Results 1 - 10 of 4047
Results 1 - 10 of 4047. Search took: 0.027 seconds
|Sort by: date | relevance|
[en] Full text of publication follows. Aim: there are a growing number of patients undergoing nuclear medicine examination each year and dose estimation becomes a very important issue. The time-activity curves (TAC) of all source organs are required before one can estimate patient-specific body dose during the whole treatment period. However, TAC is known to be difficult to obtain for each individual. The purpose of this paper is to develop a patient-specific dose estimation system from the dose measured outside the body without any TAC information. Materials and methods: the method involves two steps. First, to compute the S values on the body surface for each source organ based on nuclear image using Monte Carlo simulation. Secondly, to measure the dose externally from the TLD placed on the body surface during nuclear examination. Since the doses in TLD are contributed from all source organs, they can be expressed by simultaneous equations with the S values as known variables and the cumulative activities of source organs unknown. Solving the simultaneous equations, the cumulative activities of all source organs can be obtained and subsequently the total body dose calculated. A NEMA phantom and an ORNL mathematical phantom were used to validate this method. A static activity was used for NEMA phantom and the dynamic activity distribution of each source organ obtained from MIRD dose estimate Report 19 was used in ORNL phantom. 8 simulations were performed at 15 min, 30 min, 45 min, 60 min, 120 min, 180 min, 240 min, and 300 min after intravenous administration of 18F-FDG. Numerous TLDs were placed on the surface nearest to each source organ. After each simulation, the TLD reading and S values were used to compute the cumulated activity of each organ. Results and discussion: the percent error in estimations of cumulative activity of the source organs and the error caused by inaccurate positioning the TLD will be investigated. Preliminary results on the NEMA phantom indicate it is an accurate, robust, and efficient method. Effectiveness of this method was validated by the ORNL phantom study. (authors)
[en] The radiolytic degradation rate of DEHiBA is similar to that of TBP and malonamides, and slow compared to the DGAs, and is unaffected by contact with an aqueous phase or aeration. However, product distributions vary with irradiation conditions. Based on these results, DEHiBA apparently undergoes degradation via two pathways: an acid promoted pathway, Scheme 1, and an acid independent pathway, Scheme 2. It is clear that the monoamide degrades when irradiated in the presence of an aqueous phase to form a series of lower molecular weight species generated from the cleavage of the C-N amide bond or C-N amine bond. As this is the active site during synthesis, it is not surprising that this is the weak point in the ligand structure. The main degradation products appear to be DEHA and EHiBA. These species, and the smaller fragments produced by their radioysis have increased solubility in the aqueous phase. Another product common to all irradiation conditions was the species at m/z 310.2, which is identified as an unsaturated derivative of DEHiBA, resulting from the loss of two H-atoms. In contrast, when an aqueous phase is not present, higher molecular weight products are generated via carbon radical addition reactions under the more reducing conditions. These products have maximum abundance at 750 kGy, and then decrease with increasing absorbed dose. Their significance to a biphasic solvent extraction process is probably inconsequential. Solvent extraction results show that DEHiBA radiolytic degradation had little effect on uranium distribution ratios even at absorbed doses as high as 1 MGy. The build-up of degradation products in the aqueous phase apparently decreased stripping distribution ratios, which is not adverse to a process application. Thus, these findings for DEHiBA are in agreement with previous work that claimed good radiation stability and generation of inoffensive radiolysis products for the monoamides. This, in addition to their CHON nature suggests that they will be good candidates for the development of advanced fuel cycles. Interesting future work would include a comparison study on the n-alkane monoamide DEHBA.
[en] Highlights: • Gamma radiation can be an alternative for the treatment of archival materials. • Molds were isolated from old valuable documents in the Ottoman Archives. • Radiosensitivity of molds was determined. • A XLure MST pheromone trap was used to survey the infestations. • Radiation treatment at 6 kGy is extremely efficient in the reduction of biodeteriorating agents. - Abstract: The Ottoman Archives have one of the richest archive collections in the world. However, not all the archived documents are well preserved and some undergo biodeterioration. Therefore, a rapid and promising treatment method is necessary to preserve the collection for following generations as heritage. Radiation presents as an alternative for the treatment of archival materials for this purpose. In this study, we conducted a survey to determine the contamination species and the D10 values of the samples obtained from the shelves of the Ottoman Archives. The samples also included several insect pests collected at using a pheromone trap placed in the archive storage room. With the exception of few localized problems, no active pest presence was observed. The D10 values of mold contamination and reference mold (A. niger) were found to be 1.0 and 0.68 kGy, respectively. Based on these results, it can be concluded that an absorbed dose of 6 kGy is required to remove the contamination from the materials stored in the Ottoman Archives.
[en] Human skin is the largest organ of the body accounting for approximately 16% of the total bodyweight. Skin is readily exposed to ionizing radiation during either accidental or intentional exposure such as radiotherapy or other medical procedures because it constitutes the interface between environment and internal organs. Estimation of accurate entrance skin dose and maximum absorbed dose (MAD) is crucial to prevent serious skin injuries. Cutaneous Radiation Syndrome (CRS) is defined by a number of pathological changes manifested in the skin and severity of these changes depend on Liner Energy Transfer (LET), dose, dose-rate, geometry of exposure and volume of body part exposed. In most of the radiological accident scenarios, reconstructive dosimetry in the skin has been performed using physical (thermoluminescence and optical stimulated luminescence), biological (cytogenetics) and computational methods/models to manage radiation exposed victims.Results of the cytogenetic testing performed at the CBL on a few patients will be discussed to illustrate the potential use of DCA and other cytogenetic techniques such as micronuclei and multicolor FISH in monitoring the health of radiotherapy patients
[en] Full text of publication follows. Aim: intravenous administration of Re-186 hydroxyethylidene-diphosphonate (HEDP) is used for metastatic bone pain palliation in hormone refractory prostate cancer patients. Dosimetry for bone seeking radionuclides is challenging due to the complex structure with osteoblastic, osteolytic and mixed lesions. The aim of this study was to perform image-based patient-specific 3D convolution dosimetry to obtain a distribution of the absorbed doses to each lesion and estimate inter- and intra-patient variations. Materials and methods: 28 patients received a fixed 5 GBq activity of Re-186 HEDP followed by peripheral blood stem cell rescue at 14 days in a phase II trial. A FORTE dual-headed gamma camera was used to acquire sequential Single-Photon-Emission Computed Tomography (SPECT) data of the thorax and pelvis area at 1, 4, 24, 48 and 72 hours following administration. The projection data were reconstructed using filtered-back projection and were corrected for attenuation and scatter. Voxelised cumulated activity distributions were obtained with two different methods. First, the scans were co-registered and the time-activity curves were obtained on a voxel-by-voxel basis. Second, the clearance curve was obtained from the mean number of counts in each individual lesion and used to scale the uptake distribution taken at 24 hours. The calibration factors required for image quantification were obtained from a phantom experiment. An in-house developed EGSnrc Monte Carlo code was used for the calculation of dose voxel kernels for soft-tissue and cortical/trabecular bone used to perform convolution dosimetry. Cumulative dose-volume histograms were produced and mean absorbed doses calculated for each spinal and pelvic lesion. Results: preliminary results show that the lesion mean absorbed doses ranged from 25 to 55 Gy when the medium was soft tissue and decreased by 40% if bone was considered. The use of the cumulated activity distribution obtained from the scan acquired at 24 hours following administration reduced the number of artefacts introduced by the registration and voxelised cumulated activity calculations. Conclusion: patient-specific convolution dosimetry calculations show that the absorbed dose to each lesion changes significantly depending on the medium density considered. This suggests that specific lesion and surrounding tissue compositions should be considered to overcome the limitations of convolution dosimetry, which could explain the range of absorbed doses observed. Future work will include the correlation of absorbed dose with patient outcome. (authors)
[en] The main purpose of our study is to set up a reproducible irradiation protocol in which the absorbed dose delivered to the prostate is well known and constant. The X-ray unit used for experimental irradiation is the Faxitron CP-160 (nominal X-ray tube voltage: 160 kV). Two kinds of approaches are considered. First, an experimental measurement of the absorbed dose delivered to the prostate of a mouse. Absorbed dose measurements were performed by the use of Lif:Mg,Ti thermoluminescent dosimeters (TLD) with a sensitive range between 50 μGy and 500 Gy. Secondly, absorbed dose calculation via Monte-Carlo modelling of radiation transport and energy deposition
[en] This 2 days workshop organized for the members of the L.A.R.D. (Associated Laboratories of Radio-physics and Dosimetry) gave them the opportunity to review their most recent research in radio-physics, radio biology and dosimetry. This document gathers 6 papers. The first one is dedicated to the presentation of the activities of the CENBG (Nuclear laboratory of Bordeaux-Gradignan) center where the meeting took place. The common purpose that links all the papers is a better knowledge of the radiation doses
[en] Purpose: Dosimetric quantities such as the polarity correction factor (Ppol) are important parameters for determining the absorbed dose and can influence the choice of dosimeter. Ppol has been shown to depend on beam energy, chamber design, and field size. This study is to investigate the field size and detector orientation dependence of Ppol in small fields for several commercially available micro-chambers. Methods: We evaluate the Exradin A26, Exradin A16, PTW 31014, PTW 31016, and two prototype IBA CC-01 micro-chambers in both horizontal and vertical orientations. Measurements were taken at 10cm depth and 100cm SSD in a Wellhofer BluePhantom2. Measurements were made at square fields of 0.6, 0.8, 1.0, 1.2, 1.4, 2.0, 2.4, 3.0, and 5.0 cm on each side using 6MV with both ± 300VDC biases. PPol was evaluated as described in TG-51, reported using −300VDC bias for Mraw. Ratios of PPol measured in the clinical field to the reference field are presented. Results: A field size dependence of Ppol was observed for all chambers, with increased variations when mounted vertically. The maximum variation observed in PPol over all chambers mounted horizontally was <1%, and occurred at different field sizes for different chambers. Vertically mounted chambers demonstrated variations as large as 3.2%, always at the smallest field sizes. Conclusion: Large variations in Ppol were observed for vertically mounted chambers compared to horizontal mountings. Horizontal mountings demonstrated a complicated relationship between polarity variation and field size, probably relating to differing details in each chambers construction. Vertically mounted chambers consistently demonstrated the largest PPol variations for the smallest field sizes. Measurements obtained with a horizontal mounting appear to not need significant polarity corrections for relative measurements, while those obtained using a vertical mounting should be corrected for variations in PPol.