| 1. |
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| 2. |
- Aznar, MC, et al.
(författare)
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Real-time optical-fibre luminescence dosimetry for radiotherapy: physical characteristics and applications in photon beams
- 2004
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 49:9, s. 1655-1669
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Tidskriftsartikel (refereegranskat)abstract
- A new optical-fibre radiation dosimeter system, based on radioluminescence and optically stimulated luminescence from carbon-doped aluminium oxide, was developed and tested in clinical photon beams. This prototype offers several features, such as a small detector (1 x 1 x 2 mm), high sensitivity, real-time read-out and the ability to measure both dose rate and absorbed dose. The measurements describing reproducibility and output dependence on dose rate, field size and energy all had standard deviations smaller than 1%. The signal variation with the angle of incidence was smaller than 2% (1 SD). Measurements performed in clinical situations suggest the potential of using this real-time system for in vivo dosimetry in radiotherapy.
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| 3. |
- Baldoc, C, et al.
(författare)
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Dose resolution in radiotherapy polymer gel dosimetry: effect of echo spacing in MRI pulse sequence
- 2001
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 46:2, s. 449-460
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Tidskriftsartikel (refereegranskat)abstract
- In polymer gel dosimetry using magnetic resonance imaging, the uncertainty in absorbed dose is dependent on the experimental determination of T2. The concept of dose resolution (Dpdelta) of polymer gel dosimeters is developed and applied to the uncertainty in dose related to the uncertainty in T2 from a range of T4 encountered in polymer gel dosimetry. Dpdelta is defined as the minimal separation between two absorbed doses such that they may be distinguished with a given level of confidence, p. The minimum detectable dose (MDD) is Dpdelta as the dose approaches zero. Dpdelta and the minimum detectable dose both give a quantifiable indication of the likely practical limitations and usefulness of the dosimeter. Dpdelta of a polyacrylamide polymer gel dosimeter is presented for customized 32-echo and standard multiple-spin-echo sequences on a clinical MRI scanner. In evaluating uncertainties in T2, a parameter of particular significance in the pulse sequence is the echo spacing (ES). For optimal results, ES should be selected to minimize Dpdelta over a range of doses of interest in polymer gel dosimetry.
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| 4. |
- Bäck, Sven, et al.
(författare)
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Investigation of the NMR relaxation rate dose-response of a ceric sulphate dosimeter
- 2002
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Ingår i: Applied Radiation and Isotopes. - 0969-8043. ; 56:6, s. 895-899
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Tidskriftsartikel (refereegranskat)abstract
- The relationship between the radiation absorbed dose and the NMR longitudinal and transversal relaxation rates, R-1 and R-2, respectively, of a ceric sulphate dosimeter was examined. By adding copper sulphate, the R-1 and R-2 dose-responses were found to be linear up to 60 kGy with dose sensitivities of 13 x 10(-6) and 15 x 10(-6) s(-1) Gy-1, respectively. There is thus the potential for a three-dimensional ceric dosimeter for high dose applications. provided a suitable gelling substance is used.
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| 5. |
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| 6. |
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| 7. |
- Hill, Brendan, et al.
(författare)
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Investigation and analysis of ferrous sulfate polyvinyl alcohol (PVA) gel dosimeter
- 2002
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 47:23, s. 4233-4246
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Tidskriftsartikel (refereegranskat)abstract
- Ferrous sulfate (Fe(SO4)2) PVA gels were investigated for a range of absorbed doses up to 20 Gy using both magnetic resonance imaging (MRI) and spectrophotometry to determine R1 and optical density (OD) dose responses and G values. It was found that R1- and OD-dose sensitivities increased with O2 saturation or by the introduction of a freeze-thaw cycle during preparation of the PVA gel. The storage temperature of the Fe(SO4)2 PVA gel at -18 degrees C increased R1-dose sensitivity above that of gels stored at 5 degrees C. The addition of sucrose to the formulation was found to result in the largest increase in both R1- and OD-dose sensitivities. Fe(SO4)2 PVA gel with and without the addition of xylenol orange was demonstrated to have a G value of approximately 20 ions/100 eV and with sucrose approximately 24 ions/100 eV.
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| 8. |
- Lepag, M, et al.
(författare)
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Dose resolution optimization of polymer gel dosimeters using different monomers
- 2001
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 46:10, s. 2665-2680
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Tidskriftsartikel (refereegranskat)abstract
- Polymer gel dosimeters of different formulations were manufactured from different monomers of acrylamide, acrylic acid, methacrylic acid, 1-vinyl-2-pyrrolidinone, 2-hydroxyethyl methacrylate and 2-hydroxyethyl acrylate. Gelatin and agarose were used as the gelling agents and N,N'-methylene-bis-acrylamide was used as a co-monomer in each polymer gel dosimeter. The T2 dependence of each dosimeter was analysed using a model of fast exchange of magnetization. The influence of the half-dose and the apparent T2 of the polymer-proton pool on the dose resolution (Dpdelta) were examined. Comparisons are made with the commonly employed R2-dose sensitivity. Differences exist suggesting that experiments reported in the literature using what were thought to be more optimal dosimeters may not actually be so. Based on Dpdelta of each formulation, conclusions are drawn on the optimal formulation required for a specific range of absorbed doses. In addition, information about the extent of polymerization of the monomers used along with some characteristics of the polymer network formed are reported. The influence of the concentration of monomers and gelling agent was subsequently evaluated using a model of fast exchange of magnetization. Based on these calculations, further improvement in Dpdelta can be expected.
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| 9. |
- Lepage, M, et al.
(författare)
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Magnetization transfer imaging for polymer gel dosimetry
- 2002
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Ingår i: Physics in Medicine and Biology. - 1361-6560. ; 47:11, s. 1881-1890
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Tidskriftsartikel (refereegranskat)abstract
- Off-resonance RF pre-saturation was used to obtain contrast in MRI images of polymer gel dosimeters irradiated to doses up to 50 Gy. Two different polymer gel dosimeters composed of 2-hydroxyethyl-acryl ate or methacrylic acid monomers mixed with N, N'-methylene-bisacrylamide (BIS), dispersed in an aqueous gelatin matrix were evaluated. Radiation-induced polymerization of the co-monomers generates a fast-relaxing insoluble polymer. Saturation of the polymer using off-resonance Gaussian RF pulses prior to a spin-echo read-out with a short echo time leads to contrast that is dependent on the absorbed dose. This contrast is attributed to magnetization transfer (MT) between free water and the polymer, and direct saturation of water was found to be negligible under the prevailing experimental conditions. The usefulness of MT imaging was assessed by computing the dose resolution obtained with this technique. We found a low value of dose resolution over a wide range of doses could be obtained with a single experiment. This is an advantage over multiple spin echo (MSE) experiments using a single echo spacing where an optimal dose resolution is achieved over only very limited ranges of doses. The results suggest MT imaging protocols may be developed into a useful tool for polymer gel dosimetry.
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| 10. |
- Lepage, M, et al.
(författare)
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Modelling of post-irradiation events in polymer gel dosimeters
- 2001
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 46:11, s. 2827-2839
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Tidskriftsartikel (refereegranskat)abstract
- The nuclear magnetic resonance (NMR) spin-spin relaxation time (T2) is related to the radiation-dependent concentration of polymer formed in polymer gel dosimeters manufactured from monomers in an aqueous gelatin matrix. Changes in T2 with time post-irradiation have been reported in the literature but their nature is not fully understood. We investigated those changes with time after irradiation using FT-Raman spectroscopy and the precise determination of T2 at high magnetic field in a polymer gel dosimeter. A model of fast exchange of magnetization taking into account ongoing gelation and strengthening of the gelatin matrix as well as the polymerization of the monomers with time is presented. Published data on the changes of T2 in gelatin gels as a function of post-manufacture time are used and fitted closely by the model presented. The same set of parameters characterizing the variations of T2 in gelatin gels and the increasing concentration of polymer determined from FT-Raman spectroscopy are used successfully in the modelling of irradiated polymer gel dosimeters. Minimal variations in T2 in an irradiated PAG dosimeter are observed after 13 h.
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