Feasibility of radiochromic gels for 3D dosimetry of brachytherapy sources

Abstract

Two radiochromic gel dosimeters, Fricke-xylenol orange (FXO) gel and Turnbull Blue (TB) gel, were studied in the scope of the iMERA+ project ‘Increasing cancer treatment efficacy using 3D brachytherapy’ for their feasibility for the determination of relative 3D dose distribution of brachytherapy (BT) sources. Initially, the dose, dose rate and energy dependence of the gels were investigated. Subsequently, the gels were irradiated by a point low-dose-rate source IsoSeed I25.S16 (125I) and a high-dose-rate source GammaMed+ (192Ir) and scanned using optical computed tomography. Optical transmission images of irradiated gels were processed to obtain detailed 3D optical density maps inside the gels with voxel dimensions of 0.25 × 0.25 × 0.25 mm3. The radial dose function between 1.5 mm and 35 mm from the source and the anisotropy function at 10 mm radius were determined and compared with Monte Carlo calculations and TG-43 data, showing agreement mostly within the measurement uncertainty. Results revealed that the TB gel is feasible for measurements of the relative 3D dose distributions very close to the point BT source because it conserves sharp dose gradients as this gel does not suffer diffusion of dye created upon irradiation. On the other hand, FXO gel underestimates doses closer than 5 mm from the source due to diffusion effects, but it has a significantly higher sensitivity which enables convenient measurement of relative doses up to 35 mm from the source. Further development, especially on gel composition and corrections to optical CT images, is desirable.

Comparison of the Convolution algorithm with TMR10 for Leksell Gamma knife and dosimetric verification with radiochromic gel dosimeter

“…The TB gel dosimeter was removed from the phantom and scanned, using a homemade optical CT scanner 2 h after irradiation . The nonirradiated gel sample was also scanned to obtain a background reading.…”

Evaluation of the OSC‐TV iterative reconstruction algorithm for cone‐beam optical CT

“…1,2 Moreover, gel dosimeters are also promising candidates for application in both low-dose-rate and high-dose-rate brachytherapy. 3,4 3D dosimeters are expected to be convenient and reliable when commissioning new treatment delivery techniques or performing quality assurance procedures. The main advantages of dosimetric gels are excellent water-equivalence and exceptional spatial resolution.…”

Air kerma and absorbed dose standards for reference dosimetry in brachytherapy

“…Depending on the type of detector and the measurement distance from the source centre, the relative measurement uncertainty ranges from around 6% to 20% (k 5 2). Further high-resolution relative dosimetry methods for the accurate determination of 3D dose distributions close to brachytherapy sources [77][78][79] were developed within the EMRP T2.J06 project and compared with MC calculations. 80 Monte Carlo dosimetry MC simulation is nowadays a widely used and accepted dosimetry tool.…”