Gel Dosimeter Research Articles

Fricke-Xylenol orange-Gelatin gel characterization with dual wavelength cone-beam optical CT scanner for applications in stereotactic and dynamic radiotherapy

PurposeThis study is about the development of a new dual wavelength reading method of Fricke-Xylenol orange-Gelatin (FXG) gel dosimeters on the Vista16™ optical Computed Tomography (CT) scanner to perform 3D dose distribution measurements in stereotactic and dynamic radiotherapy treatments. MethodsThe dosimetric characteristics of an optimized FXG gel composition and its optical CT readout have been evaluated. A dual wavelength reading method has been developed on the CT scanner at wavelengths 590 nm and 633 nm. Small-field dose profile measurements with FXG gel and microDiamond (PTW) detectors were compared by γ-index analysis (0.5%/0.5 mm) to validate this method. ResultsThis reading method exhibits linear calibration curves in the 0–4 Gy and 2–10 Gy dose ranges at 590 nm and 633 nm respectively. The absorbed dose values below 4 Gy, measured at 590 nm, and those above 4 Gy, measured at 633 nm, are combined to plot a complete profile. A γ passing rate of 93.4% was achieved. ConclusionsThe new reading method of FXG gel dosimeters has been implemented on the Vista16™ scanner to span absorbed doses representative of stereotactic and dynamic radiotherapy treatments and enable 3D measurements in tumor volumes and surrounding healthy tissues. Small-field profile measurements validated this reading method as FXG gel dosimeters and microDiamond detectors were in very close agreement. This dosimetric method is a promising candidate for 3D quality assurance end-to-end tests in stereotactic and dynamic radiotherapy.

Evaluation of dose enhancement effect of bismuth oxide nanoparticles by means of MAGAT and nPAG gel dosimeters

Evaluation of dose enhancement effect of bismuth oxide nanoparticles by means of MAGAT and nPAG gel dosimeters

Applying the N-isopropylacrylamide gel dosimeter to quantify dynamic dose effects: A feasibility study.

BACKGROUND: The gel dosimeter is a chemical as well as a relative dosimeter.OBJECTIVE: To evaluate the feasibility of using N-isopropylacrylamide (NIPAM) gel dosimeter to observe the dynamic dose effects and quantification of the respiration, and to help determine the safety margins.METHODS: The NIPAM gel dosimeter combined with the dynamic phantom was used to simulate radiotherapy of lung or upper abdominal tumor. The field set to 4 5 cm, simulate respiratory rate of 4 sec/cycle, and motion range 2 cm. MRI was used for reading, and MATLAB was used for analysis. The 3%/3 mm gamma passing rate 95% was used as a clinical basis for evaluation.RESULTS: The dynamic dose curve was compared with 4 5, 4 4, 4 3 cm TPS, and gamma passing rates were 74.32%, 54.83%, 30.18%. Gamma mapping demonstrated that the highest dose region was similar to the result of the 4 4 cm TPS. After appropriate selection and comparing that the 60% part of the dose curve with TPS, the gamma passing rate was 96.49%.CONCLUSIONS: Using the NIPAM gel dosimeter with dynamic phantom to simulate organ motion during respiration for dynamic dose measurement and quantified the dynamic dose effect is feasible. The results are consistent with clinical evaluation standards.

Using NIPAM gel dosimeter and concentric swing machine to simulate the dose distribu- tion during breathing: A feasibility study.

BACKGROUND: Radiotherapy plays an important role in cancer treatment today. Successful radiotherapy includes precise positioning and accurate dosimetry.OBJECTIVE: To use NIPAM gel dosimeter and concentric swing machine to simulate and evaluate the feasibility of lung or upper abdominal tumor dose distribution during breathing.METHODS: We used a concentric swing machine to simulate actual radiotherapy for lung or upper abdomen tumors. A 4 4 cm irradiation field area was set and MRI was performed. Next, readout analysis was performed using MATLAB and the 3 mm, 3% gamma passing rate 95% was used as a basis for evaluation.RESULTS: The concentric dynamic dose curve for a simulated respiratory rate of 3 seconds/breath and 4 4 cm field was compared with 4 4, 3 3, and 2 2 cm treatment planning systems (TPS), and the 3 mm, 3% gamma passing rate was 42.87%, 54.96%, and 49.92%, respectively. Pre-simulation showed that the high-dose region dose curve was similar to the 2 2 cm TPS result. After appropriate selection and comparison, we found that the 3 mm, 3% gamma passing rate was 97.92% on comparing the 60% dose curve with the 2 2 cm TPS.CONCLUSIONS: NIPAM gel dosimeter and concentric swing machine use is feasible to simulate dose distribution during breathing and results conforming to clinical evaluation standards.

Evaluation of MAGIC-f polymer gel dosimeter for dose profile measurement in small fields and stereotactic irradiation

Background and purposeThe use of small fields in modern radiotherapy treatment techniques is increasingly growing, which has aroused the interest of researchers to use more polymer gel in small field dosimetry. Polymer gel dosimeters contain radiation-sensitive materials that are polymerized under irradiation as a function of absorption dose, and the spatial information of the radiation dose distribution is extracted by imaging of polymer gel. In this study, the performance and capability of MAGIC-f polymer gel dosimeter were evaluated for small field dosimetry and the temporal stability was investigated. MethodsMAGIC-f polymer gel was manufactured and it was poured into phantoms and calibration vials, and then phantoms were irradiated with 6 MV photons with small fields. The values of R2 maps and dose distribution in irradiated gel phantoms were obtained using MRI images taken from the gel phantoms at 1 day and 14 days after irradiation. Also, EBT3 film was used for the measurement of dose profiles at the same field shapes. The transverse dose profiles measured with polymer gel dosimeter were compared with the results of EBT3 film. ResultsThe slope of fitted lines on dose-response data at 1 day and 14 days after irradiation were equal to 0.6005 and 0.6147 respectively. By comparing the results of MAGIC-f gel and EBT3 film, the relative difference in FWHM for profile curves was observed 12.1%, 6.1%, and 4.3% for 0.5, 1.0, and 1.5 cm field size respectively. The gamma index pass rates between dose profile of polymer gel and film with criteria of 1%/0.5 mm were more than 77.1%. In the case of temporal stability, the penumbra measured by MAGIC-f at 14 days after irradiation was almost equal to that at 1 day after irradiation but in terms of FWHM, it was greater at 14 days. ConclusionThe results of this study show that the MAGIC-f polymer gel has good reliability and stability characteristics for small field dosimetry but it must be benchmarked against other dosimeters to become a three-dimensional dosimeter in small field dosimetry.

Improved Dose Response of N-(hydroxymethyl)acrylamide Gel Dosimeter with Calcium Chloride for Radiotherapy.

The impact of calcium chloride (CaCl2) on the performance of N-(hydroxymethyl)acrylamide (NHMA) polymer gel dosimeter is studied in this article. The dosimeter was exposed to doses of up to 10 Gy with radiation beam-energy of 10 MV and dose-rates of 300 cGy/min. The relaxation rate (R2) parameter was utilized to explore the performance of irradiated NHMAGAT gels. The dose response in terms of R2 increased from 0.29 to 0.63 Gy−1·s−1 with increasing calcium chloride concentration from 0 to 1000 mM. The results show no substantial impact of dose-rates as well as radiation energies on NHMAGAT samples. For the steadiness of irradiated NHMAGAT dosimeters, it was found that there is no apparent variation in R2 (less than ±3%; standard deviation) up to 3 days. The overall uncertainty of the gel dosimeter with calcium chloride is 4.96% (double standard deviation, 95% confidence level).

Characterization of Improved PASSAG Polymer Gel Dosimeter Using Magnetic Resonance Imaging

Characterization of Improved PASSAG Polymer Gel Dosimeter Using Magnetic Resonance Imaging

Dosimetric gelator probes and their application as sensors

Supramolecular gels formed by the self-assembly of organic molecules are useful in many areas from materials to medicine. Of the different applications, exploitation of gels for the visual detection of analytes is a fairly recent trend in gel chemistry. Most of the gel-based sensors rely on non-covalent interactions between the gelator molecules and the added chemical analytes and therefore, often suffer from less selectivity and long response time. In this context, dosimetric gelator probes are superior to other gel-based sensors with high selectivity and fast response time. Unlike non-covalent binding sites, dosimetric gelators typically contain a reaction centre and undergo a specific chemical reaction selective to an analyte resulting in either formation or rupturing of covalent bonds. In this review, we provide an up-to-date report of various reaction-based gel systems applied for the sensing of analytes. We elaborately discuss the concept, design principles, self-assembly properties, and reaction mechanisms of such gelators. We also highlight the limitations, challenges, and the necessity of further exploration of dosimetric gels in this domain.

Simulated design optimization of a prototype solid tank optical CT scanner for 3D radiation dosimetry

Optical computed tomography (CT) is one of the leading modalities for imaging gel dosimeters. There exist many prototype designs, as well as some commercial optical CT scanners that have showcased the value that gel dosimeters can provide to improve 3D dose verification for radiation treatments. However, due to factors including image accuracy, scan time, or demanding setup and maintenance there is currently no single scanner that has become a ubiquitous staple in a clinical setting. In this work, a prototype solid tank optical CT scanner is proposed that minimizes the need for a refractive index bath commonly found in optical CT systems. In addition to the design proposal, a ray-path simulator was created to optimize the design such that the solid tank geometry improves light collection across the detector array, maximizes the volume of the dosimeter scanned, and maximizes the dynamic range of the scanner.

Effects of PVA-GTA-I radiochromic gel dosimeter components on optical dose-response

In recent years, a novel radiochromic gel dosimeter was developed that utilizes the color development of a polyvinyl alcohol-iodide (PVA-I) complex. In this study, we explore the effects of different iodide salts (LiI, NaI, KI, CsI, NH4I, CaI2, and ZnI2) and PVAs with different degrees of polymerization (500, 1000, and 1500) and saponification (80, 88, and 98 mol%) were investigated on a PVA-GTA-I gel dosimeter using PVA that was chemically crosslinked with glutaraldehyde (GTA) as a matrix. The results showed that these substitutions had negligible effect on dose-responses, such as sensitivity and dose-rate independence.

Further investigation of lung tumour peripheral doses using normoxic polymer gel dosimetry techniques

This work builds upon previous investigations of lung tumour peripheral doses for 6 MV, 6 MV FFF, and 10 MV FFF conformal arc therapy beams calculated in the Monaco® TPS and delivered using an Elekta® Agility™ linac. An improved patient lung phantom is developed with measurements using the normoxic PAG gel dosimeter and compared against dose planes from the TPS. The gel dosimeter measurements indicate that the TPS is overestimating the secondary build-up in the lung tumour peripheral region. It has been determined that in lung tumours, 6 MV FFF is the optimal beam energy for peripheral dose coverage and that there is a dosimetric compromise using 10 MV FFF.

Dosimetry.

The dosimeters used to measure radiation dose produce a value which has to be calibrated to be in keeping with the values in an approved laboratory, which will be one of an international network of such laboratories at the center of which is the Bureau International des Poids et Mesures in France (BIPM). Dosimeters work by producing a quantitatively proportional change in status to the intensity of the radiation being measure. Amongst the techniques in use are thermoluminescent devices, radiographic film, radiochromic film, semiconductors, ionization chambers, silicon diodes and gel dosimeters. The Gamma Knife radiation has been difficult to measure directly because the beams have been to fine for accurate measurement by commonly available dosimeters. For more modern dosimeters this is less of a problem. During the treatment of a patient, a variety of indices are recorded to assist in the standardization and accuracy of treatment. Having determined the dose in the beams, it is necessary to calculate how much energy is lost during the passage of radiation from the source to the target. There has been a steady evolution of these calculations to make them more accurate.

New directions for tetrazolium - gellan gum gel dosimeters

Tetrazolium salt-based dosimeters are non-diffusing, gel dosimeters with excellent physical and chemical stability but with relatively low dose sensitivity and a dose rate dependence of the dose response. Both issues are tackled in this study by: (a) the introduction of a new tetrazolium salt with simple synthesis and dose response around 585 nm which may provide the pathway to more sensitive formulations and (b) producing gels with low gellan gum concentration, thus limiting the dose rate effects, and addition of thickening agents to restrain the liquid loss (syneresis) from the resulting gels.

End-to-End Quality Assurance of Stereotactic Radiation Therapy Using an Anthropomorphic Head Phantom

In the clinic, routine quality assurance tests ensure the proper functioning of each individual aspect of a radiation therapy treatment delivery. However, these tests may not guarantee an accurate treatment delivery. In this work, we present the design and application of a head phantom (using 3D printing technology) developed for end-to-end quality assurance of a stereotactic radiation therapy treatment for brain metastases, coupled with inserts for ion chamber, and film and gel dosimeters. The head phantom was subjected to the entire clinical workflow, with each stage of the process being performed by the appropriate clinical personnel to ensure that this quality assurance test mimics the clinical scenario.

Study of the use of gel dosimetry in combination with 3D printing phantom for personalized pretreatment QA in radiotherapy

In modern radiotherapy, pretreatment patient-specific quality assurance (PSQA) generally consists in delivering the treatment plan to a phantom equipped with a detector and in comparing the measured dose and the dose calculated by the treatment planning system (TPS) in order to detect any gap between both dose distributions. Dosimetric gels have interesting properties for QA. In this work, the use of gel dosimetry together with a patient-based 3D printed phantom for personalized PSQA is investigated. CT images of a patient with a right mesencephalic brain tumor were used to generate a 3D printed phantom. Then it was filled with water and a radiochromic gel jar and irradiated according to the patient intracranial stereotactic plan using a Novalis TrueBeam STX accelerator. Measured dose distributions agree well with the calculated ones. Regarding 3D gamma-index (1 mm – 2%) estimated within the central 85% of the jar volume, 96.3% of points pass the test. In addition, 86.5% of the points pass the local 2D 3 mm-3% gamma-index. Results are promising but further work is needed to improve the protocol and investigate the possibility to extend it to end-to-end tests.

Novel Application of Ferrous-Methylthymol Blue- Polyvinyl Alcohol- Glutaraldehyede Gel Dosimeter as a Bolus

Novel Application of Ferrous-Methylthymol Blue- Polyvinyl Alcohol- Glutaraldehyede Gel Dosimeter as a Bolus

Real time 4D Radiation Gel Dosimetry on the Australian MRI-Linac

4D radiation dosimetry using a highly radiation-sensitive polymer gel dosimeter with real-time quantitative MRI readout is presented as a technique to acquire the accumulated radiation dose distribution during image guided radiotherapy (IGRT) on an MRI-Linac. Optimized T2 weighted TSE scans are converted into quantitative ΔR2 maps and subsequently to radiation dose maps. The potential of real-time 4D radiation dosimetry in a theragnostic MRI-Linac is demonstrated in test tubes, for a square beam in a cylindrical gel phantom, for a simple step-and-shoot irradiation in a head phantom and a dynamic arc treatment on a cylindrical gel phantom using a rotating couch. The optimal sequence parameters for maximal dose resolution in the dynamic MRI acquisition will be presented and the trade off between MRI scanning speed and dose resolution will be discussed. A further improvement in temporal resolution using a keyhole imaging approach is the focus of future research.

Development of a practical clinical application of NIPAM kV-CBCT dosimetry

We report our progress towards developing a clinical application of NIPAM kV-CBCT dosimetry. The goal is to develop a practical kV-MV isocenter verification test for which the measurement and analysis can be carried out quickly (within an hour), and that eliminates the need for separate readout (other than on board kV-CBCT) or extra analysis steps such as image registration. Isocenter verification is performed using a NIPAM 3D gel dosimeter which is irradiated with a small field to ~16Gy at eight unique couch/gantry angles. Pre- and post-irradiation kV-CBCT images are acquired and dose is manifest as the intensity difference between pre- and post-CBCTs due to radiation induced changes in density. Code was developed to detect the geometry of each beam in the kV-CBCT and quantify relevant parameters. We applied this technique to verify the isocenter for MLCs as well as for SRS cones. The measured radius to encompass all beams for 4mm, 6mm, 7.5mm, 12.5mm, and 15mm cones was 0.55±0.11mm. The efficiency, robustness to setup errors, and unique ability to visualize spatial uncertainties in the kV-CBCT coordinate system make the NIPAM kV-CBCT test a practical and unique tool for kV-MV isocenter verification.

Post-processing techniques using 3D Slicer for T1-weighted MRI analysis of radiochromic gel dosimeters

Radiochromic FXG gel dosimeters were investigated for end-to-end validation of TG-119 plans delivered in the pre-clinical Elekta 1.5 T-7 MV FFF MR-Linac. Due to the noise levels in the T1-weighted MR images, this preliminary study investigated post-processing techniques available in 3D Slicer and their impact on gamma passing rates. Binomial blur and discrete Gaussian image filters were identified as the most impactful on increasing gamma passing rates for T1-weighted MR images; however, any application of image filters should be implemented with caution on the interpretation of the results.

Effective Atomic Number and Electron Density Determination for Fricke Gel Dosimeters Using Different Methods.

The effective atomic number and electron density of some Fricke gel dosimeters were calculated for photon interaction in the energy range from 10 keV to 1000 MeV using Auto-Zeff, direct and power law methods. The results are presented relative to those of water to allow direct comparison. It is found, that the effective atomic numbers and effective electron densities calculated with the Auto-Zeff and direct methods, demonstrates a good agreement in the energy interval extending from 0.1 MeV to 10 MeV. For effective atomic number relative to water, Ferrous Agarose Xylenol gel showed better water equivalence with difference up to 0.3%, while FX-PVA-GTA and Ferrous Xylenol Gelatin gels showed differences up to 2.26% and 2.25%, respectively.