Studies on tetanus toxin and toxoid. I. Isolation of tetanus toxin using DEAE-cellulose.
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Amino Acids↗
Biomedical subjects
D J Dawson
Publications and source records attributed to D J Dawson.
Tissue-maximum ratios for high-energy x rays.
The tissue-maximum ratios for high-energy betatron x rays, measured at target-axis distances of 90, 110, and 130 cm, exhibit a strong dependence on the target-axis distance in the buildup region as well as a significant dependence in the exponential region. This dependence and the field-size dependence of the tissue-maximum ratios at a fixed target-axis distance are studied with the use of phantom and collimator scatter factors. The depth and field-size dependence of these scatter factors are determined experimentally. The measurements indicate that the collimator scatter factor is dependent on both the collimator opening and the targetaxis distance. These components are quantitated separately and are associated primarily with high-energy electron scatter from the collimating system. An equation involving these components of the collimator scatter factor is derived for the conversion of tissue-maximum ratios from one target-axis distance to another. With the use of this equation, the tissue-maximum ratios measured for one target-axis distance can be used to calculate within 1% those at other target-axis distances.
Particle Accelerators↗
Elongation effects on the Therac 6 linear accelerator.
The effects of field elongation on the central-axis output at dmax and on the depth-dose curves for the 6-MV x rays from the Therac 6 linear accelerator are considered. These parameters are independent of the collimator angle for both square and elongated fields. The exchange of collimator pairs results in significant output differences but has a negligible effect on the depth-dose curves. Both the central-axis output at dmax and the depth-dose curves agree satisfactorily with the predictions of the equivalent-square technique. An alternative method of greater accuracy is also indicated for the prediction of central-axis outputs at dmax for elongated fields.
Humans↗
Analysis of physical parameters associated with the measurement of high-energy x-ray penumbra.
The effect of dosemeter type and configuration on the measured penumbral distribution for Co-60, 6-MV, and 31-MV x rays has been determined in air using equilibrium buildup caps for three commercial detection systems including a silicon diode and two ionization chambers. The diode is shown to be measuring a different parameter in the penumbral region than the ionization chambers. This fact in combination with the lateral spread of the secondary electrons and the difference in the inside diameters of the ionization chambers results in significant differences between the measured beam penumbra. The latter effect is studied in more detail with a series of specially designed ionization chambers of varying inside diameter from 0.3 to 1.4 cm. A theoretical model is described which resolves these differences, indicates a method to determine the true penumbral primary-dose distribution and introduces the concept of an effective diameter for the ionometric measurement of high-energy x-ray penumbra. Recommendations are made concerning the dosemeters of choice for penumbral measurements over this range of photon energies.
Cobalt Radioisotopes↗
A statistical analysis of ionometrically measured 6-MV x-ray beam parameters.
A statistical analysis has been made of ionometrically measured parameters related to the central-axis output, the beam symmetry, the beam flatness, and the depth dose for the 6-MV x-ray beam from the Therac-6 linear accelerator. The means and coefficients of variation of the measurements are determined on a monthly basis for each parameter. Mean coefficients of variation less than +/- 1% have been determined and are useful in establishing the optimal limits of acceptance of these parameters. The results of this study indicate that the long-term stability of the radiation parameters associated with this unit can be maintained within acceptable limits with a consistent quality-assurance program.
Humans↗
Characteristics of cobalt-60 penumbral regions.
Ionization chambers with wall materials of various electron densities have been employed to investigate the penumbral region of a cobalt-60 beam of side length 10 cm. Measurements were made in air with chambers of various inside diameters. The homogeneous walls of the ionization chambers were 0.5 g/cm2 in thickness. Extrapolation techniques to zero inside diameter and to infinite density were used, respectively, to eliminate the effect of the inside diameter of the chamber and to determine the penumbral photon-fluence distribution. The method also quantitates both the penumbral primary-dose profiles in water-equivalent media and the degradation of these profiles in media of low electron density.
Cobalt Radioisotopes↗
Analysis of utilization-related parameters on a 6-MV linear accelerator.
An analysis of unscheduled downtime and of patient treatment data for a 6-MV linear accelerator is presented for a 7-yr period. Following the initial year of clinical use, the unscheduled downtime has averaged 2.4%, with a corresponding loss of 1.3% in patient treatments. The quality assurance, preventive maintenance, and repairs are handled in-house, with an investment of approximately 500 man-hours annually.
Humans↗
Penumbral measurements in water for high-energy x rays.
Ionization chambers of varying inside diameter have been used to investigate the penumbral region of 60Co, 6-MV, and 31-MV x-ray beams. Measurements were made in water at varying depths up to 25 cm for a square field of side length 10 cm. The dependence of the penumbral widths on both the inside diameter of the ionization chamber and the depth in water is established along with the asymmetry of the penumbral distributions about the 50% level. A standard correction is indicated to eliminate the dependence of the measured penumbral widths on the inside diameter of the ionization chamber.
Cobalt Radioisotopes↗
Analysis of Mycobacterium avium complex serovars isolated from AIDS patients from southeast Brazil.
The purpose of this study was to assess the distribution of Mycobacterium avium serovars isolated from AIDS patients in São Paulo and Rio de Janeiro. Ninety single site or multiple site isolates from 75 patients were examined. The most frequent serovars found were 8 (39.2%), 4 (21.4%) and 1 (10.7%). The frequency of mixed infections with serovar 8 or 4 was 37.8%. Among the 90 strains examined, M. intracellulare serovars (7 strains) and M. scrofulaceum (4 strains) were found in 11 isolates (12%) indicating that M. avium (88%) was the major opportunistic species in the M. avium complex isolates in Brazilian AIDS patients.
AIDS-Related Opportunistic Infections↗