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PubMed2000

The effects of ionizing radiation on osteoblast-like cells in vitro.

The well-described detrimental effects of ionizing radiation on the regeneration of bone within a fracture site include decreased osteocyte number, suppressed osteoblast activity, and diminished vascularity. However, the biologic mechanisms underlying osteoradionecrosis and the impaired fracture healing of irradiated bone remain undefined. Ionizing radiation may decrease successful osseous repair by altering cytokine expression profiles resulting from or leading to a change in the osteoblastic differentiation state. These changes may, in turn, cause alterations in osteoblast proliferation and extracellular matrix formation. The purpose of this study was to investigate the effects of ionizing radiation on the proliferation, maturation, and cytokine production of MC3T3-E1 osteoblast-like cells in vitro. Specifically, the authors examined the effects of varying doses of ionizing radiation (0, 40, 400, and 800 cGy) on the expression of transforming growth factor-beta1 (TGF-beta1), vascular endothelial growth factor (VEGF), and alkaline phosphatase. In addition, the authors studied the effects of ionizing radiation on MC3T3-E1 cellular proliferation and the ability of conditioned media obtained from control and irradiated cells to regulate the proliferation of bovine aortic endothelial cells. Finally, the authors evaluated the effects of adenovirus-mediated TGF-beta1 gene therapy in an effort to "rescue" irradiated osteoblasts. The exposure of osteoblast-like cells to ionizing radiation resulted in dose-dependent decreases in cellular proliferation and promoted cellular differentiation (i.e., increased alkaline phosphatase production). Additionally, ionizing radiation caused dose-dependent decreases in total TGF-beta1 and VEGF protein production. Decreases in total TGF-beta1 production were due to a decrease in TGF-beta1 production per cell. In contrast, decreased total VEGF production was secondary to decreases in cellular proliferation, because the cellular production of VEGF by irradiated osteoblasts was moderately increased when VEGF production was corrected for cell number. Additionally, in contrast to control cells (i.e., nonirradiated), conditioned media obtained from irradiated osteoblasts failed to stimulate the proliferation of bovine aortic endothelial cells. Finally, transfection of control and irradiated cells with a replication-deficient TGF-beta1 adenovirus before irradiation resulted in an increase in cellular production of TGF-beta1 protein and VEGF. Interestingly, this intervention did not alter the effects of irradiation on cellular proliferation, which implies that alterations in TGF-beta1 expression do not underlie the deficiencies noted in cellular proliferation. The authors hypothesize that ionizing radiation-induced alterations in the cytokine profiles and differentiation states of osteoblasts may provide insights into the cellular mechanisms underlying osteoradionecrosis and impaired fracture healing.

Alkaline Phosphatase↗
PubMed2000

Ionization waves in electron-beam-assisted, shielded capillary discharge

A theory of propagation of cathode-directed ionization waves during the early stages of an electrical breakdown in a shielded, low-pressure capillary is developed. The discharge process occurs due to the ionization of the low-density gas in the capillary by an electron beam that is emanating from a hollow cathode. Due to the strong electric field in the capillary the electrons are in the fast acceleration regime. Consequently, the full momentum equation for the electrons is employed, rather than the electron drift velocity approach. The smallness of the ratio of the capillary radius to the characteristic length of the electric potential variation in the axial direction allows the construction of a quasi-one-dimensional model. The latter retains the important two-dimensional nature of the electron flow as well as the electrodynamic boundary conditions at the capillary wall and the conducting shield and results in a set of one-dimensional, time-dependent partial differential equations for the on-axis distributions of the physical quantities. It is shown that those equations admit self-similar solutions that represent ionization waves propagating with constant velocities. The resulting set of ordinary differential equations is solved numerically for various initial conditions representing a nonperturbed steady state ahead of the ionization front and the resulting features of the ionization waves are investigated and discussed. The obtained solutions describe both ionization growth and virtual anode propagation and represent fast ionization waves in plasma waveguides, for which the maximum value of the mean electron velocity is much higher than the wave velocity. The space-charge distribution associated with the ionization waves is found in the form of plasma oscillations with a continuously increasing frequency and a solitary envelope. The calculated wave velocity increases with the gas pressure and this tendency is in agreement with corresponding experimental observations.

Journal Article↗
PubMedDate not supplied

Intravenous magnesium sulfate relieves cluster headaches in patients with low serum ionized magnesium levels.

Patients with cluster headaches have been reported to have low serum ionized magnesium levels. We examined the possibility that patients with cluster headaches and low ionized magnesium levels may respond to an intravenous infusion of magnesium sulfate. Thirty-eight infusions of magnesium sulfate were given to 22 patients with cluster headaches. The mean ionized magnesium level prior to 23 infusions which provided relief for at least 2 days and enabled the patient to skip two or more attacks, was 0.521 +/- 0.016 mmol/L; this value was 0.561 +/- 0.016 prior to 15 infusions which were ineffective. These latter 15 infusions were preceded by higher total magnesium levels. The ionized magnesium level prior to the 23 effective infusions was below 0.54 mmol/L in 19 patients. Five of the 15 ineffective infusions were accompanied by basal ionized magnesium levels below 0.54 mmol/L. In 76% of the infusions, there was a correlation between a response and an ionized magnesium level below 0.54 mmol/L. Nine patients (41%) obtained clinically meaningful improvement. Spontaneous remissions and a placebo effect might have accounted for some of the improvement. However, this should have applied equally to all patients, regardless of the ionized magnesium level. Measurements of ionized magnesium may prove useful in elucidating the pathogenesis of cluster headache and in identifying patients who may benefit from treatment with magnesium.

Adult↗
PubMedDate not supplied

Serum ionized magnesium levels in type 2 diabetic patients with microalbuminuria or clinical proteinuria.

BACKGROUND/AIMS: The association between microalbuminuria and magnesium depletion is a controversial issue, and serum ionized magnesium levels have not been previously studied in patients with different grades of diabetic nephropathy. Therefore, the aim of this study was to evaluate circulating ionized magnesium concentrations in patients with non-insulin-dependent diabetes mellitus (NIDDM) and incipient or overt diabetic nephropathy. METHODS: We measured fasting plasma glucose, creatinine, creatinine clearance estimate, total cholesterol and triglycerides, and serum ionized magnesium (ion-selective electrodes, ISE) in 30 NIDDM patients with urinary albumin excretion rate (UAER) <20 microg/min (normoalbuminuria), 30 NIDDM patients with microalbuminuria (20 < UAER < 200 microg/min), 30 NIDDM patients with clinical proteinuria (UAER >200 microg/min), and 20 healthy subjects. RESULTS: Serum ionized magnesium levels were significantly reduced in diabetic patients when compared to control subjects (0.39 +/- 0.06 vs. 0.58 +/- 0.05 mmol/l, p < 0.001). Moreover, diabetic patients with microalbuminuria or clinical proteinuria showed a significant decrease in serum ionized magnesium with respect to normoalbuminuria group (normoalbuminuria: 0.45 +/- 0. 02 mmol/l; microalbuminuria: 0.36 +/- 0.05 mmol/l, p < 0.001; clinical proteinuria: 0.35 +/- 0.04 mmol/l, p < 0.001). Serum ionized magnesium showed a significant negative correlation with plasma HbA1c and triglycerides in both microalbuminuria and clinical proteinuria groups. Multiple linear regression analysis showed that circulating ionized magnesium levels decrease together with the increase of plasma HbA1c and triglycerides in NIDDM patients with incipient or overt nephropathy, also after adjusting for age, sex, BMI, diabetes duration, systolic and diastolic blood pressure, hypoglycemic therapy, plasma creatinine, creatinine clearance, plasma cholesterol and fasting glucose. CONCLUSIONS: Microalbuminuria and clinical proteinuria, as well as poor glycometabolic control and hypertriglyceridemia, are associated to relevant alterations in magnesium metabolism, and the measurement of serum ionized magnesium seems to represent a useful biochemical tool for the study of magnesium disturbances in patients with different grades of diabetic nephropathy.

Albuminuria↗
PubMed2002

Maintenance hemodialysis and circulating ionized magnesium.

BACKGROUND: Circulating magnesium exists in the bound and in the free ionized form, that is biologically active. In kidney disease the relationship between ionized and total circulating magnesium is often altered. Little information is available on the influence of hemodialysis on the relationship between ionized and total circulating magnesium in end-stage kidney disease. METHODS: Plasma total and ionized magnesium and the plasma ionized magnesium fraction were assessed before and after hemodialysis (dialysate magnesium content 0.75 mmol/l) in 46 patients with end-stage kidney disease and in a control group of 25 healthy subjects. RESULTS: In patients plasma total (from 1.19 [1.05-1.33] to 1.10 [1.02-1.16] mmol/l; median and interquartile range) and ionized (from 0.71 [0.66-0.78] to 0.65 [0.63-0.69] mmol/l) magnesium significantly decreased during dialysis (control subjects: 0.82 [0.80-0.92], respectively, 0.57 [0.54-0.59] mmol/l). The plasma ionized magnesium fraction was significantly lower in patients both before (0.61 [0.58-0.64)] and after (0.60 [0.56-0.62]) hemodialysis than in controls (0.68 [0.65-0.70]). CONCLUSIONS: The study demonstrates a tendency towards a reduced circulating ionized magnesium fraction in end-stage kidney disease that is not corrected by hemodialysis.

Acid-Base Equilibrium↗
PubMed1997

Identification of essential ionizable groups in active site of Aspergillus niger alpha-glucosidase.

A kinetic study was done to identify the ionizable groups in the active site of Aspergillus niger alpha-glucosidase (ANGase). From dependence of V and Km values on pH, we obtained the ionization constants of essential ionizable groups 1 and 2 of free enzyme; pKe1 = 3.2 and pKe2 = 6.4. When the dielectric constant of the reaction mixture was decreased, the pKe1 and pKe2 were shifted to higher values. The ionization heats (delta H's) of ionizable groups 1 and 2 were measured to be -0.4 kcal/mol and 0 kcal/mol, respectively. The water-soluble carbodiimide (WSC), a specific reagent for carboxyl groups, inactivated the enzyme activity completely, and maltose as substrate decreased the inactivation. The WSC did not modify the free Cys. These findings suggest that the essential ionizable groups of ANGase are two kinds of carboxyl groups: one is a charged type (-COO-, ionizable group 1), and the other is a protonated type (-COOH, ionizable group 2).

Aspergillus niger↗
PubMed2005

Use of laser-induced ionization to detect soot inception in premixed flames.

Experimental measurements of laser-induced ionization were performed for ethene-air premixed flames operated near the soot inception point. Soot was ionized with a pulsed laser operated at 532 nm. The ionization signal was collected with a tungsten electrode located in the postflame region. Ionization signals were collected by use of both single-electrode and dual-electrode configurations. Earlier laser-induced-ionization studies focused on the use of a single biased electrode to generate the electric field, with the burner head serving as the path to ground. In many practical combustion systems, a path to ground is not readily available. To apply the laser-induced-ionization diagnostic to these geometries, a dual-electrode geometry must be employed. The influence of electrode configuration, flame equivalence ratio, and flame height on ionization signal detection was determined. The efficacy of the laser-induced-ionization diagnostic in detecting soot inception in the postflame region of a premixed flame by use of a dual-electrode configuration was investigated. Of the dual-electrode configurations tested, the dual-electrode geometry oriented parallel to the laser beam was observed to be most sensitive for detecting the soot inception point in a premixed flame.

Carbon↗
PubMed1999

Correlation of serum HDL-cholesterol and LCAT levels with the fraction of ionized magnesium in children.

Correlation of serum lipids and apolipoprotein levels with serum total magnesium concentration and whole blood ionized magnesium level was determined in 47 children (14 female and 33 male; mean age, 8.7 +/- 4.2 years). Mean serum concentration of magnesium was 2.19 +/- 0.19 mg/dl, whole blood concentration of ionized magnesium 1.23 +/- 0.08 mg/dl, and fraction of ionized magnesium (ratio of whole blood ionized magnesium to serum total magnesium) 0.56 +/- 0.04. Neither serum total magnesium level nor whole blood ionized magnesium level had any correlation with serum albumin, lipid, and apolipoprotein levels. However, the fraction of ionized magnesium was significantly correlated with HDL-cholesterol (n = 46, r = 0.31, p = 0.0345), apolipoprotein A-1 (n = 41, r = 0.39, p = 0.0124), and lecithin-cholesterol acyltransferase (LCAT) (n = 20, r = 52, p = 0.0184). These results suggest that fraction of ionized magnesium is more closely linked to serum HDL-cholesterol and LCAT level than with the serum total magnesium level or whole blood ionized magnesium.

Apolipoprotein A-I↗
PubMed1991

Resistance patterns between cis-diamminedichloroplatinum(II) and ionizing radiation.

Cross-resistance between cis-diamminedichloroplatinum(II) (CDDP) and radiation resistance has been suggested from clinical and experimental data (C. T. Coughlin and R. C. Richmond, Semin. Oncol., 16: 31-43, 1989). To determine whether cross-resistance patterns between both cytotoxic approaches exist, resistance against CDDP and ionizing radiation was induced separately in human ovarian cancer cells in a cross-over design. Subsequently sensitivity changes were determined for both treatment modalities. CDDP resistance was induced previously (P. J. Kuppen et al., Cancer Res., 48: 3355-3359, 1988), and resistant cells were grown at three different levels of CDDP:0 ng/ml; 250 ng/ml; and 500 ng/ml. Resistance with resistance factor (RF) 3.4 to 5.1 proved to be stable, since withdrawal of CDDP pressure for at least 6 mo did not alter resistance patterns. CDDP-resistant cells also demonstrated stable resistance against ionizing radiation, with RF ranging from 1.7 to 2.0. The resistance patterns could not be explained by differences in growth kinetics and DNA content. Resistance to ionizing radiation was induced in the same human ovarian cancer cells as used for CDDP resistance studies. Exposure with 1.5 Gy of intermittent irradiation during 6 mo, at time intervals of 48 h, resulted in cells which were able to grow under chronic ionizing radiation pressure. RF was 2.0; the resistance was lost after 6 mo of culturing without ionizing radiation pressure. With intermittent radiation doses of 0.5 and 1.0 Gy, no significant resistance could be induced. Cells intermittently exposed to 0.5, 1.0, and 1.5 Gy during 6 mo demonstrated increased sensitivity to CDDP, with 0.22 less than RF less than 0.43. Increased sensitivity was associated with proportionally increased formation of the platinum-DNA adducts. Differences in sensitivity for both ionizing radiation and CDDP were lost after 6 mo of culturing without radiation pressure; therefore, resistance toward ionizing radiation and, likewise, the increased sensitivity to CDDP, were judged to be unstable. In conclusion, data of the present study demonstrated that development of stable resistance to CDDP is associated with development of stable resistance to ionizing radiation in human ovarian cancer. Contrastingly, increased sensitivity to CDDP was found when resistance against irradiation was induced in the same cells.

Cell Survival↗
PubMedDate not supplied

Measurement of serum ionized magnesium in CAPD patients.

OBJECTIVE: To evaluate the magnesium status of continuous ambulatory peritoneal dialysis (CAPD) patients using a new method for assessing the level of the ionized fraction of serum magnesium. DESIGN: Serum ionized magnesium was measured in CAPD patients using the ion-selective electrode for Mg2+. SETTING: The Dialysis Unit of Tampere University Hospital. PATIENTS: Twenty-six patients on CAPD (age: 21-81 years, mean 54 +/- 16 years; duration of CAPD: 3-52 months, mean 13 months), and 26 sex- and age-matched healthy controls. RESULTS: Both serum ionized magnesium (0.73 +/- 0.11 mmol/L vs 0.56 +/- 0.07 mmol/L, p < 0.001) and total magnesium (1.11 +/- 0.22 vs 0.81 +/- 0.08 mmol/L, p < 0.01) were higher in CAPD patients than in sex- and age-matched controls. The ionized magnesium fraction of total magnesium was slightly lower in dialysis patients in spite of the fact that 16/26 patients had serum albumin less than 36 g/L. Hypermagnesemia (mean serum ionized magnesium 0.78 +/- 0.10 mmol/L) was observed in the 13 of 26 patients with 0.75 mmol/L Mg2+ dialysate; those with lower magnesium dialysate (Mg2+ 0.50 mmol/L in 10/26 and Mg2+ 0.25 mmol/L in 3/26) had mean serum ionized magnesium at the upper normal margin (0.69 +/- 0.10 mmol/L). CONCLUSION: In CAPD patients with Mg2+ 0.5-0.75 mmol/L in their dialysis fluid, both serum ionized and total magnesium concentrations were higher but the ionized/total magnesium ratio was lower than in healthy control subjects. Use of ion-selective electrodes to measure ionized magnesium may be a more useful methodology than measuring total magnesium in the evaluation of magnesium status of CAPD patients, because it is not influenced by hypoalbuminemia or increased complexed fraction of magnesium often present in dialysis patients.

Adult↗
PubMed1998

Vacuum ultraviolet single photon versus femtosecond multiphoton ionization of sputtered germanium clusters.

Neutral atoms and clusters desorbed from a solid germanium surface by ion bombardment are detected by laser postionization and time-of-flight mass spectrometry. Two different photoionization schemes are compared which are generally believed to be candidates for the 'soft' ionization of polyatomic species without significant photon induced fragmentation. First, a single photon ionization process is employed using an F2 laser as an intense VUV source with a photon energy in excess of all relevant ionization potentials. It is shown that the available laser pulse energy is sufficient to saturate the ionization of Ge atoms and all detected Ge(n) clusters. The resulting mass spectra are compared to those obtained with a non-resonant multiphoton ionization process using a high intensity laser delivering pulses of 250 femtoseconds duration at a wavelength of 267 nm. Also in this case, the ionization process can apparently be driven into saturation. The mass spectra measured under these conditions are found to be almost identical to those obtained using single photon ionization. We take this as an indication that the results obtained with both postionization techniques closely reflect the true cluster sputtering yields and, in particular, are not dominated by photon induced fragmentation.

Absorptiometry, Photon↗
PubMed1989

The influence of negative ionization of the air on motor activity in Syrian hamsters (Mesocricetus auratus Waterhouse) in light conditions.

The motor activity of Syrian hamsters (Mesocricetus auratus Waterhouse) under the influence of negative ionization of the atmosphere applied for 10, 20 or 30 min per day was investigated. An ionizer with output of 14,000 light negative ions per 1 cm3 of air was used. Studies carried out in the light phase of a 12:12 h light/dark regime revealed a relation between the reaction of the animal and the time of day at which ionization was applied. Ionization for 20 or 30 min in the light phase decreased motor activity, while 10 min of ionization increased it compared to control animals. Ionization in the dark phase gave a more distinct rise in activity than that applied in the light phase for all three durations of ionization.

Air Ionization↗
PubMed2006

Involvement of nuclear factor of activated T cells 3 (NFAT3) in cyclin D1 induction by B[a]PDE or B[a]PDE and ionizing radiation in mouse epidermal Cl 41 cells.

The results from animal studies have shown that mouse skin is highly susceptible to both ionizing radiation and benzo[a]pyrene-7,8-diol-9,10-epoxide (B[a]PDE). Previous studies have also indicated that cyclin D1 plays a crucial role in controlling cell proliferation and tumorigenesis. We, therefore, investigated here the effect of ionizing radiation and B[a]PDE on cyclin D1 transcription and potential involvement of NFAT3 in regulation of cyclin D1 transcription in mouse epidermal Cl 41 cells. We found that B[a]PDE exposure induced a high level of NFAT activation and cyclin D1 transcription in mouse epidermal Cl 41 cells. Ionizing radiation exhibited an enhancement for NFAT activation and cyclin D1 induction by B[a]PDE, even though ionizing radiation by itself had only a marginal effect. By stably knockdown of NFAT3 protein expression using specific NFAT3 small interfering RNA (siRNA), we found that cyclin D1 induction by B[a]PDE or B[a]PDE plus ionizing radiation was dramatically impaired. These results indicate that ionizing radiation is able to enhance cyclin D1 transcription induced by B[a]PDE, and NFAT3 is involved in the regulation of cyclin D1 transcription by B[a]PDE or B[a]PDE plus ionizing radiation.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMedDate not supplied

Diminished cellular and humoral immunity in workers occupationally exposed to low levels of ionizing radiation.

BACKGROUND: It has been reported that subgroups of T-lymphocytes are affected at different levels and different cell groups of immune system give different responses in individuals exposed to long-term ionizing radiation. The aim of this study was to investigate the effect of occupational exposure to low levels of ionizing radiation in selected indices of cellular and humoral immunity in radiology workers. METHODS: Level of subgroups of peripheral blood lymphocytes, complements (C(3), C(4)), and total immunoglobulins (IgG, IgA, IgM) were analyzed in 50 radiology workers occupationally exposed to low levels of ionizing radiation and 35 age-matched healthy controls. RESULTS: CD4(+) T lymphocyte (T-helper) levels were determined as significantly low in radiology workers exposed to ionizing radiation compared with controls (p <0.05). There were no statistically significant differences in groups in terms of other subgroups of lymphocytes (p >0.05). In addition, levels of serum total IgG, IgA, IgM, C(3,) and C(4) were determined as significantly lower in workers exposed to ionizing radiation compared with controls (p <0.001). Total IgA and IgM levels in radiology workers who were smokers were determined as significantly lower compared with non-smoking radiology workers (p >0.05). CONCLUSIONS: Levels of CD4(+) T lymphocytes and humoral immune response (total immunoglobulins and complements) were determined as weaker in workers exposed to low levels of ionizing radiation compared with controls, indicating the importance of taking appropriate measures to protect radiology workers from exposure to ionizing radiation and for these workers to avoid smoking. Further studies are needed for determining the appropriateness of periodic check-ups of immune functions and the most efficient and cost-effective ways of monitoring immune functions in radiology workers for detecting early changes in the immune system.

Adult↗
PubMed2005

Electron beam ionization induced oxidative enzymatic activities in pepper (Capsicum annuum L.), associated with ultrastructure cellular damages.

Mature green pepper fruits (Capsicum annuum L.) were subjected to ionizing radiation, in the range of 1-7 kGy, with accelerated electrons. Ultrastructural changes by electron microscopy, and the activity of several oxidative metabolism-related enzymes such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), guaicol peroxidase (POX), and lipoxygenase (LOX), were determined in pericarp tissue just after the ionization treatment and during postionization storage at 7 degrees C followed by 3 days at 20 degrees C. Changes in oxidative stress during the ionization treatment was assessed by the accumulation of malondyaldehide (MDA), a lipid peroxidation product. The ionization induced modifications in the cell ultrastructure, a moderate separation of the plasma membrane from the cell wall being observed for all doses. At 5 and 7 kGy, peroxisomes were not detected and the structures of the chloroplast and vacuoles were seriously damaged. Lipid peroxidation and lipoxygenase activity increased with the ionization dose, staying constant and decreasing, respectively, during the storage period. Conversely, catalase, ascorbate peroxidase, and superoxide dismutase had lower values than in nonionized fruits and, in general, their values did not change or diminished slightly from the seventh day of storage. Peroxidase exhibited an increase in activity with the ionization dose, although these was not a linear relationship, with higher values at 3kGy. Ionization of pepper, especially at doses of 5 and 7 kGy, caused a significant oxidative damage in the fruit, since it increased oxidation and decreased the antioxidant enzymatic defense systems causing ultrastructural changes at cell level.

Ascorbate Peroxidases↗
PubMed2002

Long-range destruction of Der p 1 using experimental and commercially available ionizers.

BACKGROUND: To reduce the risk of sensitization and the elicitation of allergy symptoms, it is important to reduce the level of allergens in the home. It has previously been demonstrated that corona discharge, the process by which ionizers produce ions, can destroy the major house dust mite allergen Der p 1. OBJECTIVE: In this paper the denaturing efficacy of an experimental ionizer and two commercially available products are evaluated. METHODS: The first test was conducted in an electrically grounded chamber with samples of Der p 1 placed in various positions for 1, 2 and 3 weeks. The second test was conducted in situ in an unoccupied, furnished office room for 1 week. Der p 1 concentration was quantified by two-site monoclonal antibody enzyme-linked immunosorbent assay (ELISA). RESULTS: All ionizers in both tests caused significant reductions in allergen concentration (P < 0.05), reaching a maximum of 92% with the experimental ionizer in the chamber after 3 weeks. The percentage reductions observed in situ with the experimental and the larger commercial ionizer were similar, reaching a maximum of 32% at a distance of 4 m away from the experimental ionizer after 1 week of exposure. CONCLUSION: With a revised protocol for use, air ionizers may offer a simple, efficient and inexpensive way to reduce allergen levels in the domestic environment.

Air Ionization↗
PubMed2006

Perturbation correction factors for the NACP-02 plane-parallel ionization chamber in water in high-energy electron beams.

Recent dosimetry protocols for clinical high-energy electron beams recommend measurements of absorbed dose-to-water with a plane-parallel or cylindrical ionization chamber. For well-guarded plane-parallel ionization chambers, the ionization chamber perturbation factor in water, p(Q), has a recommended value of unity in all protocols. This assumption was investigated in detail in this study for one of the recommended ionization chambers in the protocols: the Scanditronix NACP-02 plane-parallel ionization chamber. Monte Carlo (MC) simulations of the NACP-02 ionization chamber with the EGSnrc code were validated against backscatter experiments. MC simulations were then used to calculate p(wall), p(cav) and p(Q) perturbation factors and water-to-air Spencer-Attix stopping powers in 4-19 MeV electron beams of a calibration laboratory (NPL), and in 6-22 MeV clinical electron beams from a Varian CL2300 accelerator. Differences between calculated and the currently recommended (Burns et al 1996 Med. Phys. 23 383-8) stopping powers, water-to-air, were found to be limited to 0.9% at depths between the reference depth z(ref) and the depth where the dose has decreased to 50% of the maximum dose, R50. p(wall) was found to exceed unity by 2.3% in the 4 MeV NPL calibration beam at z(ref). For higher energy electron beams p(wall) decreased to a value of about 1%. Combined with a p(cav) about 1% below unity for all energies at z(ref), this was found to cause p(Q) to exceed unity significantly for all energies. In clinical electron beams all three perturbation factors were found to increase with depth. Our findings indicate that the perturbation factors have to be taken into account in calibration procedures and for clinical depth dose measurements with the NACP-02 ionization chamber.

Aluminum↗
PubMed1999

Greater sensitivity to ionizing radiation at older age: follow-up of workers at Oak Ridge National Laboratory through 1990.

BACKGROUND: Workers at Oak Ridge National Laboratory (ORNL) were individually monitored for whole body exposure to ionizing radiation. Studies of these workers may provide valuable information about the long-term effects of occupational exposure to ionizing radiation. Since biological changes occur as adults age, a potentially important question in these investigations is whether sensitivity to the carcinogenic effects of ionizing radiation changes with age at exposure. METHODS: Vital status and cause of death were ascertained through 1990 for 8307 white males hired at ORNL from 1943 through 1972. Associations between whole body ionizing radiation dose and all-cancer mortality were quantified using life table regression methods for time dependent exposures. Analyses focused of differences in radiation-cancer associations with age at exposure. Length of follow-up, period of hire, and age at risk were considered as alternative explanations for effects of age at exposure. RESULTS: Cumulative radiation dose was associated with a 1.8% (SE = 0.9) increase in all-cancer mortality per 10 mSv, assuming a 10-year lag between exposure and mortality. However, radiation doses received at older ages exhibited larger associations with cancer mortality than doses received at younger ages. Doses received after age 45 were associated with a 5.9% (SE = 1.7) increase in cancer mortality per 10 mSv, adjusted for doses received before age 45. Dose-response associations between cancer mortality and doses received after age 45 appeared consistent across periods of follow-up, periods of hire, and ages at risk. CONCLUSIONS: Findings suggest that sensitivity to the carcinogenic effects of ionizing radiation may increase with older ages at exposure. More attention should be given to the role of age at exposure in studies of the health effects of low-level exposure to ionizing radiation, and to efforts to limit exposure to ionizing radiation.

Adult↗