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Vista scanner projection images from (a) a 1.6 cm diameter scattering finger-gelatin phantom, (b) a 5 cm diameter scattering finger-gelatin phantom, and (c) a scattering solution -filled jar phantom. (d) Vista mean attenuation value versus scatter concentration, measured within the scattering finger region-of-interest for the different phantoms, indicating the range of approximately linear behavior for each size of scattering region. Some of the error bars are smaller than symbol size
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This paper explores the combination of cone beam optical computed tomography with an N-isopropylacrylamide (NIPAM)-based polymer gel dosimeter for three-dimensional dose imaging of small field deliveries. Initial investigations indicate that cone beam optical imaging of polymer gels is complicated by scattered stray light perturbation. This can lea...
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Measurement of solar ultraviolet (UV) radiation is an important aspect of dosimetry for the improved knowledge of UV exposure and its associated health related issues. EBT2 Gafchromic film has been designed by its manufacturers as an improved tool for ionizing radiation dosimetry. The film is stated as exhibiting a significant reduction in UV respo...
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Citations
... In addition, optically stimulated luminescence dosimeters, [9] calorimeters, [10] and alanine-based dosimeters [11] contribute to the quantification of the dose administered to cancer patients. Notably, relative or spatial dosimetry is carried out through the deployment of arrays of ionization chambers/diodes, [12] films, [13] gel dosimeters, [14] and scintillation detectors. [15] A combination of absolute and relative dosimetry measurements representing dose delivery conditions guarantees both accuracy and safety in the planning and delivery of radiation therapy. ...
Radiation dosimeters play a crucial role in radiation oncology by accurately measuring radiation dose, ensuring precise and safe radiation therapy. This study presents the design and development of a low-cost printed circuit board (PCB) dosimeter and an integrated electrometer with sensitivity optimized for dose rates intended for use in megavoltage radiation therapy. The PCB dosimeter was designed in KiCad, and it uses a low-cost S5MC-13F general-purpose 1 kV 5A power diode as a radiation detector. The dosimeter is calibrated against a known dose derived from an ionization chamber and tested for dose linearity, dose rate dependence, field size dependence, and detector orientation dependence. The observed average dose differences between the delivered and measured doses for most measurements were found to be < 1.1%; the dose rate linearity between 100 MU/min and 1400 MU/min was found to be within 1.3%. This low-cost architecture could successfully be adapted further for a scalable, cost-effective dosimetry solution through firmware or circuit design.
... In the last few years, there has been a growing interest in magnetic resonance imaging based polymer gel dosimetry (MRPD) due to its tissue equivalence and potential to determine quantitatively complex 3D dose distributions with high spatial resolution [19][20][21][22][23][28][29][30][31][32][33]. ...
The photon induced radical-initiated polymerization in polymer gels can be used for high-resolution tissue equivalent dosimeters in quality control of radiation therapy. The dose (D) distribution in radiation therapy can be measured as a change of the physical measurement parameter T2 using T2-weighted magnetic resonance imaging. The detection by T2 is relying on the local change of the molecular mobility due to local polymerization initiated by radicals generated by the ionizing radiation. The dosimetric signals R2 = 1/T2 of many of the current polymer gels are dose-rate dependent, which reduces the reliability of the gel for clinical use. A novel gel dosimeter, based on methacrylic acid, gelatin and the newly added dithiothreitol (MAGADIT) as an oxygen-scavenger was analyzed for basic properties, such as sensitivity, reproducibility, accuracy and dose-rate dependence. Dithiothreitol features no toxic classification with a difference to THPC and offers a stronger negative redox-potential than ascorbic acid. Polymer gels with three different concentration levels of dithiothreitol were irradiated with a preclinical research X-ray unit and MR-scanned (T2) for quantitative dosimetry after calibration. The polymer gel with the lowest concentration of the oxygen scavenger was about factor 3 more sensitive to dose as compared to the gel with the highest concentration. The dose sensitivity (α = ∆R2/∆D) of MAGADIT gels was significantly dependent on the applied dose rate D ˙ (≈48% reduction between D ˙ = 0.6 Gy/min and D ˙ = 4 Gy/min). However, this undesirable dose-rate effect reduced between 4–8 Gy/min (≈23%) and almost disappeared in the high dose-rate range (8 ≤ D ˙ ≤ 12 Gy/min) used in flattening-filter-free (FFF) irradiations. The dose response varied for different samples within one manufacturing batch within 3%–6% (reproducibility). The accuracy ranged between 3.5% and 7.9%. The impact of the dose rate on the spatial integrity is demonstrated in the example of a linear accelerator (LINAC) small sized 5 × 10 mm2 10 MV photon field. For MAGADIT the maximum shift in the flanks in this field is limited to about 0.8 mm at a FFF dose rate of 15 Gy/min. Dose rate sensitive polymer gels likely perform better at high dose rates; MAGADIT exhibits a slightly improved performance compared to the reference normoxic polymer gel methacrylic and ascorbic acid in gelatin initiated by copper (MAGIC) using ascorbic acid.
... Optics enable x-rays X-rays enable optics Optical tools have become pervasive throughout radiation oncology, with lasers used in almost every treatment unit for daily patient alignment [20][21][22] and now surface mapping for patient setup and verification, 23 both shown in Fig. 4. Further information to aid in optimal treatment delivery comes from the original technology of (optical) film dosimetry as well as thermoluminescence. [24][25][26] Optical gel dosimeters are under active development [27][28][29][30] to enable accurate direct dose verification. Fiberoptic-based scintillation dosimetry has also been developed, [31][32][33][34] with extension to scintillating fiber arrays for dose mapping, 35,36 where the signal comes from the scintillator radioluminescence. ...
X-ray and optical technologies are the two central pillars for human imaging and therapy. The strengths of x-rays are deep tissue penetration, effective cytotoxicity, and the ability to image with robust projection and computed-tomography methods. The major limitations of x-ray use are the lack of molecular specificity and the carcinogenic risk. In comparison, optical interactions with tissue are strongly scatter dominated, leading to limited tissue penetration, making imaging and therapy largely restricted to superficial or endoscopically directed tissues. However, optical photon energies are comparable with molecular energy levels, thereby providing the strength of intrinsic molecular specificity. Additionally, optical technologies are highly advanced and diversified, being ubiquitously used throughout medicine as the single largest technology sector. Both have dominant spatial localization value, achieved with optical surface scanning or x-ray internal visualization, where one often is used with the other. Therapeutic delivery can also be enhanced by their synergy, where radio-optical and optical-radio interactions can inform about dose or amplify the clinical therapeutic value. An emerging trend is the integration of nanoparticles to serve as molecular intermediates or energy transducers for imaging and therapy, requiring careful design for the interaction either by scintillation or Cherenkov light, and the nanoscale design is impacted by the choices of optical interaction mechanism. The enhancement of optical molecular sensing or sensitization of tissue using x-rays as the energy source is an important emerging field combining x-ray tissue penetration in radiation oncology with the molecular specificity and packaging of optical probes or molecular localization. The ways in which x-rays can enable optical procedures, or optics can enable x-ray procedures, provide a range of new opportunities in both diagnostic and therapeutic medicine. Taken together, these two technologies form the basis for the vast majority of diagnostics and therapeutics in use in clinical medicine.
... Many radiotherapy centers don't pay attention to effect of ionization champers type on accuracy of quality control measurements. They use any available ionization champers in all quality control and data entry measurements (1,2) . Many studies were carried out in this field to compare different ionization champers in small fields but large fields were not completely compared before (3.4) . ...
Many radiotherapy centers don’t pay attention to effect of ionization champers type on accuracy of quality control measurements. They use any available ionization champers in all quality control and data entry measurements (1,2) . Many studies were carried out in this field to compare different ionization champers in small fields but large fields were not completely compared before (3.4). The aim of this work is to compare output factor in large field using two different sizes ionization champers connected to electrometer. Final out put were obtained from the farmer and smidflex dosimeter irradiated with 6 MV photon beams. Important field side ranging from 20 cm to 70 cm side field is measured in whole body radiation (5, 6). For all examined large field sizes a difference ranging from 1% to 5 % was found when added to other calibration errors it will exceeds the acceptable margin. The largest difference was found in field side 70 cm this may be due to large scattering radiation
... When the size of the radiation beam is small, e.g., less than 1 cm, the only currently available measurement tool is either radiographic/radiochromic films or the 3D dosimeters. There are a few publications on applications of PGD/FGD/SPD [25][26][27][28][29][30] , and more studies on this topic are needed. ...
Accurate dose measurement tools are needed to evaluate the radiation dose delivered to patients by using modern and sophisticated radiation therapy techniques. However, the adequate tools which enable us to directly measure the dose distributions in three-dimensional (3D) space are not commonly available. One such 3D dose measurement device is the polymer-based dosimeter, which changes the material property in response to radiation. These are available in the gel form as polymer gel dosimeter (PGD) and ferrous gel dosimeter (FGD) and in the solid form as solid plastic dosimeter (SPD). Those are made of a continuous uniform medium which polymerizes upon irradiation. Hence, the intrinsic spatial resolution of those dosimeters is very high, and it is only limited by the method by which one converts the dose information recorded by the medium to the absorbed dose. The current standard methods of the dose quantification are magnetic resonance imaging, optical computed tomography, and X-ray computed tomography. In particular, magnetic resonance imaging is well established as a method for obtaining clinically relevant dosimetric data by PGD and FGD. Despite the likely possibility of doing 3D dosimetry by PGD, FGD or SPD, the tools are still lacking wider usages for clinical applications. In this review article, we summarize the current status of PGD, FGD, and SPD and discuss the issue faced by these for wider acceptance in radiation oncology clinic and propose some directions for future development.
... Currently, only a few studies focused on gel dosimetric measurements of small-field dose delivery. Olding et al. [11] used the NIPAM-based gel dosimeter to measure two letter dose patterns and read the gel by a cone beam optical CT. The results of gamma evaluation with 2%/2 mm criteria showed that the dose maps had a 92.7% pass rate compared to the result of the treatment planning system (TPS). ...
With advances in therapeutic instruments and techniques, three-dimensional dose delivery has been widely used in radiotherapy. The verification of dose distribution in a small field becomes critical because of the obvious dose gradient within the field. The study investigates the dose distributions of various field sizes by using NIPAM polymer gel dosimeter. The dosimeter consists of 5% gelatin, 5% monomers, 3% cross linkers, and 5 mM THPC. After irradiation, a 24 to 96 hour delay was applied, and the gel dosimeters were read by a cone beam optical computed tomography (optical CT) scanner. The dose distributions measured by the NIPAM gel dosimeter were compared to the outputs of the treatment planning system using gamma evaluation. For the criteria of 3%/3 mm, the pass rates for 5 × 5, 3 × 3, 2 × 2, 1 × 1, and 0.5 × 0.5 cm2 were as high as 91.7%, 90.7%, 88.2%, 74.8%, and 37.3%, respectively. For the criteria of 5%/5 mm, the gamma pass rates of the 5 × 5, 3 × 3, and 2 × 2 cm2 fields were over 99%. The NIPAM gel dosimeter provides high chemical stability. With cone-beam optical CT readouts, the NIPAM polymer gel dosimeter has potential for clinical dose verification of small-field irradiation.
... These dosimeters don't perturb radiation ield because the material phantom and these detector are the same (10) . Because of these bene its several studies in radiation small ields have been accomplished by using several types of polymer gel dosimeter (3,7,(11)(12)(13)(14) but the MRI-based on MAGIC polymer gel dosimeter has not been evaluated for small ields. It is well recognized that effect of a gel is different from others; even a change in component of a unique gel causes a different response to absorbed dose. ...
Background: Accurate small radiation field dosimetry is essential in modern radiotherapy techniques such as stereotactic radiosurgery (SRS) and intensity modulated radiotherapy (IMRT). Precise measurement of dosimetric parameters such as beam profile, percentage depth doses and output factor of these beams are complicated due to the electron disequilibrium and the steep dose gradients. In the present work the MAGIC polymer gel was used for dosimetry of small circular photon beams. The results of MAGIC were compared with EBT2 measurements and Monte Carlo (MC) calculations. Materials and Methods: Experimental measurements were made by mentioned dosimeters in four small field sizes 5, 10, 20 and 30 mm. The BEAMnrc code based on EGSnrc was used for simulaion to calculate dosimetric parameters at these small fields. The phantoms were irradiated in a 6 MV photon beam Varian 2100C linear accelerator at SSD=100 cm. gel readout performed by 3 Tesla MRI scanner. Results: The results showed that the Percent depth dose (PDD) values measured and calculated by EBT2 film and MC had maximum local differences 4% and 5% with PDD values measured by MAGIC for field size of 5mm respectively. These differences decreased for larger field sizes. The measurements of output factor and penumbra (80%-20%) and (90%-10%) showed good agreement between the measurements and MC calculation. Conclusion: This study showed that the MAGIC polymer gel based on high resolution MRI images is useful detector for small field dosimetry butits agreement with MC is less than agreement of EBT2 film with MC. © 2016, Novim Medical Radiation Institute. All rights reserved.
... These dosimeters don't perturb radiation ield because the material phantom and these detector are the same (10) . Because of these bene its several studies in radiation small ields have been accomplished by using several types of polymer gel dosimeter (3,7,(11)(12)(13)(14) but the MRI-based on MAGIC polymer gel dosimeter has not been evaluated for small ields. It is well recognized that effect of a gel is different from others; even a change in component of a unique gel causes a different response to absorbed dose. ...
... In the present study, we explore such a method by using optical cone beam computed tomography of Cherenkov-excited fluorescence (CEF) for 3D dosimetry of megavoltage photon beams in water, a reconstruction technique studied previously in gel and radiochromic plastic dosimetry applications. [15][16][17][18][19] Herein, we explore the application of this device for commissioning of static beam shapes. The imaging system, image processing, and reconstruction methodology were developed here and tested on a complexly shaped radiation field, specifically examining the unique niche areas for potential use in imaging of complex beams in a fast timescale in water. ...
To test the use of a three-dimensional (3D) optical cone beam computed tomography reconstruction algorithm, for estimation of the imparted 3D dose distribution from megavoltage photon beams in a water tank for quality assurance, by imaging the induced Cherenkov-excited fluorescence (CEF).
An intensified charge-coupled device coupled to a standard nontelecentric camera lens was used to tomographically acquire two-dimensional (2D) projection images of CEF from a complex multileaf collimator (MLC) shaped 6 MV linear accelerator x-ray photon beam operating at a dose rate of 600 MU/min. The resulting projections were used to reconstruct the 3D CEF light distribution, a potential surrogate of imparted dose, using a Feldkamp-Davis-Kress cone beam back reconstruction algorithm. Finally, the reconstructed light distributions were compared to the expected dose values from one-dimensional diode scans, 2D film measurements, and the 3D distribution generated from the clinical Varian ECLIPSE treatment planning system using a gamma index analysis. A Monte Carlo derived correction was applied to the Cherenkov reconstructions to account for beam hardening artifacts.
3D light volumes were successfully reconstructed over a 400 × 400 × 350 mm(3) volume at a resolution of 1 mm. The Cherenkov reconstructions showed agreement with all comparative methods and were also able to recover both inter- and intra-MLC leaf leakage. Based upon a 3%/3 mm criterion, the experimental Cherenkov light measurements showed an 83%-99% pass fraction depending on the chosen threshold dose.
The results from this study demonstrate the use of optical cone beam computed tomography using CEF for the profiling of the imparted dose distribution from large area megavoltage photon beams in water.
... One of the gels from the batch is then used as a calibration gel. A number of calibration techniques exist [8,9,10], but here we present one calibration method which is performed by using electron depth dose data from ionization chamber measurements, and comparing to optical density depth dose measurements in a gel. Gel dosimeter response is roughly linear (see below), which allows for easy alignment of the two depth dose curves (Fig. 4), and then acquisition of calibration data. ...
An extension tailored to dose data processing and analysis has been developed in the open source imaging application 3D Slicer to aid in routine clinical use of gel dosimetry. This extension allows for registration, calibration, and comparison of 3D gel dosimeter data (imaged using an optical CT scanner) to treatment planning data. In this work, we present the accuracy and reproducibility of the gel dosimeter calibration component of the 3D Slicer extension. We examine the consistency of the calibration curves for a range of electron beam irradiations, and the inter-user variability of the gel dosimeter calibration process.
