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At least 541 records · Page 30Linked to original sources
PubMed1977

[Radiation response and radiation effects in salivary glands (author's transl)].

Using nuclear medical techniques, especially that of functional scintigraphy with the gamma camera after injection of 99mTc-pertechnetate, it is possible to objectify dose-dependent radiation effects on the salivary glands: Radiation doses from 500 to 1200 rd lead to a temporary reduction of the capacity to accumulate the 99mTc-pertechnetate. This functional restriction is reversible. With radiation doses of more than 2000 rd there appear irreversible functional disorders being proportional to dosage. Focal doses of about 6000 rd produce a complete loss of the capacity for 99mTc accumulation of the salivary glands. The chronological course of radiation response is characterized by a) an activation of the radionuclide accumulation following ca. 3000 rd in about three weeks, b) a following decrease of the capacity for accumulation of 99mTc, c) a renewed activation after the end of irradiation, and d)the progressive and irreversible loss of function of the salivary glands.

Humans↗
PubMed1996

Radiation-induced apoptosis in HL60 cells: oxygen effect, relationship between apoptosis and loss of clonogenicity, and dependence of time to apoptosis on radiation dose.

Apoptosis in HL60 human leukemia cells irradiated in vitro was quantified using a DNA fragmentation assay. Dose-response curves for induction of apoptosis in HL60 cells 6 h after irradiation with 280 kVp X rays in air and hypoxia give an oxygen enhancement ratio (OER) of 2.7. This is similar to the OER of 2.8 obtained from survival curves for HL60 cells using a soft agar clonogenic assay. However, HL60 cells are much more sensitive to radiation-induced loss of clonogenicity than to induction of apoptosis at 6 h. For example, 12 Gy in air reduces the surviving fraction to about 0.002 in a clonogenic assay, but 12 Gy does not cause any significant increase in the percentage of apoptosis-like DNA fragmentation 6 h after irradiation compared to unirradiated controls. However, if apoptosis is assayed 2-4 days after irradiation, the HL60 cells show greater sensitivity, with 5 Gy in air causing 45-50% apoptosis at 3 days. When apoptosis is measured 3 days after irradiation, the OER is similar to that obtained for survival and for apoptosis at 6 h. Although the HL60 cells exhibit radiation-induced apoptosis if one waits 2-4 days after low doses of radiation, rather than just 6 h, to conduct the assay, the amount of cells undergoing apoptosis is still not sufficient to account for all the loss of clonogenicity seen when HL60 cells are exposed to ionizing radiation.

Aerobiosis↗
PubMed2004

Role of type II pneumocytes in pathogenesis of radiation pneumonitis: dose response of radiation-induced lung changes in the transient high vascular permeability period.

We studied the dose response of pulmonary changes at 3 weeks after 1-25 Gy irradiation and we investigated the effects of an anti-inflammatory drug. Wistar rats were given a single dose of 1-25Gy irradiation to the thorax. Group one was treated with saline only, while group two was administered subcutaneously a combination of pentoxifylline (35 mg/kg) and dexamethasone (1 mg/kg) twice per week. Lungs were examined histochemically and number of neutrophile granulocytes, alveolar septal thickness, air/tissue ratio, number of alveoli per field, number of type II pneumocytes per alveolus, and occludin 1 expression were measured. A significant dose-dependent depletion of type II pneumocytes was found after irradiation with a dose of 1 Gy and higher. Alveolar neutrophils increased after 1 Gy with a dose dependency noted after 10-25Gy and alveolar septa thickening followed 5-25 Gy. A lower occludin 1 expression was observed in animals irradiated with the doses of 5 20 Gy, indicating an effect on vascular permeability. Anti-inflammatory therapy partially inhibited the increase of neutrophils at all radiation doses and the depletion of type II pneumocytes after doses of 1, 10, and 15 Gy. Occludin 1 did not decrease in the lungs of rats treated with the anti-inflammatory drugs as it did in most rats treated only with saline. Our results suggest that pneumocytes depletion is a major factor responsible for radiation pneumonitis development and that these changes may be compensated for provided radiation doses are below the threshold.

Animals↗
PubMed1987

The effect of combined treatment of HeLa cells with actinomycin D and radiation upon survival and recovery from radiation damage.

The presence of actinomycin D during irradiation of HeLa cells leads to radiosensitization under aerobic but not under hypoxic conditions. Depending on the time interval between incubation with the drug and irradiation, pre- or post-treatment with actinomycin D also increases the radiosensitivity of HeLa cells irradiation in air. Pretreatment with actinomycin D does not inhibit recovery from potentially lethal radiation damage. In split-dose experiments, recovery from sublethal radiation damage was not impaired by the drug if present during the entire fractionation interval or if it was given as a short exposure after the first radiation dose.

Cell Survival↗
PubMed2003

Structural and functional injury in minipig salivary glands following fractionated exposure to 70 Gy of ionizing radiation: an animal model for human radiation-induced salivary gland injury.

This study explored the feasibility of developing an animal model for radiation-induced salivary gland injury with a radiation protocol identical to current clinical practice. Three male Hanford minipigs were subjected to fractionated daily irradiation with a total dose of 70 Gy; structural and functional measures were compared with those of a control group of minipigs. We found that irradiated submandibular and parotid glands were one-third to one-half the gross size of control glands. Whereas no pathologic changes were noted in control glands, irradiated glands consistently demonstrated significant parenchymal loss with extensive acinar atrophy and interstitial fibrosis, enlarged nuclei in remaining acinar cells, and ductal dilatation and proliferation. Stimulated salivary flow was reduced by 81% in irradiated animals compared with preirradiation flow (P <.001); salivary flow in the control group increased by 30% during the same period (P <.001). The observed radiation-induced structural and functional salivary gland changes are comparable in every respect to those observed following irradiation of human salivary glands.

Animals↗
PubMed1996

Effects of target fragmentation on evaluation of LET spectra from space radiations: implications for space radiation protection studies.

We present calculations of linear energy transfer (LET) spectra in low earth orbit from galactic cosmic rays and trapped protons using the HZETRN/BRYNTRN computer code. The emphasis of our calculations is on the analysis of the effects of secondary nuclei produced through target fragmentation in the spacecraft shield or detectors. Recent improvements in the HZETRN/BRYNTRN radiation transport computer code are described. Calculations show that at large values of LET (> 100 keV/micrometer) the LET spectra seen in free space and low earth orbit (LEO) are dominated by target fragments and not the primary nuclei. Although the evaluation of microdosimetric spectra is not considered here, calculations of LET spectra support that the large lineal energy (y) events are dominated by the target fragments. Finally, we discuss the situation for interplanetary exposures to galactic cosmic rays and show that current radiation transport codes predict that in the region of high LET values the LET spectra at significant shield depths (> 10 g/cm2 of Al) is greatly modified by target fragments. These results suggest that studies of track structure and biological response of space radiation should place emphasis on short tracks of medium charge fragments produced in the human body by high energy protons and neutrons.

Aluminum↗
PubMed1991

A proposed biophysical framework for radiation protection calculations using summation of iso-risk contributions of different radiations.

A biophysical framework for administrative radiation protection calculation using summation of iso-risk contribution of different radiation components is presented. It addresses some of the concerns with the present system but would preserve the present linear mathematical framework and hence the massive literature of numerical calculations in radiation protection.

Biophysical Phenomena↗
PubMed2002

Studies on ultraviolet radiation and health effects: ocular exposure to ultraviolet radiation.

A wide variety of studies were conducted over the last 10 years to more carefully determine the exposure to ultraviolet (UV) radiation in the natural environment, which are especially concerned with the UV exposure to the eye. Careful measurements of global UV radiation and personal exposure were performed. A mannequin head model was developed that monitors the UV radiation to different locations on the face including at the eye. The effectiveness of hat and glasses and/or sunglasses was studied. Furthermore, models of estimating UV exposure were tested in field trials with schoolchildren, and the results were applied to the participants of epidemiological studies. In this article, these studies are briefly reviewed.

Environmental Exposure↗
PubMed2004

EEG patterns in persons exposed to ionizing radiation as a result of the chernobyl accident. Part 2: quantitative EEG analysis in patients who had acute radiation sickness.

Cross-sectional quantitative electroencephalogram (qEEG) study (1996-2001) among Chernobyl accident survivors, who had confirmed acute radiation sickness and were irradiated in dose of 1-5 Gy, revealed the neurophysiological markers of ionizing radiation. Neuropsychological markers were: left fronto-temporal dominant frequency reduction; absolute delta-power lateralization to the left (dominant) hemisphere; relative delta-power increase in the fronto-temporal areas; absolute theta-power decrease in the left temporal region; absolute and relative alpha-power diffusive decrease, which may reflect cortico-limbic dysfunction lateralized to the left, dominant hemisphere, with the fronto-temporal cortical and hippocampal damage. Quantitative electroencephalogram proposed for differentiation of radiation and nonradiation brain damages and as a new biological dosymetry method. High radiosensitivity of the brain, neocortex, and dominant hemisphere higher radiosensitivity are discussed.

Brain Mapping↗
PubMed1983

Cumulative radiation damage and cumulative radiation effect.

Different mathematical formulas capable of replacing CRE have been analyzed. The purpose was to develop an expression which would yield a value identical with CRE for regular treatment schedules, but would represent more clearly and more truthfully the radiation damage of tissue. This quantity has been called cumulative radiation damage (CRD). Its unit is adequately called CRD unit. CRD does not require a separate gap correction, as does CRE, it is easy to use, explicit and unambiguous. CRE, CRD and some other formulas have been compared in different types of radiation therapy.

Humans↗
PubMedDate not supplied

[Radiation protective agents effective in a wide range of radiation dosages].

Perspective chemical classes of prophylactic radioprotecting compounds were found from analysis of proper experimental data. Preparations effective in a wide range of radiation doses of various intensity were synthesized. Their activity are due to combination of antiradiation and many other pharmacological properties. During acute radiation these preparations protect stem cells pul of critical tissues but under prolonged radiation they normalize the hematological, immune and lipid peroxide oxidation systems. There is no strong correlation between radioprotection and increasing of functional reserve of organism.

Animals↗
PubMed1965

RADIATION PROTECTION IN CANADA. VII. SETTING STANDARDS FOR RADIATION PROTECTION.

The current recommendations of the International Commission on Radiological Protection have as a basic objective the limitation of the radiation dose to "that which involves a risk that is not unacceptable to the individual and to the population at large". The problem is to decide what degree of risk is acceptable, in relation to the benefits of a practice that necessitates a radiation exposure. At the present time it is not possible to make more than very rough estimates of some of the risks of exposure to radiation, but such estimates can be usefully compared with some of the other risks that are tolerated by society. On the assumption that it would be possible to make quantitative assessments of both the benefits and the risks, the question is raised as to how and by whom an appropriate balance should be made.

Canada↗
PubMed1991

[Radiology and radiation protection in dental medicine. 1: Biological effects resulting from exposure to ionizing radiation].

The different types of biological effects produced by ionizing radiations are reviewed. Among the early effects following an acute exposure, the bone marrow syndrome and the intestinal syndrome are briefly described. They are unlikely to appear in the current conditions encountered in dental radiology. As far as skin exposure is concerned (e.g. fingers, hands), acute reactions (moist desquamation, ulceration, etc.) require high doses which are encountered only in accidental conditions. However, chronic dermatitis after repeated low dose exposure is one of the major risks in dental radiology (even without previous acute lesions), if the recommendations of radioprotection are not followed. The danger is ultimately the transformation into a radio-induced skin cancer. Among the late effects, after chronic exposure at low doses, cancer induction and the genetic effects are the most important. The risk coefficient for cancer induction is expressed by the number of lethal cancers induced per unit dose. In his last report (1988), the UNSCEAR assessed the risk coefficient between 4.5 and 7% for an absorbed dose of 1 Gy (low-LET radiation, high dose delivered at high dose rate). A low doses and low dose rates (X-and gamma rays), the UNSCEAR recommends to reduce the above risk coefficients by a factor between 2 and 10. The risk coefficient at low doses is difficult to evaluate since the rate of radio-induced cancers is small compared to the spontaneous cancer incidence. The risk of a severe genetic effect is about 1/3-1/4 of the risk of lethality from radio-induced cancer. Finally, the characteristics of the stochastic and non-stochastic effects are described. The acute effects, the late radiodermatitis and the cataract are examples of non-stochastic effects, while cancer induction and the genetic effect are stochastic effects. In the Appendix, the most important quantities and units, used in radiation protection, are presented.

Bone Marrow↗
PubMed1990

[Radiation tolerance of normal lung-pulmonary radiation syndrome].

Radiation pneumonitis and radiation fibrosis are two distinct syndromes with probably different target cells. The ultrastructural changes occur rapidly and current evidence suggests that damage to the type II pneumocyte and the endothelial cell is linked to the pneumonia process than the fibrotic. The fibrosis process may be related to the basement membrane of both endothelial cells and alveolar type I cells. Dose time and volume data for tolerance dose are well documented in animals. Many antineoplastic agents enhances radiation lung damage. The pneumonitis and fibrosis will be discussed.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1983

[Prevention of radiation injuries during multifractionation in radiation therapy].

A radiobiological substantiation of a method of multifractionation and a review of the results of its clinical application are presented. The authors have developed a method to calculate a cumulative radiation effect and the TDF factor in radiation therapy with multiple dose fractionation in the form of several sessions daily. This method can be used to prevent the radiation-caused complications.

Dose-Response Relationship, Radiation↗
PubMed1982

Paradoxical effect of radiation on tumor incidence in the rat: implications for radiation therapy.

The high incidence of leukemia in the Fischer rat is reduced by radiation to an incidence below that seen spontaneously. Fractionating the radiation decreased this effect. In contrast, mammary tumors increased with dose until reaching a plateau at the highest doses. Fractionation had little effect. These results are consistent with a hypothesis suggesting that tumor incidence due to radiation is the result of competing processes of tumor induction and cell killing.

Animals↗
PubMed1994

Measurements on the shuttle of the LET spectra of galactic cosmic radiation and comparison with the radiation transport model.

A new class of tissue-equivalent proportional counters has been flown on two space shuttle flights. These detectors and their associated electronics cover a lineal energy range from 0.4 to 1250 keV/microns with a multichannel analyzer resolution of 0.1 keV/microns from 0.4 to 20 keV/microns and 5 keV/microns from 20 to 1250 keV/microns. These detectors provide the most complete dynamic range and highest resolution of any technique currently in use. On one mission, one detector was mounted in the Shuttle payload bay and another older model in the mid-deck, thus providing information on the depth dependence of the lineal energy spectrum. A detailed comparison of the observed lineal energy and calculated LET spectra for galactic cosmic radiation shows that, although the radiation transport models provide a rather accurate description of the dose (+/- 15%) and equivalent dose (+/- 15%), the calculations significantly underestimate the frequency of events below about 100 keV/microns. This difference cannot be explained by the inclusion of the contribution of splash protons. The contribution of the secondary pions, kaons and electrons produced in the Shuttle shielding, if included in the radiation transport model, may explain these differences. There are also significant differences between the model predictions and observations above 140 keV/microns, particularly for 28.5 degrees inclination orbit.

Aerospace Medicine↗
PubMedDate not supplied

[The measurement of scattering radiation in the radiation control of x-ray offices].

A procedure for measuring the power of an ambient and goal-oriented equivalent scattered radiation dose in the radiation control of X-ray rooms. The procedure is based on the concept of the effective solid angle of a dosimeter directivity diagram. The plots of the angular response of a S2010 selective X-ray dosimeter for studying the radionuclides 119Sn, 241Am, 57Co are exemplified. The scaling factors for dosimetric reading for isotropic and nonuniform fields of radiation were calculated from the obtained values of effective angular solid angles (0.7, 0.8, 1.2 pi).

Humans↗