Prostaglandin E2 stimulates insulin-like growth factor binding protein-4 expression and synthesis in cultured human articular chondrocytes: possible mediation by Ca(++)-calmodulin regulated processes.

Insulin-like growth factor-1, IGF-1, is believed to be an important anabolic modulator of cartilage metabolism whose action is mediated by high affinity cell surface receptors and bioactivity and bioavailability regulated, in part, by IGF-1 binding proteins (IGFBPs). Prostaglandin E2 (PGE2) stimulates collagen and proteoglycan synthesis in cartilage via an autocrine feedback loop involving IGF-1. We determined whether the eicosanoid could regulate IGFBP-4, a major form expressed by chondrocytes and, as such, act as a modifier of IGF-1 action at another level.

Against all odds: the survival strategies of Deinococcus radiodurans.

Bacteria of the genus Deinococcus exhibit an extraordinary ability to withstand the lethal and mutagenic effects of DNA damaging agents-particularly the effects of ionizing radiation. These bacteria are the most DNA damage-tolerant organisms ever identified. Relatively little is known about the biochemical basis for this phenomenon; however, available evidence indicates that efficient repair of DNA damage is, in large part, responsible for the deinococci's radioresistance.

Prostaglandin E2 stimulates incorporation of proline into collagenase digestible proteins in human articular chondrocytes: identification of an effector autocrine loop involving insulin-like growth factor I.

Prostaglandin E2 (PGE2) stimulates collagen gene promoter activity in transfected human chondrocytes though no canonical cyclic AMP (cAMP) response element has been yet identified. Human insulin-like growth factor-1 (IGF-1) induces an increase in collagen type II expression and synthesis in chondrocytes. Since our preliminary data suggested that PGE2 can stimulate IGF-1 release from human articular chondrocytes, we examined whether the eicosanoid could influence collagen synthesis and whether the effect was mediated by IGF-1.

Radioresistance of Deinococcus radiodurans: functions necessary to survive ionizing radiation are also necessary to survive prolonged desiccation.

Forty-one ionizing radiation-sensitive strains of Deinococcus radiodurans were evaluated for their ability to survive 6 weeks of desiccation. All exhibited a substantial loss of viability upon rehydration compared with wild-type D. radiodurans.

Extrafocal radiation: a unified approach to the prediction of beam penumbra and output factors for megavoltage x-ray beams.

An extrafocal source model has been developed to explain the dependence of head scatter and beam penumbra on field size. In this model, the x-ray source of a medical linear accelerator is described by two components: a small but intense focal component; and a broadly distributed extrafocal component of low intensity. The extrafocal component is so large that it can be "eclipsed" by the field-defining collimators.

Radiation dosimetry in human bone using electron paramagnetic resonance.

Accurate measurements of dose in bone are required in order to improve the dosimetry of systemic radiotherapy for osseous metastases. Bone is an integrating dosimeter which records the radiation history of the skeleton. During irradiation, electrons become trapped in the crystalline component of bone mineral (hydroxyapatite).

Genetic characterization of forty ionizing radiation-sensitive strains of Deinococcus radiodurans: linkage information from transformation.

Natural transformation was used to help define a collection of ionizing radiation-sensitive strains of Deinococcus radiodurans. Three putative rec mutations were identified, as were three pol alleles. Forty of the ionizing radiation-sensitive strains were placed into 16 linkage groups, and evidence obtained indicates that each linkage group consists of a cluster of mutations not more than 1,000 bp apart.

Monte Carlo studies of x-ray energy absorption and quantum noise in megavoltage transmission radiography.

The subject contrast of bony anatomy in megavoltage medical radiographs is very low, making detection of bony landmarks difficult if additional noise sources are introduced into the images. One source of noise, which is inherent to the x-ray detection process, is x-ray energy absorption noise. X-ray energy absorption noise results from variations in the amount of energy deposited in the imaging detector per interacting x ray.

Peroxynitrite causes DNA nicks in plasmid pBR322.

Peroxynitrite causes single-strand breaks in pBR322 supercoiled DNA as evidenced by agarose gel electrophoresis analysis. The effect of three free radical scavengers, namely mannitol, benzoate and dimethylsulfoxide, were studied. Mannitol failed to protect DNA from damage by peroxynitrite while benzoate and dimethylsulfoxide amplified the damage.

Dose distributions and dose rate constants for new ytterbium-169 brachytherapy seeds.

Relative dose distributions in the vicinities of two new prototypes of ytterbium-169 brachytherapy sources have been measured using lithium fluoride thermoluminescent dosimeters (TLD) placed in a solid water phantom. The type 6 seed consists of four Yb2O3 spheres contained in a 0.075-mm thick titanium tube, with overall dimensions of 4.

Novel ionizing radiation-sensitive mutants of Deinococcus radiodurans.

Two new loci, irrB and irrI, have been identified in Deinococcus radiodurans. Inactivation of either locus results in a partial loss of resistance to ionizing radiation. The magnitude of this loss is locus specific and differentially affected by inactivation of the uvrA gene product.

Inclusion of energy straggling in a numerical method for electron dose calculation.

Energy straggling along electron trajectories has been incorporated into a numerical algorithm for electron beam dose calculations. Landau's theory is used to predict, at any point in the absorber, the broadening of the primary electron energy spectrum due to energy loss straggling. Numerical calculations have been performed for electron beams with energies of 10-30 MeV incident upon water in order to determine the variation of dose with depth and variation of energy spectra with pathlength.

Lesion spectra: radiation signatures and biological gateways.

We describe an integrative approach to the modeling of biophysical radiation effects. The model takes aim at practical applications of the knowledge provided by molecular studies of radiation-matter interactions in DNA. The central proposition is the idea that the distribution of molecular lesions (i.

Radiance and particle fluence.

The concepts of radiance and fluence are fundamental to the description of a radiation field. The International Commission on Radiological Units and Measurements (ICRU) has defined fluence in terms of the number of the radiation particles crossing a small sampling sphere. A second definition has been proposed in which the length of track segments contained within any sampling volume are used to calculate the incident fluence.

A method for the calculation of electron energy-straggling spectra.

To calculate electron beam dose distributions accurately, numerical methods of electron transport calculations must account for the statistical variation (or "straggling") in electron energy loss. This paper shows that the various energy straggling theories that are applicable to short path lengths all derive from a single statistical model, known as the compound Poisson process. This model in turn relies on three assumptions: (1) the number of energy-loss events in a given path length is Poisson distributed; (2) events are mutually independent; and (3) each event has the same probability distribution for energy loss (i.

X-ray scatter in megavoltage transmission radiography: physical characteristics and influence on image quality.

The physical characteristics of x rays scattered by the patient and reaching the imaging detector, as well as their effect on verification (portal) image quality, were investigated for megavoltage (0.1-20 MeV) x-ray beams. Monte Carlo calculations and experimental measurements were used to characterize how the scatter and primary fluences at the detector plane were influenced by scattering geometry and the energy spectrum of the incident beam.

Dose calculations using convolution and superposition principles: the orientation of dose spread kernels in divergent x-ray beams.

The convolution/superposition method of dose calculation has the potential to become the preferred technique for radiotherapy treatment planning. When this approach is used for therapeutic x-ray beams, the dose spread kernels are usually aligned parallel to the central axis of the incident beam. While this reduces the computational burden, it is more rigorous to tilt the kernel axis to align it with the diverging beam rays that define the incident direction of primary photons.

X-ray sources of medical linear accelerators: focal and extra-focal radiation.

A computerized tomography (CT) reconstruction technique has been used to make quantitative measurements of the size and shape of the focal spot in medical linear accelerators. Using this technique, we have measured the focal spots in a total of nine accelerators, including (i) two Varian Clinac 2100c's, (ii) two Atomic Energy of Canada Ltd. (AECL) Therac-25's, (iii) two AECL Therac 6's, (iv) a Siemens KD-2, (v) a Varian Clinac 600c (4 MV), and (vi) an AECL Therac-20.

The relative biological effectiveness of ytterbium-169 for low dose rate irradiation of cultured mammalian cells.

Purpose: An important step in the development of 169Yb as a new brachytherapy source is to determine its biological effectiveness relative to other commonly used radioisotopes. The purpose of this paper is to determine the relative biological effectiveness of 169Yb, with respect to 60Co, for a range of low dose rates.

Method And Materials: The relative biological effectiveness of photon radiation from encapsulated 169Yb was determined by exposing Chinese hamster ovary cells, in exponential growth, to graded doses of radiation from either 169Yb or 60Co.

True three-dimensional dose computations for megavoltage x-ray therapy: a role for the superposition principle.

The objective of radiation therapy is to concentrate a prescribed radiation dose accurately within a target volume in the patient. Major advances in imaging technology have greatly improved our ability to plan radiation treatments in three dimensions (3D) and to verify the treatment geometrically, but there is a concomitant need to improve dosimetric accuracy. It has been recommended that radiation doses should be computed with an accuracy of 3% within the target volume and in radiosensitive normal tissues.

Ytterbium-169: calculated physical properties of a new radiation source for brachytherapy.

Seeds containing radioactive Ytterbium-169 (169Yb) have recently been manufactured for possible application to brachytherapy. Ytterbium-169 emits photons with an average energy of 93 keV (excluding energies less than 10 keV), and decays with a half-life of 32 days. Analytic and Monte Carlo computations have been used to predict physical quantities useful in treatment planning and radiation protection.

Daily monitoring and correction of radiation field placement using a video-based portal imaging system: a pilot study.

We have developed a video-based portal imaging system for radiotherapy localization. The system can acquire high quality portal images automatically using short (1-3 monitor unit) irradiations and immediately display the images. The major advantage of the imaging system is that it can be used routinely to check and correct patient positioning before much of the daily irradiation has been delivered.

Activity distribution of a cobalt-60 teletherapy source.

In the course of quantifying the effect of radiation source size on the spatial resolution of portal images, a concentric ring structure in the activity distribution of a Cobalt-60 teletherapy source has been observed. The activity distribution was measured using a strip integral technique and confirmed independently by a contact radiograph of an identical but inactive source replica. These two techniques suggested that this concentric ring structure is due to the packing configuration of the small 60Co pellets that constitute the source.

Dominant negative umuD mutations decreasing RecA-mediated cleavage suggest roles for intact UmuD in modulation of SOS mutagenesis.

The products of the SOS-regulated umuDC operon are required for most UV and chemical mutagenesis in Escherichia coli. The UmuD protein shares homology with a family of proteins that includes LexA and several bacteriophage repressors. UmuD is posttranslationally activated for its role in mutagenesis by a RecA-mediated proteolytic cleavage that yields UmuD'.

Computerized tomography versus perfusion lung scanning in canine radiation lung injury.

Computerized tomographic (CT) measurements of lung density were obtained before and serially after thoracic irradiation in dogs to detect the alterations caused by radiation therapy. Fourteen mongrel dogs were given either 2000 cGy (Group A, 10 dogs, right lower zone irradiation), 1000 cGy (Group B, 2 dogs, right lower zone irradiation), or 500 cGy (Group C, 2 dogs, right lung irradiation) in one fraction. Once before and bi-weekly after irradiation, the anesthetized dogs had thoracic CT scans.