Gel Dosimeter Research Articles

Response investigation of a new polymer gel dosimeter based on ammonium salt through MRI technique

Increasing the use of polymer gel dosimetry (PGD) in radiotherapy requires reducing its toxicity. The toxicity of the PGD components causes risks for the users as well as the environment. The aim of this study is to produce a new PGD called PAGBIT (Polymer, Amps ammonium salt, Gelatin, BIs, Thpc) based on the nontoxic monomer of 2-acrylamido-2-methylpropanesulfonic acid ammonium salt. Furthermore, this monomer is ecofriendly. The PAGBIT PGD was prepared in the laboratory in ambient conditions. PGDs were irradiated using a clinical accelerator with a dose range of 0–10 Gy. The incident photon energy and dose rate were 6-MV and 300 cGy/min, respectively. The irradiated PGDs were imaged using a 1.5T MRI scanner 9 times in a time range of 12–720 h post-irradiation. The maximum obtained sensitivity was 0.115 ± 0.005 Gy−1s−1 at 36 h post-irradiation time. The average sensitivity change as a function of post-irradiation time was 0.0017 Gy−1s−1h−1. However, the average sensitivity change as a function of scanning temperature was 0.0006 Gy−1s−1°C−1. Results showed that the differences of effective atomic number and electron density between PAGBIT and soft tissue were 2.3% and 0.3%, respectively. It was concluded that the PAGBIT is a low toxic, water equivalent PGD with noticeable temporal and temperature stabilities.

Evaluation of a novel N-(Hydroxymethyl) acrylamide polymer gel dosimeter formulation with organic glucose additive for radiotherapy

In this study, the first evaluation of organic sensitizer material on N-(Hydroxymethyl) acrylamide (NHMA) polymer gel dosimeter was presented. A novel tissue-equivalent polymer gel formula composed of NHMA containing different concentrations of organic glucose additive (GL-NHMA) was developed and evaluated for its potential use to measure 3D dose distributions to compare with treatment planning system. The new polymers of GL-NHMA were irradiated using a linear accelerator (LINAC) with a megavolt X-ray photon beam over a dose range of 2–20 Gy, energies of 6, 10, and 15 MV, and dose rates of 50, 200, and 500 cGy/min. The samples were evaluated using 0.5 T nuclear magnetic resonance (NMR) technique in terms of spin-spin relaxation rate (R2). Comparing with the conventional NHMA composition (i.e., 0 wt% GL concentration), the sensitivity of the GL-NHAM was improved by 53%, 68%, 89%, and 115% with 10, 15, 20, and 25 wt% GL, respectively, with an excellent linear dose response up to 8 Gy. There were no observable effects on the R2 dose response induced by varying the dose rate, photon energy, and irradiation temperature. The polymerization was stable after irradiation for a period of 10 days. Additionally, the R2 values decreased with increasing the scanning temperature. The dosimeter is water equivalent and is energy-independent from 0.1 to 20 MeV when considering the optimum composition. The gel dosimetry accuracy was evaluated in this study by calculating the overall uncertainty and found to be 4.64% (2σ, 95% confidence level). The GL additive acts as an excellent organic sensitizer in the GL-NHMA system, suggesting that this improved polymer formulation may be a useful tool for measuring dose distributions in radiotherapy at clinically relevant dose levels.

Dosimetric properties of PASSAG polymer gel dosimeter in electron beam radiotherapy using magnetic resonance imaging.

Several physical factors such as photon beam energy, electron beam energy, and dose rate may affect the dosimetric properties of polymer gel dosimeters. The photon beam energy and dose rate dependence of PASSAG gel dosimeter were previously evaluated. This study aims to assess the dosimetric properties of the optimized PASSAG gel samples in various electron beam energies. The optimized PASSAG gel samples are first fabricated and irradiated to various electron energies (5, 7, 10 and 12 MeV). Then, the response (R2) and sensitivity of gel samples are analyzed by magnetic resonance imaging technique at a dose range of 0 to 10 Gy, scanning room temperature range of 15 to 22 °C, and post-irradiation time range of 1 to 30 days. The R2-dose response and sensitivity of gel samples do not change under the evaluated electron beam energies (the differences are less than 5%). Furthermore, a dose resolution range of 11 to 38 cGy is obtained for the gel samples irradiated to different electron beam energies. Moreover, the findings show that the R2-dose response and sensitivity dependence of gel samples on electron beam energy varies over different scanning room temperatures and post-irradiation times. The dosimetric assessment of the optimized PASSAG gel samples provides the promising data for this dosimeter during electron beam radiotherapy.

Review of nanomaterial advances for ionizing radiation dosimetry.

There are a wide range of applications with ionizing radiation and a common theme throughout these is that accurate dosimetry is usually required, although many newer demands are provided by improved features in higher range, multi-spectral and particle type detected. Today, the array of dosimeters includes both offline and online tools, such as gel dosimeters, thermoluminescence (TL), scintillators, optically stimulated luminescence (OSL), radiochromic polymeric films, gels, ionization chambers, colorimetry, and electron spin resonance (ESR) measurement systems. Several future nanocomposite features and interpretation of their substantial behaviors are discussed that can lead to improvements in specific features, such as (1) lower sensitivity range, (2) less saturation at high range, (3) overall increased dynamic range, (4) superior linearity, (5) linear energy transfer and energy independence, (6) lower cost, (7) higher ease of use, and (8) improved tissue equivalence. Nanophase versions of TL and ESR dosimeters and scintillators each have potential for higher range of linearity, sometimes due to superior charge transfer to the trapping center. Both OSL and ESR detection of nanomaterials can have increased dose sensitivity because of their higher readout sensitivity with nanoscale sensing. New nanocrystalline scintillators, such as perovskite, have fundamentally important advantages in sensitivity and purposeful design for key new applications. Nanoparticle plasmon coupled sensors doped within a lower Zeff material have been an effective way to achieve enhanced sensitivity of many dosimetry systems while still achieving tissue equivalency. These nanomaterial processing techniques and unique combinations of them are key steps that lead to the advanced features. Each must be realized through industrial production and quality control with packaging into dosimetry systems that maximize stability and reproducibility. Ultimately, recommendations for future work in this field of radiation dosimetry were summarized throughout the review.

Iterative image reconstruction with polar coordinate discretized system matrix for optical CT radiochromic gel dosimetry.

Gel dosimeters are a potential tool for measuring the complex dose distributions that characterize modern radiotherapy. A prototype tabletop solid-tank fan-beam optical CT scanner for readout of gel dosimeters was recently developed. This scanner does not have a straight raypath from source to detector, thus images cannot be reconstructed using filtered backprojection (FBP) and iterative techniques are required. Iterative image reconstruction requires a system matrix that describes the geometry of the imaging system. Stored system matrices can become immensely large, making them impractical for storage on a typical desktopcomputer. Here we develop a method to reduce the storage size of optical CT system matrices through use of polar coordinate discretization while accounting for the refraction in optical CTsystems. A ray tracing simulator was developed to track the path of light rays as they traverse the different mediums of the optical CT scanner. Cartesian coordinate discretized system matrices (CCDSMs) and polar coordinate discretized system matrices (PCDSMs) were generated by discretizing the reconstruction area of the optical CT scanner into a Cartesian pixel grid and a polar coordinate pixel grid, respectively. The length of each ray through each pixel was calculated and used to populate the system matrices. To ensure equal weighting during iterative reconstruction, the radial rings of PCDSMs were asymmetrically spaced such that the area of each polar pixel was constant. Two clinical phantoms and several synthetic phantoms were produced and used to evaluate the reconstruction techniques under known conditions. Reconstructed images were analyzed in terms of spatial resolution, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), signal nonuniformity (SNU), and Gamma map passpercentage. A storage size reduction of 99.72% was found when comparing a PCDSM to a CCDSM with the same total number of pixels. Images reconstructed with a PCDSM were found to have superior SNR, CNR, SNU, and Gamma (1mm, 1%) pass percentage compared to those reconstructed with a CCDSM. Increasing spatial resolution in the radial direction with increasing radial distance was found in both PCDSM and CCDSM reconstructions due to the outer regions refracting light more severely. Images reconstructed with a PCDSM showed a decrease in spatial resolution in the azimuthal directions as radial distance increases, due to the widening of the polar pixels. However, this can be mitigated with only a slight increase in storage size by increasing the number of projections. A loss of spatial resolution in the radial direction within 5mm radially from center was found when reconstructing with a PCDSM, due to the large innermost pixels. However, this was remedied by increasing the number of radial rings within the PCDSM, yielding radial spatial resolution on par with images reconstructed with a CCDSM and a storage size reduction of 99.26%. Discretizing the image pixel elements in polar coordinates achieved a system matrix storage size reduction of 99.26% with only minimal reduction in the imagequality.

A real-world assessment of the robustness of gel dosimetry

The purpose of this multi-institutional study was to evaluate the robustness of a transported gel dosimeter. Six vials were filled with a normoxic N-vinylpyrrolidone-based polymer gel dosimeter containing inorganic salt as a sensitizer (iVIPET), manufactured by Triangle Products (Kashiwa, Japan). Three vials were sent to the home institution (National Cancer Center Hospital East, Chiba, Japan) and three to an external institution. At each institution, vials received a dose of 0, 5, or 10 Gy using a 10 MV X-ray beam. After irradiation, the gel in the vial was imaged using a 3 T MRI scanner, and an R2 (spin–spin relaxation rate) map was created. The dose–R2 relationship was then analyzed using linear regression and the dose uncertainty computed. Thirty-four institutions participated in the study from July 2020 to July 2021. At the home institution, dose uncertainties were constant throughout the year (95% confidence interval [mean ± 1.96σ]: 3.3 ± 2.1% at 5 Gy and 4.0 ± 2.5% at 10 Gy). The ratio of the dose uncertainties measured at the external institutions and home institution was 1.1 ± 0.4 at 5 Gy (r = 0.88) and 1.0 ± 0.3 at 10 Gy (r = 0.81). Dose uncertainties were approximately 4% within 4 d of transportation but exceeded 10% when the gels were irradiated 7 d after fabrication. Temperature variations during transportation resulted in negligible uncertainties in absorbed dose; however, extended transportation times may increase dose uncertainty. Thus, polymer gel dosimeters should be used within 2–4 d of fabrication.

Response of 2-Hydroxymethyl Methacrylate Polymer Gel Dosimeter with Maltose Additive for Radiation within Diagnostic X-Ray Energies

The use of polymer gel dosimeters (PGD) in x-ray radiography has not yet been confirmed. However, if it could be applied, it could help to improve patient dosimetry, dose optimization, and quality assurance through its three-dimensional (3D) image display. This research aimed to evaluate the response of a 2-hydroxymethyl methacrylate (HEMA) polymer gel dosimeter at lower energies for possible use in diagnostic x-ray radiography and to determine the effect of maltose concentrations on the sensitivity. The dosimeter was made under normoxic conditions using Gelatin, HEMA, N, N’- Methylene – bis – acrylamide (BIS), Ascorbic Acid, deionized water, and maltose of various concentrations (10 – 50 mM). The PGDs were then irradiated using a conventional x-ray machine with exposure settings ranging from 10-200 mA, 40-100 kV, and s = 1 s. Afterward, the irradiated dosimeters were scanned using UV-spectroscopy. The result showed that the dosimeters responded to low-energy x-rays, and the effect of the maltose concentration within the tested range was not linear with the sensitivity. We concluded that the HEMA polymer gel dosimeter could be used for clinical x-ray dosimetry, but further research on the effect of maltose concentrations on the sensitivity is needed.

Optimization of the Dose Rate Effect in Tetrazolium Gellan Gel Dosimeters.

Tetrazolium salts provide an appealing candidate for 3D gel dosimeters as they exhibit a low intrinsic color, no signal diffusion and excellent chemical stability. However, a previously developed commercial product (the ClearView 3D Dosimeter) based on a tetrazolium salt dispersed within a gellan gum matrix presented a noticeable dose rate effect. The goal of this study was to find out whether ClearView could be reformulated in order to minimize the dose rate effect by optimizing of the tetrazolium salt and gellan gum concentrations and by the addition a thickening agent, ionic crosslinkers, and radical scavengers. To that goal, a multifactorial design of experiments (DOE) was conducted in small-volume samples (4-mL cuvettes). It showed that the dose rate could be effectively minimized without sacrificing the integrity, chemical stability, or dose sensitivity of the dosimeter. The results from the DOE were used to prepare candidate formulations for larger-scale testing in 1-L samples to allow for fine-tuning the dosimeter formulation and conducting more detailed studies. Finally, an optimized formulation was scaled-up to a clinically relevant volume of 2.7 L and tested against a simulated arc treatment delivery with three spherical targets (diameter 3.0 cm), requiring different doses and dose rates. The results showed excellent geometric and dosimetric registration, with a gamma passing rate (at 10% minimum dose threshold) of 99.3% for dose difference and distance to agreement criteria of 3%/2 mm, compared to 95.7% in the previous formulation. This difference may be of clinical importance, as the new formulation may allow the quality assurance of complex treatment plans, relying on a variety of doses and dose rates; thus, expanding the potential practical application of the dosimeter.

Sensitivity of a bone-equivalent polymer gel dosimeter for measuring the dose to bone during radiation therapy.

Treatment planning systems that use the Monte Carlo algorithm can calculate the dose to the medium (Dm) in non-water-equivalent tissues such as bones. However, Dm cannot be verified using actual measurements; therefore, it is necessary to develop tissue-equivalent dosimeters. In this study, we developed a bone-equivalent polymer gel dosimeter (BPGD) that can measure the dose absorbed by the bone and investigated its sensitivity. The BPGDs were prepared by adding 3.0mol of calcium hydrogen phosphate dihydrate as a component of bone to an improved dose-sensitive polyacrylamide gelatin and tetrakis hydroxymethyl phosphonium chloride (iPAGAT). One day after preparation, the BPGDs were irradiated with a field size of 15 × 15 cm2 using a 10 MV X-ray beam to evaluate the dose sensitivity, dose-rate dependence, and dose-integration dependence. One day after dose exposure, the BPGDs were scanned using a 0.4T MRI APERTO Eterna (Hitachi, Tokyo, Japan) to obtain R2 values. The difference between the R2 values of 6Gy and 0Gy was up to 5s-1, and the R2 curve plateaued in the high-dose region. Moreover, the BPGD did not depend on the integration of the dose and dose rates. Therefore, the BPGDs that we developed can determine the radiation dose to bones.

End-to-End QA with Polymer Gel Dosimeter for Photon Beam Radiation Therapy.

With the complexity and high demands on quality assurance (QA) of photon beam radiation therapy, end-to-end (E2E) QA is necessary to validate the entire treatment workflow from pre-treatment imaging to beam delivery. A polymer gel dosimeter is a promising tool for three-dimensional (3D) dose distribution measurement. The purpose of this study is to design a fast "one delivery" polymethyl methacrylate (PMMA) phantom with a polymer gel dosimeter for the E2E QA test of the photon beam. The one delivery phantom is composed of ten calibration cuvettes for the calibration curve measurement, two 10 cm gel dosimeter inserts for the dose distribution measurement, and three 5.5 cm gel dosimeters for the square field measurement. The one delivery phantom holder is comparable in size and shape to that of a human thorax and abdomen. In addition, an anthropomorphic head phantom was employed to measure the patient-specific dose distribution of a VMAT plan. The E2E dosimetry was verified by undertaking the whole RT procedure (immobilization, CT simulation, treatment planning, phantom set-up, imaged-guided registration, and beam delivery). The calibration curve, field size, and patient-specific dose were measured with a polymer gel dosimeter. The positioning error can be mitigated with the one-delivery PMMA phantom holder. The delivered dose measured with a polymer gel dosimeter was compared with the planned dose. The gamma passing rate is 86.64% with the MAGAT-f gel dosimeter. The results ascertain the feasibility of the one delivery phantom with a polymer gel dosimeter for a photon beam in E2E QA. The QA time can be reduced with the designed one delivery phantom.

[Radiation Therapy] 3. Fabrication and Evaluation of Gel Dosimeters as 3D-Dose Distribution Phantom

[Radiation Therapy] 3. Fabrication and Evaluation of Gel Dosimeters as 3D-Dose Distribution Phantom

Dose-response dependencies of Turnbull blue, modified Fricke, VIPET, and Presage® gel dosimeters in high-dose-rate radiation fields

Dose-response dependencies of the radiochromic Turnbull blue (TB), modified Fricke gel (FXO), polymer gel VIPET, and solid-state Presage® dosimeters were investigated, in high-dose-rate radiation fields, using spectrophotometry. A sealed radionuclide source (60Co) with a dose rate up to 9 Gy s−1 was used for irradiation. Standard liquid Fricke solution was used as a reference dosimeter. It was found that the properties of different types of gel dosimeters are affected by the dose rate. The results were compared with the predictions derived from the physical-chemical irradiation response principles. Considerable dose-rate dependencies were observed for all investigated 3D dosimeters. Dose responses of TB, VIPET, and FXO were decreased by 30–40% while the Presage® response were decreased by approximately 20% for dose rates from 7.2 × 10−3 to 9.01 Gy s−1. Presented results could have practical impact on some clinical applications, and therefore proper corrections might be needed.

An investigation into the dose rate and photon energy dependence of the GENA gel dosimeter in the MeV range

PurposeIn the current study, the energy and dose rate dependence of a new genipin-based gel dosimeter, named GENA gel dosimeter, were investigated. MethodsPrepared gel dosimeters exposed using a Varian clinical linac. Beam qualities of 6 and 18 MV were applied to investigate the GENA gel dosimeter’s energy dependence. Furthermore, the gel dosimeters were exposed to 50, 100, 200, and 350 cGy/min dose rates, ranging from 0 to 8 Gy. The irradiated gel dosimeters were read out using a double beam UV–Visible spectrophotometer. The absorbance peak (AP) and area under spectrum (AUS) were evaluated. ResultsAbsorbance-dose sensitivities of (8.0 ± 0.18) × 10–3 cm–1Gy−1 and (7.8 ± 0.15) × 10–3 cm−1Gy−1 were obtained for GENA gel dosimeter for 6 and 18 MV beam qualities, respectively. Results specified no significant difference (p > 0.05) between the GENA gel dosimeter’s sensitivities irradiated using the two energies mentioned above. For the mentioned dose rates, AP-dose sensitivities of (8.2 ± 0.22) × 10−3, (8.1 ± 0.21) × 10−3, (8.1 ± 0.2) × 10−3 and (8.0 ± 0.18) × 10−3 cm−1Gy−1 were obtained, respectively. Results showed no significant difference (p > 0.05) between the GENA gel dosimeter’s sensitivities for the investigated dose rates and energies. In addition, results revealed that when the incident photon energy and dose rate changed, there were no significant differences (p > 0.05) between the GENA gel dosimeter’s dose resolution values. ConclusionsIt is concluded that the response of the GENA gel dosimeter is not dependent on the energy and dose rate (p > 0.05) within the studied energy and dose rate ranges.

Preparation of polymer gel dosimeters for low gamma irradiation dose

Abstract In this study, two separate hydrogel dosimeters were prepared for low-dose measurement. The first system is based on Congo Red (CR) dye and a blend of natural polymers (gelatin/CMC) while the second system is based on 2,6-dichlorophenol indophenol (DCP) blue dye and a hybrid polymer blend (PVA/gelatin/CMC). The sensitivity of Congo red (CR)–(gelatin/CMC) gel dosimeter and 2, 6 – di choro phenol indophenols(DCP)-(PVA/gelatin/CMC) gel dosimetry systems were examined by studying the comparative results between the two different systems through the change in optical properties upon exposure to different gamma radiation doses, which showed the sensitivity of the second system (DCP)-(PVA/gelatin/CMC) to radiation is more than the first system(CR)–(gelatin/CMC) (CR) and (DCP)dyes have absorbance crest at 492 and 622 nm respectively. With the increase of the radiation dose, the decomposition of the dyes increases, and thus the color of the prepared hydrogel changes from orange to colorless in the case of (CR) dye at the dose (0–3.5 kGy) and from blue to colorless in the case (DCP) dye at the absorbed doses ranged from (0–1000 Gy). Dose-response curves, sensitivity, FTIR analysis, and the relative stability of the prepared hydrogel before and after irradiation were studied.

Radio-fluorogenic nanoclay gel dosimeters with reduced linear energy transfer dependence for carbon-ion beam radiotherapy.

The precise assessment of the dose distribution of high linear energy transfer (LET) radiation remains a challenge, because the signal of most dosimeters will be saturated due to the high ionization density. Such measurements are particularly important for heavy-ion beam cancer therapy. On this basis, the present work examined the high LET effect associated with three-dimensional gel dosimetry based on radiation-induced chemical reactions. The purpose of this study was to create an ion beam radio-fluorogenic gel dosimeter with a reduced effect of LET. Nanoclay radio-fluorogenic gel (NC-RFG) dosimeters were prepared, typically containing 100μM dihydrorhodamine 123 (DHR123) and 2.0wt% nanoclay together with catalytic additives promoting Fenton or Fenton-like reactions. The radiological properties of NC-RFG dosimeters having different compositions in response to a carbon-ion beam were investigated using a fluorescence gel scanner. An NC-RFG dosimeter capable of generating a fluorescence intensity distribution reflecting the carbon-ion beam dose profile was obtained. It was clarified that the reduction of the unfavorable LET dependence results from an acceleration of the reactions between DHR123 and H2 O2 , which is a molecular radiolysis product. The effects of varying the preparation conditions on the radiological properties of these gels were also examined. The optimum H2 O2 catalyst was determined to include 1mM Fe3+ ions, and the addition of 100mM pyridine was also found to increase the sensitivity. This technique allows the first-ever evaluation of the depth-dose profile of a carbon-ion beam at typical therapeutic levels of several Gy without LET effect.

Small field output factor measurement and verification for CyberKnife robotic radiotherapy and radiosurgery system using 3D polymer gel, ionization chamber, diode, diamond and scintillator detectors, Gafchromic film and Monte Carlo simulation

The dosimetry of small fields has become tremendously important with the advent of intensity-modulated radiation therapy (IMRT) and stereotactic radiosurgery, where small field segments or very small fields are used to treat tumors. With high dose gradients in the stereotactic radiosurgery or radiotherapy treatment, small field dosimetry becomes challenging due to the lack of lateral electronic equilibrium in the field, x-ray source occlusion, and detector volume averaging. Small volume and tissue-equivalent detectors are recommended to overcome the challenges. With the lack of a perfect radiation detector, studies on available detectors are ongoing with reasonable disagreement and uncertainties. The joint IAEA and AAPM international code of practice (CoP) for small field dosimetry, TRS 483 (Alfonso et al., 2017) provides guidelines and recommendations for the dosimetry of small static fields in external beam radiotherapy. The CoP provides a methodology for field output factor (FOF) measurements and use of field output correction factors for a series of small field detectors and strongly recommends additional measurements, data collection and verification for CyberKnife (CK) robotic stereotactic radiotherapy/radiosurgery system using the listed detectors and more new detectors so that the FOFs can be implemented clinically. The present investigation is focused on using 3D gel along with some other commercially available detectors for the measurement and verification of field output factors (FOFs) for the small fields available in the CK system. The FOF verification was performed through a comparison with published data and Monte Carlo simulation. The results of this study have proved the suitability of an in-house developed 3D polymer gel dosimeter, several commercially available detectors, and Gafchromic films as a part of small field dosimetric measurements for the CK system.

Investigation on the long-term storage condition of the PVA-GTA-I gel dosimeter

Radiochromic gel materials are of special interest for application to three-dimensional dosimetry, particularly in clinical settings of radiation therapy. The authors previously developed a radiochromic gel complex composed of polyvinyl alcohol (PVA), glutaraldehyde (GTA) and iodide (I) which is abbreviated hereafter as the “PVA-GTA-I gel”. While showing promising features such as linear dose response and good reusability, the PVA-GTA-I gel has suffered from natural coloration due to auto-oxidation during the long-term storage for a week or more. To find a practical solution for this issue, we examined the color intensity changes of the PVA-GTA-I gel for up to nearly two months under seven storage conditions with the variables of temperature (5.5 °C or 20 °C), air flow (in air or vacuum), and lighting (under fluorescent light or in darkness). The results showed that the condition setting of the samples stored in a vacuum case at 20 °C in darkness could significantly prevent the color intensity change of the PVA-GTA-I gel during long-term storage. This finding could give a certain practical advantage to the PVA-GTA-I gel dosimeter for future applications.

Radiation‐sensitive nanogel‐incorporated Fricke hydrogel dosimeters with reduced diffusion rates

AbstractFricke gel dosimeters have great potential for three‐dimensional (3D) dose verification in radiation therapy; however, they suffer from time‐dependent ion diffusion after irradiation, severely affecting their stability and reliability. In this work, a pullulan‐based amphiphilic molecule was synthesized, characterized, and self‐assembled into nanogels. Nanogel structures were embedded into gel dosimeters to reduce the diffusion rates, and radiation‐sensitive nanogel‐incorporated Fricke hydrogel nanocomposites were prepared successfully. The results demonstrated that the diffusion coefficient of improved dosimeters was reduced to 0.125 ± 0.001 mm2 h−1, while maintaining the high optical dose sensitivity (0.0410 ± 0.0004 Gy−1 cm−1). It provides a powerful tool toward the practical application of 3D dosimeters.

Feasibility of a Novel 3D Dosimetry System for Commissioning of Single Isocenter Multitarget SRS Treatment

<h3>Purpose/Objective(s)</h3> Verification of Single Isocenter Multitarget SRS treatments (SIM-SRS) is uniquely challenging due to the combination of high dose, steep dose gradients and the requirement for very high spatial accuracy. Here we demonstrate the feasibility of a novel 3D dosimetry system for uniquely comprehensive dosimetry validation and commissioning of this exceptionally challenging technique. <h3>Materials/Methods</h3> The 3D dosimetry system utilizes a new commercially available radiochromic gel dosimeter and a state-of-art in-house telecentric optical-CT readout system DLOS (Duke Large Field of View telecentric Optical CT Scanner). The system was used to quantify the accuracy in 3D and in high resolution (isotropic 1mm) of two SIM-SRS treatments: a simpler two target treatment, and a more complex 5 target treatment. The SIM-SRS plans were created on patient anatomy and then recalculated on a CT of a 15cm diameter dosimeter, with isocenter placed such that each target was located within the dosimeter. Both treatments were delivered to the dosimeters which are gellan gum based radiochromic dosimeters containing a water-soluble tetrazolium salt which reduces into an insoluble formazan dye (with associated color change) under ionizing radiation. Optical-CT readout of the dosimeters pre and post irradiation enabled a high-resolution comprehensive evaluation of the accuracy of delivery. The DLOS is a bi-telecentric system which enables highest accuracy optical-CT readout through strong scatter and stray light rejection. The measured optical density distribution was spatially registered to the dose from the planning system and converted to dose via a calibration curve. Independent verification of treatment accuracy was also performed with a commercial Monte Carlo dose calculation algorithm. <h3>Results</h3> For the 2-target plan, the measured dose agreed with the planning system with a Gamma-Index passing rate of 99.88%, 99.27%, and 92.75%, using a 3%/3mm, 3%/2mm, 5%/1mm criteria, respectively. For the 5-target plan, the Gamma-Index passing rate was 99.59%, 97.35%, and 93.82%, using a 3%/3mm, 3%/2mm, 5%/1mm criteria, respectively. In comparison, the dose calculated using Monte Carlo agreed with the planning system with a Gamma-Index passing rate of 100.0% using 3%/1mm for both the 2 target and 5 target plans. Mean dose for the PTVs of the 2-target plan was within –0.71% and –1.53%. Mean dose for the PTVs of the 5-target plan was within (1.08±0.97)%. <h3>Conclusion</h3> This study demonstrates the feasibility of a new 3D dosimetry tool for verification of advanced radiation treatments. Application to SIM-SRS treatments has demonstrated excellent agreement between measured and predicted dose in the phantom. The combination of DLOS optical-CT with Clearview dosimeters was found to be important in obtaining accurate 3D dosimetry. The method introduced here is anticipated to be applicable to a wide range of clinically challenging treatment techniques.

Investigating the Sensitivity of New Formulation MAGAT and NIPAM Polymer Gels in the Radiation Therapy Dosimetry.

Background: Normoxic polymer gels have been used as a three dimensional (3D) dosimeter in radiation therapy, recently. The sensitivity of these gels is important in dosimetry and their improvement can be also useful.Objective: In this study, different modalities of gel reading were used and the structure of gel changed due to the best improvement of sensitivity. The sensitivities of the new formulation of Methacrylic acid gel (MAGAT) and N-isopropyl acrylamide (NIPAM) polymer gel dosimeters were studied using two different reading methods of magnetic resonance imaging (MRI) and X-ray computed tomography (X-ray CT).Material and Methods: In this experimental study, in addition to making the NIPAM polymer gel dosimeter, a new formulation of normoxic polymer gel dosimeter, which named MAGAT gel, was investigated. The gels were irradiated with 6 MV in low doses, including1, 1.5, 1.75, 2 and 2.5 Gy. MRI and X-ray CT did the reading of gel dosimeters a day after irradiation using an elevated protocol.Results: The dose sensitivities of 0.92 HGy-1 and 0.47 HGy-1 were obtained for new MAGAT and NIPAM polymer gel dosimeters, respectively, based on the X-ray CT reading modality. The use of MRI reading modality and the dose sensitivities were 0.74 S-1Gy-1 and 0.27 S-1Gy-1 for new MAGAT and NIPAM polymer gel dosimeters, respectively.Conclusion: The new formulation of MAGAT polymer gel with a suitable protocol of gel reading has a better response.