Measured Exposure Rate Research Articles

ОПЕРАТИВНАЯ ОЦЕНКА ЗНАЧЕНИЙ ДОЗЫ НАД ЩИТОВИДНОЙ ЖЕЛЕЗОЙ, СООТВЕТСТВУЮЩИХ ОПРЕДЕЛЕННЫМ УРОВНЯМ ПОГЛОЩЕННОЙ ДОЗЫ В ЩИТОВИДНОЙ ЖЕЛЕЗЕ, ДЛЯ НАСЕЛЕНИЯ В РАННИЙ ПЕРИОД ПОСЛЕ КРУПНОЙ РАДИАЦИОННОЙ АВАРИИ

In case of a large radiation accident at the nuclear power station the most important radiation hazard for the public is internal exposure to the thyroid from radioiodine. The IAEA standard published in 2013 and accounting the experience of the Chernobyl and Fukushima accidents, recommends that, in the first 1-6 days after an inhalation intake of radioiodine the exposure rate over the thyroid be measured for the public and be guided by the following operational criteria: (a) 0.5 μSv · h-1 for children under the age of 7 years, and (b) 2 μSv ·h-1 for children over 7 years and adults. These operational criteria are indicative estimates corresponding to the dose range 100–200 mGy in the thyroid for all age groups. However, a wider range of thyroid doses and a more detailed breakdown of children into five age groups according to the recommendations of the ICRP are of interest.
 The purpose of this paper is to develop a method for estimating the values of the measured exposure rate over the thyroid corresponding to certain levels of the absorbed dose in the thyroid for members of the public of different ages for various conditions of inhalation of radioiodine intake and times of measurement in the early period after a radiation accident.
 According to the method developed in the paper for the committed absorbed dose 100-200 mGy in the thyroid the exposure rates over the thyroid were calculated depending upon the time of inhalation intake after the accident and the time span between the moment of intake and the moment of measurement, which were equal to: 0.6– 4 μSv ·h-1 - for children of 1 year and 4–27 μSv · h-1 – for adults. These values are significantly higher than those recommended by the IAEA Standard 0.5 μSv · h-1 and 2 μSv · h-1, respectively. It is important to stress that the IAEA recommendations provide conservative estimates of the measured exposure rate over the thyroid in order to maximize the coverage of critical group of the public for further dosimetric and medical examination. For example, for some options of the time of radioiodine inhalation intake and the time of measurement, the IAEA recommended the values of the exposure rate over the thyroid that can lead to an overestimation of the absorbed dose in the thyroid gland by a factor of up to 10.

Radiation Safety Observations Associated with 177Lu Dotatate Patients.

Lutetium-177 dotatate, marketed under the name Lutathera®, is proving to be a valuable tool for physicians treating patients with neuroendocrine somatostatin-receptive tumors. Treatment consists of four cycles of 7.4 GBq of Lu dotatate infused intravenously over 30 to 40 minutes. This paper focuses on the radiation safety implications of patients undergoing Lu dotatate treatments at two large medical centers in the United States under the manufacturer's Expanded Access Protocol. Radiation safety precautions are described for the treatment of patients to control for radiation exposure and potential contamination. Ideally, the room used for administration should have a toilet, or one that is in close proximity, and covering should be provided to minimize contamination and clean up. The patient will meet the requirements in 10 CFR Part 35.75 for immediate release based on administered activity or measured exposure rate, but will need to be provided with written instruction on how to keep doses to other individuals ALARA. Disposal of the radioactive waste from Lu dotatate therapy can present some hazard control issues due to the long-lived Lu contaminant.Based on our experience, Lu dotatate therapy is an effective outpatient procedure that can safely occur in any hospital procedural room without the need for additional local shielding. Administration can be accomplished safely with attention paid to the administration set-up and proper administration procedures. Exposure to staff or to adjacent areas is minimal.

GIS mapping of impact of industrial activities on the terrestrial background ionizing radiation levels of Ughelli metropolis and its environs, Nigeria

The assessment of industrial activities and effluents on the external background ionizing radiation (BIR) levels of Ughelli metropolis and its environs has been conducted, using a digilert 100 nuclear radiation monitor and geographical positioning system for GIS mapping. The monitoring of the terrestrial BIR levels was carried out for 2 years (from May 2013 to June 2015) in 21 locations within the city and 21 other major villages/towns in Ughelli North local government area of Delta state. Measured exposure rate in Ughelli metropolis revealed a mean value of 15.20 ± 2.80 µRh−1 (1.28 ± 0.23 mSvy−1), while a mean value of 15.19 ± 2.70 µRh−1 (1.28 ± 0.23 mSvy−1) was obtained in the villages/towns. The estimated mean outdoor absorbed dose rate for the Ughelli metropolis and Ughelli environs is 132.16 ± 24.36 ηGyh−1 and 132.15 ± 23.50 ηGyh−1, respectively. The mean annual effective dose equivalent is 0.16 ± 0.03 mSvy−1) while the mean excess life cancer risk is (0.56 ± 0.11) × 10−3 mSvy−1. GIS maps of the study area revealing the BIR distribution and higher radiation levels were recorded in areas/communities where there are industrial activities and oil and gas facilities. The overall results of the measured exposure rates and the estimated radiological indices show that 73.5% of the sampled location exceeded their permissible limits. The mean equivalent dose rate obtained is higher than the safe exposure limit of 1.0 mSvy−1) recommended by UNSCEAR, and the mean radiation exposure levels in the study area is well above the normal background radiation level of 13.00 µRh−1 which shows that the studied area is radiologically contaminated. Though these values obtained may not cause immediate health hazard, there is the likelihood of long-term accumulating health side effects on the residents of some of these locations and communities sampled. Recommendations are made on the possible ways of reducing the impacts on the populace.

Radiological impact of oil and Gas Activities in selected oil fields in Production Land Area of Delta State, Nigeria

A study of the radiological impact of oil and gas exploration activities in the production land area of Delta State has been carried out in-situ using two synchronized and calibrated radiation meters (Digilert 50 and 100) and a geographical positioning system (GPS). Ten oil field facilities were studied. At each facility, nine sampling locations and their host communities were evaluated making a total of 100 study points. Measured exposure rate in the oil field facilities ranged from 0.011±0.003mRh -1 in Evwreni camp site to 0.031±0.01mRh -1 at the Otorogu gas plant. Mean field exposure rates/equivalent dose rates ranged from 0.016±0.006mRh -1 (0.839±0.34mSvy -1 ) to 0.0213±0.008mRh -1 (1.134±0.44mSvy -1 ). In the host communities the values ranged from 0.0115±0.003mRh -1 (0.612±0.16mSvy -1 ) in Evwreni community to 0.021±0.007mRh -1 (1.117±0.37mSvy -1 ) in Otujeremi town, while for the control study area the value obtained was 0.009±0.002mRh -1 (0.479±0.11mSvy -1 ). The results show that the radiation levels for the Ughelli East, Kokori, Eriemu, Evwreni, Eriemu, Oweh, Olomoro-Oleh oil and gas fields are within the 1mSvy -1 maximum permissible limit recommended for the public and non-nuclear industrial environment, while the levels for the fields at Otorogu, Ughelli West, Afiesere and Uzere West and East and the host communities of Olomoro, Uzere and Emeragha exceeded the maximum recommended value, an indication that the oil fields and host communities environment have been impacted radiologically. However, these results obtained may not have immediate health hazard, but will pose some long-term health side effects on the staff working in the facilities and residents of the host communities. Interim proactive measures are recommended @JASEM

Evaluation of the Effects of Scattered Radiation on Dosimeter Calibration in a Calibration Range

ISO standard 4037 specifies limits for scattered radiation for "gamma reference radiation" for the calibration of "protection-level dosemeters and rate dosemeters." More specifically, it specifies that scattered radiation should contribute less than 5% to the total exposure rate for source-center-to-dosimeter-center distances (henceforth called downrange distances) over which dosimeters are calibrated. In a previous paper by the authors, the results of an MCNP analysis of a calibration range with a Cs irradiator (henceforth called Cs calibration range) were reported. In that paper, simulations of the singly differential photon fluence rate (i.e., flux) energy spectra (henceforth called photon flux energy spectra) from the Cs (an ISO standard 4037 gamma reference radiation) irradiator were reported. In that paper, the spectra were examined to determine the contribution of scattered photons to the exposure rate in the Cs calibration range for various downrange distances. In this paper, the simulations of the photon flux energy spectra for the Cs irradiator photons for various downrange distances are convolved with response functions, creating an ideal exposure meter and two commercially available ion chamber survey meters, in order to predict the meters' response rates versus downrange distance. The simulated response rates indicate that the Cs calibration range satisfies an operational check of the contribution of scattered radiation to the exposure rate that is specified in the ISO standard 4037, although as shown in the previous paper by the authors, the Cs calibration range does not satisfy the ISO standard 4037 specification that scattered radiation should contribute less than 5% to the total exposure rate for downrange distances over which dosimeters are calibrated. The ISO standard 4037 operational check is that the measured exposure rate varies from an inverse square dependence by less than 5% for the downrange distances over which dosimeters are calibrated.

SU‐E‐T‐260: Radiation Exposure Estimation for 131Cs Prostate Implant Patient Release Determination

Due to the short half-life and high energy of Cesium-131 (131Cs), the exposure rate outside the patient could potentially increase radiation exposure to hospital staff and exceed the maximum patient release exposure rate limit. A calculation technique has been developed to estimate the exposure rate at 1 meter from the patient, for prostate patients receiving 131Cs implants. In our calculation for each patient, all 131Cs sources were treated as one single source, and the point on the prostate with the shortest distance to skin surface was selected as the effective source position. Attenuation inside the patient was calculated based on the attenuation coefficient of 30 keV photons in water, assuming homogeneous patient density. This calculation technique was evaluated on our first 25 131Cs implant patients. For comparison, the exposure rate at approximately 1 meter inferior to patient perineum was measured prior to patient release using the Inovision 451P-RYR survey meter. The distance from the edge of the prostate to skin surface along the inferior direction was the shortest in all 25 patients. The mean of the calculated exposure rates at 1 meter from skin surface was 0.53 mR/hr, 0.53 mR/hr, 0.04 mR/hr, 0.04 mR/hr and 1.5 mR/hr along the anterior, posterior, left, right and inferior directions, respectively. The mean of the measured exposure rate at 1 meter inferior to patient perineum was 1.1 mR/hr. The mean ratio of the measured versus calculated exposure rate was 0.74 (standard deviation = 0.23). Our calculation technique is useful in determining in advance whether a patient may require hospitalization after his implant. The exposure rate at 1 meter inferior to patient perineum is a good indicator for determining whether the exposure rate along any direction might exceed the maximum allowed patient release exposure rate of 6 mR/hr.

Less-restrictive, patient-specific radiation safety precautions can be safely prescribed after permanent seed implantation

Purpose To use radiation exposure rate measurements to determine patient-specific radiation safety instructions with the aim of reducing unnecessary precaution times and to evaluate potential doses to members of the public. Methods and Materials Radiation exposure rate measurements were obtained from 1279 patients with Stage T1-2 prostate cancer who underwent transperineal 125I or 103Pd seed implantation from January 1995 through July 2008. An algorithm was developed from these measurements to determine the required precaution times to maintain public effective doses below 50% of the limits for specific exposure situations. Results The median air kerma rates at 30 cm from the anterior skin surface were 4.9 μGy/h (range: 0.1–31.5) for 125I and 1.5 μGy/h (range: 0.02–14.9) for 103Pd. The derived algorithms depended primarily on the half-life T p , the measured exposure rate at 30 cm, and specific exposure situation factors. For the typical 103Pd patient, no radiation safety precautions are required. For the typical 125I patient, no precautions are required for coworkers, nonpregnant adults who do not sleep with the patient, or nonpregnant adults who sleep with the patient. Typical 125I patients should only avoid sleeping in the “spoon” position (i.e., in contact) with pregnant adults and avoid holding a child for long periods of time in the lap for about 2 months. Conclusions The large number of cases available for this study permitted the development of an algorithm to simply determine patient-specific radiation safety instructions. The resulting precaution times are significantly less restrictive than those generally prescribed currently.

Analysis of dosimetric and radiation safety results of seventeen patients treated with radioimmuno therapy using Iodine 131—Tositumomab for non-Hodgkin’s lymphoma

12513 Background: Radioimmunotherapy using radioactive Iodine -131 labeled radioimmuno conjugate called Tositumomab has been used in the treatment of non-Hodgkin’s lymphoma. Radiation dosimetry and safety aspects of this treatment modality are very critical for successful implementation of this treatment. Methods: Since year 2001, we have treated 17 patients using I-131-tositumomab. There were 11 female and 6 male patients at age range of 40 to 82 years. Patient specific dosimetry was performed on all the patents using a tracer dose of I-131. The whole body counts were performed after infusion of 5.0 mCi of I-131-tositumomab and whole body counts were taken at 0, 48 and 178 hours. The total body residence time (TBRT) for 37% of the activity to stay in the body was determined by graphical method. The activity in mCi, for delivering 65 cGy or 75 cGy whole body dose, was calculated based on the TBRT and patient’s weight. Based on the measured exposure rate, we have calculated the total effective dose equivalent (TEDE) to the public. The patients were released to home with radiation safety instructions if TEDE delivered to the public was less than 5.0 mGy. We have studied the platelet count recovery time for all the patients, following treatment. Results: The calculated TBRT ranged from 85 to 175 hours and the the mCi/Kgm varied from 1.4 to 0.6, related inverse proportion with TBRT. For both group of patients, treated with total body dose of 65 cGy and 75 cGy, the mCi/Kgm was the same, for TBRT values exceeding 100 hours. The TEDE to public varied from 1.02 to 3.22 mGy, while the exposure rate measured on the patient at 1 meter was less than the permissible value reported in the literature for safe release. Conclusion: The above results show that the patients can be treated as outpatient using I-131 -tositumomab with radiation safety restrictions lasted for one week. The radiation exposure to the public was less than the maximum permissible dose equivalent. No significant financial relationships to disclose.

TH-C-T-6C-09: Measurement of Shielding Requirements for Helical Tomotherapy

Purpose: Helical tomotherapy is a CT-based rotational delivery technique that uses intensity-modulated fan beams to deliver highly conformal intensity modulated radiation therapy (IMRT). The purpose of this work is to directly measure and map the radiation environment around a clinical TomoTherapy HI-ART system during patient treatments to determine the rate of in-room exposure. Method and Materials: Radiation exposure was measured at various positions surrounding a helical tomotherapy treatment system using a calibrated InoVision Model 451P ionization chamber. The 451P has a 300 cubic centimeter collecting volume air ionization chamber that is pressurized to 8 atmospheres (862 kPa). Prior to use in this study, the chamber was calibrated by an Accredited Dosimetry Calibration Laboratory (ADCL) and is directly traceable to the National Institute of Standards and Technology (NIST) standard. Results: A total of 225 measurements were taken during helical treatment delivery for 25 patients at various positions around the HI-ART gantry. The largest measured exposure rate is 1 mR/sec in the plane of gantry rotation from head leakage and primary beam transmission through the beam-stopper. There are 2.2 million seconds of beam-on time annually assuming an average beam-on time is 300 seconds, an average treatment slot of fifteen minutes, and patients per hour. Based on the measured scatter and leakage values, a total of 3 to 5 TVLs of secondary beam shielding is required, depending on the room geometry, patient load, occupancy factors, and dose limits. Conclusion: Based on the primary, leakage, and scatter exposures measured around the HI-ART it is possible to replace a conventional linear accelerator with a helical tomotherapy system without requiring additional primary or secondary shielding.

RADIATION EXPOSURE RATE FROM 131I-TREATED HYPERTHYROID PATIENTS???A DYNAMIC STUDY, WITH DATA FOR UP TO 42 d POST THERAPY

Hyperthyroid patients treated with radioactive 131I are a potential source of external and internal exposure to family members and others in close contact with these patients. Information on the exposure rate from the patient on any day post administration of the dosage may be helpful when implementing an effective radiation safety or ALARA strategy for the family or members of the general public. Exposure rate measurements were completed on 78 out of 128 hyperthyroid patients participating in the study. Measurements were taken at 1 m, 0.6 m, and 0.3 m from the patient for eight different dose regimens and for up to 42 d post dose administration. The measured exposure rate was plotted against days post dose administration to demonstrate how quickly the exposure rate reduced with time. As anticipated, significant positive correlation was found between exposure rate at 1 m, 0.6 m, and 0.3 m for all radioactive dose regimens. No significant correlation was found between the external exposure rate reduction post-therapy and the 131I uptake at 2 or 24 h, prior to therapy. This work is a dynamic study that provides comprehensive external radiation exposure rate measurements in hyperthyroid patients post therapy dose administration and may serve as a database for radiation safety related decision-making.

Dose-effect relationship of dicentric and ring chromosomes in lymphocytes of individuals living in the high background radiation areas in China.

Chromosomes of 39 healthy family members (3 generations from 13 families) living both in the high-level background radiation areas (HBRA) and the control areas (CA) were studied. Cumulative dose from birth to the time of blood sampling was estimated by calculating measured exposure rate in each individual. The cumulative doses ranged 30.9-358.9 and 6.0-59.2 mGy for HBRA and CA, respectively. Peripheral lymphocyte chromosome preparations were made according to our improved method. Dicentric and ring chromosomes (Dic + Rc) were scored in average 2,527 cells per individual in HBRA and 2,694 cells in CA under a microscope equipped with an automated stage. A positive correlation between Dic + Rc and age was found in HBRA, while no such dose relationship was clear in CA. The frequency of Dic + Rc linearly increases over lifetime due to chronic low dose exposure and it is likely that the activation of repair enzymes is not triggered in the present HBRA. Threshold dose (rate) of the induction of chromosome aberrations, if any, is below the present dose (rate) level.

Development of a Method to Estimate Thyroid Dose from Fallout Radioiodine in a Cohort Study

A cohort of 4831 persons aged 11-18 y in 1965 was identified among students in the schools of Washington County, UT; Lincoln County, NV; and Graham County, AZ. These children who had potentially been exposed to radioiodine from atomic weapons test fallout from the Nevada Test Site during 1951-1962 were selected for participation in a study of thyroid disease. The entire cohort was first examined during 1965-1968 for thyroid abnormalities. A total of 3,085 of these people were again reexamined during 1985-1986 to determine any subsequent occurrence of thyroid disease. In order to determine the relationship of the radiation dose to the thyroid with incidence of thyroid disease, we have developed a suite of models to calculate estimates of the internal dose received by the thyroid from fallout radioiodines. For completeness, the exposure to the thyroid from external radiation is also estimated. Dose estimates are made specific to each individual in the study using individual residential histories, the locality-specific exposure rate and radionuclide deposition, descriptions of dairy management for identified milk producers, and the subjects' sources of foods and intake rates of milk and leafy vegetables determined by interview. Other data such as the relationship of radioiodine deposition to measured exposure rate, environmental transfer parameters, and age-dependent factors for the conversion of radioiodine intake to thyroid dose were taken from work of other investigators. Dairy management information, milk distribution practices, the milk source for each study subject, as well as age-specific intake rates of milk and leafy vegetables, were determined by interview.

積雪による地殻γ線線量率の減衰

In order to clarify the diminution characteristics of terrestrial gamma ray exposure rate due to snow cover, measurements were performed on the ground with and without snow cover. The diminution factors observed were 0.36-0.17 for 12-23g/cm2 of water equivalent of the snow cover. According to a calculation by the Monte Carlo method, the corresponding diminution factors were 0.32-0.16. They agreed well as a whole, while the fluctuation of the diminution factors based on the measured exposure rate were fairly large. The fluctuation is deemed to be due to the inhomogeneity in the distribution of the snow cover as well as the gamma ray field. The fluctuation is expected to decrease with increase in the degree of their homogeneity.

Real-Time Simulation of Gamma Exposure Rate by Puff Model

The measured gamma exposure rate around nuclear power plants is due mainly to natural causes and radioactive plumes emitted from the plants. A calculation method based on a puff model has been proposed to identify the latter contribution and evaluate quantities in response to short-term fluctuations of meteorological conditions and the release rate. The calculation results have been compared with the measured exposure rate less the natural background. In general, the calculation exposure rate is one-half to twice as much as the measured exposure rate less the background. 12 refs.

原子力発電所からの放射性雲によるγ線照射線量率の短時間変動特性の評価方法

The measured γ-exposure rate around nuclear power plants is due mainly to natural causes and radioactive clouds emitted from the plants. An exposure calculation method based on puff model has been already proposed to identify the plant contributions and to estimate values in response to short-term fluctuations of meteorological condition and the release rate. However, the calculation method by this model consumes a lot of computer time, since the calculation requires a three-dimen-sional integration of the distribution of the concentration from each puff. Hence, we propose a simplified method using approximate polynominal equations and interpolations. The computer time needed for the calculation with the simplified method is reduced to 1/30 of that required by the previous method. The calculation results by simplified method are compared with those by the previous method and with the measured exposure rate less natural background. The results of two different methods are in good agreement. The calculated exposure rate is within the range from half to twice as much as the measured exposure rate less background.

Barrier transmission of 6 MV x rays for oblique angles of incidence.

Useful beam transmission data for both normal and oblique angles of incidence are required for optimum shielding design. This is particularly true for installations that utilize an isocentric source mounting. However, transmission data for 6 MV x rays are available only for normal incidence. To determine the effect of oblique angles of incidence on barrier transmission, measurements were made at a 6 MV linear accelerator installation. The useful beam was directed toward a 40-inch concrete barrier at various angles of incidence. The transmitted exposure rates were measured with a 590 cc ionization chamber rate meter. A 6.0 mm Lucite cover on the chamber was found to be sufficient to insure electronic equilibrium. All measurements were made with a 20 x 20 cm field at 1 m and with the detector 1 foot from the distal surface of the barrier. For normal incidence the detector was 3.5 m from the isocenter. The isocenter was 1 m from the source. The results for various angles of incidence are shown in Figure 1. The circle on each curve represents the point of interception of the central ray and the plane of measurement. For clarity, this point is defined as the “intercept.” As expected, for normal incidence (α = 0°) the variation of exposure rate with distance from the central ray is much greater than indicated by simple geometrical consideration. For oblique angles of incidence the experimentally determined exposure rate was compared with the rate computed from transmission data obtained with normal angle of incidence (1). The measured exposure rate at the “intercept” is in accord with the calculated value based on the barrier thickness along the central ray. However, as shown, the location of the maximum exposure rate is not coincident with the “intercept.” The ratio of the maximum exposure rate to the exposure rate at the “intercept” is very dependent upon the angle of incidence and ranges from 1.2 for 20° to 2.5 for 45° (Fig. 1). These preliminary results were obtained for the specified barrier thickness and geometrical conditions. It is intended to extend this investigation for a range of photon energies, barrier thicknesses, and geometrical conditions.

The equivalent field principle and its use in beam therapy dose calculations.

A simple approximation for equivalent squares of rectangular fields has been developed for use in different routine calculations with computers. This approximation is shown to be particularly satisfactory in the calculation of treatment times for a cobalt unit for fields of different shape and area. Parameters are presented which give the dose-rate for the Siemens “Gammatron I” as a function of the equivalent square, based upon the measured exposure rate.