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141.
G.E. Neal A.R. Mattocks D.J. Judah 《Biochimica et Biophysica Acta (BBA)/General Subjects》1979,585(1):134-142
The activation by rat liver microsomal systems in vitro of a naturally occurring and a synthetic furan-containing toxin, aflatoxin B1 and 2-(N-ethylcarbamoyloxymethyl)furan (CMF) has been examined. Both compounds are metabolised to form products which bind covalently to DNA and microsomal protein, Using a specially designed two-chamber diffusion apparatus it has been demonstrated that the active metabolite of CMF is able to bind covalently to DNA separated by a membrane barrier from the microsomal site of activation. In the case of aflatoxin B1 the DNA must be in physical contact with the microsomal system for the active metabolite of aflatoxin B1 to bind covalently. Differences between the activation of the two compounds have also been found with regard to their relative efficiencies in binding to DNA and also the effects of the nucleophile GSH. These results have suggested that if the molecular mechanisms of activation of the two compounds be similar, other factors, for example differences in lipid solubility, may play important roles in determining the relative biological activaties of the compounds. The results suggested that the subcellular site of activation of aflatoxin B1, unlike that of CMF, may need to be adjacent to the target DNA. It is proposed that this site might be the outer nuclear membrane. Alternatively a carrier molecular might exist for the activated aflatoxin B1 metabolite in vivo. 相似文献
142.
PurposeThis study optimized our previously proposed simulation program for the approximate irregular field dose distribution (SPAD) and applied it to a respiratory motion compensation system (RMCS) and respiratory motion simulation system (RMSS). The main purpose was to rapidly analyze the two-dimensional dose distribution and evaluate the compensation effect of the RMCS during radiotherapy.MethodsThis study modified the SPAD to improve the rapid analysis of the dose distribution. In the experimental setup, four different respiratory signal patterns were input to the RMSS for actuation, and an ultrasound image tracking algorithm was used to capture the real-time respiratory displacement, which was input to the RMCS for actuation. A linear accelerator simultaneously irradiated the EBT3 film. The gamma passing rate was used to verify the dose similarity between the EBT3 film and the SPAD, and conformity index (CI) and compensation rate (CR) were used to quantify the compensation effect.ResultsThe Gamma passing rates were 70.48–81.39% (2%/2mm) and 88.23–96.23% (5%/3mm) for various collimator opening patterns. However, the passing rates of the SPAD and EBT3 film ranged from 61.85% to 99.85% at each treatment time point. Under the four different respiratory signal patterns, CR ranged between 21% and 75%. After compensation, the CI for 85%, 90%, and 95% isodose constraints were 0.78, 0.57, and 0.12, respectively.ConclusionsThis study has demonstrated that the dose change during each stage of the treatment process can be analyzed rapidly using the improved SPAD. After compensation, applying the RMCS can reduce the treatment errors caused by respiratory movements. 相似文献
143.
There is a paucity of literature comparing patient and staff dose during coronary angiography (CA), implantable cardiac devices, permanent pacemakers (PPM) and electrophysiology (EP) procedures and little noting dose to staff other than cardiologists. This study sought to compare patient and occupational dose during a range of fluoroscopically guided cardiac procedures. Radiation dose levels for the patients (n = 1651), cardiologists (n = 24), scrub (n = 32) and scout nurses (n = 35) were measured in a prospective single-centre study between February 2017 and August 2019. A comparison of dose during CA, device implantation, PPM insertion and EP studies was performed. Three angiographic units were used, with dosimeters worn on the temple of staff. Results indicated that occupational dose during PPM was significantly higher than other procedures. The cardiologist had the highest mean dose during biventricular implantable cardioverter-defibrillators; levels were approximately five times that of ‘normal’ pacemaker insertions. Transcatheter aortic valve implantations (TAVI) were associated with relatively high mean doses for both staff and patients and had a statistically significant higher (>2 times) mean patient dose area product than all other categories. TAVI workups were also related to higher mean cardiologist and scrub nurse dose. It was observed that the mean scrub nurse dose can exceed that of the cardiologist. The highest mean dose for Scout nurses were recorded during EP studies. Given the significantly higher temple dose associated with PPM insertion, cardiologists should consider utilizing ceiling mounted lead shields, lead glasses and/or skull caps where possible. Efforts should also be made to minimize the use of DSA during TAVI and TAVI workups to reduce cardiologist, nurse and patient dose. 相似文献
144.
It is widely recognized that endocrine disrupting compounds, such as Bisphenol A, pose challenges for traditional paradigms in toxicology, insofar as these substances appear to have a wider range of low‐dose effects than previously recognized. These compounds also pose challenges for ethics and policymaking. When a chemical does not have significant low‐dose effects, regulators can allow it to be introduced into commerce or the environment, provided that procedures and rules are in place to keep exposures below an acceptable level. This option allows society to maximize the benefits from the use of the chemical while minimizing risks to human health or the environment, and it represents a compromise between competing values. When it is not possible to establish acceptable exposure levels for chemicals that pose significant health or environmental risks, the most reasonable options for risk management may be to enact either partial or complete bans on their use. These options create greater moral conflict than other risk management strategies, leaving policymakers difficult choices between competing values. 相似文献
145.
Paul M. O Neill Paul A. Stocks Sunil Sabbani Natalie L. Roberts Richard K. Amewu Emma R. Shore Ghaith Aljayyoussi I?igo Angulo-Barturén María Belén Santiago Ferrer Bazaga María Santos Martínez Brice Campo Raman Sharma Susan A. Charman Eileen Ryan Gong Chen David M. Shackleford Stephen A. Ward 《Bioorganic & medicinal chemistry》2018,26(11):2996-3005
A series of aryl carboxamide and benzylamino dispiro 1,2,4,5-tetraoxane analogues have been designed and synthesized in a short synthetic sequence from readily available starting materials. From this series of endoperoxides, molecules with in vitro IC50s versus Plasmodium falciparum (3D7) as low as 0.84?nM were identified. Based on an assessment of blood stability and in vitro microsomal stability, N205 (10a) was selected for rodent pharmacokinetic and in vivo antimalarial efficacy studies in the mouse Plasmodium berghei and Plasmodium falciparum Pf3D70087/N9 severe combined immunodeficiency (SCID) mouse models. The results indicate that the 4-benzylamino derivatives have excellent profiles with a representative of this series, N205, an excellent starting point for further lead optimization studies. 相似文献
146.
Annamaria Didona Valentina Lancellotta Claudio Zucchetti Bianca Moira Panizza Alessandro Frattegiani Martina Iacco Anna Concetta Di Pilato Simonetta Saldi Cynthia Aristei 《Reports of Practical Oncology and Radiotherapy》2018,23(3):175-182
Background
Intensity-modulated radiotherapy (IMRT) improves dose distribution in head and neck (HN) radiation therapy. Volumetric-modulated arc therapy (VMAT), a new form of IMRT, delivers radiation in single or multiple arcs, varying dose rates (VDR-VMAT) and gantry speeds, has gained considerable attention. Constant dose rate VMAT (CDR-VMAT) associated with a fixed gantry speed does not require a dedicated linear accelerator like VDR-VMAT. The present study explored the feasibility, efficiency and delivery accuracy of CDR-VMAT, by comparing it with IMRT and VDR-VMAT in treatment planning for HN cancer.Methods and materials
Step and shoot IMRT (SS-IMRT), CDR-VMAT and VDR-VMAT plans were created for 15 HN cancer patients and were generated by Pinnacle3 TPS (v 9.8) using 6 MV photon energy. Three PTVs were defined to receive respectively prescribed doses of 66 Gy, 60 Gy and 54 Gy, in 30 fractions. Organs at risk (OARs) included the mandible, spinal cord, brain stem, parotids, salivary glands, esophagus, larynx and thyroid. SS-IMRT plans were based on 7 co-planar beams at fixed gantry angles. CDR-VMAT and VDR-VMAT plans, generated by the SmartArc module, used a 2-arc technique: one clockwise from 182° to 178° and the other one anti-clockwise from 178° to 182°. Comparison parameters included dose distribution to PTVs (Dmean, D2%, D50%, D95%, D98% and Homogeneity Index), maximum or mean doses to OARs, specific dose-volume data, the monitor units and treatment delivery times.Results
Compared with SS-IMRT, CDR-VMAT significantly reduced the maximum doses to PTV1 and PTV2 and significantly improved all PTV3 parameters, except D98% and D95%. It significantly spared parotid and submandibular glands and was associated with a lower Dmean to the larynx. Compared with VDR-VMAT, CDR-VMAT was linked to a significantly better Dmean, to the PTV3 but results were worse for the parotids, left submandibular gland, esophagus and mandible. Furthermore, the Dmean to the larynx was also worse. Compared with SS-IMRT and VDR-VMAT, CDR-VMAT was associated with higher average monitor unit values and significantly shorter average delivery times.Conclusions
CDR-VMAT appeared to be a valid option in Radiation Therapy Centers that lack a dedicated linear accelerator for volumetric arc therapy with variable dose-rates and gantry velocities, and are unwilling or unable to sanction major expenditure at present but want to adopt volumetric techniques. 相似文献147.
Hediye Acun-Bucht Ebru Tuncay Emin Darendeliler Gönül Kemikler 《Reports of Practical Oncology and Radiotherapy》2018,23(4):242-250
Aim
This study aims at examining absolute dose verification of step-and-shoot intensity modulated radiation treatment (IMRT) of prostate and brain patients by use of ion chambers of two different volumes and thermoluminescent detectors (TLD).Background
The volume of the ion chamber (IC) is very important for absolute dose verification of IMRT plans since the IC has a volume average effect. With TLD detectors absolute dose verification can be done measuring the dose of multiple points simultaneously.Materials and methods
Ion chambers FC65-P of volume 0.65 cc and semiflex of volume 0.125 cc as well as TLDs were used to measure the central axis absolute dose of IMRT quality assurance (QA) plans. The results were compared with doses calculated by a treatment planning system (TPS). The absolute doses of off axis points located 2 cm and 4 cm away from the isocenter were measured with TLDs.Results
The measurements of the 0.125 cc ion chamber were found to be closer to TPS calculations compared to the 0.65 cc ion chamber, for both patient groups. For both groups the root mean square (RMS) differences between doses of the TPS and the TLD detectors are within 3.0% for the central axis and points 2 cm away from the isocenter of each axis. Larger deviations were found at the field edges, which have steep dose gradient.Conclusions
The 0.125 cc ion chamber measures the absolute dose of the isocenter more accurately compared to the 0.65 cc chamber. TLDs have good accuracy (within 3.0%) for absolute dose measurements of in-field points. 相似文献148.
Aim
In this study, at different fields, energies and gantry angles, treatment couch and rails dose absorption ratio and treatment couch effect on surface and build-up region doses were examined.Background
It is assumed that radiation attenuation is minimal because the carbon fiber couches have low density and it is not generally accounted for during treatment planning. Consequently, it leads to a major dosimetric mistake.Materials and methods
Solid water phantom was used for relative dose measurement. The measurements were done using a Farmer ion chamber with 0.6 cc volume and a parallel plane ion chamber starting from surface with 1 mm depth intervals at 10 × 10 cm2 field, SSD 100 cm. Measurements were taken for situations where the beams intersect the couch and couch rails.Results
Dose absorption ratio of carbon fiber couch obtained at gantry angle of 180° was 1.52%, 0.69%, 0.33% and 0.25% at different field sizes for 6 MV. For 15 MV, this ratio was 0.95%, 0.27%, 0.20% and 0.05%. The absorption ratio is between 3.4% and 1.22% when the beams intersect with couch rails. The couch effect increased surface dose from 14% to 70% for 6 MV and from 11.34% to 53.03% for 15 MV.Conclusions
The results showed that the carbon fiber couch increased surface dose during posterior irradiation. Therefore, the skin-sparing effect of the high energy beams was decreased. If the effect of couch is not considered, it may cause significant differences at dose which reaches the patient and may cause tissue problems such as erythema. 相似文献149.
Chao Fang Katie K. Lee Raymond Nietupski Robert H. Bates Raquel Fernandez-Menendez Eva Maria Lopez-Roman Laura Guijarro-Lopez Yunxing Yin Zuozhong Peng James E. Gomez Stewart Fisher David Barros-Aguirre Brian K. Hubbard Michael H. Serrano-Wu Deborah T. Hung 《Bioorganic & medicinal chemistry letters》2018,28(22):3529-3533
Previous work established a coumarin scaffold as a starting point for inhibition of Mycobacterium tuberculosis (Mtb) FadD32 enzymatic activity. After further profiling of the coumarin inhibitor 4 revealed chemical instability, we discovered that a quinoline ring circumvented this instability and had the advantage of offering additional substitution vectors to further optimize. Ensuing SAR studies gave rise to quinoline-2-carboxamides with potent anti-tubercular activity. Further optimization of ADME/PK properties culminated in 21b that exhibited compelling in vivo efficacy in a mouse model of Mtb infection. 相似文献
150.
PurposeTo compare, via Monte Carlo simulations, homogeneous and non-homogenous breast models adopted for mean glandular dose (MGD) estimates in mammography vs. patient specific digital breast phantoms.MethodsWe developed a GEANT4 Monte Carlo code simulating four homogenous cylindrical breast models featured as follows: (1) semi-cylindrical section enveloped in a 5-mm adipose layer; (2) semi-elliptical section with a 4-mm thick skin; (3) semi-cylindrical section with a 1.45-mm skin layer; (4) semi-cylindrical section in a 1.45-mm skin layer and 2-mm subcutaneous adipose layer. Twenty patient specific digital breast phantoms produced from a dedicated CT scanner were assumed as reference in the comparison. We simulated two spectra produced from two anode/filter combinations. An additional digital breast phantom was produced via BreastSimulator software.ResultsWith reference to the results for patient-specific breast phantoms and for W/Al spectra, models #1 and #3 showed higher MGD values by about 1% (ranges [–33%; +28%] and [−31%; +30%], respectively), while for model #4 it was 2% lower (range [−34%; +26%]) and for model #2 –11% (range [−39%; +14%]), on average. On the other hand, for W/Rh spectra, models #1 and #4 showed lower MGD values by 2% and 1%, while for model #2 and #3 it was 14% and 8% lower, respectively (ranges [−43%; +13%] and [−41%; +21%]). The simulation with the digital breast phantom produced with BreastSimulator showed a MGD overestimation of +33%.ConclusionsThe homogeneous breast models led to maximum MGD underestimation and overestimation of 43% and 28%, respectively, when compared to patient specific breast phantoms derived from clinical CT scans. 相似文献