisms, State-of-the-Art and Perspective from 3D to 4D

Gel dosimetry was developed in the 1990s in response to a growing need for methods to validate the radiation dose distribution delivered to cancer patients receiving high-precision radiotherapy. Three different classes of gel dosimeters were developed and extensively studied. The first class of gel dosimeters is the Fricke gel dosimeters, which consist of a hydrogel with dissolved ferrous ions that oxidize upon exposure to ionizing radiation. The oxidation results in a change in the nuclear magnetic resonance (NMR) relaxation, which makes it possible to read out Fricke gel dosimeters by use of quantitative magnetic resonance imaging (MRI). The radiation-induced oxidation in Fricke gel dosimeters can also be visualized by adding an indicator such as xylenol orange. The second class of gel dosimeters is the radiochromic gel dosimeters, which also exhibit a color change upon irradiation but do not use a metal ion. These radiochromic gel dosimeters do not demonstrate a significant radiation-induced change in NMR properties. The third class is the polymer gel dosimeters, which contain vinyl monomers that polymerize upon irradiation. Polymer gel dosimeters are predominantly read out by quantitative MRI or X-ray CT. The accuracy of the dosimeters depends on both the physico-chemical properties of the gel dosimeters and on the readout technique. Many different gel formulations have been proposed and discussed in the scientific literature in the last three decades, and scanning methods have been optimized to achieve an acceptable accuracy for clinical dosimetry. More recently, with the introduction of the MR-Linac, which combines an MRI-scanner and a clinical linear accelerator in one, it was shown possible to acquire dose maps during radiation, but new challenges arise.

Dosimetry and Radioenhancement Comparison of Gold Nanoparticles in Kilovoltage and Megavoltage Radiotherapy using MAGAT Polymer Gel Dosimeter

BACKGROUND

Numerous unique characteristics of the nanosized gold, including high atomic number, low toxicity, and high biocompatibility make it one of the most appropriate nanostructures to boost radiotherapy efficacy. Many in-vivo and in-vitro investigations have indicated that gold nanoparticles (AuNPs) can significantly increase tumor injuries in low kilovoltage radiotherapy. While deep-lying tumors require much higher energy levels with greater penetration power, and investigations carried out in megavoltage energy range show contradictory results.

OBJECTIVE

In this study, we quantitatively assess and compare dose enhancement factors (DEFs) obtained through AuNPs under radiation of Cobalt-60 source (1.25MeV) versus Iridium-192 source (380 KeV) using MAGAT gel dosimeter.

MATERIAL AND METHODS

MAGAT polymer gel in both pure and combined with 0.2 mM AuNPs was synthesized. In order to quantify the effect of energy on DEF, irradiation was carried out by Co-60 external radiotherapy and Ir-192 internal radiotherapy. Finally, readings of irradiated and non-irradiated gels were performed by MR imaging.

RESULTS

The radiation-induced R2 (1/T2) changes of the gel tubes doped with AuNPs compared to control samples, upon irradiation of beams released by Ir-192 source showed a significant dose enhancement (15.31% ±0.30) relative to the Co-60 external radiotherapy (5.85% ±0.14).

CONCLUSION

This preliminary study suggests the feasibility of using AuNPs in radiation therapy (RT), especially in low-energy sources of brachytherapy. In addition, MAGAT polymer gel, as a powerful dosimeter, could be used for 3D visualization of radiation dose distribution of AuNPs in radiotherapy.