Radiation Exposure Conditions Research Articles

Broad-Spectrum Sunscreens Provide Better Protection from the Suppression of the Elicitation Phase of Delayed-Type Hypersensitivity Response in Humans

It is well established that ultraviolet radiation has immunomodulatory effects that may be involved in skin cancer. Recent studies have shown that ultraviolet A radiation (320-400 nm) as well as ultraviolet B (290-320 nm) is immunosuppressive. This means sunscreens that mainly absorb ultraviolet B (protection against erythema) may be less effective in preventing ultraviolet radiation-induced immunosuppression than broad-spectrum products. We have studied the effects of ultraviolet A exposure on the human delayed-type hypersensitivity response and compared the efficacy of sunscreens having different levels of ultraviolet A protection under both solar-simulated radiation and outdoor real-life solar exposure conditions. Delayed-type hypersensitivity was assessed using recall antigens. In a first study, two groups of volunteers were exposed to ultraviolet A (either full spectrum ultraviolet A or ultraviolet A1) without prior application of sunscreen and they were shown to exhibit significantly reduced delayed-type hypersensitivity responses. In order to compare the efficacy of sunscreens in preventing photoimmunosuppression, three groups of subjects received 10 cumulative exposures to solar-simulated radiation; one group was exposed unprotected and the other two were exposed after being applied either a ultraviolet B or a broad-spectrum sunscreen, each with the same sun protection factor 9, but with different ultraviolet A protection factors 9 and 2. Then, an outdoor study was conducted in which delayed-type hypersensitivity was assessed before and after six daily exposures. Two different groups of subjects were treated with one of two sunscreens having the same sun protection factor 25 but different ultraviolet A-protection factors. In unprotected volunteers, responses to delayed-type hypersensitivity tests were significantly reduced irrespective of ultraviolet exposure conditions (full spectrum ultraviolet A, ultraviolet A1, solar-simulated radiation). The ultraviolet B sunscreen failed to protect from solar- simulated radiation-induced immunosuppression. In contrast, the broad-spectrum sunscreen having the same sun protection factor but providing high protection in the ultraviolet A range significantly reduced local ultraviolet-induced immunosuppression and prevented the distal effects. In the outdoor study, as compared with delayed-type hypersensitivity responses obtained before sun exposure, no alteration of immune response was detected when the skin was protected by broad-spectrum sunscreen sun protection factor 25 and ultraviolet A-protection factor 14. Conversely, a broad-spectrum sunscreen sun protection factor 25 ultraviolet A-protection factor 6 failed to protect against the sun-impaired response. The above studies clearly demonstrate the role of ultraviolet A in the induction of photoimmunosuppression together with the need for sunscreen products providing efficient photoprotection throughout the entire ultraviolet spectrum.

Radiation doses to patients during ERCP

Background: There is a scarcity of data regarding the radiation dose and associated risks to patients during ERCP. Dose area product (DAP) measurements can be used to estimate an effective dose (ED) to patients undergoing ERCP. This measure allows radiation risk associated with such procedures to be quantified. The aim of this study was to evaluate the ED to patients undergoing ERCP. Methods: A DAP meter was fitted to the x-ray tube before each ERCP. DAP reading (Gy-cm2), fluoroscopy time, average screening kVp, number of films, and kVp per film were recorded. Mean ED was estimated by using DAP readings and Monte Carlo computer software to model radiation exposure conditions. Results: Data were recorded on 20 subjects. Average DAP was 13.5 Gy-cm2 (6.8-23.9) for diagnostic and 66.8 Gy-cm2 (28.7-108.5) for therapeutic ERCP (p < 0.05). Average fluoroscopy time was 2.3 minutes (1.1-5.3) for diagnostic and 10.5 minutes (5.9-16.6) for therapeutic ERCP (p < 0.05). DAP showed a linear relationship with fluoroscopy time (R2 = 0.928). Mean number of diagnostic and therapeutic films was 2.8 and 3.7, respectively. Fluoroscopic exposure represented 69% of the DAP for diagnostic ERCP and 90% of the DAP for therapeutic ERCP. Average ED was 3.1 mSv for diagnostic and 12.4 mSv for therapeutic ERCP. Conclusions: Therapeutic ERCP is associated with significantly higher radiation exposure than diagnostic ERCP. ED in therapeutic ERCP is a result largely of fluoroscopy time as opposed to number of films. (Gastrointest Endosc 2001;53:161-4.)

Relevance of the radioprotective effect of sodium selenite

Based on the mode of action of Na2SeO3 as a radical scavenger in vitro culture experiments using normal human skin fibroblasts and squamous cell carcinoma cells were performed to investigate the potential role of Na2SeO3 as a radioprotector for normal cells. Therefore, comparative studies of combined treatment, i.e. radiation exposure +/- Na2SeO3 in single-dose (0 to 7 Gy) and multiple fractionated-dose (5 x 2 Gy), were applied to differentiate the radiation response of normal and tumor cells depending upon the treatment protocol. The results indicate that Na2SeO3 under both radiation exposure conditions positively modulates the radiation response of normal fibroblasts in a sense of the radioprotective effect. On the contrary, human tumor cells are not affected by the radioprotective capacity of Na2SeO3 neither under single-dose nor fractionated-dose irradiation. On the basis of the quantitative cell culture analyses, this study indicates for the first time the potential role of Na2SeO3 as a radioprotective compound for normal cells. It will be discussed to what degree differential expression of apoptotic cell death in normal and tumor cells contributes to the radiation response of normal and tumor cells.

Biological Dosimetry of Beta-Ray Exposure from Tritium Using Chromosome Translocations in Human Lymphocytes Analyzed by Fluorescence In Situ Hybridization

Radiation exposures from tritium make up a substantial fraction of the occupational and accidental radiation exposures associated with the nuclear power industry. Tritiated water, the most abundant form of tritium, is of particular interest because it is readily taken up by human cells and its irradiation of the cells is spread over a period of days. To approximate the prolonged exposure and the conditions that the cells of an individual would experience in vivo, we irradiated human lymphocytes with tritiated water for 48 h in a 1:1 blood:medium mix. For estimation of the tritium beta-ray dose, a cellular water content of 0.78, based on measurements of human lymphoblastoid cells in culture medium, was used. A modified dose calculation formula was developed for the radiation exposure conditions. A total of 48,014 metaphases (14,482 in irradiated samples and 33,532 in control, unirradiated samples) in human lymphocytes cultured for 72 h after exposure were analyzed for chromosome translocations using fluorescence in situ hybridization. The linear slope (alpha coefficient) of the dose-response curve was measured to be (3.93+/-0.42) x 10(-2) and (5.26+/-0.48) x 10(-2) translocations per cell per gray for complete translocations (tc) and complete translocations plus incomplete translocations [ti(Ab)], respectively, when the data were fitted to a linear model using a weighted least-squares method. The alpha coefficient for tc is significantly lower than that for conventionally measured dicentrics after tritium beta irradiation, but the alpha coefficient for tc + ti(Ab) does not differ significantly from that for dicentrics. This is in agreement with theoretical considerations. The importance of scoring criteria is stressed. The frequency of tc + ti(Ab) is proposed to be a reliable biodosimeter for tritium exposures, and its practical use in a dose reconstruction is presented.

Cancer Predisposition, Radiosensitivity and the Risk of Radiation-Induced Cancers. II. A Mendelian Single-Locus Model of Cancer Predisposition and Radiosensitivity for Predicting Cancer Risks in Populations

Individuals genetically predisposed to cancer may be more sensitive to cancers induced by ionizing radiation than those who are not so predisposed. Should this be true, under conditions of radiation exposure, a population consisting of cancer-predisposed and non-predisposed individuals will be expected to respond with a higher total frequency of induced cancers than one in which all the individuals are assumed to have the same sensitivity to radiation-induced cancers. To study this problem quantitatively, we have developed a Mendelian autosomal one-locus, two-allele model; this model assumes that one of the alleles is mutant and the genotypes carrying the mutant allele(s) are cancer-predisposed and are also more sensitive to radiation-induced cancer. Formal analytical predictions as well as numerical illustrations of this model show that: (1) when such heterogeneity with respect to cancer predisposition and radiosensitivity is present in the population, irradiation results in a greater increase in the frequency of induced cancers than when it is absent; (2) this increase is detectable only when the proportion of cancers due to genetic predisposition is large and when the degree of predisposition is considerable; and (3) even when the effect is small, most of the radiation-induced cancers will occur in predisposed individuals. These conclusions are valid for models of cancer when predisposition and radiosensitivity may be either dominant or recessive. The published data on breast cancers in Japanese A-bomb survivors show that at 1 Sv, the radiation-related excess relative risk in women irradiated before age 20 is 13 compared to about 2 for those irradiated at later ages. We examined the application of our model to the above data using two assumptions, namely, that the proportion of cancers due to genetic susceptibility at the BRCA1 locus (1/200) and the frequency of the mutant allele (0.0033) estimated for Western populations are valid for Japanese women. With our model, these results can be explained only if there are very large differences in cancer susceptibility (> 1000-fold) and radiosensitivity (> 100-fold) of the heterozygotes.

Comparison of two stocks of mice in spermatogonial response to different conditions of radiation exposure

In a previous report (Generoso et al., 1985) it was shown that the two hybrid stocks of mice, (C3H/R1 × 101/R1)F 1 and (SEC/R1 × C57BL/6)F 1, differed in their responses to induction of chromosomal aberrations following exposure of the stem-cell spermatogonia to 500 R × 4 (4-week intervals) acute X-rays. The levels of response in the two stocks were paralleled by the effects on the length of the sterile period, which presumably results from stem-cell killing and repopulation. The present study was conducted in order to determine whether the differences between the two stocks in these parameters hold true also for other conditions of radiation exposure. Thus, comparative experiments were conducted using the following acute exposure regimens: 500 R single dose, 500 R + 500 R (24-h interval), 100 R + 900 R (24-h interval), and 500 R × 4 (8-week intervals). The endpoints measured were chromosome rearrangements in diakinesis/metaphase-I meiocytes, embryonic lethality in conceptuses, length of sterile period and testis weight. Trend analysis indicated that higher frequencies of chromosome rearrangements and embryonic lethality were recovered from (C3H/R1 × 101/R1)F 1 than from (SEC/R1 × C57BL/6)F 1 males, that there were no significant differences between stocks in testis weight reductions, and that there was no consistency in the direction of the significant differences that occurred in the length of the sterile period. A definitive conclusion regarding the possible association between induction of chromosomal aberrations and induction of cell killing awaits direct histological analysis of the stem-cell population.

Song Among the Ruins

As international tensions mount in the Middle East, it is perhaps timely that we are presented with a book that reminds us of the unthinkable consequences of nuclear conflict. Spanning more than 40 years, William Schull'sSong Among the Ruinsstems from his work in Japan with the Atomic Bomb Casualty Commission—currently the Radiation Effects Research Foundation. Though they are not the primary subject of this book, the author summarizes the genetic findings of the work conducted by him and his Japanese and American colleagues. Under radiation exposure conditions similar to those in Hiroshima and Nagasaki, the results suggest that for a dose of 100 rad (1 Gy), the risk of untoward pregnancy (in children conceived after parental exposure) is increased less than 10% over natural baseline risk. While commenting on the difficulties in extrapolating to lower doses, he states that exposure to 5 rad (0.05 Gy, the current annual

Stability investigations of a chemically converted textured black copper selective surface

We report here the optical and structural investigations conducted on a stable and degraded black copper selective surface prepared by the chemical conversion technique. This surface exhibits a high initial solar absorptance ( α≈0.97−0.98) and possess a relatively low emittance ( ϵ 100≈0.2±0.02). The surface has been exposed to air and vacuum test conditions at elevated temperatures. The surface shows good and structural stability in both vacuum (10 −5 Torr) and under ambient conditions up to 250°C. In the case of a surface annealed in air between temperatures of 250 and 350°C the surface optically degrades with no structural changes. However, above 350°C drastic degradations in both optical and structural properties have been observed. These surfaces become rough along with a grain size enlargement. In contrast, upon vacuum annealing up to 370°C no significant change in the microstructure has been noticed. However, dramatic changes in the solar absorptance have been evident above 250°C. Further, these surfaces have been indicated good stability under UV radiation, external environment, humidity and steam exposure conditions. Chemical stability, such as corrosion resistance in 3% NaCl and 3% acetic acid spray have also indicated satisfactory results.

The construction of computer tomographic phantoms and their application in radiology and radiation protection.

In order to assess human organ doses for risk estimates under natural and man made radiation exposure conditions, human phantoms have to be used. As an improvement to the mathematical anthropomorphic phantoms, a new family of phantoms is proposed, constructed from computer tomographic (CT) data. A technique is developed which allows any physical phantom to be converted into computer files to be used for several applications. The new human phantoms present advantages towards the location and shape of the organs, in particular the hard bone and bone marrow. The CT phantoms were used to construct three dimensional images of high resolution; some examples are given and their potential is discussed. The use of CT phantoms is also demonstrated to assess accurately the proportion of bone marrow in the skeleton. Finally, the use of CT phantoms for Monte Carlo (MC) calculations of doses resulting from various photon exposures in radiology and radiation protection is discussed.

Epistemological problems in assessing cancer risks at low radiation doses.

Historically, biology has not been subjected to any epistemological analysis as has been the case with mathematics and physics. Our knowledge of the effects in biological systems of various stimuli proves to be dualistic in a complementary (although not mutually exclusive) way, which bears resemblance to the knowledge of phenomena in quantum physics. The dualistic "limbs" of biological knowledge are the action of stimuli and the response of the exposed, biological system. With regard to radiogenic cancer, this corresponds to the action of the ionizations and the response of the exposed mammal to that action, respectively. The following conclusions can be drawn from the present analysis: Predictions as to radiogenic cancer seem often if not always to have neglected the response variability (variations in radiosensitivity) in individuals or among individuals in populations, i.e. the predictions have been based exclusively on radiation doses and exposure conditions. The exposed individual or population, however, must be considered an "open statistical system", i.e. a system in which predictions as to the effect of an agent are only conditionally possible. The knowledge is inverse to the size of the dose or concentration of the active agent. On epistemological grounds, we can not gain knowledge about the carcinogenic capacity of very low (non-dominant) radiation doses. Based on the same principle, we can not predict cancer risks at very low (non-dominant) radiation doses merely on the basis of models, or otherwise interpolated or extrapolated high-dose effects, observed under special exposure conditions.

Histologic types of bronchogenic cancer in relation to different conditions of radiation exposure

The rish of lung cancer among the uranium miner study group was found to be not only connected with the increase in frequency of different histologic types of lung cancer, but mainly with the increase of small cell undifferentiated and epidermoid type frequencies. It appears that the frequency of these two major histologic types may be influenced by the level of cumulated radiation exposure and by the time course of cumulation of exposure in a different way. These findings, in agreement wit recent data of Archer et al., eliminate the former assumption that radiation can induce an elevated frequency of only one histologic type of lung cancer.

The relative sensitivity of the soaked seeds of nine gymnosperm species to gamma radiation

Seeds of nine gymnosperm species, soaked in water to full imbibition, were irradiated with 137Cs gamma rays in two separate experiments. Species studied were Larix laricina, Picea abies, Picea glauca, Picea mariana, Pinus banksiana, Pinus contorta, Pinus resinosa, Pinus sylvestris and Thuja occidentalis. In the first experiment exposures of 150, 300, 600, 1200, 2400, 4800, 9600, 19,200 and 38,400 R were used and the seedlings were grown for 36 days after initial germination in perlite saturated with a complete nutrient solution. In the second experiment exposures of 150, 300, 450, 600, 900, 1200, 1800, 2400, 3600, 4800, 7200, 9600, 14,400 and 19,200 R were employed and the seedlings were grown in sand for 75 days after initial germination. Endpoints scored in the first experiment were germination, survival, cotyledon length, and plant dry weight. In the second experiment germination, survival, hypocotyl length, cotyledon length, shoot length, root length, shoot dry weight, and root dry weight were scored. Seed radiosensitivity varied by a factor of 3·80–7·33 in the first experiment and from 2·67 to 5·70 in the second experiment, depending on the endpoint used. Picea abies, Picea glauca and Pinus sylvestris were the most sensitive species in both experiments and Pinus banksiana the most resistant. The average D 50 (exposure resulting in 50 per cent inhibition) for all endpoints in Experiment I varied from 2·64 kR to 9·71 kR; that in Experiment II from 2·30 kR to 10·56 kR for the nine species studied. Comparison of the results with previous reports for individual species indicated that relative radiosensitivity of seed of plant species must be investigated with all species of interest being identical in radiation exposure conditions, seed moisture content and post-irradiation storage. Germination and growing conditions optimal for each species are suggested. The more than four-fold average differences in seed radiosensitivity were found to be unrelated to differences in nuclear volume, chromosome volume, and DNA content previously reported for the same populations of these species. The relative seed sensitivity pattern showed no relation to previously reported predictions of seedling and mature plant sensitivities for the same species.

Gamma-Ray Exposure Measurements in a Man Phantom related to Personnel Film Dosimetry

The variation of exposure with depth in a man phantom, together with the performance of film dosemeters on the surface, has been determined for uncollimated photons of energies from 48 keV to 2·8 MeV. To simulate radiation exposure conditions in the atomic energy industry, measurements were made with the phantom both stationary and rotating. The front to back attenuation factor for the static phantom of thickness 21·8 cm varied from 0·6 to 0·07 for photons of energies from 2·8 MeV to 48 48 keV in general agreement with published radiotherapy data. The measurements enable an improved estimate of the dose to an organ in the body to be made from a film dosemeter reading, provided that an indication of both the energy and direction of the incident radiation is available.

Theoretical growth-rate curves for Vicia faba roots under continuous radiation exposure at low dose-rate: a comparison with experimental results.

SummaryUsing models for the meristem of Vici faba proposed previously, theoretical curves of growth-rate have been computed for conditions of continuous radiation exposure at low dose-rate (1–10 rads/hr). These have been compared with experimental results. The best agreement is obtained assuming cell death at the second division following radiation damage, allowing for some gradual increase in cell cycle time during irradiation and postulating that, at any rate at the lower dose-rates, sterilised cells differentiate and contribute to root elongation. The match between theoretical and experimental curves suggests a value for D0 of about 240 rads for the ‘single hit’ type of mechanism assumed to apply at these dose-rates. It is predicted that if the cell-cycle time is varied, similar growth-rate curves should be observed for the same dose received per cell cycle (rather than for the same dose-rate).