Biomedical subjects

P Nizin

Publications and source records attributed to P Nizin.

4 recordsLinked to original sources

PubMed1986

Induction of malignant transformation of cocultivated hematopoietic stem cells by X-irradiation of murine bone marrow stromal cells in vitro.

X-irradiation of purified primary cultures of mouse bone marrow stroma or permanent cloned marrow stromal cell lines in plateau phase decreases production of macrophage progenitor cell-specific colony-stimulating factor to a plateau minimum of 40% of control levels after doses of 50 to 500 Gy delivered at 2 Gy/min. After 50 Gy there is increased bioavailability of another growth factor(s) that is distinct from macrophage progenitor cell-specific colony-stimulating factor, granulocyte-macrophage progenitor cell colony-stimulating factor, or colony-stimulating factor for multipotential hematopoietic stem cells (interleukin 3). Liquid-phase cocultivation of irradiated stromal cells with either nonadherent cells from continuous marrow cultures or cloned dual granulocyte-macrophage progenitor cell colony-stimulating factor/interleukin 3-dependent hematopoietic progenitor cell lines induces evolution over 5 weeks of factor-independent colony-forming cells. Subcultured factor-independent colonies generated clonal malignant cell lines with multiple distinct karyotypic alterations. Inoculation of 10(6) cells s.c. from factor-independent clones into syngeneic mice produces local granulocytic monomyeloid tumors with spread to spleen, lymph nodes, and bone marrow. These data provide the first demonstration in vitro of indirect X-irradiation leukemogenesis through cells of the marrow stroma.

Animals↗

PubMedDate not supplied

Determination of nominal accelerating potential.

We present a simple linear relationship between the nominal accelerating potential (NAP) and the ratios of ionization measurements made with constant source-detector distance and at two different phantom thicknesses. This relationship can be used as a standard, unambiguous method for determining NAP for use in dosimetry and quality control.

Models, Structural↗

PubMedDate not supplied

A method of measuring the primary dose component in high-energy photon beams.

We present an approach for deriving the primary component of dose from measurements in a megavoltage gamma or x-ray beam. The theoretical development of the approach is discussed showing that primary dose can be obtained from four measurements of ionization in narrow beam geometry and two measurements of ionization in a large beam in a phantom. The uncertainty in the final result is analyzed and is about an order of magnitude greater than the uncertainty in an individual measurement.

Biophysical Phenomena↗

PubMedDate not supplied

"Zero-field" dose data for 60Co and other high-energy photon beams in water.

A procedure of separating the primary- and scatter-dose components in therapeutic photon beams is examined. It is based on the observation that the scatter-dose component is proportional to the variable z = rd/(r+d), where r and d are beam radius and depth in phantom, respectively. It is, therefore, possible to express an absorbed dose in the form of a linear equation D(r) = P+Nz, where at a fixed depth d, both primary dose P and coefficient N are constant. A method of linear extrapolation of an absorbed dose D(r) to "zero-field" size, i.e., r = 0, is utilized. Since Monte Carlo technique is capable of scoring separately the primary- and scatter-dose components, it is used to evaluate the accuracy of the linear extrapolation method within the range of 60Co-15-MV nominal photon energies. The results demonstrate that this method is sufficiently accurate to obtain the primary dose component in photon beams. For 60Co gamma radiation in water, tabulated sets of measured depth-dose data are analyzed by the linear extrapolation method to review "zero-field" dose values [percentage depth dose (PDD) and tissue-air ratio (TAR) tables of the British Journal of Radiology, Suppl. 17]. The "zero-field" PDD data are found to be accurate within limits of experimental uncertainties. Inconsistencies in the TAR table are illustrated and discussed. 60Co tables of relative doses, D(r,d)/P(dmax), including "zero-field" values for both fixed SSD and isocentric geometries, are generated. Dose calculation in irregular fields is considered. The linear extrapolation method is recommended as a standard procedure for separating primary dose from depth-dose data in high-energy photon beams.

Biophysical Phenomena↗