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R J Schulz

Publications and source records attributed to R J Schulz.

At least 19 recordsLinked to original sources
PubMed1992

Water calorimeter dosimetry for 160 MeV protons.

The absorbed dose to water from a 160 MeV proton beam as determined by a flexible, temperature regulated, sealed glass core, water calorimeter was compared to that determined from ionization chambers used in accordance with AAPM Report 16. The ratios of these doses as obtained from two experiments done over four months apart, are 0.992 +/- 0.004 and 0.990 +/- 0.004. As there are no radiation dependent parameters required for the water calorimeter, these data add to the growing body of evidence which supports the use of the calorimeter as a reliable absorbed dose standard. They also support the use of 60Co-calibrated ionization chambers used in accordance with AAPM Report 16 for the dosimetry of proton beams.

Calorimetry↗
PubMed1990

The thermal defect of A-150 plastic and graphite for low-energy protons.

The thermal defects of A-150 plastic and graphite referenced to aluminium were determined for 800 keV protons scattered by a 2 micron nickel foil (mean transmitted energy = 550 keV). Composite cores of Al/A-150, graphite/A-150 and Al/graphite which could be irradiated from one side or the other were employed. The temperature increase of a core caused by 30-100 s of irradiation (3-6 nA of proton beam current) was detected by two thermistors mounted in opposite legs of a Wheatstone bridge. The thermal defect of A-150 plastic was determined to be 0.0421 +/- 0.0036 (SE) referenced to aluminium and 0.0402 +/- 0.0034 referenced to graphite. The thermal defect of graphite referenced to aluminium is 0.0043 +/- 0.0034. No change in the thermal defect of A-150 plastic was detected for accumulated doses up to 8 x 10(5) Gy.

Aluminum↗
PubMed1990

Dose-response curves for Fricke-infused agarose gels as obtained by nuclear magnetic resonance.

The radiation-response characteristics of agarose gels prepared with Fricke dosemeter solution have been studied. The response mechanism is an increase in the NMR longitudinal relaxation rate of protons caused by ferric ions. It has been observed that: (i) oxygen saturation assures consistent and maximum sensitivity; (ii) agarose concentrations in the range 1.0-2.0% have no effect upon sensitivity; (iii) the initial G value is 150 Fe3+/100 eV for gels containing 0.5 mM Fe2+ ions; (iv) increasing NMR frequencies only causes a moderate increase in sensitivity; (v) the gel dosemeters are dose rate independent in the range 4.7-24.2 Gy min-1; (vi) sensitivity is pH dependent, being zero at pH 7; (vii) freshly prepared gels are slightly more sensitive than those more than 24 h old; and (ix) the diffusion coefficient for ferric ions in a 1.0% agarose gel containing 0.0125 M H2SO4 is 1.83 x 10(-2) cm2 h-1, and this will require consideration for the NMR imaging of dose distributions.

Dose-Response Relationship, Radiation↗
PubMed1989

The dose rate dependence of the relative biological effectiveness of 241Am versus 226Ra gamma rays.

The survival of Chinese hamster cells exposed to 59.5 keV 241Am gamma rays was compared with that obtained after exposure to 226Ra gamma rays. The Fricke dosimeter in conjunction with the calculational techniques of transition-zone dosimetry was employed to determine the dose rates to the cells at the petri dish/growth medium interface. The dose rates to the cells ranged from 11 to 133 cGy/h. In all cases, cell survival versus dose was best described by a simple exponential function of dose. For both radiations, graphs of D0 versus dose rate show complex but similar patterns of peaks and valleys. As the curve for 241Am is displaced toward lower dose rates compared with that for 226Ra, the relative biological effectiveness of 241Am vs 226Ra varies considerably with dose rate, ranging from 1.7 at 20 cGy/h to 1.1 at 40 cGy/h to 1.6 at 50 cGy/h. This phenomenon may be due to the LET-dependent accumulation of cells at the G2 + M interface in the cell cycle. The mean unrestricted track-average LET of 241Am (3.7 keV/microns) is 12 times higher than that for 226Ra (0.31 keV/microns) but only one-fifth that of carbon ions (18 keV/microns) for which G2 + M pile-up is observed. Application of the in vitro data derived from this study to the clinical situation, where the dose rate decreases rapidly with distance from the source, suggests that, dose for dose, 241Am will produce results little different from those obtained with 226Ra.

Americium↗
PubMed1985

Convection currents in a water calorimeter.

A flexible, temperature-regulated water calorimeter has been constructed containing two pairs of thermistor sensors at depths of 6.23 and 10.0 cm. It may be irradiated by vertical or horizontal beams, and operated at temperatures in the range from 3 to 40 degrees C. When irradiated at 30 degrees C with a vertically downward 19 MeV electron beam, the responses of the proximal and midline thermistors were in accordance with the depth-dose curve. When irradiated horizontally, the initial patterns of temperature rise were the same, but after about 30 s (4 Gy) the rate of temperature rise decreased at the proximal thermistors and increased at the midline thermistors. Shortly after irradiation, the temperature curve and increased at the midline thermistors. Shortly after irradiation, the temperature curve of the midline thermistors crossed that for the proximal thermistors, a pattern that suggested the presence of convection currents. To test this hypothesis, the calorimeter was operated at 4 degrees C. The temperature patterns for horizontal irradiation became the same as those obtained with vertical beams, thus demonstrating the production of convection currents in water at a temperature of 30 degrees C for temperature gradients as small as 10(-3) degrees C cm-1.

Calorimetry↗
PubMed1984

Measurement of radiation dose distributions by nuclear magnetic resonance (NMR) imaging.

A method is described for determining the spatial distribution of radiation dose in a tissue-equivalent phantom using nuclear magnetic resonance imaging. The conversion of ferrous ions to ferric by ionising radiation alters the magnetic moment and electron spin relaxation times of the metal ion. The spin relaxation times (T1 and T2) of the hydrogen nuclei in an aqueous solution of a ferrous salt are consequently reduced substantially. These changes in T1 and T2 can be measured using standard NMR techniques. The same conversion is used in conventional Fricke dosimetry, which can be used to calibrate the technique.

Humans↗
PubMed1984

Failure of 5-thio-D-glucose to alter cell survival in irradiated or unirradiated EMT6 tumors.

The antineoplastic effects of the glucose analog 5-thio-D-glucose (5TG) were tested using EMT6 mouse mammary tumors in vivo and EMT6 cells in cell culture. In vitro, 5TG selectively killed hypoxic EMT6 cells. However, administration of 5TG to mice bearing EMT6 tumors produced no significant toxicity to the cells of unirradiated tumors and did not alter the survival of cells in irradiated tumors. Fasting the mice to lower blood glucose concentrations before administration of 5TG increased the toxicity of the drug to the mice, but did not allow more efficacious treatment of the tumors. The data provided no evidence that 5-thio-D-glucose can be used effectively for the treatment of solid tumors, either as a cytotoxic agent or as a radiosensitizer.

Animals↗
PubMed1984

On the specific toxicity of 5-thio-D-glucose to hypoxic cells.

The toxicity of 5-thio-D-glucose (5TG) to mammalian cells in culture has been studied with respect to oxygen tension, concentration, and temperature. At 37 degrees C and at 5 mM concentration of the drug in normal growth medium, survival is 10(-3) for 4-hr exposure to 5 ppm O2; this increases to 0.5 for 24-hr exposure to 200 ppm O2. The relationship between survival and oxygen tension is nonlinear with the greatest change occurring between 50 and 100 ppm. The drug is essentially nontoxic to aerated cells. Drug toxicity increases with concentration up to about 5 mM at which point a plateau is reached. The effect of elevated temperature is to reduce the time required to obtain a specific level of survival, but temperatures as high as 42 degrees C had only a slight effect on drug toxicity for oxygen tensions higher than 100 ppm. The effect of D-glucose on the toxicity of 5TG was studied, and an inverse relationship was established. At D-glucose concentrations greater than 20 mM the toxicity of 5TG was nullified regardless of oxygen tension or 5TG concentration.

Animals↗
PubMed1980

Response of mammalian cells irradiated with 30 MV X-rays in the presence of a uniform 20-kilogauss magnetic field.

The effects of intense magnetic fields on the survival curves for aerated and hypoxic Chinese hamster lung cells exposed to 30 MV X-rays were investigated. A uniform 20-kilogauss magnetic field, as well as a non-uniform magnetic field with an average value of 17 . 5 kilogauss and a gradient of 2 . 3 kilogauss/cm, were employed. A study of the repair of sublethal damage for cells exposed to the magnetic field only during the split-dose irradiations, and the effect of exposure to the magnetic field alone for 2 hours, were also studied. For each of these four experiments, no effects attributable to the magnetic field were detected.

Animals↗
PubMed1976

Application of tissue-air ratios for patient dosage in diagnostic radiology.

A method for calculating organ dose form radiographic procedures which utilizes the concept of tissue-air ratio (TAR) is described. TAR's were measured for 70-120 kVp x-rays filtered by a total of 2.5 and 3.5 mm Al under conditions which simulate those in radiography. The output of the x-ray tube tube, in terms of mR/mAs at 40 inches (101.6 cm) was also measured, and these are compared with previously published data. A step-by-step procedure for calculating organ dose is described and an example given to illustrate the magnitude of the dose delivered by a typical radiographic procedure.

Female↗
PubMed1975

[Vitamin B6-deficiency and -substitution in chronic uremia (author's transl)].

In patients with chronic renal failure on potatoe-egg-diet (0.4 g protein/kg body weight) an alimentary vitamin B6-deficiency occurs, which can be overcome by 20 mg vitamin B6/day. Chronic hemodialysis causes a vitamin B6 loss which amounts to a quantity similar to the daily urinary excretion in normal persons. No hints for an inhibition of the synthesis of pyridoxal phosphate could be found.

Humans↗