MAGIC Gel Research Articles

PSOR05 Presentation Time: 4:50 PM: A Magic Gel Formulation Adapted to the Requirements of Dosimetry for Complex-Shaped Low-Dose Rate Brachytherapy Devices

PSOR05 Presentation Time: 4:50 PM: A Magic Gel Formulation Adapted to the Requirements of Dosimetry for Complex-Shaped Low-Dose Rate Brachytherapy Devices

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.

3D star shot analysis using MAGAT gel dosimeter for integrated imaging and radiation isocenter verification of MR-Linac system.

PurposeThis study aims to investigate a star shot analysis using a three‐dimensional (3D) gel dosimeter for the imaging and radiation isocenter verification of a magnetic resonance linear accelerator (MR‐Linac).MethodsA mixture of methacrylic acid, gelatin, and tetrakis (hydroxymethyl) phosphonium chloride, called MAGAT gel, was fabricated. One MAGAT gel for each Linac and MR‐Linac was irradiated under six gantry angles. A 6 MV photon beam of Linac and a 6 MV flattening filter free beam of MR‐Linac were delivered to two MAGAT gels and EBT3 films. MR images were acquired by MR‐Linac with a clinical sequence (i.e., TrueFISP). The 3D star shot analysis for seven consecutive slices of the MR images with TrueFISP was performed. The 2D star shot analysis for the central plane of the gel was compared to the results from the EBT3 films. The radius of isocircle (ICr) and the distance between the center of the circle and the center marked on the image (ICd) were evaluated.ResultsFor MR‐Linac with MAGAT gel measurements, ICd at the central plane was 0.46 mm for TrueFISP. Compared to EBT3 film measurements, the differences in ICd and ICr for both Linac and MR‐Linac were within 0.11 and 0.13 mm, respectively. For the 3D analysis, seven consecutive slices of TrueFISP images were analyzed and the maximum radii of isocircles (ICr_max) were 0.18 mm for Linac and 0.73 mm for MR‐Linac. The tilting angles of radiation axis were 0.31° for Linac and 0.10° for MR‐Linac.ConclusionThe accuracy of 3D star shot analysis using MAGAT gel was comparable to that of EBT3 film, having a capability for integrated analysis for imaging isocenter and radiation isocenter. 3D star shot analysis using MAGAT gel can provide 3D information of radiation isocenter, suggesting a quantitative extent of gantry‐tilting.

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

Fabrication and Determination of Radiation Sensitive Features of Tissue Equivalent Gels in Radiation Dosimetry and Diagnostic Radiology

Various types of gel dosimeters have been developed so far with the names PVAL gel and MAGIC gel, have been abundantly applied in medical physics. This work is divided into two parts. First, this study aims to analyze an ultrasonic imaging device for accurate patient positioning and organ motion detection during prostate radiotherapy. The images of gel were taken before and after the irradiation, using CT, ultrasound and MRI and dose profiles were plotted. This gel will be used as a prostate phantom for the applications in trans-rectal ultrasound imaging. Secondly, this work aims to develop a realistic artificial breast Using PVAL Gel. The gel was X-rayed on a digital mammography machine which has 3 different programs which will select 3 different beam energies. Results for 2 sample thicknesses were compared against Perspex. PVAL gel was confirmed to be a close match to the Perspex for three beam energies.

Stopping power and CSDA range calculations of electrons and positrons over the 20 eV–1 GeV energy range in some water equivalent polymer gel dosimeters

In this study, the stopping power, CSDA range and radiation yield calculations of electrons and positrons over the 20 eV–1 GeV energy range in some water equivalent polymer gel dosimeters were performed. For collision stopping power calculations of electrons and positrons the effective charge concept proposed by Sugiyama were considered. Here, both the effective charge of incident electrons and positrons (z*) and the effective charge (Z*) and the effective mean excitation energy (I*) of the target material were calculated. For the density effect correction the Fano model was selected. For the radiative stopping power analytical model based on the ratio between the collision and the radiative stopping power discribed by Attix was considered. For CSDA range and radition yield the continuous slowing down approximation (CSDA) was considered and the calculations were performed using numerical integral methods. Because of their water equivalent and 3D dose distribution properties, MAGIC and MAGAS polymer gels were selected as a target materials. The calculations were performed by programming all the equations discribed in this study as a computational code. The results of the stopping power, range and radiation yield were compared with those of ESTAR program and PENELOPE Monte Carlo modelling. Some deviations in low and high energy region between the calculated and reference data were observed. However, the similarity between calculated and reference data is remarkable. For the collision stopping power and CSDA range a good agreement between the calculated and reference data was observed for energies >1 keV. Whereas, for the radiative stopping power a good agreement was observed for energies >100 keV.

Investigation of isotropic radiation of low energy X-ray intra-operative radiotherapy by MAGAT gel dosimeter

PurposeIsotropy as a quality assurance aspect of intraoperative radiotherapy (IORT) needs to be evaluated accurately. There are some main problems associated with isotropy investigations by two dimensional dosimeters including limited positions and distances in which isotropy can be measured and long irradiation time needed for isotropy evaluation. In this study, isotropic radiation accuracy of spherical applicators of low energy X-ray IORT was estimated by the use of MAGAT gel as a three dimensional gel dosimeter and a specified IORT phantom. MethodsDesigned IORT phantom was manufactured by multi-axis computer numerical control machine (CNC) using Plexiglas. To investigate isotropy, methacrylic acid, gelatin and tetrakis phosphonium chloride (MAGAT) gel dosimeters embedded in the phantom holes were irradiated with a 50 kV X-ray IORT device to 18 Gy at the surface of the vials. Then, relative dose deviations of output doses from their average were extracted from MRI images of the gel vials in different positions and distances from the 50-mm spherical applicator. ResultsThe percentages of relative deviations of output doses from the average value were less than 8% in all positions which are within the 15% acceptance limit of isotropy radiation. Moreover, a Pearson-moment correlation analysis showed a Pearson's r equal to 0.99–1 for different polar and azimuth angles representing isotropic radiation emission of X-ray IORT. ConclusionIsotropy of IORT can be easily investigated using gel dosimeters by applying the produced phantom which solved the issues facing three-dimensional measurement of isotropic radiation of IORT X-ray source (XRS).

A Novel Ultrasonic Gel Phantom Dosimetry for Evaluation of the Dose Response

Ultrasonic imaging is able to detect structural changes due to chemical reactions occurring due to ionizing irradiation. The purpose of this study to create a gel phantom dosimeter (developed MAGIC gel), which has ultrasonic properties equivalent to human tissue for readout with ultrasonic imaging. The speed of sound and the attenuation coefficient were determined as a function of the absorbed dose in the range of 0–50 Gy by using this dosimeter. A gel phantom was prepared by adding MAGIC polymer gel proprietary combinations in ultrasonic soft tissue-mimicking gel. Then, the ultrasonic parameters (response) of the samples, including the propagation speed of sound (SOS) and the attenuation coefficient (BUA) were measured in the absorbed dose range of 0-50 Gy in steps 2 Gy. The dose response curve is plotted and a sigmoid function is fitted. Ultrasonic images were recorded to assess the quality of the novel gel phantom. At 24 h postirradiation, the gel samples were imaged by using a magnetic resonance (MR) scanner. The mean values of the transverse relaxation rates (R2) were taken. The sensitivities of the speed of sound and the attenuation coefficient parameters and the R2 parameter were determined for the soft tissue-mimicking ultrasonic gel phantom. The concentrations of gel phantom, including 14% gelatin, 0.25% graphite, and 2% formaldehyde, with a maximum variation in the speed of sound (21.9 ± 2.3, 20.5 ± 2.1, and 24.3 ± 3.3 m/s) and attenuation coefficient (49.6 ± 9.1, 29.5 ± 5.5, and 47.9 ± 15.4 dB/MHz·m) were selected, respectively. The sensitivities of the speed of sound and the attenuation coefficient parameters and the R2 parameter were determined for the soft tissue-mimicking ultrasonic gel phantom as 1.01 m/s, 2.9 dB/MHz-m, and 0.48 s−1 per Gy and for the MAGIC-f polymer gel as 0.79 m/s, 1.9 dB/MHz-m, and 0.26 s−1 per Gy (R = 0.98), respectively. A significant correlation was found between the MAGIC-f polymer gel and the ultrasonic soft tissue-mimicking gel phantom with the R2 parameter (R = 0.9). Thus, the ultrasonic tissue-mimicking gel phantom can be concluded to be suitable for read-out using ultrasound waves as a free radical polymerization sensor. The cost effectiveness due to the utility of edible gelatin and the formation of breast soft tissue-mimicking ultrasonic images due to the presence of graphite scattering particles are distinctive features of the gel phantom introduced in this study.

Towards real-time 4D radiation dosimetry on an MRI-Linac

4D radiation dosimetry using a highly radiation-sensitive polymer gel dosimeter with real-time quantitative magnetic resonance imaging (MRI) readout is presented as a technique to acquire the accumulated radiation dose distribution during image-guided radiotherapy on an MRI-Linac. Optimized T 2-weighted Turbo-Spin-Echo (TSE) scans are converted into quantitative ΔR 2 maps and subsequently to radiation dose maps.The concept of temporal uncertainty is introduced as a metric of effective temporal resolution. A mathematical framework is presented to optimize the echo time of the TSE sequence in terms of dose resolution, and the trade-off between temporal resolution and dose resolution is discussed. The current temporal uncertainty achieved with the MAGAT gel dosimeter on a 1 T MRI-Linac is 3.8 s which is an order of magnitude better than what has been achieved until now.The potential of real-time 4D radiation dosimetry in a theragnostic MRI-Linac is demonstrated for two scenarios: an irradiation with three coplanar beams on a head phantom and a dynamic arc treatment on a cylindrical gel phantom using a rotating couch. The dose maps acquired on the MRI-Linac are compared with a treatment plan and with dose maps acquired on a clinical 3 T MRI scanner. 3D gamma map evaluations for the different modalities are provided. While the presented method demonstrates the potential of gel dosimetry for tracking the dose delivery during radiotherapy in 4D, a shortcoming of the MAGAT gel dosimeter is a retarded dose response.The effect of non-ideal radiofrequency pulses resulting from limitations in the specific absorption rate or B1-field inhomogeneity on the TSE acquired ΔR 2 values is analysed experimentally and by use of computational modelling with a Bloch simulator.

A novel investigation of the effect of different concentrations of methacrylic acid on the dose response of MAGAT gel dosimeter in intraoperative radiotherapy

PurposeHigh dose prescription in one treatment session of intraoperative radiotherapy (IORT) requires precise monitoring of the delivered dose. Methacrylic acid, gelatin and tetrakis phosphonium chloride (MAGAT) gel with superior dose sensitivity and dose resolution seems to be a suitable tool for 3 dimensional dose verification of IORT. In the current study, the dose response of MAGAT gel dosimeter with varying concentrations of methacrylic acid (MAA) was investigated. Finally, the MAGAT with optimal concentration was subjected to dose rate and energy dependency measurements. MethodsMAGAT gel with different concentrations of 3, 5, 6, 8 and 10% was manufactured and irradiated with 50 keV produced by IORT. Gel vials were read out by MRI and R2 responses were plotted against dose. Dose rate and energy dependency of optimum MAGAT gel were assessed by irradiation by a VARIAN linear accelerator using various dose rates of 30, 40 and 50 cGy/min and diverse photon energies of 6 and 18 MV as well as 50 keV of IORT. ResultsMAGAT with a concentration of 8% MAA, exhibited a high-dose response and dose sensitivity of 5.16 Gy−1 s−1 in irradiation by IORT. Moreover, its response was independent of low dose rates (30, 40 and 50 cGy/min) and mega-voltage energies (p > 0.05). However, there was a significant difference between the R2-dose response of MAGAT irradiated by mega-voltage (6 and 18 MV) and 50 keV energy of IORT. ConclusionMAGAT is an effective tool to investigate three dimensional dose distributions of IORT independent of dose rates used in X-ray IORT. Moreover, its response is energy independent over mega-voltage energies.

The dose enhancement of MAGAT gel dosimeter doped with zinc oxide at 6 MV photon beam

The cancer treatment modalities have been developed rapidly with the aim to maximize the absorbed dose toward the cancer cells while sparing the healthy tissues. The use of high atomic number, Z nanomaterials has become interest as it offers the possibilities such as destroying cancer tumor with minimal damage to the healthy tissues. The study aimed to evaluate the role of methylene blue as it reduced the self-polymerization as well as to measure the dose enhancement effect of Zinc Oxide in MAGAT gel dosimeter. The MAGAT gel formulation is composed of 5% gelatin, 6% methacrylic acid, 10 mM THPC, 5 mg/ml of zinc oxide at different sizes of 20 nm, 40 nm and 60 nm, 0.01% of methylene blue and 89% of de-ionised water. The gel samples are irradiated at 1 Gy, 3 Gy, 5 Gy, 7 Gy, 9 Gy and 10 Gy by using 6 MV photon beam. The dose response and sensitivity of MAGAT gel doped with MB and zinc oxide is obtained from the UV–Vis absorbance. The results show that the presence of methylene blue inhibit the self-polymerization problem and the addition of zinc oxide NPs increased the dose response of MAGAT gel dosimeter. This new gel formulation showing a promising polymer gel dosimeter with an increase in radiation effectiveness.

Study of the formulation optimization and reusability of a MAGAT gel dosimeter

PurposeThis study aims to optimize the formulation of a methacrylic acid gelatine and tetrakis (hydroxymethyl) phosphonium chloride (MAGAT) gel dosimeter to achieve acceptable dosimetric characteristics and the lowest final costs. This study also evaluates the reusability of the dosimeter. MethodsThe MAGAT gel dosimeter formulation was optimized. Tetrakis (hydroxymethyl) phosphonium chloride (THPC) concentrations (2, 5, 8, 10, 20, and 65 mM), methacrylic acid (MA) concentrations (2.0, 2.5, 3.0, 3.5, and 4.0% w/w) and gelatin concentrations (4.36, 6.45, 8.36, and 10.45% w/w) were evaluated to provide an adequate dosimetric response. The final dosimeter formulation linearity and dose rate dependence were evaluated. The reutilization methodology of the optimized gel formulation, but containing 2 mM of THPC, which was previously irradiated with a dose of 2 Gy, is also presented. ResultsThe optimized mass concentration of the dosimeter consists of 88.60% deionized water, 8.36% gelatin, 3.00% of MA and 0.04% THPC (5 mM). It presents a linear response for doses up to 10 Gy with a 1.16 Gy−1 s−1 sensitivity. A maximum sensitivity variation of less than 4.0% was found when varying the dose rate of the radiation beams from 300 to 500 cGy/min. It was possible to reuse the dosimeter, however the sensitivity decreased by 15% from the first to the second irradiation. ConclusionsA low-cost MAGAT gel dosimeter with optimized formulation that responds to radiation in a dose range of 0 to 10 Gy with small dose-rate dependence is presented. The MAGAT gel can be reused after a 2 Gy irradiation.

Dosimetry and Radioenhancement Comparison of Gold Nanoparticles in Kilovoltage and Megavoltage Radiotherapy using MAGAT Polymer Gel Dosimeter

Background: Numerous unique characteristics of the nanosized gold, including high atomic number, low toxicity, and high biocompatibility make it one of the most appropriate nanostructures to boost radiotherapy efficacy. Many in-vivo and in-vitro investigations have indicated that gold nanoparticles (AuNPs) can significantly increase tumor injuries in low kilovoltage radiotherapy. While deep-lying tumors require much higher energy levels with greater penetration power, and investigations carried out in megavoltage energy range show contradictory results.Objective: In this study, we quantitatively assess and compare dose enhancement factors (DEFs) obtained through AuNPs under radiation of Cobalt-60 source (1.25MeV) versus Iridium-192 source (0.380 KeV) using MAGAT gel dosimeter.Material and Methods: MAGAT polymer gel in both pure and combined with 0.2 mM AuNPs was synthesized. In order to quantify the effect of energy on DEF, irradiation was carried out by Co-60 external radiotherapy and Ir-192 internal radiotherapy. Finally, readings of irradiated and non-irradiated gels were performed by MR imaging.Result: The radiation-induced R2 (1/T2) changes of the gel tubes doped with AuNPs compared to control samples, upon irradiation of beams released by Ir-192 source showed a significant dose enhancement (15.31% ±0.30) relative to the Co-60 external radiotherapy (5.85% ±0.14).Conclusion: This preliminary study suggests the feasibility of using AuNPs in radiation therapy (RT), especially in low-energy sources of brachytherapy. In addition, MAGAT polymer gel, as a powerful dosimeter, could be used for 3D visualization of radiation dose distribution of AuNPs in radiotherapy.

The microscopic dose enhancement factor measurment of bismuth nanoparticles in external radiation therapy using MRI polymer gel dosimetery

Introduction: Bismuth-based nanoparticles having high atomic number and electron density, besides of being utilized as CT contrast agent, stand as a strongly proposed method for dose enhancement in radiotherapy. Embedded nanoparticle in polymer gel dosimeter poses the first step to assess the dose enhancement capability in nanoparticles. To this end, MAGICA gel dosimeter, which is a modified kind of agarose-added magic gel to obtain more stiffness and stability is appropriate method. This study aims at determining the dose enhancement capability of bismuth nanoparticles in this gel under conventional external radiotherapy. Materials and Methods: In current study, the synthesized bismuth nanoparticles approximately with 20 nanometers in diameter and 0.1mM in concentration were injected into MAGICA gel and exposed to 6 MV X-rays beams from linear accelerator simultaneously with control gel samples irradiated in different five doses from 2-10Gy. Results: MAGICA polymer gel response against radiation was characterized by comparing R2 in samples lacking nanoparticles and with Bi-NPs. MAGICA response was found to be linear over the entire dose range explored from 2Gy up to 10 Gy. Results indicated the average dose enhancement factor around 9.8% ± 0.02 in the presence of Bi-NPs. Conclusion: This study investigated the dose enhancement capability of bismuth nanoparticles in external radiotherapy. As well as, MAGICA polymer gel combined with Bi-NPs was approved as a suitable tool for measuring the enhancement of radiation.

Dosimetry and Radioenhancement Comparison of Gold Nanoparticles in Kilovoltage and Megavoltage Radiotherapy using MAGAT Polymer Gel Dosimeter

Numerous unique characteristics of the nanosized gold, including high atomic number, low toxicity, and high biocompatibility make it one of the most appropriate nanostructures to boost radiotherapy efficacy. Many in-vivo and in-vitro investigations have indicated that gold nanoparticles (AuNPs) can significantly increase tumor injuries in low kilovoltage radiotherapy. While deep-lying tumors require much higher energy levels with greater penetration power, and investigations carried out in megavoltage energy range show contradictory results. In this study, we quantitatively assess and compare dose enhancement factors (DEFs) obtained through AuNPs under radiation of Cobalt-60 source (1.25MeV) versus Iridium-192 source (380 KeV) using MAGAT gel dosimeter. MAGAT polymer gel in both pure and combined with 0.2 mM AuNPs was synthesized. In order to quantify the effect of energy on DEF, irradiation was carried out by Co-60 external radiotherapy and Ir-192 internal radiotherapy. Finally, readings of irradiated and non-irradiated gels were performed by MR imaging. The radiation-induced R2 (1/T2) changes of the gel tubes doped with AuNPs compared to control samples, upon irradiation of beams released by Ir-192 source showed a significant dose enhancement (15.31% ±0.30) relative to the Co-60 external radiotherapy (5.85% ±0.14). This preliminary study suggests the feasibility of using AuNPs in radiation therapy (RT), especially in low-energy sources of brachytherapy. In addition, MAGAT polymer gel, as a powerful dosimeter, could be used for 3D visualization of radiation dose distribution of AuNPs in radiotherapy.

Monte-Carlo based assessment of MAGIC, MAGICAUG, PAGATUG and PAGATAUG polymer gel dosimeters for ovaries and uterus organ dosimetry in brachytherapy, nuclear medicine and Tele-therapy

Background and objectivesCalculation of 3D dose distribution during radiotherapy and nuclear medicine helps us for better treatment of sensitive organs such as ovaries and uterus. In this research, we investigate two groups of normoxic dosimeters based on meta-acrylic acid (MAGIC and MAGICAUG) and polyacrylamide (PAGATUG and PAGATAUG) for brachytherapy, nuclear medicine and Tele-therapy in their sensitive and critical role as organ dosimeters. MethodsThese polymer gel dosimeters are compared with soft tissue while irradiated by different energy photons in therapeutic applications. This comparison has been simulated by Monte-Carlo based MCNPX code. ORNL phantom–Female has been used to model the critical organs of kidneys, ovaries and uterus. Right kidney is proposed to be the source of irradiation and another two organs are exposed to this irradiation. ResultsEffective atomic numbers of soft tissue, MAGIC, MAGICAUG, PAGATUG and PAGATAUG are 6.86, 7.07, 6.95, 7.28, and 7.07 respectively. Results show the polymer gel dosimeters are comparable to soft tissue for using in nuclear medicine and Tele-therapy. Differences between gel dosimeters and soft tissue are defined as the dose responses. This difference is less than 4.1%, 22.6% and 71.9% for Tele-therapy, nuclear medicine and brachytherapy respectively. The results approved that gel dosimeters are the best choice for ovaries and uterus in nuclear medicine and Tele-therapy respectively. ConclusionsDue to the slight difference between the effective atomic numbers of these polymer gel dosimeters and soft tissue, these polymer gels are not suitable for brachytherapy since the dependence of photon interaction to atomic number, for low energy brachytherapy, had been so effective. Also this dependence to atomic number, decrease for photoelectric and increase for Compton. Therefore polymer gel dosimeters are not a good alternative to soft tissue replacement in brachytherapy.

Dose rate and energy dependence study of methacrylic acid gelatin tetrakis (hydroxymethyl) phosphonium chloride gel with flattened and unflattened photon beams.

The aim of this study is to evaluate the dose rate and energy dependency of methacrylic acid gelatin tetrakis (hydroxymethyl) phosphonium chloride (MAGAT) gel in unflattened photon beam using X-ray computed tomography (CT) and ultraviolet (UV)-visible spectroscopy. MAGAT gel was prepared and it was exposed to 6 MV flattened and unflattened beams. The dose selected for irradiation was ranging from 3 to 15 Gy with an increment of 3 Gy. The dose rate dependency of the gel was investigated by exposing the gel to three different dose rates of 250, 500, and 1500 cGy/min for flattening filter free (FFF). To verify the energy dependency of the gel, it was exposed by both FFF and flattening filter (FF) for constant dose rate (250 cGy/min) and different energy (6 and 10 MV X-ray photons). The exposed gels were scanned by X-ray CT and UV-visible spectrophotometer. The change in dose sensitivity observed over the dose rate from 250 cGy/min to 1500 cGy/min was 58.00% and 57.89% using a UV-visible spectrophotometer and X-ray CT analysis method. Energy dependency was evaluated with respect to dose sensitivity and the variation between 6 MV FF and FFF photon beams was found to be 2.20% and 2.21% using UV-visible spectrophotometer analysis and X-ray CT, respectively. Similarly, the variation noticed with 10 MV FF and FFF was 2.30% using UV-visible spectrophotometer analysis and 2.22% using X-ray CT analysis. The results clearly show that the MAGAT gel was highly dose rate-dependent and less dependent on energy. The beam quality variation between FF and FFF was less. The similar results obtained using X-ray CT scanner and UV-visible spectrophotometer indicate that this study can be recommended for polymer gel scanning procedure.

Feasibility study of basic characterization of MAGAT polymer gel using CBCT attached in linear accelerator: Preliminary study

The aim of this study is to evaluate the methacrylic acid, gelatin and tetrakis (hydroxymethyl) phosphonium chloride gel (MAGAT) by cone beam computed tomography (CBCT) attached with modern linear accelerator. To compare the results of standard diagnostic computed tomography (CT) with CBCT, different parameters such as linearity, sensitivity and temporal stability were checked. MAGAT gel showed good linearity for both diagnostic CT and CBCT measurements. Sensitivity and temporal stability were also comparable with diagnostic CT measurements. In both the modalities, the sensitivity of the MAGAT increased to 4 days and decreased till the 10th day of post irradiation. Since all measurements (linearity, sensitivity and temporal stability) from diagnostic CT and CBCT were comparable, CBCT could be a potential tool for dose analysis study for polymer gel dosimeter.

Accuracy and Precision of Magat Gel As a Dosimeter

Polymer gel dosimeter is a radiation sensitive chemical dosimeter that can measure 3 D dose distribution with high resolution. Due to the increasing complexity of radiotherapy treatment planning and delivery, accurate experimental radiation dosimetry plays an important role in the implementation and quality assurance of new treatment techniques. A polymer gel dosimeter must possess several important characteristics of a dosimeter to be able to measure absorbed dose precisely. two important dosimetric properties of a dosimeter were determined in this study; accuracy and precision. The MAGAT gels were made of 5% gelatin, 6% methacrylic acid and 10 mM tetrakis-hydroxy-methyl-phosphonium chloride (THPC). The irradiation of MAGAT gel was performed by 6-MV photon beam at a dose range 1 to 10 Gy and was imaged by 1.5 T Magnetic Resonance Imaging (MRI). The dose response of MAGAT gel dosimeter was obtained from spin-spin relaxation rate (R2) of MRI signal. The accuracy of MAGAT gel dosimeter has a range within 4% for doses greater than and equal to 3 Gy. The reproducibility of the MAGAT gel dosimeter at one irradiation was less than 1% whilst the long term reproducibility was within 3% over the five month period. For temporal stability, the dose sensitivity of MAGAT gel dosimeter irradiate at 1 to 11 days post-manufacturing decreased over time. While the dose sensitivity imaged at 1 to 9 days post-irradiation increased up to 4 days post-irradiation and subsequently starts decreasing after 4 days till 9 days. From the study of two dosimetric properties, MAGAT gel dosimeter shows a great dose response with a superior dose response. Thus the MAGAT gel dosimeter can be apply as a 3 D radiotherapy dosimeter.

SU‐E‐T‐716: Suitability Study of a Unique 3D Dosimeter for Commissioning Radiation Treatment Machines

Purpose:To determine the suitability of a methacrylic acid‐based MAGAT gel dosimeter to serve as a 3D commissioning toolMethods:Different sized MAGAT gel dosimeters were fabricated in‐house to perform dose response, depth dose and dose rate measurements using an orthovoltage treatment unit. Dose response data were obtained by irradiating dosimeters to six dose levels at three different effective beam energies. Depth dose measurements were taken using one dose at one energy. Dose rate dependence was measured by varying only distances for the gel irradiations while dose level and energy remained unchanged. A Bruker Biospecs 4.7T MRI scanner was used to acquire spin‐spin relaxation rates on axial slices at different depths throughout each dosimeter 24h after irradiation.Results:The dose response curves exhibited a separation when compared for the measured energies. MAGAT depth dose data, normalized to ion chamber data at 2 cm depth, showed an increasing divergence with increasing depth. The dose rate decreased when distances were increased and demonstrated a significant dose rate dependence of the measurements. Consequently, dose rate corrections were applied to all measurements, thus, aligning the dose response curves for all three energies and reducing the divergence between MAGAT and ion chamber depth dose data.Conclusion:The MAGAT dosimeter was intended to serve as a 3D commissioning tool for testing radiation treatment plans of small fields with steep dose gradients and complex treatment volumes. A suitable detector for commissioning needs to be dependent on dose but independent of dose rate. This study, however, showed a dose rate dependence of up to 30% eliminating the current composition of MAGAT as a suitable dosimeter. Further investigations of chemical compositions need to be performed.