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Gel Dosimetry
Published in Gad Shani, Radiation Dosimetry, 2017
Radiation-induced polymerization of polymer-gel dosimeters is clearly visible. Experience with optical changes in gel dosimeters has initiated a new realm in gel dosimetry, with dose measurement using optical techniques and image reconstruction in two and three dimensions. [2] Most of the reactions involving the free radicals initially produced by the radiation are very rapid and are essentially complete within a microsecond. However, subsequent reactions of non-radical products, or of large free radicals on polymer chains, may be quite slow. Figure 9.1 is an example of the agarose/ferrous system. [3]
Accuracy Requirements for 3D Dosimetry in Contemporary Radiation Therapy
Published in Ben Mijnheer, Clinical 3D Dosimetry in Modern Radiation Therapy, 2017
Jacob Van Dyk, Jerry J. Battista, Glenn S. Bauman
There is a growing commercial availability of radiochromic gels (Modus Medical Devices Inc., London, Ontario, Canada), radiochromic plastics (Heuris Pharma LLC, Skillman, New Jersey), and of turnkey-dedicated optical scanners (Modus Medical Devices Inc., London, Ontario, Canada). Application to patient-specific QA has been more limited; diode arrays in planar or cylindrical geometry provide more convenience and patient throughput, but it is recognized that these devices only sample a subset of the available 3D dose space. A full description of various dosimetry tools and techniques that can be used for evaluating the 3D quality of IMRT plans is given in a report from AAPM Task Group 120 (Low et al., 2011) and in Chapter 9. Gel dosimetry is rapidly evolving with promising impact on clinical 3D dosimetry and QA for new radiation devices and software (see also Chapters 5 and 6).
Dosimeters and Devices for IMRT QA
Published in Arash Darafsheh, Radiation Therapy Dosimetry: A Practical Handbook, 2021
Nesrin Dogan, Matthew T. Studenski, Perry B. Johnson
As noted for many of the devices above, there is an ongoing transition from 2D to 3D dosimetry for the measurement and analysis of patient-specific QA. In each case, a novel approach has been developed to derive the 3D dose distribution based, essentially, on a collection of 2D measurements. These approaches include correction-based interpolation, measurement-guided dose reconstruction, 3D back-projection/calculation, and 3D forward-projected/calculation. In contrast to such methods are 3D dosimeters, which inherently record a high resolution, 3D dose distribution through changes that occur within the composition of a 3D volume. Traditionally known as “gel dosimetry” due to the fact that the volume comprises 80–90% water and 5% gelatin, the type of change which occurs depends upon the remaining material, which may either induce a polymerization process (polymer-based gels) [61] or an oxidation process (Fricke gels) [62]. These changes are actualized through an optical-CT or MRI-based acquisition from which a 3D response map can be derived. The response map can then be converted to dose through a calibration procedure. The advantages of gel dosimetry include the 3D nature of the measurement, energy and dose-rate independence, high sensitivity and linear response, high spatial resolution, a near-tissue equivalence, and the fact that gels can be prepared in anthropomorphic forms with various densities. Limitations include a sensitivity to time, temperature and preparation method, the cost of the materials, the availability of MRI or optical-CT for processing, the need for frequent calibrations, the labor requirements of the process, and the delay between measurement and readout. At this time, the limitations of the method combined with the availability of attractive alternatives prevent 3D dosimeters from achieving widespread use as tool for patient-specific QA. 3D dosimeters do, however, offer unique solutions for the validation of new techniques and may serve a role in the future as a way to validate processes related to the use of adaptive radiotherapy.
Emerging theranostics to combat cancer: a perspective on metal-based nanomaterials
Published in Drug Development and Industrial Pharmacy, 2022
Tejas Girish Agnihotri, Shyam Sudhakar Gomte, Aakanchha Jain
AgNPs have been used for many years because of their antimicrobial properties and extended their applications in the cancer field under active targeted therapy. In the preparation of AgNPs, a stabilizer is required to assist in the biocompatibility of the nano system. Sofia et al. formulated AgNPs by polyol method, with polyvinyl pyrrolidone (PVP) being used as a stabilizer. Morphological evaluation and structural characterization were done by transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR), X ray diffraction (XRD), dynamic light scattering (DLS), and UV–visible spectroscopy. The NPs were further assessed for hemocompatibility by performing a hemolysis assay. The U87-MG and MCF7 cells were employed to understand the localization and intake process of formulation by cancer cells [85]. In an interesting study conducted by Vedelago et al. [86], AgNPs coated with gelatin (porcine skin) were synthesized using a green synthesis approach by reduction of silver nitrate. They have been found applicable in gel dosimetry by being as a fluorescent agent and X-ray enhancer which in turn, can present themselves as effective theranostics agents in cancer treatment. More research findings on the same are elaborated in Table 1.