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Lethal, potentially lethal lesion model

Description: A theoretical framework to describe the formation of lethal mutations by radiation is presented. Lesions that are repaired (and misrepaired) in each type of experiment described (delayed plating and split dose) are assumed to be the same. In this model the same (potentially lethal) lesions cause both sublethal and potentially lethal damage. Potentially lethal damage is defined as damage which may be modified by alterations in postirradiation conditions. Sublethal damage is cellular damage whose accumulation may lead to lethality. A crucial consideration in the expression of the damage is the kind of medium in which the cells are placed during the repair period. Fresh or growth medium (F-medium) is assumed to cause fixation of damage after about 3 hours, while no fixation (only misrepair) occurs in conditioned medium (C-medium).
Date: July 1, 1983
Creator: Curtis, S.B.
Partner: UNT Libraries Government Documents Department

New particles and their application in medicine

Description: In recent years there has been increasing interest in the use of new particle beams for various medical applications. The particles being used, fast neutrons, protons, helium ions, negative pions, and heavy ions, have in fact been known and studied for over forty years. They are new only in the sense that, until recently, the medical community has had little experience with them in the clinic. The applications of these new particles to clinical medicine, primarily in the areas of tumor radiotherapy and diagnostic radiography are reviewed.
Date: September 1, 1979
Creator: Curtis, S.B.
Partner: UNT Libraries Government Documents Department

Application of the LPL model to mixed radiations

Description: The LPL (Lethal, Potentially Lethal) formulation was used to analyze sets of cell survival data from mixes of (1) alpha particles and X rays and (2) neon ions and X rays. The hypothesis tested was whether survival after mixed radiation could be predicted by simply adding the total number of lethal and potentially lethal lesions from each radiation in the theoretical survival expression. Results show that all data appear to conform satisfactorily to the LPL hypothesis except for the mixed neon-ion and X-ray results with a large dose of X rays (8 Gy) given first. 8 refs., 6 figs., 1 tab.
Date: September 1, 1991
Creator: Curtis, S.B.
Partner: UNT Libraries Government Documents Department

Mechanistic models

Description: Several models and theories are reviewed that incorporate the idea of radiation-induced lesions (repairable and/or irreparable) that can be related to molecular lesions in the DNA molecule. Usually the DNA double-strand or chromatin break is suggested as the critical lesion. In the models, the shoulder on the low-LET survival curve is hypothesized as being due to one (or more) of the following three mechanisms: (1) interaction'' of lesions produced by statistically independent particle tracks; (2) nonlinear (i.e., linear-quadratic) increase in the yield of initial lesions, and (3) saturation of repair processes at high dose. Comparisons are made between the various approaches. Several significant advances in model development are discussed; in particular, a description of the matrix formulation of the Markov versions of the RMR and LPL models is given. The more advanced theories have incorporated statistical fluctuations in various aspects of the energy-loss and lesion-formation process. An important direction is the inclusion of physical and chemical processes into the formulations by incorporating relevant track structure theory (Monte Carlo track simulations) and chemical reactions of radiation-induced radicals. At the biological end, identification of repair genes and how they operate as well as a better understanding of how DNA misjoinings lead to lethal chromosome aberrations are needed for appropriate inclusion into the theories. More effort is necessary to model the complex end point of radiation-induced carcinogenesis.
Date: September 1, 1990
Creator: Curtis, S.B.
Partner: UNT Libraries Government Documents Department

Wobbler facility for biomedical experiments at the Bevalac

Description: A new wobbler facility has been developed to deliver large uniform fields of relativistic heavy ions at the Bevalc without resorting to the use of scattering material in the beam. The charged particle beams are made to wobble and 'paint' a ring at the target by a pair of dipole magnets, which are placed tandem with their fields orthogonal to each other. The magnets are powered sinusoidally 90/sup 0/ out of phase with each other. By superimposing several rings of appropriate sizes and intensities, large uniform fields are produced. Up to 30 cm diameter fields with less than 5% variation in uniformity have been achived. Physics and biology measurements have been made to characterize the radiation field. 5 refs., 4 figs., 1 tab.
Date: May 1, 1985
Creator: Chu, W.T.; Curtis, S.B.; Llacer, J.; Renner, T.R. & Sorensen, R.W.
Partner: UNT Libraries Government Documents Department

Effect of negative pions on the proliferative capacity of ascites tumor cells (lymphoma) grown in vivo

Description: We have attempted to determine the relative biological effectiveness (RBE) of negative pions in the Bragg-peak region as compared to the plateau region and to gamma rays. We irradiated LAF{sub 1} mice, bearing 5-day-old lymphoma ascites tumors, in the peak and plateau regions of a 90-MeV pion beam for 40 hours in temperature-controlled holders. The animals were then sacrificed; lymphoma cells were withdrawn and titrated into adult female LAF{sub 1} mice. The proliferative capacity of the irradiated tumor cells was evaluated after 8 weeks by observing the percentage of animals developing ascites tumors. Surviving fractions were then calculated from LD{sub 50}`s of control and irradiated animals. Radiation doses in the 50 plateau region were measured with LiF dosimeters calibrated against cobalt-60 gamma rays. We calculated peak doses from those at the plateau, using a measured average peak-to-plateau ionization ratio of 1.5. Doses in the plateau region ranged from 145 to 250 rads; doses in the peak region ranged from 220 to 380 rads. The survival curve for cells irradiated in the peak region gave a D{sub 0} of 65 {plus_minus} 15 rads. The plateau points were not reliable. A replicate experiment was performed using Co{sup 60} {gamma}-rays, yielding a survival-curve D{sub 0} of 350 {plus_minus} 50 rads. If the {gamma}-ray D{sub 0} is taken as a baseline, an RBE of 5.4 {plus_minus} 1.8 is obtained for negative pions in the peak region, based on the ratio of-peak-region D{sub 0} to Co{sup 60} D{sub 0}.
Date: March 30, 1967
Creator: Feola, J.M.; Richman, C.; Raju, M.R.; Curtis, S.B. & Lawrence, J.H.
Partner: UNT Libraries Government Documents Department

Relating space radiation environments to risk estimates

Description: This lecture will provide a bridge from the physical energy or LET spectra as might be calculated in an organ to the risk of carcinogenesis, a particular concern for extended missions to the moon or beyond to Mars. Topics covered will include (1) LET spectra expected from galactic cosmic rays, (2) probabilities that individual cell nuclei in the body will be hit by heavy galactic cosmic ray particles, (3) the conventional methods of calculating risks from a mixed environment of high and low LET radiation, (4) an alternate method which provides certain advantages using fluence-related risk coefficients (risk cross sections), and (5) directions for future research and development of these ideas.
Date: October 1, 1991
Creator: Curtis, S.B.
Partner: UNT Libraries Government Documents Department

Calculating survival curves in spread-peaks of heavy ion beams and comparison with experiment

Description: In preparing for treating patients with high-energy ion beams, it is important first to determine the composition of the beam, that is, the relative mixes of the various primary and secondary particles and their LET spectra, and secondly to estimate the cell killing expected during a treatment schedule. This requires measurements of the beam composition at various depths through the spread-peak region, and a calculation of cell survival using a cell-killing model designed to accommodate the mixed LET nature of the beam in the spread-peak region. This talk presents results of an experiment in which a particle identification telescope, the BEPKLET, was used to measure the LET spectra of the primary and secondary particles at two positions in a 12-cm-spread-peak of a 585 MeV/amu neon ion beam at the Bevalac. Cell survival measurements were made at the same positions at which the LET-spectra were measured. The survival curves obtained were compared with calculations using the LPL (Lethal, Potentially Lethal) model of cell-killing. Results agree quite well at doses up to about 4 Gy. A quantity proportional to the RBE at 10% survival, when plotted against dose-averaged LET for a number of different beams and energies, appears to be a fairly good predictor of biological effect. This would not be expected if the difference in biological effect due to differences in track structure between various ions at the same LET played a significant role in modifying cell-killing in the range of LETs covered by this experiment.
Date: August 1, 1995
Creator: Curtis, S.B.; Chu, W.T.; Llacer, J.; Renner, T.R.; Rodriguez, A. & Yang, T.C.H.
Partner: UNT Libraries Government Documents Department