Dose-response Sensitivity Research Articles

Thermoluminescent materials for medical applications: LiF:Mg,Ti and LiF:Mg,Cu,P

Thermoluminescent dosimeters are used in a variety of medical applications including radiation therapy, diagnostic radiology, and radiotherapy mailed dosimetry. For many years LiF:Mg,Ti has been dominating the field of TL medical dosimetry. In recent years, however, a relatively new material, LiF:Mg,Cu,P, has attracted the attention of the medical dosimetry community and its usefulness in a variety of applications was demonstrated. In this article we discuss and explain in detail the dosimetric properties of these two materials, emphasizing the characteristics that are particularly relevant to medical dosimetry, with special emphasis on the sensitivity (including fading) dose response, and the photon energy dependence.

PRESAGE - A Promising New Material for 3D Dosimetry

Purpose/Objective: Comprehensive treatment verification is a key pre-requisite to achieving high quality and accuracy of modern radiation treatment techniques including IMRT and IGRT. The complexity of these techniques has created a gross need for a practical and accurate 3D dosimeter that can comprehensively measure dose distributions in 3D. PRESAGE is a new machineable plastic material with promising characteristics as a 3D dosimeter. Chiefly, insensitivity to environment (oxygen), ability to machine the dosimeter for customized applications, and a sensitive dose response to ionizing radiation.

Investigations in x‐ray computed tomography polyacrylamide gel dosimetry

Polyacrylamide gels (PAGs) are radiosensitive materials currently under development for use as three‐dimensional (3D) dosimeters in radiation therapy. Dose information is recorded in the gels and extracted through imaging. X‐ray computed tomography (CT) has emerged as a promising gel imaging method due to a change in gel density that occurs upon irradiation. The accessibility of CT technology to cancer hospitals makes CT read out clinically attractive; however, the technique remains of limited clinical use due in part to poor dose resolution. This thesis investigates the use of CT for extracting dose information from PAGs with an overall goal of improving achievable dose resolution. Thesis results are divided into three studies: a gel‐compositional study, a study of noise and dose resolution, and a digital filtering study. The first study investigates the effects of gel composition on PAG CT dose response and the underlying density change. Results indicate dramatic variation in CT dose response sensitivity and range with gel composition. A model is developed to describe gel density change with dose, revealing two fundamental properties of the density to dose response: the density change per unit polymer yield is highest for gels with low and high concentrations of crosslinking molecules, and dose response sensitivity is linearly dependent on the total concentration of monomers in the gel. The second study investigates strategies for minimizing noise in CT polymer gel dosimetry and assesses system performance. Specifically, the effects of phantom design, scanning technique, and voxel size on image noise are investigated and the effect of scanning protocol on imaging time is established. The dose resolution achievable with an optimized system is then calculated, given voxel size and imaging time constraints, and compared with published values for magnetic resonance imaging (MRI) and optical CT gel dosimetry. The third study investigates the potential of image filtering for improved dose resolution in CT gel dosimetry. CT image noise is characterized and appropriate filters are tested on a CT image of a PAG irradiated with a clinically relevant dose distribution. Filter performance is found to vary dramatically, with the best filters more than halving the dose resolution without significantly distorting the spatial distribution of dose. In summary, this thesis provides insight into the fundamental nature of PAG density to dose response, develops strategies for minimizing image noise, quantifies system performance, and demonstrates that digital image filtering is an effective tool to provide additional improvements to dose resolution.

Phase I/II dose escalation study of angiotensin 1-7 [A(1-7)] administered before and after chemotherapy in patients with newly diagnosed breast cancer

Multilineage cytopenias occur following myelosuppressive chemotherapy. Most hematopoietic agents differentiate along a single lineage and fail to prevent progressive cytopenias. Angiotensin 1-7 [A(1-7)] is a hematopoietic agent that stimulates the proliferation of multipotential and differentiated progenitor cells in cultured bone marrow and human cord blood. The purpose of this study was to determine the optimal biologic dose and the maximum tolerated dose of A(1-7). This study determined the safety and activity of A(1-7) following chemotherapy in patients with breast cancer. Toxicity was assessed by administering A(1-7) daily for 7 days followed by a 7-day washout prior to the first cycle of chemotherapy. Beginning 2 days after chemotherapy and continuing daily for at least 10 days, fifteen patients received five different A(1-7) doses and five patients received filgrastim as a comparator group over three cycles of chemotherapy. No dose-limiting toxicity was observed following A(1-7). The frequency of adverse events was slightly lower in A(1-7) than in filgrastim patients. No patient required a chemotherapy modification due to hematologic toxicity. There was an apparent differential dose-response sensitivity of the various lineages to A(1-7). At a dose of 100 microg/kg, A(1-7) reduced the frequency of grade 2-4 thrombocytopenia, anemia, and grade 3-4 lymphopenia as compared to filgrastim. These data suggest that A(1-7) may be beneficial in attenuating multilineage cytopenias following chemotherapy at a dose of 100 mug/kg per day.

Development and initial evaluation of a spectral microdensitometer for analysing radiochromic films

Radiation dose deposited on a radiochromic film is considered as a dose image. A precise image extraction system with commensurate capabilities is required to measure the transmittance of the image and translate it to radiation dose. This paper describes the development of a spectral microdensitometer which has been designed to achieve this goal under the conditions of (a) the linearity and sensitivity of the dose response curve of the radiochromic film being highly dependent on the wavelength of the analysing light, and (b) the inherent high spatial resolution of the film. The microdensitometer consists of a monochromator which provides an analysing light of variable wavelength, a film tray on a high-precision scanning stage, a transmission microscope coupled to a thermoelectrically cooled CCD camera, a microcomputer and corresponding interfaces. The measurement of the transmittance of the radiochromic film is made at the two absorption peaks with maximum sensitivities. The high spatial resolution of the instrument, of the order of micrometres, is achieved through the use of the microscope combined with a measure-and-step technique to cover the whole film. The performance of the instrument in regard to the positional accuracy, system reproducibility and dual-peak film calibration was evaluated. The results show that the instrument fulfils the design objective of providing a precise image extraction system for radiochromic films with micrometre spatial resolution and sensitive dose response.

C. elegans metallothioneins: new insights into the phenotypic effects of cadmium toxicosis.

Metallothioneins are considered to be the primary player in the detoxification of and protection from cadmium, a teratogen, mutagen and potentially lethal heavy metal. The nematode Caenorhabditis elegans has only two metallothioneins, mtl-i and mtIl-2, thus making it an ideal organism to investigate the phenotypic effects of cadmium toxicosis. The functional importance of metallothioneins in cadmium trafficking was highlighted through the generation of viable green fluorescent protein (GFP) expressing transgenes, a metallothionein null allele, as well as RNAi mediated metallothionein knock-downs. A highly sensitive dose and temporal transcriptional response to cadmium, but not copper or zinc, was shown to be equally prevalent in both isoforms. No measurable compensatory up-regulation of mtl-l could be observed in the null allele of mtl-2, suggesting that both isoforms are independent and not synergistic in their mode of action. Exposure to cadmium affected all demographic indices measured, manifested by a reduction in body size, generation time, brood size and lifespan. These effects were magnified in the knock-out or wild-type subjected to a knock down by RNAi, however, only in the presence of cadmium. This substantiates the notion that metallothioneins play a pivotal role in the protection from cadmium toxicosis. Finally, an earthworm metallothionein-GFP construct could be activated in C. elegans upon exposure to cadmium, the results providing further evidence that the transcriptional control of metallothioneins is fundamentally divergent in lower invertebrates and not mediated via MTF-1 as in more complex organisms.

Sensitivity to drug effects on prepulse inhibition in inbred and outbred rat strains

Genetic differences in the neurochemical regulation of PPI in rats may help clarify the neural basis of inherited PPI differences in neuropsychiatric disorders. We reported and characterized substantial heritable differences in sensitivity to PPI-disruptive effects of DA agonists in outbred Sprague Dawley (SDH) versus Long–Evans (LEH) rats. Other strains might yield large group separations and facilitate studies of the neural basis for these strain differences; inbred strains might also allow us to map genes associated with differential PPI sensitivity. Sensitivity to the PPI-disruptive effects of the DA agonist apomorphine (APO) and the NMDA antagonist phencyclidine (PCP) were compared across inbred and outbred strains. APO sensitivity was greatest in SDH and buffalo rats, but the effect in buffalo rats was complicated by significant APO-induced startle suppression. PPI APO sensitivity was least in ACI and LEH rats; F344s exhibited intermediate sensitivity and Lewis rats showed a nonlinear dose response (sensitivity at low but not higher doses). PPI APO insensitivity in ACI rats developed over time, with ACI pups exhibiting robust sensitivity. Substantial strain differences were observed in short-interval (10–30 ms) prepulse effects, and APO-induced increases in short-interval PPI occurred in SDH, LEH, and Lewis rats, but not in F344, ACI, or buffalo rats. Sensitivity to PPI-disruptive effects of PCP was generally greater in outbred than inbred rats. These findings identify strains suitable for comparisons of PPI neural circuitry and others for whom such comparisons would be complex and perhaps less informative.

1H NMR AND OPTICAL SPECTROSCOPY STUDY OF THE RADIODOSIMETRIC PROPERTIES OF THE PIRA GEL

The radiation-response of the Fricke-doped protein-polymer gel (PIRA) was studied by 1H NMR, as well as with spectrophotometric and fluorescence methods. In this gel, the ionizing radiation induces an increase in the NMR longitudinal relaxation rate, R1, of protons. It was observed that: I) the main mechanism responsible for the increase in R1 was the oxidation of ferrous to ferric ions; ii) the total amount of acrylamide with the same weight fraction (50%C) of the crosslinker N,N′-methylene-bis-acrylamide in the range 6%–12% by weight had no effect upon the R1 dose sensitivity; iii) the increase in the bovine serum albumin (BSA) concentration caused a drop in the R1 dose response sensitivity; iv) the R1 dose sensitivity was pH dependent. The four-site fast exchange model for R1 dose response was applied to calculate the ferric ions chemical yield G(Fe3+). The G(Fe3+) value obtained from the NMR data agreed with that determined independently from spectrophotometric measurements.

How Useful Is Linear Regression Analysis in Detecting the Existence of Dose–Response Relationships in Large-Scale Epidemiologic Studies When Only a Fraction of the Population Is Sensitive? The Case of Methylmercury

The existence of a dose response in epidemiologic studies is generally determined from the linear regression slope after controlling for covariates. This approach assumes the entire population is equally sensitive to the toxicant and that response is a function only of dose and a random error function. However, sensitive subpopulations have been identified for a variety of toxicants possibly including methylmercury (MeHg). The study of MeHg exposure in the Seychelles Islands has failed to find significant effects (dose–response slope not significantly different from zero) while other studies have found such effects. Using data on the error function in developmental test scores and MeHg exposure distributions from that study, and assuming plausible dose–response relationships for sensitive subpopulations, we conducted Monte-Carlo simulations of the power of linear regression analysis to detect a dose–response relationship from the total sample (n=700), and to compare dose–response slopes in the total and sensitive populations. Linear regression did not reliably detect a dose–response relationship for most scenarios when sensitives were 5% of the total and for some scenarios when sensitives were 10% of the total. We also found that the dose–response slope for the total population underestimated the sensitive dose–response slope in all cases by about an order of magnitude. These findings may have important implications for detection and quantification of dose–response relationships from epidemiologic studies.

Superlinearity of synthetic quartz: Dependence on the firing temperature

In the present work, the sensitivity and thermoluminescence (TL) dose response behaviour of glow-peaks of synthetic quartz are studied as a function of the firing temperature between 300°C and 900°C in steps of 100°C. Complete TL dose response curves in the dose region, 0.1 up to 170 Gy were obtained at each firing temperature. Each TL dose response curve consists of two dose regions, which on a log–log scale have different slopes, k, indicating two different degrees of superlinearity. In the case of the glow-peak at 110°C, the TL dose response curves were fitted with an analytical expression. From the fitting procedure the superlinearity index g( D) was evaluated as a function of dose. The results show that the firing temperature influences the TL dose response behaviour of all glow-peaks. However, the effects are more profound on the glow-peak at 110°C. The superlinearity index g( D) is strongly reduced as the firing temperature increases.

Purkinje cell inhibitory responses to 3-APPA (3-aminopropylphosphinic acid) in RAT cerebellar slices.

3-APPA is considered to be a GABA(B) agonist more potent than baclofen. We report here the results obtained by applying this agonist to Purkinje cells (PCs) recorded in current clamp mode on cerebellar slices. The responses were compared to those obtained with other GABA agonists and antagonists. The drugs were delivered either in the perfusion solution or by pressure to the molecular layer near the recorded cell. When applied to the PCs either in the bathing medium or by pressure, 3-APPA evoked a potent inhibitory response which was however different from that obtained with baclofen. The response was complex and similar to that evoked by application of GABA, the endogenous neurotransmitter. In fact it showed: (1) very sensitive dose-response not affected by TTX in the bath; (2) an equilibrium potential compatible with Cl-channel conductance; (3) a massive reduction with the competitive GABA(A) antagonist bicuculline; (4) a small reduction, if any, with the potent competitive GABA(B) antagonist CGP55845A; (5) persistence of the responses under 4-AP (4-aminopyridine), the potassium channel blocker, and inhibition of the 4-AP-induced calcium bursts of spikes. The conclusion was reached that the inhibitory response of PCs to 3-APPA is induced, like GABA inhibition, by binding to both GABA(A) and GABA(B) postsynaptic receptors.

The Unified Interaction Model Applied to the Gamma Induced Supralinearity and Sensitisation of Peaks 4 and 5 in LiF:Mg,Ti (TLD-100)

A comprehensive theory of thermoluminescence (TL) supralinearity and sensitisation, the Unified Interaction Model (UNIM) is described, based on both radiation absorption stage and recombination stage mechanisms. The UNIM can be applied to both heavy charged particles and isotropically ionising gamma rays and electrons, in a unified and self-consistent conceptual and mathematical formalism. The model is applied to explain the unique features of gamma induced supralinearity and sensitisation of peaks 4 and 5 in LiF:Mg,Ti, especially the strictly linear, then supralinear behaviour and the dependence of the supralinearity on ionisation density (gamma ray energy and particle type). A model is proposed for peak 4, based on its mainly 'hole-trapping' characteristics, which explains its diametrically opposed behaviour in sensitised material, i.e. a decreased sensitivity and supralinear dose response. All features arise from a localised trapping entity (the track for HCPs), spatially correlated trapping centres and luminescent centres (TC/LC pairs) for gamma rays and electrons, which dominate the dose response at low dose and are not subject to intra-track competitive processes, thus leading to linear dose-response behaviour. The decrease of the supralinearity with decreasing gamma ray energy (increasing ionisation density) arises from the increasing probability of the TC/LC pair to capture simultaneously an electron-hole pair, leading to geminate recombination not subject to competitive processes. The UNIM is shown to be capable of yielding excellent fits to the experimental data with many of the variable parameters of the model strongly constrained by ancillary measurements.

Production and characterization of group-specific monoclonal antibodies recognizing nonamidated, glycine- and taurine-amidated ursodeoxycholic acid 7- N-acetylglucosaminides

Ursodeoxycholic acid 7- N-acetylglucosaminides (UDCA 7-NAGs) are novel conjugated metabolites whose urine levels are expected to be a specific diagnostic index for primary biliary cirrhosis. To obtain a specific antibody which is useful for developing immunochemical analytical methods of UDCA 7-NAGs, a variety of monoclonal antibodies have been generated. Spleen cells from an A/J mouse, which had been immunized with a conjugate of nonamidated UDCA 7-NAG and bovine serum albumin, were fused with P3/NS1/1-Ag4-1 myeloma cells. After screening by an enzyme-linked immunosorbent assay (ELISA) using a β-galactosidase-labeled antigen, thirteen kinds of antibody-secreting hybridoma clones were established. Binding properties of these monoclonal antibodies were investigated in detail by ELISA. One of these antibodies, Ab-#8 ( γ 1, κ) had the most favorable characteristics for clinical application, which was group-specific to the 7-NAG conjugates of nonamidated, glycine- and taurine-amidated UDCAs providing a highly sensitive dose–response curve for each conjugate (midpoint 17 pg per assay for nonamidated UDCA 7-NAG). Cross-reactivities with eleven kinds of bile acids, including some potential interfering metabolites as UDCA 3-sulfate, were negligibly low. By using direct ELISA based on Ab-#8, daily urinary excretion rates of UDCA 7-NAGs of two healthy subjects were determined to be 1030 and 469 μg as GUDCA 7-NAG equivalent.

Nitric oxide and energy production in articular chondrocytes

Addition of human, recombinant interleukin-1 beta (hrIL-1 beta) to cultures of lapine articular chondrocytes provoked a delayed increase in the production of both nitric oxide (NO) and lactate. These two phenomena followed a similar time course and shared a parallel dose-response sensitivity to hrIL-1 beta. A causal relationship is suggested by the ability of N-monomethyl-L-arginine (NMA), an inhibitor of NO synthase, to blunt the glycolytic response to hrIL-1 beta. Furthermore, addition of S-nitroso-N-acetylpenicillamine (SNAP), which spontaneously generates NO in culture, increased lactate production to the same degree as IL-1. However, 8-Br-cGMP and isobutylmethylxanthine (IBMX) had no effect either in the presence or absence of IL-1. Even under standard, aerobic, cell culture conditions, chondrocytes consumed little oxygen, either in the presence or absence of IL-1 or NMA. Furthermore, cyanide at concentrations up to 100 microM had no effect upon NO synthesis or lactate production. Thus, the increases in glycolysis under study were not secondary to reduced mitochondrial activity. Although cells treated with IL-1 had increased rates of glycolysis, their concentrations of ATP fell below those of untreated chondrocytes in a time-dependent, but NMA-independent, manner. Transforming growth factor-beta (TGF-beta) and synovial cytokines (CAF) also increased lactate production. However, TGF-beta failed to induce NO, and its effect on glycolysis was independent of NMA. Furthermore, cells treated with TGF-beta were not depleted in ATP. These data are consistent with hypotheses that rates of proteoglycan synthesis are, in part, regulated by the intracellular concentration of ATP or by changes in pericellular pH. These two possibilities are not mutually exclusive.

Photoreceptor-specific efficiencies of ?-carotene, zeaxanthin and lutein for photopigment formation deduced from receptor mutant Drosophila melanogaster

Drosophila rearing media had only beta-carotene, zeaxanthin or lutein as precursors for photopigment chromophores. Zeaxanthin and lutein are potentially optimum sources of the 3-hydroxylated retinoids of visual and accessory photopigments. Mutants made the electroretinogram in white (w) eyes selective for compound eye photoreceptors R1-6, R7 and R8: R1-6 dominates w's electroretinogram; R7/8 generates w;ora's (ora = outer rhabdomeres absent); R8 generates w sev;- ora's (sev = sevenless). Microspectrophotometry revealed R1-6's visual pigment. In w, all 3 carotenoids yielded monotonic dose-responses for sensitivity or visual pigment. An ultraviolet sensitivity peak from R1-6's sensitizing pigment was present at high but not low doses. In w;ora, all 3 carotenoids gave similar spectra dominated by R7's high ultraviolet sensitivity. For w sev;ora, all spectra were the shape expected for R8, peaking around 510 nm. The sensitivity dose-response was at its ceiling except for low doses in w;ora and zero supplementation in w sev;ora. Hence, without R1-6, most of our dose range mediated maximal visual pigment formation. In Drosophila, beta-carotene, zeaxanthin and lutein mediate the formation of all major photopigments in R1-6, R7 and R8.

Manganese Activation of CaSO4:Dy

The influence of Mn activation on CaSO4:Dy thermoluminescent (TL) phosphor has been observed to study the basic TL characteristics such as TL output, fading, sensitivity, and dose response. The experimental results indicate that the TL characteristics are strongly influenced by the concentration of Mn dopant in CaSO4:Dy, especially for the low temperature trapping peak of the glow curves. The TL properties of CaSO4:Dy:Mn phosphor with a concentration ratio of 1:4 of Dy to Mn include not only high sensitivity, negligible fading, and linear dose response as compared to the CaSO4:Dy phosphor, but also two well-separated peaks and relative peak heights. This suggests that it can be used for accidental dose and elapsed time evaluations as well as for a routine personnel dosimeter. It was also found that 350 degrees C to 400 degrees C for 30 min is the optimum temperature and time in annealing treatment for this phosphor.

Autocrine β-related interferon controls c- myc suppression and growth arrest during hematopoietic cell differentiation

Different hematopoietic cells produce minute amounts of β-related interferon (IFN) following induction of differentiation by chemical or natural inducers. The endogenous IFN binds to type I cell surface receptors and modulates gene expression in the producer ceils. We show that self-induction of two members of the IFN-induced gene family differs in the dose response sensitivity and the prolonged kinetics of mRNA accumulation from the response to exogenous IFN- β 1. Production and response to endogenous IFN are also detected when bone marrow precursor cells differentiate to macrophages after exposure to colony stimulating factor 1. In M1 myeloid cells induced to differentiate by lung-conditioned medium, addition of antibodies against IFN-β partially abrogates the reduction of c- myc mRNA and the loss in cell proliferative activity, which both occur during differentiation. The endogenous IFN therefore functions as an autocrine growth inhibitor that participates in controlling c- myc suppression and the specific G0 G1 arrest during terminal differentiation of hematopoietic cells.

In vivo modulation of leukotaxis by non-steroidal anti-inflammatory drugs.

Since non-steroidal anti-inflammatory drugs (NSAIDs) are widely used for inhibition of inflammation, an in vivo assay for leukotaxis would be of use in comparing the biological activity effects of the agents. Here, the effects of 4 different NSAIDs on in vivo leukocyte accumulation was determined by quantitating N-formyl-methionyl-leucylphenylalanine induced leukotaxis in the rabbit anterior eye chamber. New Zealand white female rabbits were treated for three days with the following regimens: ibuprofen or aspirin, 0.1, 1.0, 10.0 or 100.0 mg/kg/day, indomethacin or flurbiprofen, 0.01, 0.1, 1.0, or 10.0 mg/kg/day. Indomethacin and flurbiprofen significantly reduced leukotaxis in a dose of 10.0 mg/kg/day. Aspirin was associated with a weak inhibition of leukotaxis. Ibuprofen had biphasic effects, 1.0 mg/kg/day potentiated and 10 mg/kg/day inhibited leukotaxis, whereas leukocyte accumulation was uneffected by a high dose (100.0 mg/kg/day). These results suggest that modulation of leukotaxis by NSAIDs may reflect a differential dose-response sensitivity of lipoxygenase and cycloxygenase pathways.

Evaluation of beta-D-galactosidase from Escherichia coli and horseradish peroxidase as labels by sandwich enzyme immunoassay technique.

beta-D-galactosidase from Escherichia coli and horseradish peroxidase were evaluated as labels of Fab' in dose-response curves for human alpha-fetoprotein and human chorionic gonadotropin by sandwich enzyme immunoassay technique using fluorogenic substrates for enzyme assay. The non-specific binding of Fab'-peroxidase conjugates to IgG-coated polystyrene balls was less than that of Fab'-beta-D-galactosidase conjugates, and the affinity-purified Fab'-peroxidase conjugates gave more sensitive dose-response curves for these antigens than the corresponding beta-D-galactosidase conjugates. However, a large quantity of Fab'-peroxidase conjugates was required and a longer incubation was necessary for the peroxidase assay, since the peroxidase assay was much less sensitive than the beta-D-galactosidase assay. Other advantages and disadvantages of the two enzymes are discussed.

Endotoxin dose. I. Hemodynamic, metabolic, and lethal consequences in Yucatan minipigs.

This study was performed in part to establish an endotoxin dosage in miniature swine that would yield reproducible cardiovascular and metabolic aberrations over a specific 6-h sampling period, minimizing lethality during that time. Five groups of three 6-mo-old Yucatan miniature pigs were surgically fitted with jugular vein and carotid artery catheters. One week later they were placed in slings and infused for 6 h with Difco 055:B5 endotoxin at dosages of 0, 2.5, 7.5, 15, and 25 micrograms X kg-1 X h-1. Significant (P less than or equal to 0.05) time-dose interactions were observed in mean arterial pressure, plasma glucose, serum potassium, blood lactate, pyruvate, bicarbonate, pH, PO2, PCO2, and urea nitrogen. Significant (P less than or equal to 0.05) differences were seen in lethality by 5 days postendotoxin: 0 = 0%, 2.5 = 0%, 7.5 = 33%, 15 = 67%, and 25 = 100% lethal. These animals exhibited a sensitive dose response to endotoxin, often at two- or threefold dose differences. The 15 and 25 micrograms X kg-1 X h-1 groups consistently demonstrated the most profound changes in the parameters measured.