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Biomedical subjects

P O'Brien

Publications and source records attributed to P O'Brien.

At least 235 records · Page 13Linked to original sources
PubMed1971

Inhibition of growth of leukemia cells by enzymic folate depletion.

A new bacterial enzyme, designated as carboxypeptidase G(1), inhibited growth of the L5178Y and L1210 murine leukemias, as well as the Walker carcinoma and the human lymphoblastoid line (RPMI 4265), propogated in vitro. This enzyme hydrolyzes the glutamate moiety from both oxidized and reduced folate forms, and thus it may prove to be of value in creating rapid folate depletion in vivo.

Animals↗
PubMedDate not supplied

Spectral karyotyping, a 24-colour FISH technique for the identification of chromosomal rearrangements.

Spectral karyotyping (SKY) is a new fluorescence in situ hybridisation (FISH) technique that refers to the molecular cytogenetic analysis of metaphase preparations by means of spectral microscopy. For SKY of human metaphase chromosomes, 24 chromosome-specific painting probes are used in just one FISH experiment. The probes are labelled by degenerate oligonucleotide-primed PCR using three fluorochromes and two haptens. Each probe is differentially labelled with one, two, three or four fluorescent dyes, resulting in a unique spectral signature for every chromosome. After in situ hybridisation and immunodetection, a spectral image is acquired using a conventional fluorescence light microscope equipped with a custom-designed triple-bandpass filter and the SpectraCube, which is able to retrieve spectral information for every pixel in a digital CCD image. The 24-colour display and chromosome classification are based on the unique emission spectra of the chromosomes. Together with chromosome banding information from an inverted DAPI or a G-banded metaphase, a comprehensive overview of chromosomal aberrations is presented.

Color↗
PubMedDate not supplied

Characteristics of electron beams from a new 25-MeV linear accelerator.

Clinically useful electron fields are produced on the Atomic Energy of Canada, Limited Therac 25 linear accelerator by computer-controlled scanning of the electron beam. Measurements were made to determine the properties of these electron fields. Central axis percentage depth dose and bremsstrahlung background were compared for these fields and for the fields from selected machines that use scattering foils. Dose calibrations were made in both water and polystyrene using the American Association of Physicists in Medicine Task Group 21 protocol. Measurements were made to determine the relative output factors, virtual source position, and the attenuation of the electron fields by lead.

Electrons↗
PubMedDate not supplied

Radiation protection aspects of a new high-energy linear accelerator.

The Therac-25 is a new 25-MeV linear accelerator manufactured by Atomic Energy of Canada, Ltd. The first two units have recently been installed in Toronto, Ontario and Halifax, Nova Scotia. Calculations and measurements of primary and secondary radiation levels were made. Neutron dose-equivalent rates were measured inside and outside the room. The maximum leakage rate at 1 m from the accelerator target was 0.4% Sv per peak photon Gy. The tenth value layer for neutrons from the Therac-25, at the entrance to a one-legged maze was found to be 5.5 cm of polyethylene. Measurements were done to estimate daily technologist exposure due to induced activity in the treatment room.

Electrons↗
PubMedDate not supplied

Treatment planning for asymmetric jaws on a commercial TP system.

In this work, the accuracy of the asymmetric jaws planning feature in a commercial treatment planning (TP) system is assessed. In the latest version of this software, the off-axis beam quality variation is handled by a function g(d,r), which is derived from measured horizontal beam profiles at four different depths. The calculated and measured isodoses for a 6-MV linear accelerator with asymmetric jaws agree to +/- 0.5% along the central axis and to within 2 mm at the beam edge. Formulas for treatment time calculations using the output data reported by the computer program are described, as well as formulas for manual calculations based on pregenerated data tables. Doses calculated based on these formulas are compared to measurement and the accuracy is +/- 1% and +/- 2% for the computer and manual calculations, respectively. It is concluded that this version of the treatment planning system as well as the treatment time calculation formulas can be used adequately for asymmetric jaw computerized and manual treatment planning.

Humans↗
PubMedDate not supplied

Mechanical and radiation isocenter coincidence: an experience in linear accelerator alignment.

As part of the commissioning procedure of a linear accelerator at our cancer center, the defining laser lines were aligned with the optical and radiation isocenter of the linac. When a mechanical checkout jig was set up at the same point, a discrepancy of 4 mm resulted when the gantry was moved from 0 degrees to 180 degrees. Extensive measurements, some with custom-designed devices, confirmed the observations and provided an explanation. Even though the mechanical isocenter is within the specified tolerance of 1-mm radius, the clinically observable discrepancy of 4-mm results from the noncoincidence of the mechanical and radiation isocenters. The clinical significance of the final setup is discussed and future commissioning procedures are recommended.

Particle Accelerators↗
PubMedDate not supplied

Upping the ante: relative caregivers' perceptions of changes in child welfare policies.

Thirty-five caregivers of related children who were in the custody of the child welfare system were interviewed individually or in focus groups as the state child welfare system implemented new federal and state policies encouraging these caregivers to adopt or assume guardianship of the children in their care. Interviews were transcribed and analyzed using qualitative methods. Issues of concern included emergency entrance into caregiving; the simultaneous satisfaction and burden of caregiving; obstacles to caregiving, adoption, or guardianship; complex changes in family dynamics following placement of children; sources of support; and caution regarding adoption or guardianship. The caregivers also offered recommendations for the child welfare system. Policy, practice, and research implications are discussed.

Adoption↗