ABSTRACT
There is a need to calculate specific absorbed fractions (SAFs) in voxel phantoms for internal dosimetry. For this purpose, an EGS4 user code for calculating SAFs using voxel phantoms was developed on the basis of an existing EGS4 user code for external dosimetry (UCPIXEL). In the developed code, the transport of photons, electrons and positrons in voxel phantoms can be simulated, particularly the transport simulations of secondary electrons in voxel phantoms. The evaluated SAFs for the GSF 'Child' voxel phantom using the developed code were found to be in good agreement with the GSF evaluated data. In addition, SAFs in adult voxel phantoms developed at JAERI were evaluated using the developed code and were compared with several published data. It was found that SAFs for organ self-absorption depend on the organ masses and would be affected by differences in the structure of the human body.
Subject(s)
Models, Biological , Models, Statistical , Radioisotopes/analysis , Radioisotopes/pharmacokinetics , Whole-Body Counting/methods , Whole-Body Counting/standards , Absorption , Computer Simulation , Female , Humans , Japan , Male , Monte Carlo Method , Organ Specificity , Phantoms, Imaging , Radiation Dosage , Reproducibility of Results , Sensitivity and Specificity , Tomography, X-Ray Computed/methodsABSTRACT
Absorbed dose to tooth enamel was examined against external photon exposure by measurements with thermoluminescence dosemeters (TLDs) and Monte Carlo calculations. TLDs were placed in a realistic physical phantom to measure dose to the teeth region in a head. A voxel-type phantom was constructed from computed tomography (CT) images of the physical phantom. Monte Carlo calculations with this voxel-type phantom were performed to analyse the results of the experiments. The data obtained were compared to the enamel doses, which were calculated with a modified MIRD-type phantom and already given in a previous paper. It was confirmed that the data derived with the MIRD-type phantom are applicable for retrospective individual dose assessments by electron spin resonance (ESR) dosimetry using teeth for the photon energy region above 300 keV. The analysis, however, indicated that the configuration of the head can affect the enamel dose relative to external exposure to photons with energy below 100 keV.
Subject(s)
Dental Enamel/radiation effects , Gamma Rays , Thermoluminescent Dosimetry/methods , Calibration , Cesium Radioisotopes , Cobalt Radioisotopes , Dose-Response Relationship, Radiation , Electron Spin Resonance Spectroscopy , Equipment Design , Humans , Male , Monte Carlo Method , Phantoms, Imaging , Polyurethanes , Radiation Dosage , Skull , Thermoluminescent Dosimetry/instrumentation , Tomography, X-Ray ComputedABSTRACT
Computational human phantoms have been widely used to estimate organ doses and other dosimetric quantities related to the human body where direct measurements are difficult to perform. In recent years, voxel phantoms (voxel = volume element) based on computed tomographic (CT) data of real persons have been constructed which provide a realistic description of the human anatomy. A CT phantom of a Japanese male adult with an average body size was developed as the first Asian voxel phantom. The segmented phantom consists of more than 100 regions enabling the calculation of doses for various parts of the body. The bone marrow distribution was precisely modelled according to the CT values. The EGS4 Monte Carlo transport code was combined with the phantom to calculate organ doses for external exposure due to photons and electrons up to 1 TeV. The calculated organ doses were compared with respective data using MIRD-type mathematical phantoms. In some cases, significant discrepancies in doses were observed, demonstrating the necessity of sophisticated models for accurate dose calculations.
Subject(s)
Phantoms, Imaging , Radiation Dosage , Tomography, X-Ray Computed , Adult , Asian People , Electrons , Humans , Japan , Male , Monte Carlo Method , PhotonsABSTRACT
BL191, a newly developed phosphodiesterase inhibitor, markedly potentiated a differentiation of neuroblastoma cell clones (Neuro2a, NS-20Y, and N1E115) induced by dibutyryl cyclic adensoine 3?:5?-monophosphate(dibutyryl cAMP) and prostaglandin E(1) (PGE(1)). BL191 (1 mM) inhibited DNA synthesis more strongly when used together with PGE(1) (0.5 ?g/ml) and dibutyryl cAMP (0.5 mM) than papaverine (1.6 ?g/ml) alone did. The inhibition rates of DNA synthesis were 72.5% for N1E-115, 75.3% for Neuro2a, and 82.5% for NS-20Y. After the treatment with BL191. PGE(1), and dibutyryl cAMP for 48 h all of three cell lines became enlarged and flattened, and extended long processes. The specific activities of choline acetyl transferase (EC 2.3.1.9) of NS-20Y and dopamine ?-hydroxylase (EC 1.14.17.1) of N1E-115 increased about 3-fold as compared to the controls. The tumorigenicities of Neuro2a and N1E-115 cells were decreased, but not of NS-20Y. These data suggest the heterogenous responsiveness in neuroblastoma cells to drug treatment.
