Evaluation of absorbed dose in thyroid follicles due to short-lived iodines irradiation using the Monte Carlo method

Summary Thyroid cells are arranged in spheres called follicles of different sizes, in which most of the iodine in the body concentrates. For dose assessment in follicles, it is necessary to consider specific emissions of iodine isotopes in the calculation. Hence, the aim of this work was to evaluate the contribution of ¹³¹I and short-lived iodines to the absorbed dose in thyroid cells. Thus, the interaction of emissions from isotopes with follicles was carried out using the MCNP4C code. The results showed that the contribution of short-lived iodines for absorbed dose per disintegration is about 70%.     

EFFECT OF SPLIT-DOSE U.V. IRRADIATION ON DIPLOID YEAST

Abstract— Recovery from sublethal damage by u.v. irradiation as measured by the split-dose technique was investigated in stationary phase populations of diploid yeast Saccharomyces cerevisiae. Ft has been found that only about 35 per cent of the irradiated population is able to undergo recovery before the first subsequent cell division. The qualitative pattern is not changed if maximum photoreactivation is allowed after the first dose. Measurements of the decay of photoreactibility show that primary photo-products are still present up to six hours after irradiation.     

Chemical dosimeters for electron beam dosimetry of microtron accelerator

The variable energy microtron at Mangalore University has been used to study the effect of radiation on different materials and biological systems. While studying the effects of radiation, it is essential to have complete knowledge of absorbed dose. In the present study the dose due to 8 MeV electron beam from microtron accelerator has been calculated using chemical dosimeters. The uniformity of dose distribution at various points of the irradiation area also has been calibrated. From the dosimetry studies it is observed that there is a linear relation between dose and electron numbers over a wide range of absorbed doses. It is evaluated that the electron counts of about 1.15 × 10¹⁴ corresponds to an absorbed dose of 100 Gy and a field size of about 4 × 4 cm is available at 30 cm distance from the beam exit window over which the dose distribution is uniform.     

Study of the formation of the dispersed phase in aqueous solutions of Cu(II)

The formation of the dispersed phase in aqueous solutions of Cu(II) in the presence of formate and alcohols is studied using the pulse radiolysis method. The incubation time and the half-life for the formation depend on the absorbed dose and on the number of applied pulses as well as on the solution composition itself (Cu concentration, pH, OH-scavenger etc.). With increasing dose per pulse or number of pulses, the incubation time and the half-life for colloid formation decrease. The nature of the colloids formed is discussed.     

Evaluation of micronuclei induced by energetic electrons delivered at different dose rates per pulse

The severity of the cell damage induced by electrons is mainly depends upon absorbed dose and dose rate. This severity of the damage can be analysed by estimating micronuclei frequency in a binucleated cell (MN/BNC), which is a simple, standard and extensively used assay. In the present study, quantification of multiple MN within a cell along with quantification of binucleated cells with micronuclei (BNC with MN), the number of micronuclei per micro-nucleated binucleated cell (MN/(BNC with MN)), percentage of BNC and Nuclear Division Index (NDI) in lymphocytes, exposed to single 2 µs, 500, 50 and 25 ns pulses of 7 MV electrons at various doe rate per pulse from 1 × 10⁶ to 3.2 × 108 Gy s^?1, were carried out to assess the cell damage. A comparison study amongst end points, multiple MN, BNC with MN, MN/(BNC with MN), percentage of BNC, NDI and MN/BNC was also made. Present study suggests that the quantification of multiple MN, BNC with MN, MN/(BNC with MN), percentage of BNC and NDI along with MN/BNC provided vital information, while assessing cell damage at high doses and dose rates.     

Establishment and characterization of cell lines (Kagura-1 and Kagura-2) from aflatoxin B1-induced rat hepatoma

Two hepatoma cell lines designated Kagura-1 and Kagura-2 were established from rat hepatocellular carcinomas induced by aflatoxin B1, and have been propagated for over two years. Both cell lines grew as monolayered sheets with a population doubling time of about 20 h. Chromosome counts of Kagura-1 cells ranged from 34 to 45 with a modal number of 40, while that of Kagura-2 cells ranged widely from 40 to 130 with a modal number of 65. Subcutaneous inoculation of cultured cells of both these lines into nude mice resulted in tumor formation. The histopathological appearances of the induced tumors were similar to those of the original tumors. Kagura-1 and Kagura-2 cell lines express at least two tumor markers, glutathione-S-transferase P and gamma-glutamyl transpeptidase; the level of c-myc messenger ribonucleic acid was also highly elevated.     

Studies on the optimal immunization schedule of experimental animals. VI. Antigen dose-response of aluminum hydroxide-aided immunization and booster effect under low antigen dose

The dose-response relationships of a viomycin (VM) immunogen for total immunoglobulin (Ig) G and anti-VM antibody response of mouse using aluminum hydroxide as adjuvant was studied. The condition required to absorb a protein on aluminum gel was first established. The effective immunogen dose for total and specific IgG response of mouse using aluminum hydroxide as the adjuvant was found to be in the narrow range of 5 to 20 micrograms, and 10 micrograms per mouse was optimal. The most effective number and intervals of booster injections were studied; when mice were immunized with a lower antigen dose than the optimal, both the number and interval period of booster injections greatly affected the immune response; the more boosters were given, the higher was the response level of specific IgG. The results are contrary to those obtained by immunizing with the optimal or a higher antigen dose.     

Photochemical studies of thymine in ice

Abstract— Solutions containing various concentrations of thymine have been irradiated (254 nm) at — 196°, and the corresponding absorbance changes at 315 nm due to thymine-thymine adduct formation have been followed as a function of dose. The maximum yield of the adduct is about 3–2 per cent. Additional irradiation leads to a reduction in the yield of adduct and to an increase in the yield of the proposed trimer, which shows a sigmoid dose response curve. Not more than 10 per cent of the thymine is converted to trimer. Irradiation of the trimer in solution converts it into adduct plus thymine. Fluorescence due to the adduct does not appear directly after irradiation at — 196°, but comes about upon annealing at elevated temperatures (T > - 80°).     

Neutron dose estimation for 1H+9Be and 1H+12C reactions at 20 MeV proton energy via LET spectrometry using CR-39 detectors

The neutron dose is estimated by linear energy transfer (LET) spectrometry method for two reactions, viz. ¹H+⁹Be and ¹H+¹²C at 20 MeV proton energy using CR-39 track detectors. The LET spectrum is generated from the major, minor radii of each track and thickness of removed surface from each side of the detector due to chemical etching. Microdosimetric distributions of absorbed dose and dose equivalents are obtained from the LET spectrum. The absorbed dose and dose equivalent per incident proton obtained from the LET spectra are found to be about 12.5 and 8 times higher in ¹H+⁹Be reaction than ¹H+¹²C reaction.     

EVALUATION OF SULFONATED ALUMINUM PHTHALOCYANINES FOR USE IN PHOTOCHEMOTHERAPY. A STUDY ON THE RELATIVE EFFICIENCIES OF PHOTOINACTIVATION

The cellular photosensitivity caused by aluminum phthalocyanines sulfonated to different degrees (AlPcSn) has been investigated. The phototoxic effect increased with decreasing number of sulfonate groups on the macrocycle, with the exception of AlPcS1 which was less phototoxic than AlPcS2 but more phototoxic than AlPcS3 and AlPcS4. The tendency of the AlPcSns to aggregate in our cellular system increased with increasing lipophilicity of the sensitizers. The aggregates had little or no photosensitizing activity. The low efficiency of cell inactivation caused by AlPcS1 can be explained by the highly aggregated state of this sensitizer in the cells. AlPcS2 and AlPcS3 induced a lower degree of cell inactivation per fluorescing quantum and per quantum absorbed by monomeric species than did AlPcS2 and AlPcS1. AlPcS4 and AlPcS3 are therefore suggested to be in different intracellular locations than AlPcS2 and AlPcS1.     

Methodology for evaluation of melanin content and production of pigment cells in vitro

Melanin has a photo-screening, a biophysical/biochemical and a cosmetic effect. Melanin content of cultured pigmented cells can be measured by spectrophotometry and expressed either as melanin content per cell or melanin content per culture (area). Melanin production can be calculated from melanin content and cell number at the beginning and at the end of a culture using various formulas and expressed as melanin production per cell per day or melanin production per culture per day. Melanin content or production per cell have been used widely to compare melanin content in various cell lines or to compare the melanin content during different stages in the culture (e.g. growing stage and senescent stage). For the evaluation of changes in melanin content and production in a given pigment cell line after treatment with a special chemical, physical or biological stimulator or inhibitor, different parameters used for the evaluation of experimental data can lead to conflicting results. Melanin content per area is determined by melanin content per cell and the number of cells in this area. The biological and cosmetic effects of melanin in vivo are determined mainly by melanin content per area, not melanin content per cell. For example, if melanin content per cell is the same, but the number of cells in a given area is increased after the treatment, then the melanin content per area is also increased. Under this circumstance, the color of skin turns darker and the total antioxidant activity provided by melanin in this area is increased even though the melanin content per cell measured remains the same; therefore, melanin content or production per culture is more important than melanin content or production per cell under this circumstance.     

Radiation-induced grafting of styrene onto ultra-high molecular weight polyethylene powder and subsequent film fabrication for application as polymer electrolyte membranes: I. Influence of grafting conditions

Ultra-high molecular weight polyethylene (UHMWPE) powder was irradiated by gamma rays using a ⁶⁰Co source. Simultaneous and pre-irradiation grafting was performed in air and in inert atmosphere at room temperature. The monomer selected for grafting was styrene, since the styrene-grafted UHMWPE could be readily post-sulfonated to afford proton exchange membranes (PEMs). The effect of absorbed radiation dose and monomer concentration in methanol on the degree of grafting (DG) is discussed. It was found that the DG increases linearly with increase in the absorbed dose, grafting time and monomer concentration, reaching a maximum at a certain level. The order of rate dependence of grafting on monomer concentration was found to be 2.32. Furthermore, the apparent activation energy, calculated by plotting the Arrhenius curve, was 11.5 kJ/mole. Lower activation energy and high rate dependence on monomer concentration shows the facilitation of grafting onto powder substrate compared with film. The particle size of UHMWPE powder was measured before and after grafting and found to increase linearly with increase in level of grafting. FTIR-ATR analysis confirmed the styrene grafting. The grafted UHMWPE powder was then fabricated into film and post-sulfonated using chlorosulfonic acid for the purposes of evaluating the products as inexpensive PEM materials for fuel cells. The relationship of DG with degree of substitution (DS) of styrene per UHMWPE repeat unit and ion exchange capacity (IEC) is also presented.     

THE EFFECT OF CHANGES IN CELL GEOMETRY ON THE SENSITIVITY TO ULTRAVIOLET RADIATION OF MAMMALIAN CELLULAR CAPACITY

Abstract— We have measured a calcium and magnesium dependent change in cell shape when mammalian cell monolayers are being prepared for irradiation by replacing their growth medium with certain buffers. In some cases, flattened cells (umbonate) assumed a spherical configuration. In order to assume a centrally located target molecule, we used a DNA-dependent cellular function–pacity for herpes viral growth–as the parameter to measure ultraviolet (UV) sensitivity of cells irradiated while in either of the two shapes. Umbonate cells were more sensitive to UV than were spherical cells. Exposures to the cell that lowered the cellular capacity of umbonate cells to the 10% survival level only lowered spherical cells to the 50% level. Twenty-seven per cent additional UV exposure to spherical cells was required to get the same effect as with umbonate cells. Included in the text are photographs of both cell types, survival curves for cellular capacity, a measure of the absorbance of cell homogenates, and a calculation of the relative number of photons absorbed by each cell nucleus.     

Preservation of fresh noodles by irradiation

At the present paper, it is studied to preserve fresh noodles by irradiation. The noodles which were irradiated by 10 kGy of ⁶⁰Co-γ rays and stored at room temperature (18–24°C). The appearance of the noodles was observed, the bacteria in the noodles were examines, and the acidity of the noodles was measured during 10 days after irradiation. The results showed that the number of bacteria and the extent of acidification of the noodles were in inverse proportion to radiation dose. When the absorbed dose was less than 8 kGy, the residual bacteria in the noodles could proliferate massively in several days and acidified the noodles. The pH of these noodles decreased from 6.2 to 5.0 or less and the noodles turned into sticky during storage. When the absorbed dose reached 8–10 kGy, most of bacteria were killed and the acidity of the noodles kept about pH 6.0. The appearance of the noodles looks fresh within 10 days after irradiation. They smelled as good as fresh ones.     

Dosimetry by a cellulose triacetate film dosimeter in proton-beam irradiation

The basic characteristics of cellulose triacetate (CTA) film dosimeter have been investigated with 5, 8, and 15 MeV proton beams. The optical density change per unit absorbed dose for 8 and 15 MeV protons is the same as that given for electron beams, but a little smaller for 5 MeV protons. The CTA dosimeter was found to be useful to obtain dose distributions with high spatial resolution in samples exposed to proton beams.     

Multiplex polymerase chain reaction analysis of UV-A- and UV-B-induced delayed and early mutations in V79 Chinese hamster cells

We previously reported that approximately 10% of V79 Chinese hamster fibroblast populations clonally derived from single cells immediately after irradiation with either ultraviolet B (UV-B, 290-320 nm, mainly 311 nm) or ultraviolet A (UV-A, 320-400 nm, mainly 350-390 nm) radiation exhibit genomic instability. The instability is revealed by relatively high mutation frequencies in the hypoxanthine phosphoribosyl transferase (hprt) gene up to 23 cell generations after irradiation. These delayed mutant clones exhibited higher levels of oxidative stress than normal cells. Therefore, persistently increased oxidative stress has been proposed as a mechanism for UV-induced genomic instability. This study investigates whether this mechanism is reflected in the deletion spectrum of delayed mutant clones. Eighty-eight percent of the delayed mutant clones derived from UV-A-irradiated populations were found to have total deletion of the hprt gene. Correspondingly, 81% of UV-A-induced early mutations (i.e. detected shortly after irradiation) also had total deletions. Among delayed UV-B-induced mutant clones, 23% had total deletions and 8% had deletion of one exon, whereas all early UV-B events were either point mutations or small deletions or insertions. In conclusion, the multiplex polymerase chain reaction deletion screen showed that there were explicit differences in the occurrence of large gene alterations between early and delayed mutations induced by UV-B radiation. For UV-A radiation the deletion spectra were similar for delayed and early mutations. UV-A radiation is, in contrast to UV-B radiation, only weakly absorbed by DNA and probably induces mutation almost solely via production of reactive oxygen species. Therefore, the present results support the hypothesis that persistent increase in oxidative stress is involved in the mechanism of UV-induced genomic instability.     

UV-induced unscheduled DNA synthesis in human skin: dose response, correlation with erythema, time course and split dose exposure in vivo

Unscheduled DNA synthesis (UDS) has been shown to be saturated above a threshold dose of UV-C in human fibroblasts in vitro. We have investigated by autoradiography whether a similar saturation occurs in human skin in vivo with UV-B and whether this phenomenon correlates with the erythemal response. In addition, we determined the time course of UDS at 24 h after exposure and the effect of dual exposures separated by 24 h. The dose-response curve was established by exposure to 1/16, 1/8, 1/4, 1/2, 1, 2, 3, 4 and 6 MEDs UV-B. For the time-course study, areas exposed to 1/2 and 2 MEDs were biopsied after 1, 3, 6, 12 and 24 h. Autoradiography was performed in vitro. The dose-response curve showed a significant increase in UDS from 1/16 to 1 minimal erythema dose (MED), whereas no significant difference was observed between 1 MED and the higher UV-B doses tested. The 24 h time sequence revealed a gradual decrease in UDS activity. The 1/2 MED curve declined more rapidly and reached the zero-level between 12 h and 24 h, whereas about 50% of the initial UDS value was still retained 24 h after 2 MEDs. The dual-dose study revealed that a second hit of fractions of the MED resulted in lower levels of UDS than induced by these fractions alone in previously untreated areas. UDS increases with the erythemal dose between 1/16 and 1 MED. It reaches a plateau after 1 MED and cannot be increased by doses up to 6 MEDs, suggesting a saturation of excision repair in vivo. Time course studies support such a saturation phenomenon. The failure to increase significantly UDS by a second irradiation 24 h after the first exposure needs further clarification. Since persistence of DNA lesions may lead to an accumulation after repeated exposures, additional mechanisms other than excision repair may protect human skin by error-free removal of possibly mutagenic sites. Photoreactivation may be important in this respect.     

Calculation of singlet oxygen dose using explicit and implicit dose metrics during benzoporphyrin derivative monoacid ring A (BPD-MA)-PDT in vitro and correlation with MLL cell survival

Photodynamic therapy (PDT) oxygen consumption, clonogenic cell survival, fluorescence photobleaching and photoproduct formation were investigated during benzoporphyrin derivative monoacid (BPD-MA)-PDT of MAT-LyLu cells in vitro. Cells were incubated with BPD-MA concentrations of 0.1, 0.5 or 2.5 μg mL(-1) for 2 h and then treated with 405 nm light under oxygenated and hypoxic conditions. Fluorescence spectra were acquired during treatment, and photobleaching and photoproduct generation were quantified using singular value decomposition of the spectra. Cell survival was measured at set times during the treatment using a colony-forming assay. The amount of oxygen consumed by PDT per photon absorbed decreased with BPD-MA intracellular concentration. Survival was correlated with the total amount of oxygen consumed by PDT per unit volume, which is assumed to be equivalent to the amount of singlet oxygen that reacted. A photobleaching-based singlet oxygen dose metric was also found to predict survival independent of intracellular BPD-MA concentration. The BPD-MA photoproduct was bleached during the treatment. Two singlet oxygen dose metrics based on photoproduct kinetics could not be correlated with cell survival over the full range of intracellular BPD-MA concentrations used.     

Radiation degradation of polychlorinated biphenyls

Gradual dechlorination of the polychlorinated biphenyls (PCBs) in alkaline solutions in 2-propanol under the effect of high energy electrons (4.5 MeV) produced by electron accelerator has been studied using a flow-through apparatus of the volume of about 50 L. The dependence of both relative radiation chemical yield and the dechlorination degree on the initial concentration of OH⁻ ions or PCBs, absorbed dose as well as on dose rate has been investigated.     

A study of dosimetry characteristics of GAF DM-1260 radiochromic films

The dosimetric characteristics of gamma-ray, x-ray and electron irradiated GAF-DM-1260 radiochromic film have been studied, and the dependence of radiation-induced film absorbance on irradiation temperature and reading temperature and the changes of the absorption spectrum peaks at different reading temperatures and absorbed doses (3×10¹ to 5×10⁴ Gy) are reported. It is shown that the responses are independent of the gamma-ray dose rate in the dose rate range considered in the experiment. The film response characteristics as a function of the absorbed dose to ⁶⁰Co gamma irradiation at the spectrophotometric reading wavelengths of 400, 580, 600, 650 and 670 nm and two absorption peaks are determined as well as the response characteristics to the electron beam at the reading wavelength of 400 nm. The results demonstrate that the film responses to gamma rays, x-rays and a 3.8 MeV electron beam are equivalent, over the absorbed dose rate range of about 0.8 Gy·s⁻¹ to 5×10⁸ Gy·s⁻¹. Some advice and points of view about the dosimetric characteristics of the film and some problems in usage are provided according to the experimental results.