Electron contamination due to Lucite in a 45-MV photon beam

The presence of the Lucite blocking tray in a 45-MV betatron beam leads to a considerable loss in the skin-sparing properties of this unit. Measurements conducted with a parallel-plate chamber show that the surface dose is approximately doubled (up to 58% of the maximum absorbed dose) and the depth of maximum dose is reduced by as much as 1.5 cm by the Lucite. These results suggest that separate dosimetry data should be kept for blocked and unblocked fields. The penetration of the electron contamination to the open field depth of maximum dose can lead to erroneous results if attenuation measurements are made at that depth. Studies of the effect of the lead sheet and leaded acrylic on the surface dose showed that under normal circumstances the presence of high-Z materials increases the surface dose, hence these materials cannot in general be used as electron filters on very high energy x-ray units. A Luciteless blocking tray with universal triangular corner blocks has been designed for use in special cases requiring a reduced surface dose.

Dosimetry characteristics of large wedges for 4- and 6-MV x rays

Two sets of newly designed large wedge filters for field sizes up to 20 X 20 cm2 have become commercially available for use with 4- and 6-MV linear accelerators. Such field sizes are sometimes required to ensure adequate coverage in certain treatment techniques. This work reports base line data resulting from an investigation of the dosimetric properties of these wedges. Measurements of wedge angles, transmission factors, and beam hardening effects are described, and comparisons are made with the smaller standard wedges.

Rationale for the use of hypnotic agents in a general hospital

A survey at a teaching hospital found that 46% of medical patients had prescriptions written specifically for sleep and 31% received a hypnotic agent at least once during hospitalization. Physicians for 96% of surgical patients ordered hypnotic agents and 88% received such a drug. The rationale for prescribing hypnotic agents was not well documented. Administration did not correlate with requests by patients, with previous use of hypnotic agents, or with recorded indications of sleep disturbance; however, the chance of receiving a hypnotic agent was greater if the patient was on a private instead of a ward service and if nurses were more inclined to fill as-needed prescriptions. Patients who received a hypnotic agent did not rate the quality of their sleep as being any better than those who did not, and they complained of as many awakenings during the night. Further studies are necessary to ascertain the indications and efficacy of hypnotic agents for hospitalized patients.

Generation time of leukaemic blast progenitor cells

Previous studies have indicated that the generation time of human leukaemic cells is longer than that of normal haematopoietic cells. We have employed a modification of the thymidine (TdR)-suicide technique to measure directly the generation time of leukaemic progenitor cells capable of colony formation. The results obtained with two human leukaemic cell lines (KG-1 and HL-60) and with blast progenitor cells from two patients with acute myelogenous leukaemia indicate generation times ranging from 9 X 0-22 X 0 hr and S-phase durations ranging from 5 X 5-8 X 0 hr. Using the same technique, the generation time of normal bone marrow CFU-c was determined to be 9-11 hr. These findings suggest that the proliferation rate of human leukaemic blast progenitor cells is similar to that of normal haematopoietic stem cells.

UV-induced second readout of LiF thermoluminescent dosimeters in the therapeutic dose range

A previously developed technique for reading out LiF thermoluminescent dosimeters (TLD) a second and subsequent time by means of ultraviolet (UV)-induced repopulation of dosimetry traps was studied to determine the feasibility of maintaining a second readout capability in a radiotherapy clinical setting. It was found that with grouping of the TLDs according to second readout sensitivity, the UV-induced readout attained a precision comparable to that of the initial readout. However, the UV-induced TL response retained a strong previous dose memory following a standard high-temperature anneal, and routine calibration before each reuse is recommended.

The effects of halothane on sympathetic ganglionic transmission

The effects of halothane on ganglionic transmission were studied in the stellate ganglion of the guinea pig using intracellular recordings in vitro. Depression of synaptic transmission is one of the actions common to many general anesthetics. The aim of this study was to investigate which of the processes involved in synaptic transmission are affected by halothane in concentrations comparable to those used during surgical anesthesia. The neurons of the stellate ganglion were depolarized using preganglionic nerve stimulation, postganglionic nerve stimulation, and intracellular stimulation before ad after introduction of halothane (vaporizer settings of 0.75% and 1.5% produced bath concentrations of 8 and 18 mg/dl, respectively). Halothane at both concentrations depressed sympathetic ganglionic transmission which was induced by stimulation of preganglionic nerves. Axonal transmission and the excitability of the postganglionic neurons to direct intracellular stimulation was far less sensitive to halothane than synaptic transmission. The depression of ganglionic transmission seen in the present study was most likely due to a decrease in transmitter release although alterations in postsynaptic receptor properties could have been involved as well. The decrease in sympathetic activity resulting from depression of ganglionic transmission probably contributes to the arterial hypotension seen during halothane anesthesia, along with direct myocardial depression, inhibition of catecholamine release from the adrenal medulla, direct action on vascular smooth muscle, and central sympathetic depression.

Isolation of genome-enzyme complex from cytoplasmic polyhedrosis virus of silkworm Bombyx mori

The genome-enzyme complex is isolated from the silkworm cytoplasmic polyhedrosis virus with DEAE-Sephadex column chromatography after ultraviolet irradiation. The genome-enzyme complex shows both RNA-polymerase and methyltransferase activities while using 3H-UTP and [3H-methyl]-S-adenosyle-L-methionine as substrates. Like the double-stranded RNA genome of CPV, the genome-enzyme complex could be separated into nine segments on polyacrylamide gel electrophoresis. It is demonstrated that the RNA polymerase and methyl-transferase are tightly bound to the double-stranded RNA genome and that the individual segments of the genome-enzyme complex all possess RNA-polymerase and methyltransferase activities. It appears that each segment of the double-stranded RNA genome is transcribed independently.

The morphological changes of the endothelium to venous stasis as observed under the scanning electron microscope

In this study using the pig, venous stasis is produced artificially by placing a pneumatic cuff around the hind leg of the anaesthetised animal and the cuff inflated intermittently. The period of stasis is three hours. The leg vein distal to the cuff is biopsied before and at intervals after the onset of stasis. The endothelium of the vein is examined under the scanning electron microscope. These findings suggest that venous stasis has a traumatic effect on the endothelium and cell injury is demonstrated within three minutes of the onset of stasis. With increasing period of stasis the endothelial cells are desquamated resulting in the exposure of the subendothelial basement membrane and collagen fibres. This is followed by aggregation of platelets and fibrin. It is postulated that the effect of venous stasis on the endothelium is a primary factor and may be important in the aetiology of clinical thrombogenesis.

Hemoglobin affinity for oxygen during short-term exhaustive exercise

We assessed hemoglobin affinity for oxygen (standard P50: pH 7.40, PCO2 40 Torr, temperature 37 degrees C) in 3 series of studies of 16 male subjects who performed exhaustive treadmill exercise of 10 min duration. Standard P50 was significantly elevated (0.7--2.5 Torr) during the last minute of and for 30 min following exercise. Exercise while carboxyhemoglobin (HbCO) was acutely elevated to 5% did not affect std P50 any differently than exercise alone. 2,3-Diphosphoglycerate (2,3-DPG) was significantly elevated after exercise, but not during or 30 min postexercise, and it correlated significantly with P50 in 2 studies (r, 0.43--0.68). ATP (mumol/100 ml) was significantly elevated only 3 min postexercise. Serum [Na+], [K+], [Cl-], osmolarity, and hemoglobin (Hb) concentration were significantly elevated during exercise with [Na+] osmolarity, and [Hb] remaining significantly elevated postexercise. There was no significant correlation between std P50 and any of these variables. Multiple correlation regression analysis between P50 and 2,3-DPG, ATP, and [Na+] yields a coefficient of 0.86. We conclude this type of exercise is unique in causing a small change in std P50 that appears to be mediated by several factors.

A simple method of producing a monolayer of cervical cells for digital image processing

A manual method of producing a monolayer of isolated and evenly distributed cervical epithelial cells has been developed for use in an automated digital image analysis system. The cervical scrape specimen is vortexed from the spatula into a solution of Mucosol. The suspension is filtered through a 10 micro nylon mesh to remove polys and debris and then syringed to disaggregate epithelial clumps. The cells are plated out on a Nuclepore filter. The filter is touched directly onto a glass microscopic slide to transfer cells, which are then fixed and stained in a routine manner. Cell counts reveal elimination of 92% polys, with only 2% loss of squamous cells.

Stereoelectronic factors in the binding of substrate analogues and inhibitors to purine nucleoside phosphorylase isolated from human erythrocytes

Several aspects of the stereoelectronic requirements of substrates of human erythrocytic purine nucleoside phosphorylase (E.C. 2.4.2.1) were elucidated providing the following information: (a) the N1 position cannot have a nonhydrogen substituent; (b) the 5'-OH group must be present for catalytic activity to be exhibited but is not an essential functional group for inhibitory action to be observed; (c) on the C8 position groups larger than -NH2 or -Br cannot be accommodated; (d) the syn-glycosyl conformation (i.e., 8-bromoguanosine) is acceptable but may not be an absolute requirement for phosphorolysis; (e) among nucleic base inhibitors methylation at N3, N7, or N9 vastly decreases the inhibitory properties as does a nitrogen in lieu of C-H in the 8 position. The results clearly indicate that this enzyme differs in its stereoelectronic requirements from the Escherichia coli enzyme.

Mass fragmentographic determination of pentachlorophenol in rainbow trout

Pentachlorophenol (PCP) is extracted from selected tissues of rainbow trout and converted to pentachloroanisole (PCA) by means of alkylation in the presence of potassium carbonate as a condensing agent. Pentachlorophenetole (PPT) is used as an internal standard. The electron impact mass fragmentography is carried out by monitoring m/e 280 (PCA), 294 (PPT), and 237. A plot of peak height vs. concentration is linear from 0.03 to 4.0 ng. Accuracy and precision of the method is +/-2% (N - 36). The results are accurate enough to warrant the use of this method for determining PCP in fish, as well as for monitoring PCP from various environmental sources. In addition, this technique provides a simple and rapid method by which a mixture of PCA and PCP can be determined simultaneously.