137Cs Irradiation Research Articles

Simulating the response of ionization chamber system to 137Cs irradiator using the artificial neural network modeling algorithm

The artificial neural network algorithm has been used to simulate the response of an ionization chamber dosimetric system to the 137Cs irradiator facility at the National Institute for Standards, Egypt. The performance of the designed model has been investigated over different processes functions and a wide range of parameters till the optimum performance has been approached. The standard uncertainty of the designed model has been evaluated for different dose-rate levels. It has been found that the dose-rate can be evaluated using the designed model with an uncertainty < 2.0% for the dose-rate level $$<\,10^{2} \,{\text{mGy/h}}$$ and with an uncertainty < 0.5% for the dose-rate level $$[10^{2} {-}10^{3} ]\,{\text{mGy/h}}$$ . The bias of the designed model has been evaluated and compared with the usual interpolation algorithms. The errors in the evaluated dose-rate using these methods have exceeded the 100% error level and approached the 20% error level for the dose rates less and greater than $$10\, {\text{mGy/h}}$$ , respectively. While, the error in the evaluated dose-rate using the designed model did not exceed 7% and 2% for the same dose-rate levels, respectively.

Experimental study on gamma ray induced light output deterioration in LaBr3:Ce scintillator

In this paper, the effects of dose and dose rate on the light output of LaBr3:Ce scintillator are studied in detail. The relative light output of the crystal is measured in real time by measuring the photoelectric current of the detector during irradiation at a 137Cs irradiation facility. It is found that the light output of the LaBr3:Ce scintillator continues to decrease with the increase in dose. Permanent radiation damage in LaBr3:Ce is also observed at a cumulative dose of 100kGy.

A Comparison of Cs-137 γ Rays and 320-kV X-Rays in a Mouse Bone Marrow Transplantation Model.

US homeland security concerns regarding the potential misuse of some radiation sources used in radiobiological research, for example, cesium-137 (137Cs), have resulted in recommendations by the National Research Council to conduct studies into replacing these sources with suitable X-ray instruments. The objective of this research is to compare the effectiveness of an X-RAD 320 irradiator (PXINC 2010) with a 137Cs irradiator (Gammacell-1000 Unit) using an established bone marrow chimeric model. Using measured radiation doses for each instrument, we characterized the dose–response relationships for bone marrow and splenocyte ablation, using a cytotoxicity-hazard model. Our results show that the X-RAD 320 photon energy spectrum was suitable for ablating bone marrow at the 3 exposure levels used, similar to that of 137Cs photons. However, the 320-kV X-rays were not as effective as the much higher energy γ rays at depleting mouse splenocytes. Furthermore, the 3 X-ray levels used were less effective than the higher energy γ rays in allowing the successful engraftment of donor bone marrow, potentially as a result of the incomplete depletion of the spleen cells. More defined studies are warranted for determining whether bone marrow transplantation in mice can be successfully achieved using 320-kV X-rays. A higher X-ray dose then used is likely needed for transplantation success.

Discorea nipponica saponins restore the Th17/Treg balance in aplastic anemia through the Notch/RBPJκ/FOXP3/RORγt axis

T cell differentiation is a key pathological process of aplastic anemia (AA). Tregs and Th17 must be balanced for efficient immune tolerance. Discorea nipponica saponins (DNS) improves the recovery from hematopoiesis in AA models through its ability to increase the number of T-helper cells whilst decreasing the percentage of T-cytotoxic cells in AA mice. However, the mechanisms by which DNS leads to these therapeutic effects remains largely undefined. Here, we explored the mechanism(s) by which DNS regulates T cell subsets in mouse AA models. BALB/c male mice were used to establish the AA model using 137Cs irradiation and intraperitoneal injection with cyclophosphamides and Chloramphenicol. Mice were administrated DNS/Tripterygium wilfordii polyglycoside tablets (TW)/cyclosporine A (CsA)/distilled water via gavage each day for 14 days. Peripheral blood, spleen and bone marrow were obtained. Bone marrow morphology, Notch/RBPJκ/FOXP3/RORγt signaling and molecules regulating Th17/Treg balance were evaluated. We found that DNS-M attenuated pancytopenia in mouse AA models. DNS-M could not only suppressed Th 17 cell numbers and RORγt expression, but enhanced the prevalence of Treg cells and Foxp3 expression. Moreover, DNS-M modulated the level of Notch1, Jagged1, RBPJκ, FOXP3, RORγt, DLL4 in AA models. These data suggest that the administration of DNS-M exhibits therapeutic effects through restoring the Th17/Treg cell balance in AA mice through its regulation of the Notch/RBPJκ/FOXP3/RORγt pathway.

DNA damage response in peripheral mouse blood leukocytes in vivo after variable, low-dose rate exposure.

Environmental contamination and ingestion of the radionuclide Cesium-137 (137Cs) is a large concern in fallout from a nuclear reactor accident or improvised nuclear device, and highlights the need to develop biological assays for low-dose rate, internal emitter radiation. To mimic low-dose rates attributable to fallout, we have developed a VAriable Dose-rate External 137Cs irradiatoR (VADER), which can provide arbitrarily varying and progressive low-dose rate irradiations in the range of 0.1-1.2Gy/day, while circumventing the complexities of dealing with radioactively contaminated biomaterials. We investigated the kinetics of mouse peripheral leukocytes DNA damage response in vivo after variable, low-dose rate 137Cs exposure. C57BL/6 mice were placed in the VADER over 7days with total accumulated dose up to 2.7Gy. Peripheral blood response including the leukocyte depletion, apoptosis as well as its signal protein p53 and DNA repair biomarker γ-H2AX was measured. The results illustrated that blood leukocyte numbers had significantly dropped by day 7. P53 levels peaked at day 2 (total dose = 0.91Gy) and then declined; whereas, γ-H2AX fluorescence intensity (MFI) and foci number generally increased with accumulated dose and peaked at day 5 (total dose = 2.08Gy). ROC curve analysis for γ-H2AX provided a good discrimination of accumulated dose < 2Gy and ≥ 2Gy, highlighting the potential of γ-H2AX MFI as a biomarker fordosimetry in a protracted, environmental exposure scenario.

Additive effects of a small molecular PCNA inhibitor PCNA-I1Sand DNA damaging agents on growth inhibition and DNA damagein prostate and lung cancer cells.

Proliferating cell nuclear antigen (PCNA) is essential for DNA replication and repair, and cell growth and survival. Previously, we identified a novel class of small molecules that bind directly to PCNA, stabilize PCNA trimer structure, reduce chromatin-associated PCNA, selectively inhibit tumor cell growth, and induce apoptosis. The purpose of this study was to investigate the combinatorial effects of lead compound PCNA-I1S with DNA damaging agents on cell growth, DNA damage, and DNA repair in four lines of human prostate and lung cancer cells. The DNA damage agents used in the study include ionizing radiation source cesium-137 (Cs-137), chemotherapy drug cisplatin (cisPt), ultraviolet-C (UV-C), and oxidative compound H2O2. DNA damage was assessed using immunofluorescent staining of γH2AX and the Comet assay. The homologous recombination repair (HRR) was determined using a plasmid-based HRR reporter assay and the nucleotide excision repair (NER) was indirectly examined by the removal of UV-induced cyclobutane pyrimidine dimers (CPD). We found that PCNA-I1S inhibited cell growth in a dose-dependent manner and significantly enhanced the cell growth inhibition induced by pretreatment with DNA damaging agents Cs-137 irradiation, UV-C, and cisPt. However, the additive growth inhibitory effects were not observed in cells pre-treated with PCNA-I1S, followed by treatment with cisPt. H2O2 enhanced the level of chromatin-bound PCNA in quiescent cells, which was attenuated by PCNA-I1S. DNA damage was induced in cells treated with either PCNA-I1S or cisPt alone and was significantly elevated in cells exposed to the combination of PCNA-I1S and cisPt. Finally, PCNA-I1S attenuated repair of DNA double strand breaks (DSBs) by HRR and the removal of CPD by NER. These data suggest that targeting PCNA with PCNA-I1S may provide a novel approach for enhancing the efficacy of chemotherapy and radiation therapy in treatment of human prostate and lung cancer.

Effect of high dose irradiation on thermoluminescence detector

Objective To investigate effect of high dose irradiation on the performances of thermolumines- cence detectors (LiF:Mg, Cu, P). Methods The high-dose irradiated thermoluminescence detector was annealed by a thermoluminescence annealing furnace until the annealing was completed, and then the annealed thermoluminescent detector was irradiated 0.5Gy by 137Cs irradiator to verify the accuracy of the thermoluminescentdetector. Results The thermoluminescence detector after high-dose irradiation could not be completely annealed under the temperature condition of 240 °C, and it could be completely annealed at a high temperature as 400 ℃. After 0.5 Gy irradiation by 137Cs irradiator, the measurement results of the annealed thermoluminescence detector were significantly smaller, and the dose response and dispersion of the detector were also changed significantly. Conclusions After a more than 5 Gy irradiation, the crystal structure of the thermoluminescence detector has changed, and a high temperature peak above 240 ℃ has appeared, which leads to the failure to completely anneal at normal temperature. Therefore, the thermoluminescence detector can no longer be used for dosimetry after high-dose irradiation. Key words: Thermoluminescent detector; High dose; Annealing; Dose response

Abstract LB-041: Targeting AKT2 and ERK decline the drug/radiation resistance in neuroblastoma

Abstract Introduction: Neuroblastoma is highly heterogeneous, containing cancer cells with very different molecular characteristics. Activation of distinct signal transduction pathways can induce neuroblastoma cells to transform cells with neuronal, chromaffin, or schwannian phenotypes, further supporting the existence of cancer stem cells. We previously demonstrated that AKT2 plays critical roles in regulation of neuroblastoma tumorigenesis. Here we hypotheize that targeting AKT2 would block the signal transduction pathways enhanced in drug/radiation resistant neuroblastoma cancer stem cells. Methods: We generated cisplatin (CDDP) resistant and radiation (Rad) resistant neuroblastoma cells under the treatment or irradiation with a concentration of IC 50 of CDDP and 137Cs irradiator respectively. Cell viability was assessed with CCK-8 kit daily. Extreme limiting dilution analysis (ELDA) was performed for quantification of tumor sphere formation. Immunoblotting detected the expression of stem cell markers CD133, Sox2, ALDH, ALDH, Nestin, Oct4 and Nanog, as well as survival signaling pathway key molecules AKT2, MAPK and P38 MAPK. Results: We founded that two important cell proliferation and survival signaling pathways mTOR, downstream of AKT2 and MAPK enhanced in CDDP-resistant and Rad-resistant neuroblastoma cells. Blocking these two pathways with chemical inhibitors, CCT128930, AKT2 selective inhibitor and PD98059, MEK inhibitor decreased cell proliferation, angiogenesis, cell migration and soft agar conoly growth in these resistant cells. We further demonstrated that these resistant cells showed higher capacity of sphere-forming with increased expression of stem cell markers CD133, Sox2, ALDH, ALDH, Nestin, Oct4 and Nanog. Improtantly, the sphere formation of these resistant cells is sensitive to the inhibitors of AKT2 and MAPK. Conclusion: Our results suggest that selected CDDP-resistant and radiation-resistant neuroblastoma cells might serve as an useful tool to improve understanding of the molecular mechanisms of therapeutic resistance and develop more effective novel treatment strategies, and further to reaching better clinical outcomes of patients with neuroblastoma. Citation Format: Kwang Woon Kim, Dai Chung, Jingbo Qiao, Julia Kim, Camille Poewers, Hernan Correa, Kyungho Park, Sora Lee. Targeting AKT2 and ERK decline the drug/radiation resistance in neuroblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr LB-041.

Dose-Rate Dependence of the Total-Ionizing-Dose Response of GaN-Based HEMTs

Significant threshold voltage $V_{\mathrm {th}}$ shifts are observed during 10-keV X-ray irradiation of AlGaN/GaN high-electron mobility transistors (HEMTs). Shifts are much smaller for lower dose-rate Cs-137 irradiation than that for higher dose-rate X-ray irradiation. This occurs because hydrogen transport and interactions with defects and impurities in these crystalline wide bandgap semiconductor materials differ fundamentally from those in amorphous SiO2. The electric field is also higher in GaN-based HEMTs than in bipolar base oxides. The absence of enhanced low-dose-rate sensitivity in these devices simplifies testing of GaN-based HEMTs for space applications. No significant X-ray-induced $V_{\mathrm {th}}$ shifts are observed in development stage InAlN/GaN HEMTs.

Gemcitabine-Based Chemoradiotherapy Gets Improved with PARP Inhibitor in Pancreatic Cancer Cells

Pancreatic ductal adenocarcinoma (PDAC) is a devastating disease with a cumulative 5-year overall survival of less than 5% for all stages. Thirty percent of patients diagnosed with PDAC present with a locally advanced disease could benefit from chemoradiotherapy with gemcitabine, which is effective but toxic. Over the past few years, studies have focused on the development of targeted radiosensitizer such as poly(ADP-ribose) polymerase (PARP) inhibitor. We conducted an in vitro study to determine whether PARP inhibition enhances radiation-induced cytotoxicity of PDAC cell lines. Three human pancreatic cancer lines, MIA PaCa-2, AsPC-1 and PANC-1 were treated in their exponential growth phase at room temperature. Low-LET gamma radiations were carried out using a 137Cs irradiator (Biobeam GM 8000) with a dose rate of 3.4 Gy/min and increasing doses of 2, 5 and 10 Gy. Cells were previously treated with non-cytotoxic concentration of gemcitabine (10 nM) and/or olaparib (1 μM). Clonogenic assay, cell cycle distribution and γ-H2AX quantifications were performed. In vitro , treatment with olaparib alone was not cytotoxic but highly radiosensitized cell lines (standard enhancement ratio (SER) = 1.21±0.06 for AsPc-1, SER = 1.27±0.02 for MIA PaCa-2, and SER=1.38±0.01 for PANC-1), particularly at high dose per fraction (10 Gy). In contrast, a non-cytotoxic concentration of gemcitabine also radiosensitized cells, but clearly less than olaparib (SER= 1.22±0.01 for AsPc-1, SER=1.11±0.04 for MIA PaCa-2 and SER=1.03±0.04 for PANC-1). Interestingly, gemcitabine and olaparib combination had a synergistic radiosensitive effect on PANC-1 cells, but not on MIA PaCa-2 cells. AsPC-1 cell line was radiosensitive with high irradiation dose, and no colonies were formed after 10 Gy. In addition, combination of olaparib and irradiation induced a G2/M arrest in all tested cell lines. Radiosensitization by gemcitabine was associated with percentage of cells blocked in early S-phase. Finally, 24h after treatment, the number of remaining γ-H2AX stained cells was higher with cells treated with a combination of olaparib and 10 Gy irradiation, compared to irradiation or olaparib alone. Our results showed that MIA PaCa-2, AsPC-1 and PANC-1 cell lines could be radiosensitized by the combination of olaparib, through an increase of unrepaired double-strand breaks and a block in G2 phase. The radiosensitization was increased with high dose of radiation. This combination of olaparib with gemcitabine based chemoradiotherapy could lead to an enhancement of local control in vivo and an improvement in disease-free survival.

Characterization of the energy spectrum of a 137Cs irradiator through measurements using a pulse-mode detector

137Cs irradiators are used for many different applications including food processing, radiobiological experiments, and calibrations of radiation detectors at standards labs. Air-kerma modulation techniques including varying source size, adding attenuation, or varying source-to-detector distance, combined with the geometry of the collimation in the irradiator, may change the energy spectrum of the irradiator. This is unaccounted for during beam characterization, which is completed using a spherical ionization chamber with a minimal energy dependence in the 662 keV 137Cs gamma-ray emission region. This work incorporated a high-purity germanium (HPGe) detector collimated using a lead aperture to measure the energy spectrum of a 5 Ci source in a Hopewell Designs G-10 dual source irradiator with 4.08 cm and 5.54 cm of attenuating material. The measured pulse-height distributions (PHDs) were compared with simulations in MCNP6 to provide validation of the geometry of the irradiator model. PHD measurements were corrected for detector response using MCNP and the true spectrum was obtained using Gold's deconvolution method. Due to the fluence limitations and collimation of the HPGe detector, measurements represented the primary photon energy spectrum. The impact of scattered photons on the energy spectrum was investigated using MCNP6 simulations. In addition, simulations were run to determine the effects of attenuation and source-to-detector distance (SDD) on the energy spectrum. Comparisons of spectra were made in terms of mean energy. Simulated and measured PHDs showed good agreement when comparing spectral features including FWHM of the 662 keV photopeak, mean energy, and the total area under the curve. After deconvolution of the PHDs, the primary energy spectrum mimicked an encapsulated 137Cs source with emission of only the 662 keV photopeak. For 5.54 cm of attenuation, simulations showed that if scattered photons were taken into account, the average energy decreased from 662 keV to 656 keV, which was a 2% difference. Simulations showed that as attenuation increased from 0 cm to 5.54 cm, the mean energy of the spectrum increased 9% from 605 keV to 656 keV. The SDD did not affect the mean energy. This work used spectrum measurements to validate a 137Cs irradiator model in MCNP6, which represents a method that is more sensitive to geometry errors than conventional PDD and profile comparisons. Using the validated model, simulations were run to improve the understanding of the output of the Hopewell G-10 137Cs irradiator.

Small gold nanoparticles presenting linear and looped Cilengitide analogues as radiosensitizers of cells expressing ανβ3 integrin

This work uses linear and looped RGDfV sequences attached to the surface of small (1.8 nm in diameter) gold nanoparticles (AuNPs) to enhance the radiosensitizating effects of Cilengitide, a cyclic RGDf (NMe)V pentapeptide that targets αvβ3 integrin which is overexpressed in certain cancers. Following synthesis and purification, the AuNPs were evaluated in vitro against HUVEC, H460, and MCF7 cells in clonogenic assays using a 137Cs irradiator. Untargeted AuNPs induced no significant dose enhancement factors (DEFs) in any of the cell types when compared to radiation treatment alone, whereas all evaluated AuNPs functionalized with targeting peptides performed at least as well as controls (irradiation after Cilengitide treatment). The observed DEFs also suggest that cyclizing the linear peptides into more spatially constrained, looped structures may facilitate target binding. These greater dose enhancements merit future in vivo studies of drug-AuNP conjugates to assess the ability of the nanostructures to provide an improved therapeutic benefit over treatment with drug candidates and radiation alone.

Paradoxical effects of 137Cs irradiation on pharmacological stimulation of reactive oxygen species in hippocampal slices from apoE2 and apoE4 mice.

In humans, apoE, which plays a role in repair, is expressed in three isoforms: E2, E3, and E4. E4 is a risk factor for age-related cognitive decline (ACD) and Alzheimer's disease (AD), particularly in women. In contrast, E2 is a protective factor for ACD and AD. E2 and E4 might also differ in their response to cranial 137Cs irradiation, a form of radiation typically used in a clinical setting for the treatment of cancer. This might be mediated by reactive oxygen species (ROS) in an-apoE isoform-dependent fashion. E2 and E4 female mice received sham-irradiation or cranial irradiation at 8 weeks of age and a standard mouse chow or a diet supplemented with the antioxidant alpha-lipoic acid (ALA) starting at 6 weeks of age. Behavioral and cognitive performance of the mice were assessed 12 weeks later. Subsequently, the generation of ROS in hippocampal slices was analyzed. Compared to sham-irradiated E4 mice, irradiated E4 mice showed enhanced spatial memory in the water maze. This was associated with increased hippocampal PMA-induction of ROS. Similar effects were not seen in E2 mice. Irradiation increased endogenous hippocampal ROS levels in E2 mice while decreasing those in E4 mice. NADPH activity and MnSOD levels were higher in sham-irradiated E2 than E4 mice. Irradiation increased NADPH activity and MnSOD levels in hemi brains of E4 mice but not in those of E2 mice. ALA did not affect behavioral and cognitive performance or hippocampal formation of ROS in either genotype. Thus, apoE isoforms modulate the radiation response.

Radio-Optically- and Thermally Stimulated Luminescence of Zn(BO2)2:Tb3+ exposed to Ionizing Radiation

The optical absorption of zinc tetraborate at different concentrations of the terbium impurity (0, 0.5, 1, 2, 4, 8 mol%) was analyzed. The radioluminescence (RL) emission spectra was obtained after beta irradiation of a 90Sr/90Y source. The RL spectrum showed the characteristics bands of Tb3+ with two main emissions at 489 nm and 546 nm which corresponding to the5D4→7F6 and 5D4→7F5 transitions respectively in this ion. The OSL and TL characteristics have been analyzed. The stimulation blue light (497 nm) of a diode laser at 500 mA was used to bleach the thermoluminescent (TL) signals obtained with 5Gy of 60Co source. The two main glow peaks (79 and 161 °C) are sensitives under 497 nm stimulation, and they were shifted to higher temperature values and faded their TL intensities. Similar behavior of TL glow curves before and after OSL stimulation with blue light was observed when the samples were exposed to 30 Gy gamma dose of 137Cs irradiator. The OSL signal response was linear with the dose range of 1-10 Gy and increased their response up to 200 Gy gamma dose. The OSL shows a bleaching sensitive shallow traps and diminishing the intensity of the TL glow curves remaining a complex traps distribution. The RL, TL and OSL properties were investigated in Zn(BO2)2:Tb3+ phosphor.

Non-destructive analysis of ancient bimetal swords from western Asia by γ-ray radiography and X-ray fluorescence

Eight ancient bimetal swords held by Hiroshima University, Japan were analyzed non-destructively through γ-ray radiography and X-ray fluorescence (XRF). 137Cs and 60Co γ-ray irradiation sources were used to obtain transmission images of swords. A scanning radiography method using a 60Co γ-ray source was developed. XRF was used for qualitative elemental analysis of the swords. The presence of iron cores in the hilts of some swords had been observed and it was assumed that the cores were a ritual symbol or had a functional purpose. However, our work reveals that these swords were originally bronze-hilted iron swords and that the rusty blades were replaced with bronze blades to maintain the swords’ commercial value as an antique. Consequently, the rest of the iron blade was left in the hilt as an iron tang. The junction of the blade and the guard was soldered and painted to match the patina color. XRF analysis clearly showed that the elemental Sn/Cu ratios of the blades and the hilts were different. These findings are useful for clarifying the later modifications of the swords and are important for interpreting Bronze Age and Iron Age history correctly.

Low-Dose Ionizing γ-Radiation Promotes Proliferation of Human Mesenchymal Stem Cells and Maintains Their Stem Cell Characteristics.

Mesenchymal stem cells (MSCs), which are multipotent and have self-renewal ability, support the regeneration of damaged normal tissue. A number of external stimuli promote migration of MSCs into peripheral blood and support their participation in wound healing. In an attempt to harness the potential beneficial effects of such external stimuli, we exposed human MSCs (hMSCs) to one such stimulus-low-dose ionizing radiation (LDIR)-and examined their biological properties. To this end, we evaluated differences in proliferation, cell cycle, DNA damage, expression of surface markers (CD29, CD34, CD90, and CD105), and differentiation potential of hMSCs before and after irradiation with γ-rays generated using a 137CS irradiator. At doses less than 50mGy, LDIR had no significant effect on the viability or apoptosis of hMSCs. Interestingly, 10mGy of LDIR increased hMSC viability by 8% (p<0.001) compared with non-irradiated hMSCs. At doses less than 50mGy, LDIR did not induce DNA damage, including DNA strand breaks, or cause cellular senescence or cell-cycle arrest. Surface marker expression and in vitro differentiation potential of hMSCs were maintained after two exposures to LDIR at 10mGy per dose. In conclusion, a two-dose exposure to LDIR at 10mGy per dose not only facilitates proliferation of hMSCs, it also maintains the stem cell characteristics of hMSCs without affecting their viability. These results provide evidence for the potential of LDIR as an external stimulus for in vitro expansion of hMSCs and application in tissue engineering and regenerative medicine.

Enhancement of IUdR Radiosensitization by Low-Energy Photons Results from Increased and Persistent DNA Damage.

Low-energy X-rays induce Auger cascades by photoelectric absorption in iodine present in the DNA of cells labeled with 5-iodo-2’-deoxyuridine (IUdR). This photoactivation therapy results in enhanced cellular sensitivity to radiation which reaches its maximum with 50 keV photons. Synchrotron core facilities are the only way to generate such monochromatic beams. However, these structures are not adapted for the routine treatment of patients. In this study, we generated two beams emitting photon energy means of 42 and 50 keV respectively, from a conventional 225 kV X-ray source. Viability assays performed after pre-exposure to 10 μM of IUdR for 48h suggest that complex lethal damage is generated after low energy photons irradiation compared to 137Cs irradiation (662KeV). To further decipher the molecular mechanisms leading to IUdR-mediated radiosensitization, we analyzed the content of DNA damage-induced foci in two glioblastoma cell lines and showed that the decrease in survival under these conditions was correlated with an increase in the content of DNA damage-induced foci in cell lines. Moreover, the follow-up of repair kinetics of the induced double-strand breaks showed the maximum delay in cells labeled with IUdR and exposed to X-ray irradiation. Thus, there appears to be a direct relationship between the reduction of radiation survival parameters and the production of DNA damage with impaired repair of these breaks. These results further support the clinical potential use of a halogenated pyrimidine analog combined with low-energy X-ray therapy.

Scintillation and dosimeter properties of CaF2 translucent ceramic produced by SPS

We have developed CaF2 translucent ceramics by spark plasma sintering (SPS) and investigated the scintillation and dosimeter properties, in comparison with a CaF2 single crystal. Under X-ray irradiation, light emission was observed at 270 and 300nm, due to self-trapped exciton (STE). The scintillation light yield of CaF2 translucent ceramic was measured to be about 6000photons/MeV under 137Cs irradiation, and this value was smaller than that of the single crystal by a factor of approximately 2. The afterglow level, after X-ray irradiation, of the ceramic sample was lower than that of the single crystal. Thermally stimulated luminescence (TSL) glow peaks were observed at 100 and 150°C in both ceramic and single crystal samples, however the TSL intensity was much stronger than that of the single crystal sample.

Air-kerma modulation effects on the energy spectrum of a 137CS irradiator using Monte-Carlo techniques

Calibration of radiation protection instrumentation such as survey meters is typically performed using 137Cs irradiators. During calibration, various thicknesses of lead attenuators are added and the source-to-detector distance is adjusted to modulate air-kerma rate. Variations in the energy spectrum as a result of these modulation techniques are unknown, and may affect the response of energy-dependent survey meters during calibration. The purpose of this work was to characterize the spectral changes that result from modulation of the air-kerma rate for the Hopewell Designs G-10 dual source irradiator at the University of Wisconsin Accredited Dosimetry Calibration Laboratory (UWADCL). An experimentally validated Monte-Carlo model of the irradiator geometry was used to investigate energy spectra variations as a function of attenuation and distance. Lead attenuator thicknesses of (0, 0.64, 1.22, 2.22, 4.32, and 5.54) cm were used in this study. The irradiator geometry was modeled using MCNP6 Monte Carlo (MC) transport code and validated by comparing simulated and measured percent depth dose (PDD) curves and cross-field profiles. Spectra were tallied at (100, 200, 300, and 400) cm from the source. The effects of room scatter on the energy spectrum were also investigated. Simulated and measured PDDs agreed within the associated uncertainty and profiles agreed within 3% or 3 mm distance to agreement. The mean energy for simulated spectra at 100 cm from the source varied from 593 keV to 654 keV as attenuation increased from no attenuation to 5.54 cm of lead. The mean energy of the spectra remained consistent at distances ranging from 100 cm to 400 cm for all attenuation thicknesses and for both geometries in which the vault walls were defined and undefined. This study used MC methods to show that the modulation of air-kerma rate using attenuation and source-detector distance significantly changes the energy spectrum. This knowledge may improve the accuracy of any calibrations using this source.

Scintillation and dosimeter properties of CaF2 transparent ceramic doped with Eu2+

We have developed CaF2 transparent ceramics doped with Eu2+(CaF2:Eu) by using spark plasma sintering (SPS), and investigated the scintillation, dosimeter and photoluminescence (PL) properties. Under X-ray irradiation, all the samples showed emission due to self-trapped excitons (STE) and 5d-4f transition of Eu2+ at 300 and 430nm, respectively. In addition, weak emission due to the 4f-4f transitions of Eu3+ at 570, 590, 615 and 625nm were also present in all the samples. Under 137Cs irradiation, the light yields of the 0.01, 0.02, 0.05 and 0.1 Eu-doped samples were estimated to be 16,400, 15,400, 17,700 and 14,300 photons/MeV, respectively. Thermally stimulated luminescence (TSL) glow curves of all the samples exhibited glow peaks at 100 and 180°C, and these intensities increased linearity as a function of X-ray dose from 0.1 to 1000mGy. Furthermore, the CaF2:Eu showed not only TSL but also optically stimulated luminescence (OSL).