The present study is aimed at exploring different scanning parameters, detectors and their orientations for time-efficient and accurate commissioning of a 6 MV clinical linear accelerator (LINAC). Beam profiles and percentage depth dose (PDD) curves were measured with a PTW dosimetry diode, a PTW Semiflex and a PinPoint ion chamber in different orientations. To acquire beam data, equidistant (step size of 0.5 mm, 1 mm, 2 mm and 3 mm) and fanline (step size of 2–0.5 mm, 2–1 mm, 3–0.5 mm and 3-1 mm) scanning modes were employed and data measurement time was recorded. Scan time per measurement point was also varied (0.2 s, 0.5 s and 1.0 s) to investigate its effect on the accuracy and acquisition time of beam data. Accuracy of the measured data was analyzed on the basis of the variation between measured data and data modeled by a treatment planning system. Beam profiles (particularly in penumbra region) were found to be sensitive to variation in scanning resolution and showed an improved accuracy with decrease in step size, while PDD curves were affected negligibly. The accuracy of beam data obtained with the PTW dosimetry diode and the PinPoint ion chamber was higher than those obtained with the PTW Semiflex ion chamber for small fields (2?×?2 cm2 and 3?×?3 cm2). However, the response of the PTW diode and the PinPoint ion chamber was significantly indifferent in these fields. Furthermore, axial orientation of the PTW Semiflex ion chamber improved accuracy of profiles and PDDs as compared to radial orientation, while such a difference was not significant for the PinPoint ion chamber. It is concluded that a scan time of 0.2 s/point with a fanline scanning resolution of 2–1 mm for beam profiles and 3 mm for PDDs are most favorable in terms of accuracy and time efficiency. For small fields (2?×?2 cm2 and 3?×?3 cm2), a PinPoint ion chamber in radial orientation or a dosimetry diode in axial orientation are recommended for both beam profiles and PDDs. If a PinPoint ion chamber and a PTW dosimetry diode are not available, a Semiflex ion chamber in axial orientation may be used for small fields.
We have investigated the effects of Ca2+ diffusion, mobile and stationary Ca2+ buffers in the cytosol, and Ca2+ handling by the endoplasmic reticulum on inositol 1,4,5-trisphosphate-induced Ca2+ wave propagation. Rapid equilibration of free and bound Ca2+ is used to describe Ca2+ sequestration by buffers in both the cytosol and endoplasmic reticulum (ER) lumen. Cytosolic Ca2+ regulation is based on a kinetic model of the inositol 1,4,5-trisphosphate (IP3) receptor of De Young and Keizer that includes activation and inhibition of the IP3 receptor Ca2+ channel in the ER membrane and SERCA Ca2+ pumps in the ER. Diffusion of Ca2+ in the cytosol and the ER and the breakdown and diffusion of IP3 are also included in our calculations. Although Ca2+ diffusion is severely limited because of buffering, when conditions are chosen just below the threshold for Ca2+ oscillations, a pulse of IP3 or Ca2+ results in a solitary trigger wave that requires diffusion of Ca2+ for its propagation. In the oscillatory regime repetitive wave trains are observed, but for this type of wave neither the wave shape nor the speed is strongly dependent on the diffusion of Ca2+. Local phase differences lead to waves that are predominately kinematic in nature, so that the wave speed (c) is related to the wavelength (lambda) and the period of the oscillations (tau) approximately by the formula c = lambda/tau. The period is determined by features that control the oscillations, including [IP3] and pump activity, which are related to recent experiments. Both solitary waves and wave trains are accompanied by a Ca2+ depletion wave in the ER lumen, similar to that observed in cortical preparations from sea urchin eggs. We explore the effect of endogenous and exogenous Ca2+ buffers on wave speed and wave shape, which can be explained in terms of three distinct effects of buffering, and show that exogenous buffers or Ca2+ dyes can have considerable influence on the amplitude and width of the waves. 相似文献
Gentamicin is a very useful antimicrobial agent for the treatment of serious infections caused by gram-negative bacteria. However, it's low therapeutic index and potential ototoxic and nephrotoxic side effects necessitate frequent determinations of serum concentration to assist in maintaining therapeutic levels and avoiding toxic levels. Two bioassays and a latex agglutination inhibition card (LAIC) test were evaluated to determine gentamicin levels in nearly 100 patient sera. Results were compared with a radioimmunoassay (RIA). Two bioassays, the Bio-Monitor and the GentaSak, gave correlation coefficients of 0.987 and 0.982, respectively. The correlation coefficient for the LAIC test was 0.987. All three tests compared well with RIA in accurately detecting gentamicin levels in patient as well as simulated sera. The LAIC test, however, was more rapid, giving results within half an hour whereas bioassays required 6–8 hours for completion. The LAIC test was also found to be more economical. It provides a suitable alternative to RIA procedures in small laboratories and for performing stat tests since batching is not necessary. 相似文献
A procedure has been developed for transforming protoplasts of the novobiocin producing strain Streptomyces niveus at high frequency. This required the isolation of strains LH13 and LH20 defective in DNA restriction from the wild type (ATCC 19793) which is transformed at very low frequencies. The LH13 and LH20 derivatives were obtained by curing pIJ702 DNA from the few S. niveus transformed protoplasts obtained by transformation of the wild type with high concentrations of pIJ702 DNA. Protoplasts of S. niveus strains LH13 and LH20 produced about 10(6) transformants/micrograms DNA with modified pIJ702 DNA derived by replication in S. niveus. Unmodified DNA (derived from replication in S: lividans) from a series of pIJ101, SCP2 and pSN2-based derivatives, gave transformation frequencies in the range of 10(2)-10(3) transformants/micrograms DNA. Optimal conditions for the formation and transformation of S. niveus protoplasts are described. 相似文献
A sensitive, specific and reproducible high-performance liquid chromatographic technique is described for the simultaneous determination in human plasma of diltiazem (DZ) and six of its primary and secondary metabolites which are products of N- and O-demethylation, deacetylation and N-oxidation. The method involves addition of excess KHCO3 to 1 ml of plasma, followed by extraction with 4 ml of ethyl acetate. The organic layer was extracted with 0.01 M HCl and the aqueous layer was dried under nitrogen and then reconstituted with 0.002 M HCl. DZ and its metabolites were free from interference and were baseline-separated. Calibration curves were linear in the concentration range studied (5–500 ng/ml for all the species). The lower limit of quantification of the assay was 5 ng/ml for DZ and the metabolites. Inter-day and intra-day coefficients of variation were less than 10%. The applicability of this procedure is shown by evaluating the kinetics of DZ and its metabolites in three patients receiving chronic DZ therapy. N-Demethyldiltiazem, deacetyldiltiazem and N-demethyldeacetyldiltiazem were found to be the major metabolites, as previously described. Deacetyldiltiazem N-oxide was found in two of the patients. The other two known but unreported metabolites in human, O-demethyldeacetyldiltiazem and N,O-didemethyldeacetyldiltiazem, were found in the plasma of all three patients. 相似文献
To assess the effect of diaphragmatic ischemia on the inspiratory motor drive, we studied the in situ isolated and innervated left diaphragm in anesthetized, vagotomized, and mechanically ventilated dogs. The arterial and venous vessels of the left diaphragm were catheterized and isolated from the systemic circulation. Inspiratory muscle activation was assessed by recording the integrated electromyographic (EMG) activity of the left and right costal diaphragms and parasternal intercostal and alae nasi muscles. Tension generated by the left diaphragm during spontaneous breathing attempts was also measured. In eight animals, left diaphragmatic ischemia was induced by occluding the phrenic artery for 20 min, followed by 10 min of reperfusion. This elicited a progressive increase in EMG activity of the left and right diaphragms and parasternal and alae nasi muscles to 170, 157, 152, and 128% of baseline values, respectively, an increase in the frequency of breathing efforts, and no change in left diaphragmatic spontaneous tension. Thus the ratio of left diaphragmatic EMG to tension rose progressively during ischemia. During reperfusion, only the frequency of breathing efforts and alae nasi EMG recovered completely. In four additional animals, left diaphragmatic ischemia was induced after the left phrenic nerve was sectioned. Neither EMG activity of inspiratory muscles nor respiratory timing changed significantly during ischemia. In conclusion, diaphragmatic ischemia increases inspiratory motor drive through activation of phrenic afferents. The changes in alae nasi activity and respiratory timing indicate that this influence is achieved through supraspinal pathways. 相似文献
Ventilation and electromyogram (EMG) activities of the right hemidiaphragm, parasternal intercostal, triangularis sterni, transversus abdominis, genioglossus, and alae nasi muscles were measured before and during central stimulation of the left thoracic phrenic nerve in 10 alpha-chloralose anesthetized vagotomized dogs. Pressure in the carotid sinuses was fixed to maintain baroreflex activity constant. The nerve was stimulated for 1 min with a frequency of 40 Hz and stimulus duration of 1 ms at voltages of 5, 10, 20, and 30 times twitch threshold (TT). At five times TT, no change in ventilation or EMG activity occurred. At 10 times TT, neither tidal volume nor breathing frequency increased sufficiently to reach statistical significance, although the change in their product (minute ventilation) was significant (P less than 0.05). At 20 and 30 times TT, increases in both breathing frequency and tidal volume were significant. At these stimulus intensities, the increases in ventilation were accompanied by approximately equal increases in the activity of the diaphragm, parasternal, and alae nasi muscles. The increase in genioglossus activity was much greater than that of the other inspiratory muscles. Phrenic nerve stimulation also elicited inhomogeneous activation of the expiratory muscles. The transversus abdominis activity increased significantly at intensities from 10 to 30 times TT, whereas the activity of the triangularis sterni remained unchanged. The high stimulation intensities required suggest that the activation of afferent fiber groups III and IV is involved in the response. We conclude that thin-fiber phrenic afferent activation exerts a nonuniform effect on the upper airway, rib cage, and abdominal muscles and may play a role in the control of respiratory muscle recruitment. 相似文献