Hwang, S-L., Hwang, J-S., Yang, Y-T., Hsieh, W. A., Chang, T-C., Guo, H-R., Tsai, M-H., Tang, J-L. Lin, I-F. and Chang, W. P. Estimates of Relative Risks for Cancers in a Population after Prolonged Low-Dose-Rate Radiation Exposure: A Follow-up Assessment from 1983 to 2005. Radiat. Res. 170, 143–148 (2008).

Radiation effects on cancer risks in a cohort of Taiwanese residents who received protracted low-dose-rate γ-radiation exposures from ⁶⁰Co-contaminated reinforcing steel used to build their apartments were studied, and risks were compared to those in other radiation-exposed cohorts. Analyses were based on a more extended follow-up of the cohort population in which 117 cancer cases diagnosed between 1983 and 2005 among 6,242 people with an average excess cumulative exposure estimate of about 48 mGy. Cases were identified from Taiwan's National Cancer Registry. Radiation effects on cancer risk were estimated using proportional hazards models and were summarized in terms of the hazard ratio associated with a 100-mGy increase in dose (HR_100mGy). A significant radiation risk was observed for leukemia excluding chronic lymphocytic leukemia (HR_100mGy 1.19, 90% CI 1.01–1.31). Breast cancer exhibited a marginally significant dose response (HR_100mGy 1.12, 90% CI 0.99–1.21). The results further strengthen the association between protracted low-dose radiation and cancer risks, especially for breast cancers and leukemia, in this unique cohort population.

Bhatti, P., Doody, M. M., Preston, D. L., Kampa, D., Ron, E., Weinstock, R. W., Simon, S., Edwards, A. A. and Sigurdson, A. J. Increased Frequency of Chromosome Translocations Associated with Diagnostic X-Ray Examinations. Radiat. Res. 170, 149–155 (2008).

Informative studies of cancer risks associated with medical radiation are difficult to conduct owing to low radiation doses, poor recall of diagnostic X rays, and long intervals before cancers occur. Chromosome aberrations have been associated with increased cancer risk and translocations are a known radiation biomarker. Seventy-nine U.S. radiologic technologists were selected for blood collection, and translocations were enumerated by whole chromosome painting. We developed a dose score to the red bone marrow for medical radiation exposure from X-ray examinations reported by the technologists that they received as patients. Using Poisson regression, we analyzed translocations in relation to the dose scores. Each dose score unit approximated 1 mGy. The estimated mean cumulative red bone marrow radiation dose score was 42 (range 1–265). After adjustment for age, occupational radiation, and radiotherapy for benign conditions, translocation frequencies significantly increased with increasing red bone marrow dose score with an estimate of 0.007 translocations per 100 CEs per score unit (95% CI, 0.002 to 0.013; P = 0.01). Chromosome damage has been linked with elevated cancer risk, and we found that cumulative radiation exposure from medical X-ray examinations was associated with increased numbers of chromosome translocations.

Sharma, K. K. K., Milligan, J. R. and Bernhard, W. A. Multiplicity of DNA Single-Strand Breaks Produced in pUC18 Exposed to the Direct Effects of Ionizing Radiation. Radiat. Res. 170, 156–162 (2008).

The transition of plasmid DNA from a supercoiled to an open circle conformation, as detected by gel electrophoresis, affords an extraordinarily sensitive method for detecting single-strand breaks (SSBs), one measure of deoxyribose damage. To determine the yield of SSBs, G(ssb), by this method, it is commonly assumed that Poisson statistics apply such that, on average, one SSB occurs per supercoiled plasmid lost. For the direct effect, at a large enough plasmid size, this assumption may be invalid. In this report, the assumption that one SSB occurs per pUC18 plasmid (2686 bp) is tested by measuring free base release (fbr), which is also a measure of deoxyribose damage in films prepared under controlled relative humidity so as to produce known levels of DNA hydration. The level of DNA hydration, Γ, is expressed in mol water/mol nucleotide. The yield of free base release, G(fbr), was measured by HPLC after exposure of the films to 70 kV X rays and subsequent dissolution in water. It is well known that damage in deoxyribose leads to SSBs and free base release. Based on known mechanisms, there exists a close correspondence between free base release and SSBs, i.e., G(fbr) ≅ G(ssb). Following this assumption, the SSB multiplicity, m(ssb), was determined, where m(ssb) was defined as the mean number of SSBs per supercoiled plasmid lost. The yield of lost supercoil was determined previously (S. Purkayastha et al., J. Phys. Chem. B 110, 26286–26291, 2006). We found that m(ssb) = 1.4 ± 0.2 at Γ = 2.5 and m(ssb) = 2.8 ± 0.5 to 3.1 ± 0.5 at Γ = 22.5, indicating that the assumption of one SSB per lost supercoil is not likely to hold for a 2686-bp plasmid exposed to the direct effect. In addition, an increase in G(fbr), upon stepping from Γ = 2.5 to Γ = 22.5, was paralleled by an increase in the yield of trapped deoxyribose radicals, G_dRib(fr), also measured previously. As a consequence, the shortfall between SSBs and trapped radicals, G(diff) = G(ssb) − G_dRib(fr), remained relatively constant at 90–110 nmol/J. The lack of change between the two extremes of hydration is in keeping with the suggestion that non-radical species, such as doubly oxidized deoxyribose, are responsible for the shortfall.

Tsuruoka, C., Suzuki, M., Hande, M. P., Furusawa, Y., Anzai, K. and Okayasu, R. The Difference in LET and Ion Species Dependence for Induction of Initially Measured and Non-rejoined Chromatin Breaks in Normal Human Fibroblasts. Radiat. Res. 170, 163–171 (2008).

We studied the LET and ion species dependence of the induction of chromatin breaks measured immediately after irradiation as initially measured breaks and after 24 h postirradiation incubation (37°C) as non-rejoined breaks in normal human fibroblasts with different heavy ions, such as carbon, neon, silicon and iron, generated by the Heavy Ion Medical Accelerator in Chiba (HIMAC) at the National Institute of Radiological Science (NIRS). Chromatin breaks were measured as an excess number of fragments of prematurely condensed chromosomes using premature chromosome condensation (PCC). The results showed that the number of excess fragments per cell per Gy for initially measured chromatin breaks was dependent on LET in the range from 13.3 to 113.1 keV/μm but was not dependent on ion species. On the other hand, the number of non-rejoined chromatin breaks detected after 24 h postirradiation incubation was clearly dependent on both LET and ion species. No significant difference was observed in the cross section for initially measured breaks, but a statistically significant difference was observed in the cross section for non-rejoined breaks among carbon, neon, silicon and iron ions. This suggests that the LET-dependent structure in the biological effects is reflected in biological consequences of repair processes.

Saintigny, Y., Roche, S., Meynard, D. and Lopez, B. S. Homologous Recombination is Involved in the Repair Response of Mammalian Cells to Low Doses of Tritium. Radiat. Res. 170, 172–183 (2008).

Radioactive compounds incorporated in tissues can have biological effects resulting from energy deposition in subcellular compartments. We addressed the genetic consequences of [³H] or [¹⁴C]thymidine incorporation into mammalian DNA. Low doses of [³H]thymidine in CHO cells led to enhanced sensitivity compared with [¹⁴C]thymidine. Compared with wild-type cells, homologous recombination (HR)-deficient cells were more sensitive to lower doses of [³H]thymidine but not to any dose of [¹⁴C]thymidine. XRCC4-defective cells, however, were sensitive to both low and high doses of [³H] and [¹⁴C]thymidine, suggesting introduction of DNA double-strand breaks, which were confirmed by γ-H2AX focus formation. While γ rays induced measurable HR only at toxic doses, sublethal levels of [³H] or [¹⁴C]thymidine strongly induced HR. The level of stimulation was in an inverse relationship to the emitted energies. The RAD51 gene conversion pathway was involved, because [³H]thymidine induced RAD51 foci, and [³H]thymidine-induced HR was abrogated by expression of dominant negative RAD51. In conclusion, both HR and non-homologous end-joining pathways were involved after labeled nucleotide incorporation (low doses); genetic effects were negatively correlated with the energy emitted but were positively correlated with the energy deposited in the nucleus, suggesting that low-energy β-particle emitters, at non-toxic doses, may induce genomic instability.

van Bree, C., Rodermond, H. M., ten Cate, R., de Vos, J., Stalpers, L. J. A., Haveman, J., Medema, J. P. and Franken, N. A. P. G₀ Cell Cycle Arrest Alone is Insufficient for Enabling the Repair of Ionizing Radiation-Induced Potentially Lethal Damage. Radiat. Res. 170, 184–191 (2008).

The repair of ionizing radiation-induced potentially lethal damage (PLD) is suggested to be important for the clinical response to radiotherapy. PLD repair is usually studied in quiescent cultures prepared by growing cells to confluence with an accumulation of cells in G₀ phase of the cell cycle, but the biological pathways enabling PLD repair are still unknown. In this study, we examined whether the controlled expression of two different inducers of G₀ cell cycle arrest, the human tumor suppressor gene growth arrest specific 1 (GAS1) in murine fibroblasts and the forkhead transcription factor FOXO3a in human colon carcinoma cells, is sufficient to enable PLD repair. We found that GAS1 and FOXO3a induced a cell cycle arrest in G₀ phase with a concomitant reduction of proliferation of log-phase cells. In both cell systems, this cell cycle arrest in G₀ phase did not enable PLD repair in log-phase cells. Significant PLD repair was found in all confluent cultures that showed similar cell cycle distributions, while GAS1 and FOXO3a in confluent cells did not influence PLD repair. No differences were found in cell cycle re-entry after replating cells with different capacities for PLD repair. Our data suggest that the induction of G₀ cell cycle arrest and the reduction of proliferation are not sufficient to enable PLD repair.

Pouget, J-P., Santoro, L., Raymond, L., Chouin, N., Bardiès, M., Bascoul-Mollevi, C., Huguet, H., Azria, D., Kotzki, P-O., Pè legrin, M., Vivès, E. and Pèlegrin, A. Cell Membrane is a More Sensitive Target than Cytoplasm to Dense Ionization Produced by Auger Electrons. Radiat. Res. 170, 192–200 (2008).

To improve radioimmunotherapy with Auger electron emitters, we assessed whether the biological efficiency of ¹²⁵I varied according to its localization. A-431 and SK-OV-3 carcinoma cells were incubated with increasing activities (0–4 MBq/ml) of ¹²⁵I-labeled vectors targeting the cell membrane, the cytoplasm or the nucleus. We then measured cell survival by clonogenic assay and the mean radiation dose to the nucleus by assessing the cellular medical internal radiation dose (MIRD). The relationship between survival and the radiation dose delivered was investigated with a linear mixed regression model. For each cell line, we obtained dose–response curves for the three targets and the reference values (i.e., the dose leading to 75, 50 or 37% survival). When cell survival was expressed as a function of the total cumulative decays, nuclear ¹²⁵I disintegrations were more harmful than disintegrations in the cytoplasm or at the cell membrane. However, when survival was expressed as a function of the mean radiation dose to the nucleus, toxicity was significantly higher when ¹²⁵I was targeted to the cell membrane than to the cytoplasm. These findings indicate that the membrane is a more sensitive target than the cytoplasm for the dense ionization produced by Auger electrons. Moreover, cell membrane targeting is as cytotoxic as nuclear targeting in SK-OV-3 cells. We suggest that targeting the membrane rather than the cytoplasm may contribute to the development of more efficient radioimmunotherapies based on Auger electron radiation, also because most of the available vectors are directed against cell surface antigens.

Willey, J. S., Grilly, L. G., Howard, S. H., Pecaut, M. J., Obenaus, A., Gridley, D. S., Nelson, G. A. and Bateman, T. A. Bone Architectural and Structural Properties after ⁵⁶Fe²⁶ Radiation-Induced Changes in Body Mass. Radiat. Res. 170, 201– 207 (2008).

High-energy, high-charge (HZE) radiation, including iron ions (⁵⁶Fe²⁶ ), is a component of the space environment. We recently observed a profound loss of trabecular bone in mice after whole-body HZE irradiation. The goal of this study was to examine morphology in bones that were excluded from a ⁵⁶Fe²⁶ beam used to irradiate the body. Using 10-week-old male Sprague-Dawley rats and excluding the hind limbs and pelvis, we irradiated animals with 0, 1, 2 and 4 Gy ⁵⁶Fe²⁶ ions and killed them humanely after 9 months. Animals grew throughout the experiment. Trabecular bone volume, connectivity and thickness within the proximal tibiae were significantly lower than control in a dose-dependent manner. Irradiated animals generally had less body mass than controls, which largely accounted for the variability in bone parameters as determined by ANCOVA. Likewise, lower cortical parameters were associated with reduced mass. However, lesser trabecular thickness in the 4-Gy group could not be attributed to body mass alone. Indicators of bone metabolism were generally unchanged, suggesting stabilized turnover. Exposure to ⁵⁶Fe²⁶ ions can alter trabecular microarchitecture in shielded bones. Reduced body mass seems to be correlated with these deficits of trabecular and cortical bone.

Sérandour, A. L., Grémy, O., Fréchou, M., Renault, D., Poncy, J. L. and Fritsch, P. In Vitro and In Vivo Assessment of Plutonium Speciation and Decorporation in Blood and Target Retention Tissues after a Systemic Contamination followed by an Early Treatment with DTPA. Radiat. Res. 170, 208–215 (2008).

This study identifies the main sources of systemic plutonium decorporated in the rat after DTPA i.v. at the dose recommended for humans (30 μmol kg⁻¹). For this purpose, standard biokinetic approaches are combined to plasma ultrafiltration for separation of plutonium complexes according to their molecular weight. In vitro studies show that at the recommended DTPA dose, less than 5% of the plasma plutonium of contaminated rats can be displaced from high-molecular-weight ligands. After i.v. administration of Pu-DTPA, early ultrafiltrability of plutonium in plasma decreases with total DTPA dose, which is associated with an increase in plutonium bone retention. This demonstrates the instability of Pu-DTPA complexes, injected in vivo, below the minimal Ca-DTPA dose of 30 μmol kg⁻¹. Plutonium biokinetics is compared in rats contaminated by plutonium-citrate i.v. and treated or not with DTPA after 1 h. No significant decrease in plasma plutonium is observed for the first hour after treatment, and the fraction of low-molecular-weight plutonium in plasma is nearly constant [5.4% compared with 90% in Pu-DTPA i.v. (30 μmol kg⁻¹) and 0.7% in controls]. Thus plutonium decorporation by DTPA is a slow process that mainly involves retention compartments other than the blood. Plutonium-ligand complexes formed during plutonium deposition in the retention organs appear to be the main source of decorporated plutonium.

Uehara, Y., Ikehata, H., Komura, J-I., Ito, A., Ogata, M., Itoh, T., Hirayama, R., Furusawa, Y., Ando, K., Paunesku, T., Woloschak, G. E., Komatsu, K., Matsuura, S., Ikura, T., Kamiya, K. and Ono, T. Absence of Ku70 Gene Obliterates X-Ray-Induced lacZ Mutagenesis of Small Deletions in Mouse Tissues. Radiat. Res. 170, 216–223 (2008).

With the goal of understanding the role of non-homologous end-joining repair in the maintenance of genetic information at the tissue level, we studied mutations induced by radiation and subsequent repair of DNA double-strand breaks in Ku70 gene-deficient lacZ transgenic mice. The local mutation frequencies and types of mutations were analyzed on a lacZ gene that had been chromosomally integrated, which allowed us to monitor DNA sequence alterations within this 3.1-kbp region. The mutagenic process leading to the development of the most frequently observed small deletions in wild-type mice after exposure to 20 Gy of X rays was suppressed in Ku70^−/− mice in the three tissues examined: spleen, liver and brain. Examination of DNA break rejoining and the phosphorylation of histone H2AX in Ku70-deficient and -proficient mice revealed that Ku70 deficiency decreased the frequency of DNA rejoining, suggesting that DNA rejoining is one of the causes of radiation-induced deletion mutations. Limited but statistically significant DNA rejoining was found in the liver and brain of Ku70-deficient mice 3.5 days after irradiation, showing the presence of a DNA double-strand break repair system other than non-homologous end joining. These data indicate a predominant role of non-homologous end joining in the production of radiation-induced mutations in vivo.

Korenstein-Ilan, A., Barbul, A., Hasin, P., Eliran, A., Gover, A. and Korenstein, R. Terahertz Radiation Increases Genomic Instability in Human Lymphocytes. Radiat. Res. 170, 224–234 (2008).

Terahertz radiation is increasingly being applied in new and evolving technologies applied in areas such as homeland security and medical imaging. Thus a timely assessment of the potential hazards and health effects of occupational and general population exposure to THz radiation is required. We applied continuous-wave (CW) 0.1 THz radiation (0.031 mW/ cm²) to dividing lymphocytes for 1, 2 and 24 h and examined the changes in chromosome number of chromosomes 1, 10, 11 and 17 and changes in the replication timing of their centromeres using interphase fluorescence in situ hybridization (FISH). Chromosomes 11 and 17 were most vulnerable (about 30% increase in aneuploidy after 2 and 24 h of exposure), while chromosomes 1 and 10 were not affected. We observed changes in the asynchronous mode of replication of centromeres 11, 17 and 1 (by 40%) after 2 h of exposure and of all four centromeres after 24 h of exposure (by 50%). It is speculated that these effects are caused by radiation-induced low-frequency collective vibrational modes of proteins and DNA. Our results demonstrate that exposure of lymphocytes in vitro to a low power density of 0.1 THz radiation induces genomic instability. These findings, if verified, may suggest that such exposure may result in an increased risk of cancer.

Höytö, A., Luukkonen, J., Juutilainen, J. and Naarala, J. Proliferation, Oxidative Stress and Cell Death in Cells Exposed to 872 MHz Radiofrequency Radiation and Oxidants. Radiat. Res. 170, 235–243 (2008).

Human SH-SY5Y neuroblastoma and mouse L929 fibroblast cells were exposed to 872 MHz radiofrequency (RF) radiation using continuous waves (CW) or a modulated signal similar to that emitted by GSM mobile phones at a specific absorption rate (SAR) of 5 W/kg in isothermal conditions. To investigate possible combined effects with other agents, menadione was used to induce reactive oxygen species, and tert-butylhydroperoxide (t-BOOH) was used to induce lipid peroxidation. After 1 or 24 h of exposure, reduced cellular glutathione levels, lipid peroxidation, proliferation, caspase 3 activity, DNA fragmentation and viability were measured. Two statistically significant differences related to RF radiation were observed: Lipid peroxidation induced by t-BOOH was increased in SH-SY5Y (but not in L929) cells, and menadione-induced caspase 3 activity was increased in L929 (but not in SH-SY5Y) cells. Both differences were statistically significant only for the GSM-modulated signal. The other end points were not significantly affected in any of the experimental conditions, and no effects were observed from exposure to RF radiation alone. The positive findings may be due to chance, but they may also reflect effects that occur only in cells sensitized by chemical stress. Further studies are required to investigate the reproducibility and dose response of the possible effects.

Sato, T., Yasuda, H., Niita, K., Endo, A. and Sihver, L. Development of PARMA: PHITS-based Analytical Radiation Model in the Atmosphere. Radiat. Res. 170, 244–259 (2008).

Estimation of cosmic-ray spectra in the atmosphere has been essential for the evaluation of aviation doses. We therefore calculated these spectra by performing Monte Carlo simulation of cosmic-ray propagation in the atmosphere using the PHITS code. The accuracy of the simulation was well verified by experimental data taken under various conditions, even near sea level. Based on a comprehensive analysis of the simulation results, we proposed an analytical model for estimating the cosmic-ray spectra of neutrons, protons, helium ions, muons, electrons, positrons and photons applicable to any location in the atmosphere at altitudes below 20 km. Our model, named PARMA, enables us to calculate the cosmic radiation doses rapidly with a precision equivalent to that of the Monte Carlo simulation, which requires much more computational time. With these properties, PARMA is capable of improving the accuracy and efficiency of the cosmic-ray exposure dose estimations not only for aircrews but also for the public on the ground.

Lin, M. D., Toncheva, G., Nguyen, G., Kim, S., Anderson-Evans, C., Johnson, G. A. and Yoshizumi, T. T. Application of MOSFET Detectors for Dosimetry in Small Animal Radiography Using Short Exposure Times. Radiat. Res. 170, 260– 263 (2008).

Digital subtraction angiography (DSA) X-ray imaging for small animals can be used for functional phenotyping given its ability to capture rapid physiological changes at high spatial and temporal resolution. The higher temporal and spatial requirements for small-animal imaging drive the need for short, high-flux X-ray pulses. However, high doses of ionizing radiation can affect the physiology. The purpose of this study was to verify and apply metal oxide semiconductor field effect transistor (MOSFET) technology to dosimetry for small-animal diagnostic imaging. A tungsten anode X-ray source was used to expose a tissue-equivalent mouse phantom. Dose measurements were made on the phantom surface and interior. The MOSFETs were verified with thermoluminescence dosimeters (TLDs). Bland-Altman analysis showed that the MOSFET results agreed with the TLD results (bias, 0.0625). Using typical small animal DSA scan parameters, the dose ranged from 0.7 to 2.2 cGy. Application of the MOSFETs in the small animal environment provided two main benefits: (1) the availability of results in near real-time instead of the hours needed for TLD processes and (2) the ability to support multiple exposures with different X-ray techniques (various of kVp, mA and ms) using the same MOSFET. This MOSFET technology has proven to be a fast, reliable small animal dosimetry method for DSA imaging and is a good system for dose monitoring for serial and gene expression studies.

Kozin, S. V., Niemierko, A., Huang, P., Silva, J., Doppke, K. P. and Suit, H. D. Inter- and Intramouse Heterogeneity of Radiation Response for a Growing Paired Organ. Radiat. Res. 170, 264–267 (2008).

An intensive search for predictive markers of individual radiation response of apparently normal tissues in cancer patients is in progress at the genetic and epigenetic levels. However, the relative impact of variability at these levels is not clear. Experimental results obtained in inbred rodents, which have significantly reduced genetic heterogeneity relative to a population of human patients, may help to clarify this issue. We investigated a paired-organ mouse system in a strain of inbred mice to evaluate the intermouse variability of normal tissue radiation response, singled out from measurement errors and stochastic effects. The legs of 5-day-old C3H mice were homogeneously γ-irradiated with a range of single doses. The lengths of the right and left tibiae were measured in 30 kVp X-ray images taken at the time of irradiation and at 84 days postirradiation. The dose–effect curves were smooth and well defined, with bone growth retardation evident at ∼14 Gy and higher, and were marginally gender-dependent. The intramouse (left compared to right) variability of the tibia length on day 89, which characterized stochastic effects, was not distinguishable from the measurement error for doses less than 16–18 Gy and slightly exceeded measurement errors only at the largest doses of 20–22 Gy. The corresponding intermouse variability was greater than the measurement error and stochastic effects at all doses used. Interestingly, the total variability, judged by the γ₅₀ values of ∼7 we obtained, was similar to that reported for severe late reactions in human normal tissue. If the variations of response determined by epigenetic events in human patients free of known factors associated with altered radiation sensitivity are comparable to those observed in this mouse model, our results imply a relatively low power of genetic approaches alone to predict individual side effects in radiotherapy.