Uncertainties In Dose Assessment Research Articles

Reduction of uncertainties in exposure assessment based on environmental monitoring data

Emergency preparedness and response systems for nuclear and radiological emergencies have to deal with decision-making in situations with relevant uncertainties. Consistent and appropriate protective measures must be decided before, during and after emergency situations. CONFIDENCE WP2 research helps to improve this decision-making process in the urgent response and the early response phase of emergency situations with potential major releases to atmosphere. This paper describes methods to reduce uncertainties in dose assessment for the population using data from stationary and mobile environmental monitoring programs. A special focus is given to identification of the measurement uncertainties of stationary and mobile monitoring systems. Methods to reduce these uncertainties and procedures to optimise mobile monitoring strategies are discussed. A first contribution towards assessing the quality of dose-rate measurements performed by the general population is made. In addition, the paper introduces approaches for advanced dose assessment tools using monitoring data and concepts for identifying critically exposed groups.

Variations in radon dosimetry under different assessment approaches in the Altamira Cave

The atmosphere of caves is a special environment where it is necessary to take into account some particular characteristics when assessing the radon dose. The equilibrium factor (F) between radon and its progeny, and especially its unattached fraction (fp), is a key parameter in radon dose evaluation. In order to consider the specific features of the atmosphere in the Altamira Cave, the radon and particle concentrations have been measured. The mean annual radon concentration inside the cave over the period 2013–2019 is around 3500 Bq m−3 with a standard deviation of 1833 Bq m−3 and this exhibits seasonal variations. This value surpasses all international (WHO, IAEA, ICRP) upper action and reference levels (occupational and non-occupational). Dose rate levels expressed in μSv h−1 were estimated for four different equilibrium scenarios between radon and its progeny 218Po, 214Pb, 214Bi and 214Po. The most recent dose conversion factors have been used and the contribution made to the dose by the unattached fraction of radon progeny fp has been also assessed from the particle concentration. The results suggest that the mean annual dose levels show variations of up to 500% due to the range of F and the fp considered in this study. Given the high radon concentrations usually found in show caves, the best way to reduce this variability and its associated uncertainty in dose assessment is to conduct specific studies aimed at determining both F and fp.

A new EPR dosimeter based on glutamic acid for radiation processing application.

L-Glutamic acid (L-GA) pellets (3.8mm × 4mm) and powder dosimeters were studied in the dose range of 0.1-150kGy using the electron paramagnetic resonance (EPR) technique. The EPR spectra of irradiated L-GA pellets showed an EPR signal with eight lines, and the intensity of the signal increased with an increase of absorbed dose. The results obtained in terms of the energy-absorption coefficients suggest a similar performance of the L-GA pellets as compared to alanine pellets. The value of the temperature coefficient for the L-GA pellets during irradiation was around - 0.08%/°C which is lower than that reported for alanine dosimeter, 0.14%/°C. The influence of humidity on the pellet response was found to be negligible; i.e., the increase in response was only about 2% for a relative humidity of up to 94%. The response of L-GA powder reached stability 4h after irradiation and continued to be stable until 47days after irradiation. In contrast, the response of the L-GA pellet dosimeter reached stability 22h after irradiation and continued to be stable until 8days after irradiation. For routine applications, the L-GA pellet dosimeter should be analyzed during the stable period after irradiation, to minimize the uncertainties in dose assessment. The overall two-sigma uncertainties in absorbed dose estimation were 5.1% and 3.9% for the dose ranges of 0.1-15kGy and 15-150kGy, respectively. It is concluded that L-GA pellets represent a promising dosimeter material for quantification of radiation doses in food irradiation, medical sterilization and polymer modification.

Phototransferred TL properties of alumina substrates

Alumina substrates, such as those found as surface-mount resistors in mobile phones, are currently the strongest candidate as a surrogate dosimeter material in emergency radiological scenarios using luminescence techniques. However, the rate of fading of the luminescence signal (TL or OSL) imposes a limitation on their longer term use, and also increases the uncertainty in dose assessment. The potential of phototransferred thermoluminescence (PTTL) techniques to access deep traps in alumina substrate samples is reported here. A measurement procedure employing blue (470 nm) illumination was found to produce a PTTL signal with a detection limit of ca 100 mGy, but with a supralinear dose response below 10 Gy. By using a UV source with emission between 307 and 575 nm a linear dose response was obtained within this dose range, although the detection limit was higher (ca 200 mGy), partly arising from the presence of a non-radiation-induced photostimulated TL signal. Pulse annealing experiments indicate that deep traps providing a reservoir of charge are thermally accessible above 500 °C and require annealing to ca 700 °C to thermally clean them. Significantly, using blue illumination, storage experiments performed under dark conditions at room temperature indicate that the loss of charge in the deep traps accessed by the PTTL measurement procedure was less than 30% for storage periods of up to 224 days. Although the physical mechanisms associated with the transfer of charge from the deep traps probed by the PTTL measurements require further clarification, the possibility of significantly reducing the fading observed in conventional TL or OSL measurements introduces a potentially valuable tool in the use of this material for both short and long term dosimetry.

EXTERNAL AND INTERNAL EXPOSURE TO FUKUSHIMA RESIDENTS.

The Great East Japan Earthquake of 11 March 2011, caused the Fukushima Daiichi Nuclear Power Plant Accident, which resulted in the release of a large amount of radioactive materials into the environment, and there is a serious concern about the radiation effects on the health of residents living in the affected areas. The evaluation of exposure dose is fundamental for the estimation of health effects, and whenever possible, the exposure dose should be evaluated by actual measurements as opposed to estimations. Here,the outline of the exposure doses of residents estimated from surveys or obtained by measurements is described. Fukushima Health Management Survey reported the results for 460 408 residents during the first 4 months after the accident; 66.3% received doses <1 mSv, 94.9% received <2 mSv, 99.7% received <5 mSv and the maximum dose was 25 mSv. Thus, it was demonstrated that the results from personal dosemeter measurements were comparable to the estimations. The dose assessment of internal exposure of 184 205 residents conducted by Fukushima Prefecture by using whole body counter showed that 99.986% received<1 mSv, with the maximum dose being 3 mSv. Regarding exposure of the thyroid, there is not enough data for the Fukushima accident, but it is presumed that thyroid doses are much lower than those from Chernobyl. The outline of exposure doses of residents in result of the accident is still being clarified, questions and uncertainties in dose assessment remain and further efforts for more accurate dosimetry are required continuously.

Characterization of XR-RV3 GafChromic(®) films in standard laboratory and in clinical conditions and means to evaluate uncertainties and reduce errors.

To investigate the optimal use of XR-RV3 GafChromic(®) films to assess patient skin dose in interventional radiology while addressing the means to reduce uncertainties in dose assessment. XR-Type R GafChromic films have been shown to represent the most efficient and suitable solution to determine patient skin dose in interventional procedures. As film dosimetry can be associated with high uncertainty, this paper presents the EURADOS WG 12 initiative to carry out a comprehensive study of film characteristics with a multisite approach. The considered sources of uncertainties include scanner, film, and fitting-related errors. The work focused on studying film behavior with clinical high-dose-rate pulsed beams (previously unavailable in the literature) together with reference standard laboratory beams. First, the performance analysis of six different scanner models has shown that scan uniformity perpendicular to the lamp motion axis and that long term stability are the main sources of scanner-related uncertainties. These could induce errors of up to 7% on the film readings unless regularly checked and corrected. Typically, scan uniformity correction matrices and reading normalization to the scanner-specific and daily background reading should be done. In addition, the analysis on multiple film batches has shown that XR-RV3 films have generally good uniformity within one batch (<1.5%), require 24 h to stabilize after the irradiation and their response is roughly independent of dose rate (<5%). However, XR-RV3 films showed large variations (up to 15%) with radiation quality both in standard laboratory and in clinical conditions. As such, and prior to conducting patient skin dose measurements, it is mandatory to choose the appropriate calibration beam quality depending on the characteristics of the x-ray systems that will be used clinically. In addition, yellow side film irradiations should be preferentially used since they showed a lower dependence on beam parameters compared to white side film irradiations. Finally, among the six different fit equations tested in this work, typically used third order polynomials and more rational and simplistic equations, of the form dose inversely proportional to pixel value, were both found to provide satisfactory results. Fitting-related uncertainty was clearly identified as a major contributor to the overall film dosimetry uncertainty with up to 40% error on the dose estimate. The overall uncertainty associated with the use of XR-RV3 films to determine skin dose in the interventional environment can realistically be estimated to be around 20% (k = 1). This uncertainty can be reduced to within 5% if carefully monitoring scanner, film, and fitting-related errors or it can easily increase to over 40% if minimal care is not taken. This work demonstrates the importance of appropriate calibration, reading, fitting, and other film-related and scan-related processes, which will help improve the accuracy of skin dose measurements in interventional procedures.

A dosimetric study of prostate brachytherapy using Monte Carlo simulations with a voxel phantom, measurements and a comparison with a treatment planning procedure

In prostate brachytherapy treatments, there is an initial swelling of the prostate of the patient due to an oedema related to the insertion of the seeds. The variation of the prostate volume can lead to variations in the final prescribed dose in treatment planning procedures. As such, it is important to understand their influence for dose optimisation purposes. This work reports on a dosimetric study of the swelling of the prostate in prostate brachytherapy using Monte Carlo simulations. Dosimetric measurements performed on a physical anthropomorphic tissue-equivalent prostate phantom and thermoluminescent dosimeters (TLDs) were used to validate the MC model. Finally the MC model was also used to simulate prostate swelling in a real treatment planning procedure. The obtained results indicate that the parameters mentioned above represent a source of uncertainty in dose assessment in prostate brachytherapy, and can be detrimental to a correct dose evaluation in treatment plannings, and that these parameters can be accurately determined by means of MC simulations with a voxel phantom.

ICRP PUBLICATION 123: Assessment of Radiation Exposure of Astronauts in Space

During their occupational activities in space, astronauts are exposed to ionising radiation from natural radiation sources present in this environment. They are, however, not usually classified as being occupationally exposed in the sense of the general ICRP system for radiation protection of workers applied on Earth. The exposure assessment and risk-related approach described in this report is clearly restricted to the special situation in space, and should not be applied to any other exposure situation on Earth. The report describes the terms and methods used to assess the radiation exposure of astronauts, and provides data for the assessment of organ doses. Chapter 1 describes the specific situation of astronauts in space, and the differences in the radiation fields compared with those on Earth. In Chapter 2, the radiation fields in space are described in detail, including galactic cosmic radiation, radiation from the Sun and its special solar particle events, and the radiation belts surrounding the Earth. Chapter 3 deals with the quantities used in radiological protection, describing the Publication 103 (ICRP, 2007) system of dose quantities, and subsequently presenting the special approach for applications in space; due to the strong contribution of heavy ions in the radiation field, radiation weighting is based on the radiation quality factor, Q, instead of the radiation weighting factor, wR. In Chapter 4, the methods of fluence and dose measurement in space are described, including instrumentation for fluence measurements, radiation spectrometry, and area and individual monitoring. The use of biomarkers for the assessment of mission doses is also described. The methods of determining quantities describing the radiation fields within a spacecraft are given in Chapter 5. Radiation transport calculations are the most important tool. Some physical data used in radiation transport codes are presented, and the various codes used for calculations in high-energy radiation fields in space are described. Results of calculations and measurements of radiation fields in spacecraft are given. Some data for shielding possibilities are also presented. Chapter 6 addresses methods of determining mean absorbed doses and dose equivalents in organs and tissues of the human body. Calculated conversion coefficients of fluence to mean absorbed dose in an organ or tissue are given for heavy ions up to Z=28 for energies from 10MeV/u to 100GeV/u. For the same set of ions and ion energies, mean quality factors in organs and tissues are presented using, on the one hand, the Q(L) function defined in Publication 60 (ICRP, 1991), and, on the other hand, a Q function proposed by the National Aeronautics and Space Administration. Doses in the body obtained by measurements are compared with results from calculations, and biodosimetric measurements for the assessment of mission doses are also presented. In Chapter 7, operational measures are considered for assessment of the exposure of astronauts during space missions. This includes preflight mission design, area and individual monitoring during flights in space, and dose recording. The importance of the magnitude of uncertainties in dose assessment is considered. Annex A shows conversion coefficients and mean quality factors for protons, charged pions, neutrons, alpha particles, and heavy ions(2<Z≤28), and particle energies up to 100GeV/u.

Simple DVH parameter addition as compared to deformable registration for bladder dose accumulation in cervix cancer brachytherapy

Background and purposeVariations in organ position, shape, and volume cause uncertainties in dose assessment for brachytherapy (BT) in cervix cancer. The purpose of this study was to evaluate uncertainties associated with bladder dose accumulation based on DVH parameter addition (previously called “the worst case assumption”) in fractionated BT. Materials and methodsForty-seven patients treated for locally advanced cervical cancer were included. All patients received EBRT combined with two individually planned 3D image-guided adaptive BT fractions. D2cm3 and D0.1cm3were estimated by DVH parameter addition and compared to dose accumulations based on an in-house developed biomechanical deformable image registration (DIR) algorithm. ResultsDIR-based DVH analysis was possible in 42/47 patients. DVH parameter addition resulted in mean dose deviations relative to DIR of 0.4±0.3Gyαβ3 (1.5±1.8%) and 1.9±1.6Gyαβ3 (5.2±4.2%) for D2cm3 and D0.1cm3, respectively. Dose deviations greater than 5% occurred in 2% and 38% of the patients for D2cm3 and D0.1cm3, respectively. Visual inspection of the dose distributions showed that hotspots were located in the same region of the bladder during both BT fractions for the majority of patients. ConclusionDVH parameter addition provides a good estimate for D2cm3, whereas D0.1cm3 is less robust to this approximation.

Modeling of Uncertainty in Dose Assessment using Probability-Possibility Transformation

Uncertainty parameters in risk assessment can be modeled by different ways viz. probability distribution, possibility distribution, belief measure, depending upon the nature and availability of the data. Different transformations exist for converting expression of one form of uncertainty to another form. In this paper, we reviewed the consistency principles as given by different researchers. Then we have carried out dose assessment using probability- possibility transformation satisfying consistency conditions.

Biokinetic models for rats exposed to repeated inhalation of uranium: implications for the monitoring of nuclear workers

For dose assessment following chronic or accidental inhalation of radioactive aerosols, the dosimetric models of the International Commission on Radiological Protection (ICRP) provide dose coefficients, retention and excretion functions. Unknown date or dates of intake is the major source of uncertainty in dose assessment during routine monitoring of nuclear workers. The two assumptions commonly made in dose assessment from an unknown time pattern of intake have been tested experimentally with a model of repeated inhalation by rats. The hypothetical intake derived from lung measurement was relatively reliable under the two hypotheses. The hypothetical intake derived from excreta measurement depended on the choice of hypothesis and on the real time pattern of intake.

Use of alanine for dosimetry intercomparisons among Italian radiotherapy centers

A pilot program of postal dosimetry intercomparison among 16 Italian Radiotherapy Centers was performed using the ISS Alanine/EPR dosimetry as a transfer system. Dosimeters were irradiated at 10 Gy with high-energy photon beams, both in reference condition in a water phantom and in an anthropomorphic phantom during the simulated treatment of rectum cancer. Intercomparison design along with alanine performances analyzing the different contributions to the combined uncertainty in dose assessment are reported. Main results of the pilot intercomparison, terminated in 2002, are also presented.

Development of Probabilistic Multimedia Multipathway Computer Codes

The deterministic multimedia dose/risk assessment codes RESRAD and RESRAD-BUILD have been widely used for many years for evaluation of sites contaminated with residual radioactive materials. The RESRAD code applies to the cleanup of sites ~soils! and the RESRAD-BUILD code applies to the cleanup of buildings and structures. This work describes the procedure used to enhance the deterministic RESRAD and RESRAD-BUILD codes for probabilistic dose analysis. A six-step procedure was used in developing default parameter distributions and the probabilistic analysis modules. These six steps include ~1! listing and categorizing parameters; ~2! ranking parameters; ~3! developing parameter distributions; ~4! testing parameter distributions for probabilistic analysis; ~5! developing probabi- listic software modules; and ~6! testing probabilistic modules and integrated codes. The procedures used can be applied to the develop- ment of other multimedia probabilistic codes. The probabilistic versions of RESRAD and RESRAD-BUILD codes provide tools for studying the uncertainty in dose assessment caused by uncertain input parameters. The parameter distribution data collected in this work can also be applied to other multimedia assessment tasks and multimedia computer codes.

The use of track registration detectors to reconstruct contemporary and historical airborne radon ( 222RN) and radon progeny concentrations for radon-lung cancer epidemiologic study

Epidemiologic studies that investigate the relationship between radon and lung cancer require accurate estimates for the long-term average concentrations of radon progeny in dwellings. Year-to-year and home-to-home variations of radon in domestic environments pose serious difficulties for reconstructing an individual's long-term radon-related exposure. The use of contemporary radon gas concentrations as a surrogate for radon-related dose introduces additional uncertainty in dose assessment. Studies of glass exposed in radon chambers and in a home show that radon progeny deposited on, and implanted in, glass hold promise for reconstructing past radon concentrations in a variety of atmospheres. We developed an inexpensive track registration detector for the Iowa Radon Lung Cancer Study (IRLCS) that simultaneously measures contemporary airborne radon concentrations, surface deposited alpha activity density, and implanted 210Po activity density. The implanted activity is used to reconstruct the cumulative radon and radon progeny exposure from the age of the glass and the ratios of the contemporary deposited activiteis to airborne radon gas activity. We placed over 2500 of these detectors in more than 1000 homes and retrieved 97% of them after a one-year exposure period. A preliminary analysis of the 1280 detectors that have undergone quality assurance review shows that the modules are meeting their accuracy and precision goals (10%). There is good correlation (r 2∼0.5) between the total radon exposure estimated from contemporary radon gas measurements and historical average reconstructed from the implanted 210Po surface activity. The linear regression slope of the airborne radon exposure to implanted activity is the same as the room model slope based on typical room parameters. This correlation improves (r 2∼0.7) when the deposited surface activity measurements are added to the linear regression. Thus, track-registration detectors can contribute to accurate radon-related dose assessment in epidemiologic studies. Additional work is planned to incorporate the deposited activities in a more sophisticated reconstruction model.

The Limitations of Atmospheric Dispersion Data and Their Contribution to Uncertainties in Dose Assessment

The calculation of atmospheric dispersion patterns is often an important component of radiation dose estimates. These dispersion calculations are a possible source of error and such errors or uncertainties need to be quantified. An important source of uncertainty is the meteorological data used in the calculations. Such data may be less than ideal because of constraints imposed by both availability and by the variances associated with population from which the data are obtained. We have studied a simple and much used model of atmospheric dispersion--the Gaussian plume. We discuss the uncertainties on the meteorological data which are input to the model and how these uncertainties could be used to estimate uncertainties for the modeling results. In doing this we have addressed both the uncertainty associated with a recorded climatology and the added uncertainty arising from the year-to-year variability at any given location.