Polymer gel dosimeters record radiation-induced changes throughout a three-dimensional volume, enabling the visualization and quantitative evaluation of delivered dose distributions. They can be applied to quality assurance in external beam radiotherapy, brachytherapy, and particle therapy, particularly when conventional point or planar measurements cannot fully characterize a complex three-dimensional dose distribution.
General info
Specifications
dGEL™ is an X-ray CT-based polymer gel dosimeter developed for three-dimensional radiotherapy dosimetry. Its CT number increases rapidly after irradiation, and the dosimeter remains solid at room temperature, approximately 24°C.[1]
dGEL™ has a polymer gel composition and physical properties comparable to those of soft tissue. Table 1 compares its elemental composition, mass density, relative electron density, and effective atomic number with the corresponding values for soft tissue reported in ICRU Report 44. Figure 1 compares their mass attenuation coefficients.
| Elemental composition (% by weight) | ρ [g/cm-3] |
ρe / NA | Zeff | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| H | C | N | O | Na | P | S | Cl | K | ||||
| dGEL™ | 10.2 | 17.5 | 3.9 | 68.3 | – | 0.0131 | 0.0068 | – | – | 1.02 | 0.563 | 7.23 |
| Soft tissue (ICRU 44) |
10.2 | 14.3 | 3.4 | 70.8 | 0.2 | 0.3 | 0.3 | 0.2 | 0.3 | 1.06 | 0.583 | 7.64 |
Figure 1. Mass attenuation coefficients of dGEL™ and soft tissue, based on ICRU Report 44, and the ratio between them.
External Beam Radiotherapy
Modern high-precision radiotherapy, particularly stereotactic radiosurgery and stereotactic radiotherapy, requires accurate alignment of the imaging and radiation isocenters.
The dGEL™-based three-dimensional starshot method reconstructs multiple beam axes in three-dimensional space and evaluates their spatial relationship with the imaging isocenter.[2] Its clinical relevance has been demonstrated in a multi-institutional study evaluating the effect of dose-delivery accuracy on the planning target volume margin in intracranial stereotactic radiosurgery.[3]
The effects of cone-beam CT acquisition and reconstruction parameters on three-dimensional starshot analysis have also been investigated.[4] More recently, dual-energy cone-beam CT combined with background subtraction and correction was evaluated as a method for improving three-dimensional dGEL™ readout.[5]
Figure 2. Three-dimensional reconstruction of the beam axes and treatment isocenter with and without an intentional positional error. The blue sphere represents the treatment-isocenter region. GA, gantry angle; CA, couch angle.
Brachytherapy
Image-guided high-dose-rate brachytherapy involves a complex clinical workflow that includes imaging, applicator or needle reconstruction, treatment planning, and source delivery. Comprehensive quality assurance should therefore evaluate both geometric and dosimetric accuracy throughout the treatment process.
After irradiation, localized changes corresponding to the source dwell positions can be visualized in dGEL™ using X-ray CT. This enables three-dimensional verification of source positions and supports end-to-end quality assurance of image-guided HDR brachytherapy.[6]
Figure 3. Irradiated dGEL™ after needle insertion, treatment planning, and HDR brachytherapy irradiation. The localized high-CT-number regions indicate the source dwell positions along the needles.
vGEL™ and mGEL™ are MRI-based polymer gel dosimeters incorporating patented proprietary technology developed by Triangle Products. These dosimeters incorporate our original formulation technology to achieve high sensitivity and reliable visualization of complex dose distributions.
After irradiation, radiation-induced changes within the gel are measured using MRI and converted into a three-dimensional dose distribution. This enables comprehensive dose evaluation that is difficult to achieve using conventional point or planar dosimeters.
Our MRI-based gel dosimetry program has been evaluated through multi-institutional end-to-end testing for image-guided HDR brachytherapy[7] and an investigation of the robustness of transported gel dosimeters under real-world conditions.[8] A dedicated three-dimensional printed phantom has also been developed to verify MRI acquisition performance for polymer gel dosimetry across different MRI systems.[9]
The potential applications of MRI-based polymer gel dosimetry have expanded to proton therapy. Recent studies have evaluated the fundamental dose and spatial measurement characteristics of an iVIPET gel dosimeter for proton beams[10] and have used a tissue-equivalent polymer gel as an independent reference for protoacoustic proton-range verification.[11]
We provide an integrated service covering gel fabrication, irradiation support, MRI acquisition, and dose-distribution analysis. Please contact us to discuss the appropriate gel formulation, dose range, container geometry, and imaging method for your application.
Figure 4. Irradiated vGEL™ dosimeter used for brachytherapy dose evaluation.
Figure 5. mGEL™ dosimeter in a cubic container.
Please contact us regarding the type of gel dosimeter,
desired dose range, container, etc.
