Small Doses Of Radiation Research Articles

Abstract 67: A novel survivin-mediated adaptive response induced by very low dose imaging-level exposures and radiation therapy.

Abstract Exposure of cells to a very low dose of ionizing radiation can induce an enhanced resistance or adaptive response to a subsequent larger radiation dose as evidenced by an increase in cell survival. This expression of an adaptive response has been attributed to the result of signaling processes induced by very low radiation doses in the range of 0.5 to 100 mGy. The radiation-induced adaptive response is garnering considerable attention now due in part to the burgeoning increase in the use of imaging technologies such as computerized axial tomography and portal imaging to monitor tumor response and positioning during multi-dose standard radiation therapy protocols. The focus of this study was to investigate whether this process could occur when the delivery of the very small radiation dose was administered before or in between the administration of two typically used radiation therapy level doses. Specifically, could this signaling process be perturbed by the addition of a second 2 Gy dose of ionizing radiation delivered at a relatively short time interval from the exposure of cells to the very low dose? A human colon carcinoma cell line (RKO36) along with transformed mouse embryo fibroblasts (MEF), both wild type (WT) or tumor necrosis factor receptor 1 and 2 knockout cells (TNFR1−2−) were grown to confluence in vitro or as MEF tumors in the flank of C57BL/6 mice. Changes in SOD2 enzymatic activity, survivin protein, apoptosis, and cell survival as a function of radiation conditions and transfection of cells with SOD2-or survivin siRNA were determined. An adaptive response was induced in cells at all doses tested from 5 to 100 mGy. The adaptive responses measured in all three cell lines were associated with a reduction in apoptosis frequencies, a 5 to 20% increase in cell survival, and a rapid 2 to 3 fold elevation in survivin protein levels. Very low dose radiation-induced elevation in survivin levels was completely inhibited by transfection of cells with survivin siRNA. This was accompanied by an increase in apoptosis and a loss of the expression of these survival related adaptive responses. We have identified a very low radiation dose-induced survivin-mediated adaptive response that may affect therapeutic outcomes associated with increased usage of imaging procedures in radiation therapy. This work was supported by NIH/NCI grant R01 CA132998 and DOE Low Dose Program/Project Grant DE-SC0001271 (D.J.G.) Citation Format: Jeffrey S. Murley, Richard C. Miller, Helena J. Mauceri, Harold G. Sutton, Ralph R. Weichselbaum, David J. Grdina. A novel survivin-mediated adaptive response induced by very low dose imaging-level exposures and radiation therapy. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 67. doi:10.1158/1538-7445.AM2013-67

Processes in afterglow responsible for initiation of electrical breakdown in xenon at low pressure

AbstractThe processes responsible for initiation of electrical breakdown in xenon-filled tube with two spherical iron electrodes at 2.7-mbar pressure have been analyzed. The analysis is based on the experimental data of electrical breakdown time delay as a function of afterglow period. It is shown that positive ions remaining from previous discharge, as well as positive ions created in mutual collisions of metastable atoms in afterglow, have a dominant role in secondary emission of electrons from the cathode which lead to initiation of breakdown in early afterglow. In late afterglow, dominant role in initiation of breakdown is taken by N(4S) atoms formed during the discharge by dissociation of ground state nitrogen molecules that are present as impurities in xenon. When the concentration of N(4S) atoms decreases sufficiently, the initiation of breakdown is caused by cosmic radiation. Small doses of gamma-ray irradiation also contribute to the initiation of breakdown, but only for large values of the afterglow period.

Epitaxial Graphene Sensors for Detection of Small Magnetic Moments

Micron-sized Hall sensors made of epitaxial graphene grown on 4H-SiC(0001) have been fabricated and studied at room temperature using transport and noise spectrum measurements. We report detection of 1-μm Dynal bead with the magnetic moment of ~4×108 μB, using a 2-μm epitaxial graphene device. A phase-sensitive AC-DC Hall magnetometry method was used to reliably detect the bead with a relatively large response of VxAC ~ 7 μV. Bead positioning was performed using a nanomanipulator inside of the FIB system. Long-term effect of the small dose of e-beam irradiation (~4 × 1014 e/cm2) on the performance of graphene Hall devices is reported.

Treatment of Onychomycosis Using Radiation of Excimer Laser

It is known that UV-C radiation kills fungus by radiating their DNA. We wanted to verify, if we could use radiation produced by excimer laser as an alternative method for the treatment of onychomycosis – nail fungus. Medical procedure like this should meet certain conditions such as perfectly and reliably destroying the fungi and to make no harm to the patient (in this case overheating of the under-nail tissue). The main part of the first stage of this work was to determine the coefficients for transmission, reflection and absorption of nails to determine the quantity of energy going through and absorbed by the nail – that means quantity of energy which could harm the healthy tissue. In the following stage we focused on the irradiation of the fungi. Our final task was to assess whether is it possible to determine the parameters of the radiation (total dose, dose per pulse frequency, repetition rate and number of pulses) for which the elimination of the fungi would be most effective without damaging the nail and the soft tissue underneath it. The results so far have proven that UV-C radiation does not pass through a fingernail to such extent that it could damage the soft tissue beneath it. We've measured the absorption and transmission spectrum for the nail tissue at the first time and we've determined the value of absorption coefficient is α = 1.7 mm-1 at the wavelength of 700 nm (transmission max.). Fungi are destroyed by the application of small doses of radiation using the excimer laser. The goal of the last phase of our work was to determine the modulation parameters of the excimer laser radiation for the treatment of onychomycosis. Refining the parameters and finding out the optimal values for different ranges and types of illnesses will require additional measurements.

Abstract P4-02-10: Molecular Breast Imaging: A multicenter clinical registry to compare breast-specific gamma imaging (BSGI) and breast MRI in the detection of breast carcinoma

Abstract Purpose: Breast-Specific Gamma Imaging (BSGI), also known as molecular breast imaging (MBI), is a diagnostic breast imaging procedure using that is becoming more common in clinical practice. In the BSGI procedure, a patient receives an intravenous injection of Tc99m-Sestamibi (MIBI) and imaging is conducted with a breast-optimized gamma camera. According to the clinical literature, the largest advantage of BSGI when compared to mammography is that the sensitivity of the examination is not influenced by breast tissue density. The goal of this work is to quantify the clinical sensitivity of BSGI against that of MRI, another diagnostic imaging modality capable of detecting mammographically occult malignancies. Methods: A multi-center patient registry was maintained for all patients routinely sent to BSGI and MRI as part of their diagnostic work up. All patients who had a malignant finding on subsequent needle biopsy or surgery within 12 months post imaging were included in this analysis. The BIRADS rating schematic was used for MRI and a similar, 6-category system was used for the BSGI images. For each modality, the reports were classified as Negative: category 1–3 and positive: category 4–6. Results: There were 60 patients with 63 malignant breast lesions. MRI was negative in 6 lesions (2 DCIS, 3 IDC and 1 ILC) while BSGI was negative in 6 lesions (5 IDC and one mixed IDC/DCIS). Both BSGI and MRI detected 56 of the 63 malignancies providing a sensitivity of 89% for both modalities. The combination of BSGI and MRI detected 63 of the 63 malignancies for a sensitivity of 100%.[table 1] Conclusions: According to the results of this patient registry, BSGI provides equal sensitivity to that of MRI however each modality was false-negative in different patients. As a result, while each modality provided a sensitivity of 89%, the combination of BSGI and MRI provided a sensitivity of 100%. The MBI/BSGI procedure does involve a relatively small dose of radiation, but this dose is less than the dose patients receive from other common diagnostic examinations such as a chest CT scan. According to RadiologyInfo.org, a website co-developed by the American College of Radiology and Radiological Society of North America, “…there are no known long-term adverse effects from such low-dose exposure.” In comparison, MRI does not involve exposure to radiation but utilizes a contrast agent that has been reported to cause adverse reactions in a very small number of patients, especially those with insufficient kidney or liver function. In addition, MRI cannot be performed in some types of patients such as those with metal implants, or those with claustrophobia. In our experience, BSGI is a low-cost imaging procedure (the procedure costing approximately 1/3 that of MRI) that is well tolerated by patients and can be used in patients who for whom MRI is contraindicated or very challenging. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P4-02-10.

Physical Interactions of Charged Particles for Radiotherapy and Space Applications

In this paper, the basic physics by which energetic charged particles deposit energy in matter is reviewed. Energetic charged particles are used for radiotherapy and are encountered in spaceflight, where they pose a health risk to astronauts. They interact with matter through nuclear and electromagnetic forces. Deposition of energy occurs mostly along the trajectory of the incoming particle, but depending on the type of incident particle and its energy, there is some nonzero probability for energy deposition relatively far from the nominal trajectory, either due to long-ranged knock-on electrons (sometimes called delta rays) or from the products of nuclear fragmentation, including neutrons. In the therapy setting, dose localization is of paramount importance, and the deposition of energy outside nominal treatment volumes complicates planning and increases the risk of secondary cancers as well as noncancer effects in normal tissue. Statistical effects are also important and will be discussed. In contrast to radiation therapy patients, astronauts in space receive comparatively small whole-body radiation doses from energetic charged particles and associated secondary radiation. A unique aspect of space radiation exposures is the high-energy heavy-ion component of the dose. This is not present in terrestrial exposures except in carbon-ion radiotherapy. Designers of space missions must limit exposures to keep risk within acceptable limits. These limits are, at present, defined for low-Earth orbit, but not for deep-space missions outside the geomagnetosphere. Most of the uncertainty in risk assessment for such missions comes from the lack of understanding of the biological effectiveness of the heavy-ion component, with a smaller component due to uncertainties in transport physics and dosimetry. These same uncertainties are also critical in the therapy setting.

Effects of gamma radiation on the mechanical properties of and susceptibility to biodegradation of natural fibers

The effect of gamma radiation on the mechanical properties and surface structure of woven fabrics made of cotton, flax, and silk fibers was investigated. It was found that small radiation doses (up to 15 kGy), sufficient for effective disinfection of textiles, caused only insignificant changes in the fiber parameters tested. However, it was found that doses increased to 100 kGy bring about a considerable weakening of the tested fabrics——their tensile strength decreases by 26–33%. Microbiological examination has shown that preradiation of cotton and linen fabric samples with a dose of 100 kGy does not affect the susceptibility of these fabrics to fungal biodegradation. A silk fabric irradiated under the same conditions shows clear susceptibility to bacterial biodegradation.

Radiographic examination of patients with dehiscence of semicircular canals with digital volume tomography

Digital volume tomography (DVT) is an extension of panoramic tomography. With this diagnostic technique, characterized by high resolution, a narrow section width (0.125 mm), and three-dimensional display, small pathological processes can be well visualized. We examined 434 patients with DVT (Accu-I-tomo, Morita, Japan). Eleven patients with a history of peripheral vertigo presented a fistula of the labyrinth. The results were compared with intraoperative findings to evaluate the diagnostic value of DVT in cases of erosion of the semicircular canals. With high resolution and artifact-free demonstration of the labyrinth and inner ear structures, it was possible to determine the presence of a fistula of the semicircular canals in all 11 patients. An erosion of the lateral semicircular canal was found in nine patients with additional fistulae of the superior and posterior semicircular canals in one patient, a dehiscence of bone of the superior semicircular canal in one patient, and a dehiscence of the posterior semicircular canal in another patient. The predicted erosion of semicircular canals was verified in all patients during surgery where a closure of the fistulae was performed. DVT is an excellent technique to examine the semicircular canal structures in patients with peripheral vertigo, and expand the application of diagnostic possibilities in the lateral skull base. With this method, the preoperative diagnosis is improved allowing more accurate planning of the surgical procedure. DVT delivers a small radiation dose with a high resolution and a low purchase price for the equipment.

Low-Dose Radiation Treatment in Pulmonary Mucosa-Associated Lymphoid Tissue Lymphoma: A Plausible Approach? A Single-Institution Experience in 10 Patients

To propose an alternative approach for treatment of pulmonary marginal zone lymphoma, using a very small radiation dose (2 × 2 Gy) delivered exclusively to tumor sites. Patients had localized pulmonary mucosa-associated lymphoid tissue (MALT) lymphoma according to the World Health Organization classification. The 6-MV radiation treatments were delivered using tumor-limited fields, except in cases of diffuse bilateral involvement. Two daily fractions of 2 Gy were delivered to tumor-limited fields using a 6-MV linear accelerator. Ten patients with pulmonary MALT lymphoma entered the study. All but 1 had localized tumor masses. The median follow-up was 56 months (range, 2-103 months). Complete remission or an unconfirmed complete remission was obtained in 60% of patients within the first 2 months, and two additional partial responses were converted into a long-term unconfirmed complete remission. All patients are well and alive, no local progression was observed, and the 5-year progression-free survival rate was 87.5% (95% confidence interval 49%-97%). Our results suggest that extremely low radiation doses delivered exclusively to tumor sites might be a treatment option in pulmonary MALT lymphoma.

Electrical Conductivity Enhancement of PTFE (Teflon) Induced by Homogeneous Low Voltage Electron Beam Irradiation (HLEBI)

Electrical conductivity (·) enhancement, control, aging stability, and linear relation between · and reciprocal temperature (1/T) in PTFE (Teflon) had been examined by homogeneous low potential electron beam irradiation (HLEBI). Irradiations up to 0.432MGy were found to raise the · of PTFE more than two orders of magnitude. In addition, control of electron movement or Fermi level by HLEBI on polymers seems possible since at low HLEBI levels up to 0.216MGy, a strong dependence on · was observed. Aging stability investigation showed the saturated conductivities at 10 6 s( ·s) (2.5 © 10 ¹16 and 3.6 © 10 ¹15 Sm ¹1 ) obtained at EB doses of 0.0432 and 0.432MGy, respectively were approximately 4.9 and 70.6 times higher than · of untreated PTFE (5.1 © 10 ¹17 Sm ¹1 ). Although the aging initially reduced the · of irradiated samples, ·s were remarkably higher than the untreated. For example, the lower dose 0.0432MGy samples decayed significantly, but its ·s value (2.5 © 10 ¹16 Sm ¹1 ) was still about 490% above untreated condition at 5.1 © 10 ¹17 Sm ¹1 . ESR (electron spin resonance) measurements showed aging for 10 6 s only slightly reduced the peak intensity of irradiated PTFE. This indicated the charge carriers generated did not easily decay. Results agree with the literature where PTFE was irradiated with VUVand radicals such as CF3 + did not substantially decay with aging. Since the slopes of linear relationships between logarithmic electrical conductivity (ln·) and reciprocal temperature (1/T) of all PTFE samples irradiated were approximately equal to that before treatment from 303 to 375K, HLEBI didn’t convert the · system. The small irradiation dose of 0.0432MGy raised the electrical conductivity at room temperature. At higher temperatures above ³375K, the 0.0432 and 0.432MGy-HLEBI generated drops in conductivity ·. When unstable dangling bonds with isolated radicals at terminated sites are assumed to be formed in irradiated PTFE, the · recovery by heating to 424K as well as high · of irradiated PTFE could be explained. HLEBI probably generated dangling bonds in the form of radicals acting as acceptors to carry charge. Since a chemical dopant was not needed to act as a charge carrier, HLEBI could probably be an attractive method to attain homogeneous doping of organic films. [doi:10.2320/matertrans.M2011273]

Repeated small perturbation approach reveals transcriptomic steady states.

The study of biological systems dynamics requires elucidation of the transitions of steady states. A “small perturbation” approach can provide important information on the “steady state” of a biological system. In our experiments, small perturbations were generated by applying a series of repeating small doses of ultraviolet radiation to a human keratinocyte cell line, HaCaT. The biological response was assessed by monitoring the gene expression profiles using cDNA microarrays. Repeated small doses (10 J/m2) of ultraviolet B (UVB) exposure modulated the expression profiles of two groups of genes in opposite directions. The genes that were up-regulated have functions mainly associated with anti-proliferation/anti-mitogenesis/apoptosis, and the genes that were down-regulated were mainly related to proliferation/mitogenesis/anti-apoptosis. For both groups of genes, repetition of the small doses of UVB caused an immediate response followed by relaxation between successive small perturbations. This cyclic pattern was suppressed when large doses (233 or 582.5 J/m2) of UVB were applied. Our method and results contribute to a foundation for computational systems biology, which implicitly uses the concept of steady state.

Magnetic Resonance Imaging to Guide Surgical Practice

Magnetic resonance (MR) imaging can provide functional and anatomical information in a single non-ionising examination and represents a rapidly expanding area of innovation and technology research. The lymphatic system is a complex network of lymph vessels, nodes and organs, and is essential for the maintenance of fluid homeostasis and immunocompetence. Failure of lymph clearance from the limb can be caused bycongenital absence of lymph vessels or valve incompetence, which are relatively uncommon compared to acquired obliteration of the lymph vessels (infection, trauma, radiotherapy) and obstruction of the lymph nodes by primary and secondary malignant disease, and nodal hilar fibrosis. Adequate imaging of the lymphatic system in the lower limbs should therefore be able to delineate the anatomy of the lymph vessels and nodes, both proximal and distal to the area of interest, and also provide functional information on the rate of lymph clearance. X-ray lymphangiography was one of the first techniques developed to visualise the lymphatics. 1 Patent blue dye is first injected subcutaneously into each of the web spaces in the foot (visual lymphangiography), to stain and localise the deep lymphatic vessels. The skin on the dorsum of the footis then incised and a large lymph vessel is cannulated. Oily X-ray contrast medium is injected directly into the lymph vessel and serial images are acquired; initial images show the lymph vessels whereas later ones delineate the lymph nodes. Abdominal films are required for the iliac and aortic lymph nodes and a chest film to assess the thoracic duct. This technique can give high spatial resolution anatomical and functional information, however it is hampered by: the use of ionising radiation; a single vessel is cannulated and so only some of the lymph vessels are shown; the 2D acquisition is a projection and therefore some vessels may be superimposed on others; the procedure is relatively invasive; the injected contrast media may cause inflammation and fibrosis of the lymph vessels; pulmonary complications such as pulmonary embolus and adult respiratory distress syndrome have been reported; and the contrast media may take several years to be removed from the body. 2e4

Radiation and risk: Is it time for a regulatory threshold dose?

This editorial follows somewhat from Madhava Bhat’s guest editorial published in the Sept 2010 issue entitled ‘‘‘‘Fear of radiation’’ is frightening’’ [1]. As Madhava suggests, there is a heightened level of fear in the general community regarding radiation, and this is not just confined to ionising radiation (IR) but also non-ionising radiation (NIR), such as electromagnetic fields and mobile phones. I am not going to discuss NIR here except to say that I believe this area also has some worrying developments from a regulatory perspective, and in particular the use of the precautionary principle where there is a very limited scientific evidence of a biological effect. It is understandable why the general community fears radiation. For instance, you cannot see it or feel it, but due to the sensitivity of detectors we can measure the tiniest amount of it. Over the last 60 years or so, we have been bombarded with images of atomic bombs, people in ‘‘radiation suits’’ and pictures of the known damaging effects of high dose radiation. In addition, images of Homer Simpson ‘‘working’’ in the Springfield nuclear power plant, and the subliminal messages found in many of our comic books suggest that radiation will mutate you into a superhero or villain. Currently, there approximately 221 comic characters who’s powers originated from radiation [2]. As well as the images, there are many conflicting reports or opinions regarding the biological effects of radiation and these are often based on either some ideological or political belief or differences within the scientific and regulatory community itself. This situation is not helped by the current media cycle of unbalanced reporting; often with farleft or far-right political views getting more publicity due to their controversy rather than the facts. As a radiation regulator, I often encounter people who are unaware that they are exposed to background levels of radiation from cosmic, terrestrial and internal (body) radiation sources. Many also don’t know that life has evolved on Earth in which natural background radiation levels some 3.5 billion years ago were about three times higher than they are now [3]. For some reason scientists and regulators have failed to remind the general community, or have been unable to get the message across, about the basics of radiation and that it’s a natural phenomenon. Although the population is ‘‘bathed’’ in background radiation, the fact remains that most will only ever receive a small additional radiation dose from the activities they undertake or the medical procedures they require. The only time a person is likely to be exposed to high or dangerous doses of radiation is when they are undergoing medical treatment e.g. radiotherapy or involved in a radiation incident. However, what is deemed ‘‘dangerous’’ depends on what side of the Linear No Threshold (LNT) fence you sit on! A. M. Hooker (&) Faculty of Health Sciences, School of Medicine, Flinders University, Adelaide, SA 5042, Australia e-mail: tony.hooker@epa.sa.gov.au

Évaluation des connaissances des prescripteurs de scanner en matière de radioprotection des patients

Purpose To evaluate the knowledge of physicians prescribing CT examinations on the radiation protection of patients. Materials and methods A questionnaire was distributed to all clinicians on medical staff who prescribe CT examinations. Several questions related to their prescription pattern and their knowledge of radiation protection. Results Forty-four questionnaires were analyzed. While 70% of physicians claimed that they considered the risks from exposure to ionizing radiation when prescribing a CT examination, only 25% informed their patients about those risks. Knowledge of the radiation dose delivered during CT evaluation of the abdomen and pelvis was poorly understood and the risks related to small doses of radiation were grossly underestimated. Finally, only a third of clinicians had received training with regards to radiation protection. Conclusion While most clinicians claim that they consider the risks from exposure to ionizing radiation when prescribing a CT examination, the risks are either not well known or not known at all. Increased formation of clinicians with regards to the radiation protection of patients, maybe through a dedicated clinical rotation while in medical school, could be a solution to improve the knowledge of hospital clinicians with regards to radiation protection.

Chemical genoprotection: reducing biological damage to as low as reasonably achievable levels

The aim of this study was to evaluate the antioxidant substances present in the human diet with an antimutagenic protective capacity against genotoxic damage induced by exposure to X-rays in an attempt to reduce biological damage to as low a level as reasonably possible. Ten compounds were assessed using the lymphocyte cytokinesis-block micronucleus (MN) cytome test. The compounds studied were added to human blood at 25 μM 5 min before exposure to irradiation by 2 Gy of X-rays. The protective capacity of the antioxidant substances assessed was from highest to lowest according to the frequency of the MN generated by X-ray exposure: rosmarinic acid = carnosic acid = δ-tocopherol = l-acid ascorbic = apigenin = amifostine (P < 0.001) > green tea extract = diosmine = rutin = dimetylsulfoxide (P < 0.05) > irradiated control. The reduction in genotoxic damage with the radiation doses administered reached 58%, which represents a significant reduction in X-ray-induced chromosomal damage (P < 0.001). This degree of protection is greater than that obtained with amifostine, a radioprotective compound used in radiotherapy and which is characterised by its high toxicity. Several antioxidant substances, common components of the human diet and lacking toxicity, offer protection from the biological harm induced by ionizing radiation. Administering these protective substances to patients before radiological exploration should be considered, even in the case of small radiation doses and regardless of the biological damage expected.

Dependences of HTS tape critical parameters on fluences under irradiation with heavy ions and high energy electrons

Experimental data on the study of modifications of two types of the YBCO(123)-based composite tape under irradiation with electrons with the energy of 23 MeV and 132Xe27+ (167 MeV), 84Kr17+ (107 MeV), and 40Ar8+ (48 MeV) ions in a wide range of irradiation doses are presented. It is shown that no changes in the HTS transition temperature and critical current occurred under electron irradiation up to the dose D ≈ 10−4 disp/a (displacements per atom). The threshold dose of irradiation with 132Xe27+ ions, at which superconductivity disappears, is determined. In comparison with the initial value, the critical current of 40Ar8+ ions is found to increase by ≈18% in the zero magnetic field at T = 77 K. This effect can be explained by the pinning centers for Abrikosov vortices induced by relatively small ion irradiation doses. High doses of heavy ions lead to partial or complete amorphization of a superconductor, which results first in a decrease in the critical current and transition temperature and then in a total disappearance of superconductivity. X-ray diffraction is used to study the changes in the crystal structure of the YBCO(123) superconductor under ion irradiation.

Modification of Self-Assembled Monolayers of Perfluoroterphenyl-Substituted Alkanethiols by Low-Energy Electrons

Using self-assembled monolayers (SAMs) of perfluoroterphenyl-substituted alkanethiols (FTPn) on Au(111) as test systems, we studied the effect of low-energy (10 eV) electron irradiation on fluorinated aromatic SAMs. FTPn films were found to mimic the typical behavior of aromatic hydrocarbon SAMs under ionizing radiation. The dominant process is the cleavage of C−F bonds in the FTP moieties followed by desorption of the released fluorine atoms, rapid conformational and orientational disordering, and cross-linking between the residual skeletons of the FTP backbones. The stability of these skeletons and the development of a cross-linked network hinder other typical irradiation-induced processes such as desorption of molecular fragments and damage of the headgroup−substrate interface. Along with these findings, FTPn SAMs gave a unique possibility to monitor the destiny of the fluorine atoms, which are analogues of the hydrogen atoms in the respective hydrocarbon systems. The extent of fluorine release upon irradiation was estimated and the cleavage of C−F bonds was found to be the main channel of this release, which is in striking contrast to fluorocarbon aliphatic monolayers for which such a release is dominated by the desorption of fluorocarbon fragments. Finally, irradiation-induced reorientation of FTPn films at very small irradiation doses was observed suggesting that their structure is kinetically trapped and can be relaxed toward the thermodynamic minimum by physical means.

Effects of Gamma Irradiation on the Structure and Mechanical Properties of Wild Silkworms and Bombyx Mori Silk Fibroin Films

The structure and mechanical properties of A. yamamai, A. perny and B. mori silk fibroin films irradiated by gamma ray with various doses of 0, 25, 50, 100 and 200 kGy, respectively were determined by XRD, FT-IR, DSC and Instron 3365 equipment. Results showed that the aggregation structure and molecular conformation of A. yamamai, A. perny and B. mori silk fibroin films irradiated by gamma ray with those doses mentioned above were not significantly changed. However, with the increase of radiation intensity, the thermal stability of silk fibroin films declined slightly, and the breaking strength and extensibility reduced significantly, due to the breakdown of parts of secondary bonds and covalent bonds. These results suggested that, when these silk fibroin materials were sterilized by gamma irradiation, smaller radiation doses should be used, otherwise irreversible damages on these materials would be caused.

Response to Multiple Radiation Doses of Human Colorectal Carcinoma Cells Infected With Recombinant Adenovirus Containing Dominant-Negative Ku70 Fragment

To investigate the effect of recombinant replication-defective adenovirus containing dominant-negative Ku70 fragment on the response of tumor cells to multiple small radiation doses. Our ultimate goal is to demonstrate the feasibility of using this virus in gene-radiotherapy to enhance the radiation response of tumor cells. Human colorectal HCT8 and HT29 carcinoma cells were plated in glass tubes, infected with virus (25 multiplicity of infection), and irradiated with a single dose or zero to five doses of 3 Gy each at 6-h intervals. Hypoxia was induced by flushing with 100% nitrogen gas. The cells were trypsinized 0 or 6 h after the final irradiation, and cell survival was determined by colony formation. The survival data were fitted to linear-quadratic model or exponential line. Virus infection enhanced the radiation response of the HCT8 and HT29 cells. The virus enhancement ratio for single-dose irradiation at a surviving fraction of 0.1 was approximately 1.3 for oxic and hypoxic HCT8 and 1.4 and 1.1 for oxic and hypoxic HT29, respectively. A similar virus enhancement ratio of 1.2-1.3 was observed for both oxic and hypoxic cells irradiated with multiple doses; however, these values were smaller than the values found for dominant-negative Ku70-transfected Rat-1 cells. This difference has been discussed. The oxygen enhancement ratio for HCT8 and HT29 receiving fractionated doses was 1.2 and 2.0, respectively, and virus infection altered them slightly. Infection of recombinant replication-defective adenovirus containing dominant-negative Ku70 fragment enhanced the response of human colorectal cancer cells to single and multiple radiation doses.

THE CONSTITUTIONAL FEATURES OF CHILDREN AND ADOLESCENTS, CONSTANTLY LIVING IN THE CONDITIONS OF CHRONIC RADIATION INFLUENCE AS DIAGNOSTIC CRITERIA OF THEIR HEALTH (literature review)

In the survey have been presented the data of the numerous scientific researches, held on the territory, which had suffered from the Chernobyl Catastrophe. The authors tried to assess the degree of the chronic influence of small radiation doses on anatomical, neuro-psychic, immune and endocrine constitution of the children and adolescents, who are constantly living on the territories of radiation control.