The relationship of effective dose to personnel and monitor reading for simulated fluoroscopic irradiation conditions

The exposure of staff during fluoroscopic procedures was simulated for overcouch x-ray tube/undercouch image intensifier and undercouch x-ray tube/overcouch image intensifier geometries. A Rando phantom with film badge dosimeters attached to the skin surface at seven commonly used monitoring sites and loaded with lithium fluoride thermoluminescent dosimeters was irradiated for an extended period in the vicinity of a patient couch. Scattered radiation generated from the irradiation of an anthropomorphic phantom using primary radiation in the range of 70 kVp-110 kVp was used. The radiation dose to organs which were shielded by a lead apron was estimated from the unattenuated organ dose readings by applying an experimentally determined scattered radiation transmission factor. The ratio of effective dose to film badge reading was obtained for a range of irradiation conditions and lead apron thicknesses. For most irradiation conditions studied, a dosimeter worn above the lead apron will significantly overestimate effective dose by a factor of between 2 and 60, depending on the irradiation conditions. A dosimeter worn under the apron at either waist or chest level, will generally yield a closer (although usually an underestimate of) effective dose, typically within a factor of 7 for the most common lead apron thicknesses and irradiation conditions. No single dosimeter can accurately monitor effective dose for all irradiation conditions in fluoroscopy.     

Evidence into practice, experimentation and quasi experimentation: are the methods up to the task?

PURPOSE: To assess the suitability of the cytokinesis block micronucleus assay as a biological dosimeter following in-vivo radiation using cancer patients undergoing radiotherapy. METHODS: Blood from 4 healthy donors was irradiated in vitro with gamma-rays and the dose response of induced micronuclei in binucleate lymphocytes following cytokinesis block was determined. Micronucleus frequency was ascertained before and at intervals during radiotherapy treatment in 6 patients with various tumors in the pelvic region. Equivalent whole body doses (physical doses) at these times were calculated from radiation treatment plans and cumulative dose volume histograms. RESULTS: Linear dose response relationships were found for induced micronucleus frequency in lymphocytes resulting from both in-vitro and in-vivo irradiation. Doses resulting from in-vivo irradiation (biological doses) were estimated by substitution of micronucleus frequency observed in radiotherapy patients into the dose response curve from in-vitro irradiation of blood. The relationship between the biologically estimated dose (BD) and the calculated equivalent whole body dose (PD) was BD = 0.868 (+/- 0.043)PD + 0.117 (+/- 0.075). CONCLUSION: The micronucleus assay appears to offer a reliable and consistent method for equivalent whole body radiation dose estimation, although our findings should be confirmed using lymphocytes from radiotherapy patients with tumors at anatomical sites other than the pelvis. Except at doses lower than about ).4 Gy, the method yields dose estimates acceptably close to "true" physically determined doses. The assay can be performed relatively rapidly and can be used as a "first line" biological dosimeter in situations where accidental exposure to relatively high radiation doses has occurred.     

Alanine-ESR dosimetry for radiotherapy. IAEA experience

At present, the most commonly used transfer dosimeters for radiotherapy applications are TL dosimeters. They are being used for intercomparison between SSDLs (about 70) and the IAEA dosimetry laboratory. However, there are some undesirable characteristics of this dosimetry system. We have a study in progress at the IAEA to evaluate the alanine-ESR system as an alternative to TLDs. There are several desirable qualities which make alanine an attractive dosimeter. Preliminary data suggest that the alanine-ESR dosimetry system has the potential to replace TLDs for intercomparison amongst SSDLs in the therapy-level dose region.     

Determination of serine hydroxymethyltransferase and reduced folate pools in tissue extracts

The ferrous sulfate-doped gel dosimeters have been developed for three-dimensional magnetic resonance imaging of radiation dose distributions. When the gel dosimeter is irradiated, ferrous ions are converted to ferric ions and the nuclear magnetic spin relaxation of the dosimeter varies with dose. In this paper, a model is presented for the dose dependence of the spin-lattice relaxation rate R1 of the ferrous sulfate doped-gelatin dosimeter. The model is based on three basic physical quantities: the ferric ion yield and the ferrous and ferric ion relaxivities, r2+ and r3+, respectively. These relaxivities specify the ability of the ions to enhance the spin-lattice relaxation of water protons. The effects of gelatin and sulfuric acid concentration on the ferric ion yield and ion relaxivities are presented. The measured r2+ values agree with those predicted by a model in which the measured spin relaxation is considered the result of the fast exchange of water hydrating the ferrous ion with water in the bulk. The r3+ values are lower than predicted by the fast exchange model. The discrepancies in the measured and predicted r3+ values are shown to result from the complexing of ferric ions arising from pH variation caused by changes in gelatin or sulfuric acid concentrations. A modified version of the R1-dose response model accounting for ferric ion complexing is presented and tested spectrophotometrically.     

Diagnosis of disseminated intravascular coagulation

The variations of the measured dose rate in air should be recognized especially where background radiation is used as a comparative benchmark to assess radiation surveillance and environmental remediation work. In this note, the natural variations of the combined gamma and cosmic-ray background air-dose rate as measured by lithium fluoride thermoluminescence dosimeters are reported. The dosimeters were deployed monthly at locations within 150 km of the Environmental Measurements Laboratory in New York City. Urban and suburban stations were established with simultaneous indoor and outdoor measurements at some locations. Measurements were obtained over 10 to 18 years. The mean air-dose rates from the six outdoor and four indoor stations vary from 50.8 to 123.1 nGy h(-1). The range of the annual dose rates expressed as a percent-difference of the minimum and maximum is 5.3 to 18.0%. Commonly, 1-mo deviations from the long term mean of about +/-10 to +/-25% are observed. An abrupt decrease in the annual dose rate at one of the measurement sites was attributed to a minor relocation of a dosimeter. Structural shielding factors for the first and second floors of a residence are reported. The ground level location of a dosimeter inside another residence apparently resulted in a very high shielding factor. Finally, a gradual decrease of the dose rate at most of the stations is shown to exist (approximately -0.3 nGy h(-1) y(-1) for the outdoor stations). Plausible causes of this trend are briefly discussed.     

Use of uracil thin layer for measuring biologically effective UV dose

Dimerization of uracil monomers in a polycrystalline state by UV radiation changes the absorption characteristics of a thin layer of the material. The change in optical density, measured by spectrophotometry in the 250-400 nm range, as a function of the exposure time is evaluated in terms of the biologically effective UV dose. A statistical evaluation of a great number of uracil dosimeters irradiated with a TL01 lamp from Philips establishes the possibility of evaluating the biologically effective UV dose using a uracil dosimeter. Nonlinear regression procedures were introduced to correct the absorption spectra for contributions due to light scattering and to determine the optical density values required to calculate the UV dose expressed in HU units. Comparison of cumulative daily doses and long-term monitoring measured by the uracil thin-layer dosimeter and a phage T7 dosimeter are given, which allow the determination of conversion factors between various biological dosimeters under different irradiation conditions.     

Radiotherapy of plantar heel spurs: indications, technique, clinical results at different dose concepts

BACKGROUND: In a retrospective study the efficacy of orthovoltage radiotherapy for refractory painful plantar heel spur was analyzed for 3 different radiation dose concepts. PATIENTS AND METHODS: From 1.1 1984 through 1.3.1994, 182 patients with refractory painful heel symptoms and radiologically proven plantar heel spur received radiotherapy. A total of 141 patients and 170 heels (due to double-sided symptoms) were completely documented in long-term follow-up. Clearly defined semi-quantitative criteria (9-point score) were used to analyze heel pain and ankle function prior to RT, 6 to 12 weeks post-radiation, and at last follow-up. The treatment outcome, i.e. (un)favourable response, of 3 radiation dose concepts were compared: Group A (n = 72 heels) received 12 Gy total radiation dose in 3 fractions per week and 2 series (6 x 1 Gy per series) separated by 6 weeks; group B (n = 98 heels) received 3 Gy total radiation dose in 10 fractions of 0.3 Gy (n = 50) or 5 Gy (10 x 0.5 Gy) (n = 48) with conventional fractionation in 1 series. RESULTS: Radiotherapy was very effective: at last follow-up 67% (group A) and 71% (group B) remained completely free of pain. The rate of "complete pain relief" (i.e. free of any pain symptoms) was not different between the 3 radiation concepts. However, significant differences were observed with regard to "incomplete or insufficient pain relief", i.e. a subjective pain relief of less than 80%, a delayed pain relief after more than 4 weeks or a relapse of pain symptoms in long-term follow-up. More favourable results were achieved in patients receiving 5 Gy or 12 Gy total dose, while patients with 3 Gy total dose had significantly worse results. Prognostic factors for "complete pain relief" were short duration of pain symptoms and acute pain symptoms prior to radiotherapy; with regard to "in-complete or insufficient pain relief" the total dose was found to be a prognostic parameter. CONCLUSIONS: Patients with refractory heel pain can yield a high response to radiotherapy even after failing various conventional treatments previously. Thus, radiotherapy should not be solely regarded as a last resort due to its low costs and high efficacy at low radiation doses.     

Bilateral ureteral inverted papilloma with synchronous transitional cell tumor of the bladder

A procedure for measuring the power of an ambient and goal-oriented equivalent scattered radiation dose in the radiation control of X-ray rooms. The procedure is based on the concept of the effective solid angle of a dosimeter directivity diagram. The plots of the angular response of a S2010 selective X-ray dosimeter for studying the radionuclides 119Sn, 241Am, 57Co are exemplified. The scaling factors for dosimetric reading for isotropic and nonuniform fields of radiation were calculated from the obtained values of effective angular solid angles (0.7, 0.8, 1.2 pi).     

Effect of continuous subcutaneous insulin infusion with lispro on hepatic responsiveness to glucagon in type 1 diabetes

OBJECTIVE: People with type 1 diabetes frequently develop a blunted counterregulatory hormone response to hypoglycemia coupled with a decreased hepatic response to glucagon, and consequently, they have an increased risk of severe hypoglycemia. We have evaluated the effect of insulin lispro (Humalog) versus regular human insulin (Humulin R) on the hepatic glucose production (HGP) response to glucagon in type 1 diabetic patients on intensive insulin therapy with continuous subcutaneous insulin infusion (CSII). RESEARCH DESIGN AND METHODS: Ten subjects on CSII were treated for 3 months with lispro and 3 months with regular insulin in a double-blind randomized crossover study After 3 months of treatment with each insulin, hepatic sensitivity to glucagon was measured in each subject. The test consisted of a 4-h simultaneous infusion of somatostatin (450 microg/h) to suppress endogenous glucagon, regular insulin (0.15 mU x kg(-1) x min(-1)), glucose at a variable rate to maintain plasma glucose near 5 mmol/l, and D-[6,6-2H2]glucose to measure HGP During the last 2 h, glucagon was infused at 1.5 ng x kg(-1) x min(-1). Eight nondiabetic people served as control subjects. RESULTS: During the glucagon infusion period, free plasma insulin levels in the diabetic subjects were 71.7+/-1.6 vs. 74.8+/-0.5 pmol/l after lispro and regular insulin treatment, with plasma glucagon levels of 88.3+/-1.8 and 83.7+/-1.5 ng/l for insulin:glucagon ratios of 2.8 and 3.0. respectively (NS). However, plasma glucose increased to 9.2+/-1.1 mmo/l after lispro insulin compared with 7.1+/-0.9 mmol/l after regular insulin (P < 0.01), and the rise in HGP was 5.7 +/-2.8 micromol x kg(-1) x min(-1) after lispro insulin versus 3.1+/-2.9 micromol x kg(-1) x min(-1) after regular insulin treatment (P=0.02). In the control subjects, HGP increased by 10.7+/-4.2 micromol x kg(-1) x min(-1) under glucagon infusion. CONCLUSIONS: Insulin lispro treatment by CSII was associated with a heightened response in HGP to glucagon compared with regular human insulin. This suggests that insulin lispro increases the sensitivity of the liver to glucagon and could potentially decrease the risk of severe hypoglycemia.     

A filtration method for improving film dosimetry in photon radiation therapy

Successful radiotherapy requires accurate dosimetry for treatment verification. Existing dosimeters such as ion chambers, TLD, and diodes have drawbacks such as relatively long measurement time and poor spatial resolution. These disadvantages become serious problems for dynamic-wedged beams. Thus the clinical use of dynamic wedges requires an improved dosimetry method. X-ray film may serve this purpose. However, x-ray film is not clinically accepted as a dosimeter for photon beams, because it overresponds to photons with energies below about 400 keV. This paper presents and develops a method which was initially proposed by Burch to improve the dose response of x-ray film in a phantom. The method is based on placing high-atomic number foils next to the film. The foils are used as filters to preferentially remove low-energy photons. The optimal film and filter configuration in a phantom was determined using a mathematical scheme derived in this study and a Monte Carlo technique (ITS code). The optimal configuration thus determined is as follows: the filter-to-film distance of 6 mm and the filter thickness of 0.15 mm for percent depth-dose measurement; the distance of 1 cm and the thickness of 0.25 mm for off-axis (dose) ratio measurement. The configuration was then tested with photon beams from a 4 MV linac. The test result indicates that the in-phantom dose distribution based on the optimal configuration agrees well with those measured by ion chambers.     

Pharmacokinetics of a new reversible proton pump inhibitor, YH1885, after intravenous and oral administrations to rats and dogs: hepatic first-pass effect in rats

The pharmacokinetics of YH1885 were evaluated after intravenous (iv) and oral administrations of the drug to rats and dogs. The reason for the low extent of bioavailability (F) of YH1885 after oral administration of the drug to rats and the absorption of the drug from various rat gastrointestinal (GI) segments were also investigated. After iv administration of YH1885, 5-20 mg kg(-1), to rats, the pharmacokinetic parameters of YH1885 seem to be independent of the drug at the dose ranges studied. After oral administration of YH1885, 50-200 mg kg(-1), to rats, the area under the plasma concentration-time curve from time zero to 12 or 24 h (AUC(0-12 h) or AUC(0-24 h)) was proportional to the oral dose of the drug, 50-100 mg kg(-1), however, the AUC(0-24 h) value at 200 mg kg(-1) increased with less proportion to the dose increase (324, 689, and 815 microg x min mL(-1) for 50, 100, and 200 mg kg(-1), respectively) due to the poor water solubility of the drug. This was proved by the considerable increase in the percentages of the oral dose remaining in the entire GI tract as unchanged YH1885 at 24 h (11.8, 15.3, and 42.8% for 50, 100, and 200 mg kg(-1), respectively). The F value after oral administration of YH1885 to rats was relatively low; the value was approximately 40% at the oral dose of 50 and 100 mg kg(-1). The reason for the low F in rats was investigated. The liver showed the highest metabolic activity for YH1885 based on an in vitro rat tissue homogenate study; hence, the liver first-pass effect was estimated. The value of AUC after intraportal administration of the drug, 5 mg kg(-1), was approximately 70% (116 versus 163 microg x min mL(-1)) of that after iv administration of the drug, 5 mg kg(-1), to rats; the liver first-pass effect of YH1885 in rats was estimated to be approximately 30%. The total body clearance of YH1885 after iv administration of the drug, 5-20 mg kg(-1), to rats were considerably lower than the cardiac output of rats, indicating that the lung and/or heart first-pass effect of YH1885 could be negligible in rats. After oral administration of YH1885, 50 and 100 mg kg(-1), to rats, the F value was approximately 40%, and approximately 15% of the oral dose was recovered from the entire GI tract as unchanged YH1885 at 24 h, and 30% of the oral dose disappeared with the liver first-pass effect. Therefore, the remainder, approximately 15% of the oral dose, could have disappeared with the small intestine first-pass effect and/or degradation of the drug in the GI tract. YH1885 was absorbed from ileum, duodenum, and jejunum of rat, however, YH1885 was under the detection limit in plasma when the drug was instilled into the rat stomach and large intestine. After iv administration of YH1885, 5-20 mg kg(-1), to dogs, the pharmacokinetic parameters of YH1885 also seemed to be independent of the drug at the dose ranges studied. However, after oral administration of YH1885, 0.5 and 2 g per whole body weight, to dogs, the AUC(0-10 h) values were not significantly different (96.8 versus 98.2 microg x min mL(-1)) and this could be due to the poor water-solubility of the drug. YH1885 was not detected in the urine after both iv and oral administration of the drug to both rats and dogs.     

Sensitivity of amorphous selenium to x rays from 40 kVp to 18 MV: measurements and implications for portal imaging

Recently, the clinical application of electronic portal imaging devices has enabled more frequent verification of patient setup for radiation treatment. However, the image quality has sometimes proven to be inadequate, motivating the investigation of alternative sensors with better image quality. Amorphous selenium (a-Se) is potentially one such sensor since the electrostatic image formation process has high resolution. To fully evaluate the potential of a-Se for portal imaging, it is necessary to investigate all the imaging properties at high x-ray energies. Here, measurements of the sensitivity of a-Se to incident x-ray spectra ranging in energy from 40 kVp to 18 MV and for a-Se thicknesses ranging from approximately 10 to 300 microns under full buildup conditions are described. When x rays or energetic electrons deposit energy in a photoconductor with an applied electric field, F, electrons and holes are released. The x-ray conversion sensitivity may be defined as 1/W +/-, where W +/- is the energy required to release an electron-hole pair. Consistent with the results of previous investigators, W +/- is found to vary approximately with F-2/3. Unexpectedly, over the energy range of 40 kVp to 18 MV, W +/- was found to decrease by a factor of nearly 3. These dependencies are compared to the predictions of two competing charge recombination models, geminate and columnar. The results are explained by a microdosimetric model in which the sensitivity at megavoltage energies is governed by geminate recombination, but at lower energies, both mechanisms are involved. Thus, the sensitivity of a-Se to x rays spanning the diagnostic and radiotherapy range has been measured and the physical basis for this behavior established.     

Human immunodeficiency virus and resistance]

CONTEXT: Racial differences in tobacco-related diseases are not fully explained by cigarette-smoking behavior. Despite smoking fewer cigarettes per day, blacks have higher levels of serum cotinine, the proximate metabolite of nicotine. OBJECTIVE: To compare the rates of metabolism and the daily intake of nicotine in black smokers and white smokers. DESIGN: Participants received simultaneous infusions of deuterium-labeled nicotine and cotinine. Urine was collected for determination of total clearance of nicotine and cotinine, fractional conversion of nicotine to cotinine, and cotinine elimination rate. Using cotinine levels during ad libitum smoking and clearance data, the daily intake of nicotine from smoking was estimated. SETTING: Metabolic ward of a university-affiliated public hospital. PARTICIPANTS: A total of 40 black and 39 white smokers, average consumption of 14 and 14.7 cigarettes per day, respectively, of similar age (mean, 32.5 and 32.3 years, respectively) and body weight (mean, 73.3 and 68.8 kg, respectively). MAIN OUTCOME MEASURES: Clearance (renal and nonrenal), half-life, and volume of distribution of nicotine and cotinine and the calculated daily intake of nicotine. RESULTS: The total and nonrenal clearances of nicotine were not significantly different, respectively, in blacks (17.7 and 17.2 mL x min(-1) x kg(-1)) compared with whites (19.6 and 18.9 mL x min(-1) x kg(-1)) (P=.11 and .20). However, the total and nonrenal clearances of cotinine were significantly lower, respectively, in blacks (0.56 and 0.47 mL x min(-1) x kg(-1)) than in whites (0.68 vs 0.61 mL x min(-1) x kg(-1); P=.009 for each comparison). The nicotine intake per cigarette was 30% greater in blacks compared with whites (1.41 vs 1.09 mg per cigarette, respectively; P=.02). Volume of distribution did not differ for the 2 groups, but cotinine half-life was higher in blacks than in whites (1064 vs 950 minutes, respectively; P = .07). CONCLUSIONS: Higher levels of cotinine per cigarette smoked by blacks compared with whites can be explained by both slower clearance of cotinine and higher intake of nicotine per cigarette in blacks. Greater nicotine and therefore greater tobacco smoke intake per cigarette could, in part, explain some of the ethnic differences in smoking-related disease risks.     

Synchrotron radiation in the study of the variation of dose response in thermoluminescence dosimeters with radiation energy

Thermoluminescence dosimetry (TLD) is a versatile technique with many applications for dosimetry of ionising radiation. However, in the range of kilovoltage x-rays which is widely used for diagnostic and therapeutic medical applications, problems arise from the differing dose response of most TL dosimeters with the radiation energy. The dose response of various TL detector types was investigated in mono-energetic x-ray beams of 26.8, 33.2, 40, 80.4 and 99.6keV from a synchrotron radiation source at the National Laboratory for High Energy Physics in Japan. This response was studied as a function of TL material (LiF:Mg,Ti, LiF:Mg,Cu,P and Al2O3), the detector geometry and size, and their thermal history. Due to the asymmetric diffraction from a Si crystal employed to produce monoenergetic photons there was more than 50% dose inhomogeneity in some of radiation fields used. Therefore, the different TL dosimeter types were rotated around and the results related to the reading of a set of "standard" LiF:Mg,Ti ribbons which were included in all experiments as reference detectors. No significant influence of the detector shape (physical size, thickness) on the dose response with energy could be found. However, the pre-irradiation thermal history influences the dose response with radiation energy: a fast cool down of LiF:Mg,Ti after a high temperature anneal will increase the sensitivity by more than a factor of two. The relatively new TLD material LiF:Mg,Cu,P (GR-200, obtained from Solid Dosimeter & Detector Laboratories, Beijing) was found to be approximately 100 times more sensitive than the standard LiF:Mg,Ti. In addition it proved to be more tissue equivalent for photon radiation between 27keV and 40keV. The performance of LiF:Mg,Cu,P makes it a very interesting TL material deserving further evaluation for applications in diagnostic and therapeutic x-rays.     

Small amounts of fructose markedly augment net hepatic glucose uptake in the conscious dog

Fructose activates glucokinase by releasing the enzyme from its inhibitory protein in liver. To examine the importance of acute activation of glucokinase in regulating hepatic glucose uptake, the effect of intraportal infusion of a small amount of fructose on net hepatic glucose uptake (NHGU) was examined in 42 h-fasted conscious dogs. Isotopic ([3-3H] and [U-14C]glucose) and arteriovenous difference methods were used. Each study consisted of an equilibration period (-90 to -30 min), a control period (-30 to 0 min), and a hyperglycemic/hyperinsulinemic period (0-390 min). During the latter period, somatostatin (489 pmol x kg(-1) x min(-1)) was given, along with intraportal insulin (7.2 pmol x kg(-1) x min(-1)) and glucagon (0.5 ng x kg(-1) x min(-1)). In this way, the liver sinusoidal insulin level was fixed at four times basal (456 +/- 60 pmol/l), and liver sinusoidal glucagon level was kept basal (46 +/- 6 ng/l). Glucose was infused through a peripheral vein to create hyperglycemia (12.5 mmol/l plasma). Hyperglycemic hyperinsulinemia (no fructose) switched net hepatic glucose balance (micromoles per kilogram per minute) from output (11.3 +/- 1.4) to uptake (14.7 +/- 1.7) and net lactate balance (micromoles per kilogram per minute) from uptake (6.5 +/- 2.1) to output (4.4 +/- 1.5). Fructose was infused intraportally at a rate of 1.7, 3.3, or 6.7 micromol x kg(-1) x min(-1), starting at 120, 210, or 300 min, respectively. In the three periods, portal blood fructose increased from <6 to 113 +/- 14, 209 +/- 29, and 426 +/- 62 micromol/l, and net hepatic fructose uptake increased from 0.03 +/- 0.01 to 1.3 +/- 0.4, 2.3 +/- 0.7, and 5.1 +/- 0.6 micromol x kg(-1) x min(-1), respectively. NHGU increased to 41 +/- 3, 54 +/- 5, and 69 +/- 8 micromol x kg(-1) x min(-1), respectively, and net hepatic lactate output increased to 11.0 +/- 3.2, 15.3 +/- 2.7, and 22.4 +/- 2.8 micromol x kg(-1) x min(-1) in the three fructose periods, respectively. The amount of [3H]glucose incorporated into glycogen was equivalent to 69 +/- 3% of [3H]glucose taken up by the liver. These data suggest that glucokinase translocation within the hepatocyte is a major determinant of hepatic glucose uptake by the dog in vivo.     

The application of non-annealing thermoluminescent dosimetry (TLD)

Conventional use of Thermoluminescence (TL) in radiation dosimetry is very time-consuming. It requires repeating the procedures of preheating and annealing. In an attempt to simplify these procedures, we conducted an experiment of non-annealing TL dosimetry. This article reports the experiment's results. We adopted Lithium Fluoride (LiF) chip (TLD-100) in polystyrene under the exposure of Co-60, and the result was taken by HAR-SHAW-4000 TL reading system. The TL response was analyzed, including linearity, reproducibility and fading test. Because non-annealing TL response was greatly influenced by residual electron, TLD calibration curves were separated into two parts: (1) high dose region (HDR, 50-1500 cGy); (2) low dose region (LDR, 0-50 cGy). When TL dosimeters were exposed to a single high does (about 500 cGy), the HDR could be reproduced within 3% and fit a good linearity. For LDR, we had to give up the tail of glow curve in the high temperature region. We could then get good linearity and reproducibility. Furthermore, fading of non-annealing was apparently larger than annealing. We could control the fading of non-annealing was apparently larger than annealing. We could control the fading influence within 1% by taking the TL reading one hour after exposure. On the other hand, a combination of photon and electron exposure was also performed by non-annealing TL dosimetry. The results were compatible with Co-60 exposure in the same system.     

Calculation of effective doses for broad parallel photon beams

Values of effective dose (E) were calculated for the entire range of incident directions of broad parallel photon beams for selected photon energies using the Monte Carlo N-Particle (MCNP) transport code with a hermaphroditic phantom. The calculated results are presented in terms of conversion coefficients transforming air kerma to effective dose. This study also compared the numerical values of E and H(E) over the entire range of incident beam directions. E was always less than H(E) considering all beam directions and photon energies, but the differences were not significant except when a photon beam approaches some specific directions (overhead and underfoot). This result suggests that the current H(E) values can be directly interpreted as E or, at least, as a conservative value of E without knowing the details of irradiation geometries. Finally, based on the distributions of H(E) and E over the beam directions, this study proposes ideal angular response factors for personal dosimeters that can be used to improve the angular response properties of personal dosimeters for off-normal incident photons.     

Intravenous glucose suppresses glucose production but not proteolysis in extremely premature newborns

To ascertain whether the inability to suppress glucose production and increase glucose utilization in response to glucose infusion is an inherent characteristic of immature individuals, we determined glucose rate of appearance (R(a)) in minimally stressed, clinically stable, extremely premature infants (approximately 26-wk gestation) at two glucose infusion rates (6.2 +/- 0.4 and 9.5 +/- 0.5 mg/kg per min). We also assessed whether an increase in glucose delivery suppresses proteolysis by measuring the R(a) of phenylalanine and leucine. Glucose R(a) (and utilization) increased significantly at the higher glucose infusion rate (7.9 +/- 0.5 vs. 9.8 +/- 0.6 mg/kg per min). Glucose production persisted at the lower glucose infusion rate but was suppressed to nearly zero at the higher rate (1.7 +/- 0.5 vs. 0.3 +/- 0.1 mg/kg per min). Proteolysis was unaffected by the higher glucose infusion rate as reflected by no change in the rates of appearance of either phenylalanine (96 +/- 5 vs. 95 +/- 3 mumol/kg per h) or leucine (285 +/- 20 vs. 283 +/- 14 mumol/kg per h). Thus, clinically stable, extremely premature infants suppress glucose production and increase glucose utilization in response to increased glucose infusion, demonstrating no inherent immaturity of these processes. In contrast, increasing the rate of glucose delivery results in no change in whole body proteolysis in these infants. The regulation of proteolysis in this population remains to be defined.     

Calibration of a mosfet detection system for 6-MV in vivo dosimetry

PURPOSE: Metal oxide semiconductor field-effect transistor (MOSFET) detectors were calibrated to perform in vivo dosimetry during 6-MV treatments, both in normal setup and total body irradiation (TBI) conditions. METHODS AND MATERIALS: MOSFET water-equivalent depth, dependence of the calibration factors (CFs) on the field sizes, MOSFET orientation, bias supply, accumulated dose, incidence angle, temperature, and spoiler-skin distance in TBI setup were investigated. MOSFET reproducibility was verified. The correlation between the water-equivalent midplane depth and the ratio of the exit MOSFET readout divided by the entrance MOSFET readout was studied. MOSFET midplane dosimetry in TBI setup was compared with thermoluminescent dosimetry in an anthropomorphic phantom. By using ionization chamber measurements, the TBI midplane dosimetry was also verified in the presence of cork as a lung substitute. RESULTS: The water-equivalent depth of the MOSFET is about 0.8 mm or 1.8 mm, depending on which sensor side faces the beam. The field size also affects this quantity; Monte Carlo simulations allow driving this behavior by changes in the contaminating electron mean energy. The CFs vary linearly as a function of the square field side, for fields ranging from 5 x 5 to 30 x 30 cm2. In TBI setup, varying the spoiler-skin distance between 5 mm and 10 cm affects the CFs within 5%. The MOSFET reproducibility is about 3% (2 SD) for the doses normally delivered to the patients. The effect of the accumulated dose on the sensor response is negligible. For beam incidence ranging from 0 degrees to 90 degrees, the MOSFET response varies within 7%. No monotonic correlation between the sensor response and the temperature is apparent. Good correlation between the water-equivalent midplane depth and the ratio of the exit MOSFET readout divided by the entrance MOSFET readout was found (the correlation coefficient is about 1). The MOSFET midplane dosimetry relevant to the anthropomorphic phantom irradiation is in agreement with TLD dosimetry within 5%. Ionization chamber and MOSFET midplane dosimetry in inhomogeneous phantoms are in agreement within 2%. CONCLUSION: MOSFET characteristics are suitable for the in vivo dosimetry relevant to 6-MV treatments, both in normal and TBI setup. The TBI midplane dosimetry using MOSFETs is valid also in the presence of the lung, which is the most critical organ, and allows verifying that calculation of the lung attenuator thicknesses based only on the density is not correct. Our MOSFET dosimetry system can be used also to determine the surface dose by using the water-equivalent depth and extrapolation methods. This procedure depends on the field size used.