Quadratic Dose Response Research Articles

Radiosensitivity of new and established human melanoma cell lines: Comparison of [ 3H]thymidine incorporation and soft agar clonogenic assays

Seven new low-passage melanoma lines were developed in this laboratory from clinical melanoma specimens and characterised for chromosome complement, DNA ploidy and S-phase content. The radiosensitivity of these lines was compared with that of eight established melanoma cell lines, FME, MM-96, SK-MEL-5, SK-MEL-28, SK-MEL-2, MALME-3M, M19-MEL and LOX-IMVI, using a 96-well microculture assay technique. Dose-response curves were determined using a 5-day incubation period and 6-h terminal [3H]thymidine-labelling period. Radiation (60Co source) was carried out under a lead wedge to provide a radiation dose range of 0-10 Gy, or by irradiating part of the plate (radiation dose 0 or 2 Gy). Data for a range of cell densities in a single 96-well plate were combined into a single regression equation incorporating linear quadratic terms for radiation dose and cell density. SF2 values were defined as the amount of thymidine incorporated following a radiation dose of 2 Gy, expressed as a fraction of that of unirradiated cells, and varied from 0.36 to 0.93. The reproducibility in repeat assays, as defined by the standard error of determinations at different passage numbers, was +/- 0.04. The newly developed lines exhibited a similar range of radiosensitivity to that of the established lines, and melanin content did not correlate with resistance. For nine of the lines, radiation parameters were also determined using a modified Courtenay clonogenic soft agar assay technique, and the results compared with the thymidine incorporation results, and a significant linear correlation was found between SF2 and SF2' (r = 0.89). The linear (alpha) and quadratic (beta) terms of the best-fit linear quadratic dose-response curves, were significantly correlated between the two assays. It is concluded for this series of human melanoma lines that proliferation assays in 96-well plates provide radiosensitivity parameters comparable to those using clonogenic assays.

Radiation dosimetry by automatic image analysis of dicentric chromosomes

A system for scoring dicentric chromosomes by image analysis comprised fully automatic location of mitotic cells, automatic retrieval, focus and digitization at high resolution, automatic rejection of nuclei and debris and detection and segmentation of chromosome clusters, automatic centromere location, and subsequent rapid interactive visual review of potential dicentric chromosomes to confirm positives and reject false positives. A calibration set of about 15,000 cells was used to establish the quadratic dose response for 60Co gamma-irradiation. The dose-response function parameters were established by a maximum likelihood technique, and confidence limits in the dose response and in the corresponding inverse curve, of estimated dose for observed dicentric frequency, were established by Monte Carlo techniques. The system was validated in a blind trial by analysing a test set comprising a total of about 8000 cells irradiated to 1 of 10 dose levels, and estimating the doses from the observed dicentric frequency. There was a close correspondence between the estimated and true doses. The overall sensitivity of the system in terms of the proportion of the total population of dicentrics present in the cells analysed that were detected by the system was measured to be about 40%. This implies that about 2.5 times more cells must be analysed by machine than by visual analysis. Taking this factor into account, the measured review time and false positive rates imply that analysis by the system of sufficient cells to provide the equivalent of a visual analysis of 500 cells would require about 1 h for operator review.

LH and FSH response of Holstein heifers to fertirelin acetate, gonadorelin and buserelin

This study was conducted to describe the changes in serum LH and FSH concentrations in Holstein heifers following intramuscular (i.m.) injection of various dosages of fertirelin acetate and other commercially available GnRH products at their labeled dosages. The design was an incomplete Latin-square which gave nine replicates of each treatment. Treatments administered on Days 8 to 16 of the estrous cycle consisted of saline; 25, 50, 100 or 200 microg fertirelin acetate; 100, 250 or 500 microg gonadorelin; and 10 or 20 microg buserelin. Blood samples were collected via jugular catheters from 1 h before to 8 h after each injection. Log (Base 2) area under the LH and FSH curves (log AUC) were used to evaluate response to fertirelin acetate dosages and to determine difference (LSD: 0.05) and bioequivalence (alpha = 0.05) between the various dosages of GnRH products tested. Significant quadratic dose response relationships were detected for the LH and FSH log AUC data. Plots of the LH log AUC but not the FSH log AUC data suggested that a response plateau was being approached at the higher dosages of fertirelin acetate. Bioequivalence (alpha = 0.05) was based on the assumption that two means are equivalent if they differ by no more than 20% of the reference log AUC mean. Using these criteria fertirelin acetate is 2.5 to 10 times more potent than gonadorelin, whereas buserelin is approximately 10 to 20 times more potent than fertirelin acetate in the bovine for LH and FSH release.

Biological effects of low level radiation: Values, dose-response models, risk estimates

Predictions about the health risks of low level radiation combine two sorts of measures. One estimates the amount and kinds of radiation released into the environment, and the other estimates the adverse health effects. A new field called health physics integrates and applies nuclear physics to cytology to supply both these estimates. It does so by first determining the kinds of effects different types of radiation produce in biological organisms, and second, by monitoring the extent of these effects produced by given levels of exposure. This essay examines the interplay between evidential constraints and external, contextual interests and values in studying the biological hazards of radiation. By analyzing the debate over linear vs. quadratic dose response models, the essay focuses on problems of developing quantitative, rather than qualitative, estimates of the risks of increased cancer incidence in an exposed population.

An Approximate Closed Form Solution for a Quadratic Dose–Response Model*

The quadratic dose–response model is often used in radiobiology studies. Since the model is nonlinear, the least squares estimators of the parameters of the model are determined by an iterative procedure. We give a simple closed form approximation for estimating the parameters of the model.

Modeling for Comparison of Leukemia Incidence Risk between Nuclear and Coal Power Industries

The leukemia incidence risk for a single coal plant, a single nuclear plant, and a single nuclear accident is used to compute the total industry leukemia incidence risk. In the absence of a nuclear power plant accident, the leukemia incidence risk is normally lower for a nuclear industry than for a coal industry of equivalent size. The nuclear industry risk with accidents was compared to the coal industry risk for six proposed dose response curves. Simplifying assumptions about the negligible effect of the cell-killing term and the linear nature of the linear quadratic curve allowed derivation of risk models for the assumption of both linear and quadratic dose response. These derived models, representing leukemia incidence risk bounds, are used to estimate the total industry risk comparison. Evaluation of an accident's impact on the leukemia incidence risk comparison is done with the risk bounds and compared to the risk evaluations calculated during all six dose response curves. The overlapping plot of the number of nuclear accidents required for equivalent industry environment risks versus the accident fraction allows the conservative function to be defined.

Multifraction Radiation Response of Mouse Lung

The response of mouse lung to repeated doses of 60Co gamma-rays of as low as 115 cGy per fraction was measured using death from pneumonitis between 80 and 120 days after irradiation as the endpoint. A fractionation interval of 3 h was maintained for most regimens but in the longer experiments some 12 h intervals were introduced for logistic reasons. The longest overall duration (for a 43 fraction regimen) was 8 days. The total doses required to produce 50 per cent mortality increased continuously as dose/fraction was decreased, even from 160 to 115 cGy per fraction. Of clinical relevance, the steepness of the isoeffect curve over the dose range 115-500 cGy indicates that the lung shows greater sparing from dose fractionation than is characteristic of more rapidly-responding normal tissues, resembling, in this respect, other more slowly-responding tissues such as spinal cord. The plot of the reciprocal of the LD50 values as a function of dose per fraction was non-linear, suggesting that a linear quadratic dose response model may not be appropriate or that repair of cellular injury in lung is not complete in 3 h, or both.

Blood lymphocyte culture system: Quantitative analysis of X-ray-induced chromosome aberrations in man, muntjac and cattle

Peripheral blood lymphocytes of 3 mammalian species, man, muntjac and cattle, which have various amounts of DNA and divergent karyotypes, were exposed to 100-400 rad of X-rays, and frequencies of dicentrics and other aberrations were analysed at first post-irradiation metaphases. During experiments, various preparative or physical and biological factors that could influence the yield of chromosome aberrations were taken into account. The frequency of dicentrics scored at first post-irradiation metaphases showed best fit to both linear and quadratic dose-response curves, y = a + bD and y = bD + cD2 with a high correlation coefficient of 0.98 (P less than 0.001). The frequency of dicentrics obtained at different post-irradiation fixation times did not show significant variation, indicating a homogeneous sensitivity of peripheral lymphocytes to X-irradiation. BrdU incorporation following X-irradiation showed no increase in the frequency of chromosome aberrations. The frequency of dicentrics in man, muntjac and cattle showed a close correlation with their DNA content, but no meaningful correlation was found between the yield of dicentrics and the chromosome arm number or the nuclear volume. The ratio of dicentric yields, 1.00:0.67:1.04 obtained in man, muntjac and cattle were comparable to the ratio of their DNA contents, 1.00: 0.65: 1.07. The base-line frequency of SCEs was similar in the 3 species and no significant variation in SCE frequency was noticed even after administration of 400 rad of X-rays.

On the dose response in B. subtilis transfection

Transfection with phi 29 DNA is predominantly caused by multimolecular, protease-sensitive aggregates of DNA. A minority of transfecting DNA molecules having properties of unit-length phi 29 genome molecules show a quadratic dose response in transfection.

A quantitative theory of transfection in B. subtilis.

A theory of transfection is developed which describes three different types of experiments in transfection: The concentration dependence of transfection, transfection with marker rescue, and the mapping function in transfection crosses. The theory is applicable to transfection systems exhibiting quadratic or higher order dose response (APP1, AP50, SP82). It pictures the essential process in transfection as follows: transfecting DNA molecules, having suffered inactivating events during uptake or intracellularly, have to recombine prior to replication under elimination of these lesions. The probability for recombination, successful in this sense, is calculated as a function of the number of DNA molecules within the competent cell, the mean number of inactivating events per DNA molecule, and the crossover probability per nucleotide. Under the assumption of random distribution of inactivating events over the population of DNA molecules and homogeneous crossover probabilities the theory explains on a quantitative basis a number of experimental observations in transfection, as for instance the relative efficiencies of different helper phage in transfection with marker rescue, the third order concentration dependence in SP50 transfection, and the high recombination frequencies observed in transfection crosses.