Fricke gel as a tool for dose distribution verification: optimization and characterization

Abstract

With the introduction of conformal techniques in radiation therapy, gel dosimetry plays an important role as a 3D dose verification system. There are two main types of gels in use for dosimetry: Fricke gels and polymer gels. The advantages of polymer gels are improved dose response and stability with no diffusion problems. However, the more complicated fabrication procedure and the greater cost compared to Fricke gels makes polymer gels less attractive in routine clinical use. Dose resolution has recently been introduced as a concept for comparing and optimizing the performance of different types of gel dosimeters. This parameter has not yet been investigated for Fricke gels. In this study, the effect on the dose resolution and the diffusion from different gelatine- and Fe2+-concentrations and different pH was evaluated. Increasing the concentration of gelatine from 6 wt% to 10 wt% influenced the diffusion coefficient the most, while reducing the pH from 2.0 to 1.5 had the largest effect on the dose resolution. For a gel consisting of 10 wt% gelatine, 1.0 mM Fe2+ and pH 1.5 the diffusion coefficient was found to be 1.5 mm2 h-1 and the dose resolution was about 4.1% (at 95% confidence level), for a dose of 40 Gy. By evaluating different dose gradients by the gamma-method, the diffusion was shown to have no clinically relevant impact on the dose distribution and plan acceptance within 3 h of irradiation. The results indicate a potential use of Fricke gels for IMRT verification.

Dose response of three-dimensional silicone-based radiochromic dosimeters for photon irradiation in the presence of a magnetic field

“…Fricke gels are an interesting alternative for 3D dosimetry of MRgRT systems as these dosimeters could be read out by the MRI system during or immediately after irradiation without moving the dosimeter from the treatment device to an auxiliary imaging system [21]. Compared to optical CT read-out, the Fricke dosimeter thus eliminates positioning errors associated with pre-and post-scanning, and the known limitations of diffusion-induced dose smearing for these dosimeters [22] may be of less importance for the described workflow.…”

On Radiotherapy Dose Verification With a Flat-Panel Imager

“…A number of research groups has reported good results comparing planned and measured dose distributions in 3D. 29,105,137 While being able to directly…”

Effective atomic number and electron density determination for fricke gel dosimeters using different methods

“…Fricke and polymer gel dosimetry has emerged as a suitable tool to measure three-dimensional dose distribution for complex delivery verification and quality assurance of modern radiotherapy techniques such as IMRT. [ 1 2 ] For external-beam radiotherapy international protocol recommend calibration be carried out in terms of absorbed dose to water. [ 3 ] Therefore, it is preferable to use a gel dosimeter with the composition to be very close to that of water.…”