Low-Diffusion Fricke Gel Dosimeters with Core-Shell Structure Based on Spatial Confinement.

Wei Zhang,Yufeng Zeng,Xiaodan Hu,Xiaohong Zhang,Kaikai Wang,Shuquan Chang,Haiqian Zhang

doi:10.3390/ma14143932

Abstract

The diffusion of ferric ions is an important challenge to limit the application of Fricke gel dosimeters in accurate three-dimensional dose verification of modern radiotherapy. In this work, low-diffusion Fricke gel dosimeters, with a core-shell structure based on spatial confinement, were constructed by utilizing microdroplet ultrarapid freezing and coating technology. Polydimethylsiloxane (PDMS), with its excellent hydrophobicity, was coated on the surface of the pellets. The concentration gradient of the ferric ion was realized through shielding half of a Co-60 photon beam field size, and ion diffusion was measured by both ultraviolet-visible spectrophotometry and magnetic resonance imaging. No diffusion occurred between the core-shell pellets, even at 96 h after irradiation, and the diffusion length at the irradiation boundary was limited to the diameter (2–3 mm) of the pellets. Furthermore, Monte Carlo calculations were conducted to study dosimetric properties of the core-shell dosimeter, which indicated that a PDMS shell hardly affected the performance of the dosimeter.

Highlights

Modern radiation therapy technologies, including intensity modulated radiation therapy and stereotactic radiotherapy, play a critical role for tumor treatment [1]
Determining the dose distribution accurately is vital for local tumor control [3,4]; dosimetry measurement is presently realized by the ionization chamber and the film dosimeter
High-quality Fricke-Poly(vinyl alcohol) (PVA)-xylenol orange (FPX) pellets are a prerequisite for subsequent dosimeter preparation, and the optimization of preparation parameters related to reducing the diameter and improving the monodispersibility of the FPX pellets is necessary

Summary

Introduction

Modern radiation therapy technologies, including intensity modulated radiation therapy and stereotactic radiotherapy, play a critical role for tumor treatment [1]. Determining the dose distribution accurately is vital for local tumor control [3,4]; dosimetry measurement is presently realized by the ionization chamber and the film dosimeter. It is challenging to accurately and rapidly map the complex 3D dose [5]. The dose distribution maps proved that a honeycomb-like structure prevents ion diffusion from one to another. The large size of the cells (5 mm) and the walls (~0.8 mm) was not beneficial to high-resolution dose measurement. Our group [31] assembled W1 /O/W2 multiple emulsions coated with Fricke hydrogel, where diffusion coefficient of Fe3+ was reduced to 0.17 mm2 /h. Hydrophobic coatings were significantly beneficial in suppressing diffusion [32,33], it was largely ignored in the study of Fricke gel dosimeters

Methods

Results

Conclusion