IAEA Technical Reports Series Research Articles

Comparison of directly and indirectly estimated entrance skin dose (ESD) for diagnostic radiation qualities (RQR, RQA and RQT) using water phantom and shadowfree diagnostic chamber (SFD)

BackgroundThe aim of this study was to find the entrance skin dose (ESD) for diagnostic radiation qualities RQRs, RQAs and RQTs given in IAEA technical report series No. 457 using direct and indirect methods of measurement. Measurements were done for 5 × 5, 10 × 10, 15 × 15, 20 × 20 and 25 × 25 cm2 field sizes and 70, 80, 90 and 100 cm source to surface distance (SSD) using shadow-free diagnostic (SFD) chamber and water phantom having dimension 30 × 30 × 30 cm3. ESD direct measurements were done by placing SFD chamber on the surface of water phantom, while in the case of indirect measurements, air kerma values were obtained.ResultsESD values for different selected radiation qualities RQR2, RQR5, RQR8, RQR10, RQA2, RQA5, RQA8, RQA10, RQT8, RQT9 and RQT10 were found to be in the range of 0.0045–5.11 mGy per examination.ConclusionsResults obtained were found to be comparable with ESD values published in the literature. The obtained results in this research would help in establishing the national diagnostic reference levels (DRLs) which would help in the optimization of diagnostic imaging procedures. It would also help the radiographers to optimize field sizes and SSDs in order to reduce dose to the patients thereby ensuring good radiological practices, and this would reduce the stochastic risk to the patients caused by the ionizing radiations.

Establishment of beam qualities for medical applications (mammography and CT) in the gamma and X calibration laboratory of CNESTEN according to EN 61267 standards

The present study aimed to validate the different radiodiagnostic beam qualities (RQT, WAH and WAV) by the measurements of the X-ray beams HVL of a HOPEWELL generator, X80-225 kV from a high voltage range of 10 at 200 kV, at CNESTEN Gamma and X Calibration Laboratory. The experiments were carried out using the PTW TN 32005 ionization chamber, established at 100 cm from the center of the X-ray tube and connected to a SUPERMAX electrometer. The HVL values were measured by applying the attenuation law to the flow of Kair air kerma, including their uncertainties. The obtained HVL values were compared with standard values of diagnostic levels. It was observed that the HVL of the present X-ray machine in most qualities are smaller than the standard ones. An approved method (described in the STANDARD EN 61267 and IAEA TECHNICAL REPORTS SERIES n° 457) was applied to determine the amount of additional filtration required to meet the standard values, and by checking their compliance with the maximum absolute deviation. The results indicate the adequacy of the LEGX laboratory for the calibration of the radiation detection instruments used in computed tomography and mammography with an expanded uncertainty in the best measurement capability of ±4 % (k = 2).

Determination of small-field output factors for beam-matched linear accelerators using various detectors and comparison of detector-specific output correction factors using IAEA Technical Report Series 483 protocol.

Beam matching is widely used to ensure that linear accelerators used in radiotherapy have equal dosimetry characteristics. Small-field output factors (OF) were measured using different detectors infour beam-matched linear accelerators and the measured OFs were compared with existing treatment planning system (TPS) Monte Carlo algorithm calculated OFs. Three Elekta Versa HDTM and one Elekta InfinityTMlinear accelerators with photon energies of 6 MV flattening filter (FF), 10 MVFF, 6 MV flattening filter free (FFF) and 10 MVFFF were used in this study. All the Linac'swere beam-matched, Dosimetry beam data were ± 1% compare with Reference Linac. Ten different type of detectors (four ionizationchambers and six diode detectors) were used for small-field OF measurements. The OFs were measured for field sizes of 1 × 1 to 10 × 10 cm2, and normalized to 10 × 10 cm2 field size. The uncorrected and corrected OFs were calculated from these measurements. The corrected OF was compare with existing treatment planning system (TPS) Monte Carlo algorithm calculated OFs. The small-field corrected and Uncorrected OF variations among the linear accelerators was within 1% for all energies and detectors. An increase in field size led to a reduction in the difference between OFs among the detectors, which was the case for all energies. The RSD values decreased with increasing field size. The TRS 483 provided Detector-specificoutput-correction factor (OCF) reduced uncertainty in small-field measurements. It is necessary to implement the OF-correction of small fields in a TPS. Special care must be taken to incorporate the corrected small-field OF in a TPS.

Development and experimental validation of a fast neutron spectrometry system based on Superheated Drop Detectors (SDDs) operating under different external pressures

In this paper, the spectrum of 241Am-Be neutron source was measured by developing and using a neutron spectrometer system based on Superheated Drop Detectors (SDDs) operating under various external pressures. The system consisted of a set of SDDs fabricated by in situ polymerization method. The external pressures were controlled by the amount of Freon-12 added onto the surface of detectors. Also, this system includes a Geant4 simulation application capable of calculating the response of SDDs made from various materials at various temperatures and pressures. Ultimately, the system contained a customized program to design and train the Adaptive Network-based Fuzzy Inference System (ANFIS) for fast neutron spectrum unfolding. This program has the capability of designing the ANFIS with different rule structures and various parameters of the fuzzy inference system.In the present study, the simulation application was used to calculate the response matrix of five SDDs under external pressures of 0.86, 1.93, 2.72, 3.48, and 3.85 atm in 20 energy bins from 0.5 MeV to 514 MeV at 28 °C. Furthermore, the customized program was utilized to design a FIS structure using the FCM method with six membership functions for each input.Neutron spectra published in the IAEA technical reports series no. 403 and 318 were utilized as the Target data. The response matrix was used to obtain the input data of ANFIS by multiplying the target data by the response matrix. 99% of data (373 out of 377) was considered as the train data and the rest as the test data.After fabrication of SDDs, they were exposed to an 241Am-Be neutron source. The average numbers of the formed bubbles in SDDs with different external pressures were introduced to the trained ANFIS, and finally, the unfolded spectrum was the output of the ANFIS. The RMSE for the measured neutron spectrum was the acceptable value of 0.016. The reasonable agreement between the unfolded and reference 241Am-Be neutron spectra shows that the developed neutron spectrometry system can be a suitable candidate for fast neutron spectrometry.

Output factor measurements with multiple detectors in CyberKnife® Robotic Radiosurgery System.

The aim of this study was to measure and compare the output factor (OF) of a CyberKnife Robotic Radiosurgery System with eight different small field detectors and validate with Technical Report Series (TRS) report 483. Accurate dosimetry of CyberKnife system is limited due to the challenges in small field dosimetry. OF is a vital dosimetric parameter used in the photon beam modeling and any error would affect the dose calculation accuracy. In this study, the OF was measured with eight different small-field detectors for the 12 IRIS collimators at 800 mm SAD setup at 15 mm depth. The detectors used were PTW 31016 PinPoint 3D, IBA PFD shielded diode, IBA EFD unshielded diode, IBA SFD unshielded diode (stereotactic), PTW 60008 shielded diode, PTW 60012 unshielded diode, PTW 60018 unshielded diode (stereotactic), and PTW 60019 CVD diamond detector. OF was obtained after correcting for field output correction factors from IAEA TRS No. 483. The field OFs in CyberKnife are derived from the measured data by applying the correction factors from Table 23 in TRS 483 for the eight small field detectors. These field OFs matched within 2% of peer-reviewed published values. The range and standard deviation showed a decreasing trend with collimator diameter. The field OF obtained after applying the appropriate correction factor from TRS 483 matched well with the peer-reviewed published OFs. The inter-detector variation showed a decreasing trend with increasing collimator field size. This study gives physicists confidence in measuring field OFs while using small field detectors mentioned in this work.

High spatial resolution inorganic scintillator detector for high-energy X-ray beam at small field irradiation.

PurposeSmall field dosimetry for radiotherapy is one of the major challenges due to the size of most dosimeters, for example, sufficient spatial resolution, accurate dose distribution and energy dependency of the detector. In this context, the purpose of this research is to develop a small size scintillating detector targeting small field dosimetry and compare its performance with other commercial detectors.MethodAn inorganic scintillator detector (ISD) of about 200 µm outer diameter was developed and tested through different small field dosimetric characterizations under high‐energy photons (6 and 15 MV) delivered by an Elekta Linear Accelerator (LINAC). Percentage depth dose (PDD) and beam profile measurements were compared using dosimeters from PTW namely, microdiamond and PinPoint three‐dimensional (PP3D) detector. A background fiber method has been considered to quantitate and eliminate the minimal Cerenkov effect from the total optical signal magnitude. Measurements were performed inside a water phantom under IAEA Technical Reports Series recommendations (IAEA TRS 381 and TRS 483).ResultsSmall fields ranging from 3 × 3 cm2, down to 0.5 × 0.5 cm2 were sequentially measured using the ISD and commercial dosimeters, and a good agreement was obtained among all measurements. The result also shows that, scintillating detector has good repeatability and reproducibility of the output signal with maximum deviation of 0.26% and 0.5% respectively. The Full Width Half Maximum (FWHM) was measured 0.55 cm for the smallest available square size field of 0.5 × 0.5 cm2, where the discrepancy of 0.05 cm is due to the scattering effects inside the water and convolution effect between field and detector geometries. Percentage depth dose factor dependence variation with water depth exhibits nearly the same behavior for all tested detectors. The ISD allows to perform dose measurements at a very high accuracy from low (50 cGy/min) to high dose rates (800 cGy/min) and was found to be independent of dose rate variation. The detection system also showed an excellent linearity with dose; hence, calibration was easily achieved.ConclusionsThe developed detector can be used to accurately measure the delivered dose at small fields during the treatment of small volume tumors. The author's measurement shows that despite using a nonwater‐equivalent detector, the detector can be a powerful candidate for beam characterization and quality assurance in, for example, radiosurgery, Intensity‐Modulated Radiotherapy (IMRT), and brachytherapy. Our detector can provide real‐time dose measurement and good spatial resolution with immediate readout, simplicity, flexibility, and robustness.

Comparison of Hi-Art Tomotherapy Machine Outputs Using AAPM TG-148 and IAEA TRS 483 Codes of Practice

Comparison of Hi-Art Tomotherapy Machine Outputs using AAPM TG-148 and IAEA TRS 483 Codes of Practice. This paper describes a short history and technological aspect from a Hi-Art tomotherapy machine. The comparison between the tomotherapy machine and conventional linear accelerator machine in the technological aspect and therapy features was also described. There are two codes of practice to determinate the absorbed dose to water from the Hi-Art tomotherapy machine, The AAPM TG-148 and IAEA Technical Report Series No. 483. Determination of the absorbed dose to water was carried out at the machine specific reference condition by using the ionization chamber type of PTW TW 30013 SN 6367 volume 0.6 cc, and electrometer PTW Webline T10022/268. The results obtained show that the value of absorbed dose to water using the AAPM TG-148 was 8507 ± 2.4 mGy/minute and while using the IAEA TRS 483 the value of absorbed dose to water was 8485 ± 2.4 mGy/minute. The comparison result of the determination of the absorbed dose to water using AAPM TG-148 and IAEA TRS 483 protocol has a deviation of 0.2%.

Dosimetric response of fabricated Ge-doped optical fibres in computed tomography RQT beam quality x-ray beams

Novel germanium (Ge)-doped silica glass fibres tailor-made in Malaysia are fast gaining recognition as potential media for thermoluminescence (TL) dosimetry, with active research ongoing into exploitation of their various beneficial characteristics. Investigation is made herein of the capability of these media for use in diagnostic imaging dosimetry, specifically at the radiation dose levels typically obtained in conduct of Computed Tomography (CT). As a first step within such efforts, there is need to investigate the performance of the fibres using tightly defined spectra, use being made of a Philips constant potential industrial x-ray facility, Model MG165, located at the Malaysian Nuclear Agency Secondary Standards Dosimetry Lab (SSDL). Standard radiation beam qualities (termed RQT) have been established for CT, in accord with IEC 61267: 2003 and IAEA Technical Reports Series No. 457: 2007. A calibrated ionisation chamber has also been utilised, forming a component part of the SSDL equipment. The fabricated fibres used in this study are 2.3 mol% flat fibre (FF) of dimensions 643 × 356 μm2 and 2.3 mol% cylindrical fibre (CF) of 481 μm diameter, while the commercial fibre used is 4 mol% with core diameter of 50 μm. The dopant concentrations are nominal preform values. The fibres have been irradiated to doses of 20, 30 and 40 milligray (mGy) for each of the beam qualities RQT 8, RQT 9 and RQT 10. For x-rays generated at constant potential values from 100 to 150 kV, a discernible energy-dependent response is seen, comparisons being made with that of lithium fluoride (LiF) thermoluminescence dosimeters (TLD-100). TL yield versus dose has also been investigated for x-ray doses from 2 to 40 mGy, all exhibiting linearity. Compared to TLD-100, greater sensitivity is observed for the fibres.

Direct and indirect entrance surface dose measurement in X-ray diagnostics using nanoDot OSL dosimeters

This study investigated the suitability of nanoDot optically stimulated luminescence (OSL) dosimeters for entrance surface dose (ESD) measurements in common X-ray diagnostics. OSL dosimetry system supplied by Landauer Inc, (Glenwood, IL, USA) consisting of nanoDot OSL dosimeters and microStar reader were used. ESDs were measured with nanoDots placed on whole-body anthropomorphic phantom (for direct measurements) and in free air without backscatter material (for indirect measurements) in accordance with the IAEA Technical Report Series No. 457. Measurements were carried out in five X-ray projections including AP abdomen, AP chest, PA chest, AP thoracic spine and AP skull. The mean ESD for each projection was evaluated from multiple measurements with three different field sizes. Mean ESDs (direct measurements) for AP abdomen, AP chest, PA chest, AP thoracic spine and AP skull were 4.3 mGy, 0.7 mGy, 0.3 mGy, 6.8 mGy and 2.8 mGy respectively. While in the case of indirect measurements, the corresponding mean ESD values were 4.8 mGy, 0.7 mGy, 0.2 mGy, 7.2 mGy and 3.7 mGy respectively. The results were found to be within IAEA and European Commission (EC) diagnostic reference levels (DRLs) range. The percentage difference of the ESDs measured by direct and indirect methods in all projections were between 0 to 40%. It was affirmed that nanoDot OSL dosimeter is a good candidate for ESD measurement in common radiographic examinations, while taking into account the effect of energy dependence.

The transfer of fallout plutonium from paddy soil to rice: A field study in Japan

Reported transfer factor (TF) values of Pu from paddy soil to rice are rather scarce, despite the radiotoxicity of Pu and the irreplaceable role of rice in Asian peoples’ diets. Here, we conducted a field study to investigate the transfer of global fallout Pu from paddy soil to rice grain (hulled rice) in Japan. The 240Pu/239Pu atomic ratios in two rice grain samples out of 16 samples were determined and the ratios corresponded well with the global fallout value. The soil-to-rice TFPu in 12 Japanese prefectures ranged from 4.5 × 10−6 to 1.2 × 10−4 with a geometric mean of 3.3 × 10−5. The TFs of rice obtained in this study were compatible to the TFs for the broad heading “cereals” compiled in the IAEA Technical Report Series No. 472. Weak correlations were found between the TF and the investigated soil characteristics such as soil pH and loss on ignition. Regarding the TFs for cerium (Ce) and thorium (Th) which are commonly considered as Pu analogues, we observed no significant correlations between the log(TFPu) and log(TFCe) or log(TFPu) and log(TFTh). On the other hand, interestingly, a significantly positive correlation (r = 0.795, p < 0.001) was observed between log(TFPu) and log(TFU). In view of the observed similarity of TF values for U and Pu from soil to rice, we thought that using the easy-to-measure TFU to estimate TFPu from soil to rice might be suggested although the mechanism was unclear.

Development of a cell-laden 3D hydrogel scaffold assessing neuronal function through microelectrode array recordings

Reported transfer factor (TF) values of Pu from paddy soil to rice are rather scarce, despite the radiotoxicity of Pu and the irreplaceable role of rice in Asian peoples’ diets. Here, we conducted a field study to investigate the transfer of global fallout Pu from paddy soil to rice grain (hulled rice) in Japan. The 240Pu/239Pu atomic ratios in two rice grain samples out of 16 samples were determined and the ratios corresponded well with the global fallout value. The soil-to-rice TFPu in 12 Japanese prefectures ranged from 4.5 × 10−6 to 1.2 × 10−4 with a geometric mean of 3.3 × 10−5. The TFs of rice obtained in this study were compatible to the TFs for the broad heading “cereals” compiled in the IAEA Technical Report Series No. 472. Weak correlations were found between the TF and the investigated soil characteristics such as soil pH and loss on ignition. Regarding the TFs for cerium (Ce) and thorium (Th) which are commonly considered as Pu analogues, we observed no significant correlations between the log(TFPu) and log(TFCe) or log(TFPu) and log(TFTh). On the other hand, interestingly, a significantly positive correlation (r = 0.795, p < 0.001) was observed between log(TFPu) and log(TFU). In view of the observed similarity of TF values for U and Pu from soil to rice, we thought that using the easy-to-measure TFU to estimate TFPu from soil to rice might be suggested although the mechanism was unclear.

P265] Small field dosimetry comparison of 6 MV beam profiles aquired with diodesrs vs 0.125cc ionization chamber

Purpose Compare TPS calculated profiles based on 0.125 cc ionization chamber measurements for linac commissioning with beam profiles acquired using IAEA small beam recommendations with DiodeSRS. Methods At Eclipse™ 11.0 we calculated dose distribution for 2 × 2 cm, 3 × 3 cm and 4 × 4 cm MLC collimated fields at 100 cm SSD with AAA algorithm based on data acquired with 0.125cc PTW ionization chamber. Using TPS dose profile tool, we got the dose values at 10 cm depth. 2 × 2 cm, 3 × 3 cm and 4 × 4 cm MLC collimated field profiles with SSD = 100 cm at 10 cm depth, were acquired following IAEA Technical Reports Series N° 483, in water phantom using DiodeSRS PTW and Mephysto™ mc2 PTW. Transverse beam profiles were compared measuring the full with at half maximum (FWHM). Results For each field, we found a decrease in the FWHM between 2% and 10% for the DiodeSRS measurements. Conclusions Using the IAEA protocol for small field measurements we found that DiodeSRS detectors are more accurate measuring small field relative dosimetry. We intend to recommission our linac small fields according to IAEA report and evaluate the impact on our IMRT/VMAT plans quality assurance.

Neutronic modeling and calculations of the ETRR-2 MTR reactor using COMSOL multiphysics code

The second Egyptian Test and Research Reactor (ETRR-2) is a 22MWth light water cooled and moderated open pool multipurpose reactor, with isotope production, thermal neutron scattering, neutron activation and materials irradiation capabilities. COMSOL Multiphysics is powerful finite element computational tool with diversified physics and engineering applications, and coupling phenomena capabilities, a feature that is very attractive for simulating nuclear reactors as well as neutronics and thermal-hydraulics calculations. In this work, a full core, three-dimensional, multi-group model of ETRR-2 reactor is developed using detailed specifications and quality experimental data from IAEA Technical Report Series. This paper presents COMSOL-based neutronics calculations performed to study reactor physics parameters. The WIMS-D5 with 69-group neutron cross section library, was used to calculate the five-group constants for different reactor regions essential to solve the diffusion equations. The multi-group constants were applied in the COMSOL model to perform neutronics calculations using adaptive mesh refinement technique to increase the accuracy of the solution. The calculated effective multiplication factor (keff) for three specified cases compare well with experimental measurements. The study found a slight difference between the calculated $8.70 excess reactivity and the measured value of $9.11 for the core. The calculated reactivity worth of CR-1 at different positions, are in agreement with experimental measured values. The spectrums of thermal and fast fluxes were also calculated by the COMSOL model and are presented in this paper.

Full 3-D core calculations with refueling for the OPAL Research Reactor using Monte Carlo Code Serpent 2

Monte Carlo (MC) neutron transport codes have been extensively used for more than three decades to perform criticality calculations and to solve shielding problems due to their capability to model complex systems without major approximations. The irruption of affordable low-cost high performance computer resources in the last decade allows to consider some initially unexpected applications, such as full core burnup calculations or cell level modeling for few group parameters calculations. In this work the concern of the potential use of Monte Carlo codes to perform full 3-D calculations including burnup for a state of art Research Reactor is analyzed, regarding aspects related to accuracy, performance and resources requirements. For such purpose Serpent 2 v.1.24 Code, developed by VTT Technical Research Centre of Finland is used for full core burnup calculations of the 20MWth OPAL Research Reactor. This code is the second version of a brand-new Monte Carlo code designed to perform burn dependent cell-level and full 3-D core calculations using optimized schemes to diminish the computational effort. In past works the first version of Serpent Code was tested as a cell-level-code to model the MTR-type fuel assemblies from OPAL Research Reactor, obtaining fairly good results. Further works were developed for full 3-D models, where several parameters such as critical configurations, in-core thermal neutron flux profiles and effective delayed neutron parameters were obtained and compared to experimental data and other codes results, showing a very good performance. In the present work, a full 3-D model is developed using specifications and high quality experimental data from IAEA Technical Report Series. This model is used to perform full-core 3-D calculations including burnup and refueling for the first six operating cycles without the aim of an external calculation code. To perform such task, an ad hoc code to manipulate Serpent 2 restart files was developed in order to model the overall full core burnup problem without the help of any other calculation code. The results were compared with the experimental data available showing a very good agreement. Finally several aspects of the computational issues related with this modeling such performance, scalability and resources requirements are discussed, showing that the use of full core 3-D MC models including burnup for small cores represents nowadays a feasible alternative for specific calculations.

SPECTRUM WEIGHTED RESPONSES OF SEVERAL DETECTORS IN MIXED FIELDS OF FAST AND THERMAL NEUTRONS

The spectrum weighted responses of various detectors were calculated to provide guidance on the proper selection and use of survey instruments on the basis of their energy response characteristics on the neutron fields. To yield the spectrum weighted response, the detector response functions of 17 neutron-measuring devices were numerically folded with each of the produced calibration neutron spectra through the in-house developed software ‘K-SWR’. The detectors’ response functions were taken from the IAEA Technical Reports Series No. 403 (TRS-403). The reference neutron fields of 21 kinds with 2 spectra groups with different proportions of thermal and fast neutrons have been produced using neutrons from the 241Am-Be sources held in a graphite pile, a bare 241Am-Be source, and a DT neutron generator. Fluence-average energy (Eave) varied from 3.8 MeV to 16.9 MeV, and the ambient-dose-equivalent rate [H*(10)/h] varied from 0.99 to 16.5 mSv/h.

Fast neutron calibration fields constructed using a proton accelerator of KIRAMS and spectrumweighted response of various neutron detectors

This paper presents the dosimetric quantities, realistic neutron calibration fields and spectrum-weighted response (SWR) of several neutron-measuring devices to provide guidance to health physicists and dosimetry specialists on the proper selection and use of survey meters in neutron fields of varying energy spectra. To yield the SWR, the detector response functions of 17 neutron-measuring devices were numerically folded with each of the produced calibration neutron spectra through the in-house developed software 'K-SWR'. The detectors' response functions were taken from the IAEA Technical Reports Series No. 403. Eight kinds of calibration neutron fields with high energy and high dose rates were produced using a proton accelerator (MC50 cyclotron) of Korea Institute of Radiological and Medical Sciences (KIRAMS). The fluence-average energy (Eave) varied from 3.8 to 16.9 MeV, and the ambient-dose-equivalent rate [H(*)(10) h(-1)] varied from 0.99 to 16.5 mSv h(-1).

Concentration ratios of stable elements for selected biota in Japanese estuarine areas

For the estimation of radiation doses to organisms, concentration ratios (C ( R )s) of radionuclides are required. In the present study, C(R)s of various elements were obtained as analogues of radionuclides for algae, molluscs, and crustaceans, in eight estuarine areas around Japan. The elements measured were Na, Mg, K, Ca, V, Mn, Fe, Co, Ni, Cu, Rb, Sr, Y, Mo, Cd, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Pb, and U. The geometric mean (GM) values of C(R)s (GM-C(R)s) for alkali and alkaline earth elements, Mo, and U for all biota, as well as V for crustaceans, were less than 100 L/kg, while GM-C(R)s for the other elements were higher. When the obtained GM-C(R)s were compared with the C(R)s recommended in IAEA Technical Report Series 422 for marine organisms, no big differences between them were found; however, several elements (i.e. Cd and U for algae, Mn for molluscs, and Pb for crustaceans) were lower than the recommended C(R)s. In the present study, conversion factors (the ratio of C(R) for the whole body to that for muscle) for molluscs and crustaceans were also calculated, since data on edible parts of these organisms are generally available in the literature. For crustaceans, GM conversion factors of all the elements were more than one. For molluscs, GM conversion factors of rare earth elements and U were slightly higher than those for crustaceans, while GM conversion factors of the other elements were almost the same and less than 10. These results indicate that some elements tend to be concentrated in the internal organs of biota collected in the estuarine areas. For environmental radiological assessment, conversion factors from tissue to whole-body C(R) values are useful parameters.

Sediment-Water Distribution Coefficients of Stable Elements in Four Estuarine Areas in Japan

Sediment-water distribution coefficients (Kds) were obtained in estuarine areas of four A-class rivers in Japan. The total concentrations of stable elements and naturally occurring radionuclide (i.e., Na, Mg, K, Ca, V, Mn, Fe, Co, Ni, Cu, Rb, Sr, Y, Mo, Cd, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Pb, and U) in the estuarine water at each sampling point and in the corresponding sediment sample were measured. Kds of most of the elements varied within one order of magnitude regarding their differences between minimum and maximum values of each element at all the stations. However, a wide variation of Kds of Mn, Fe, Co, Cu, Rb, and La was observed. In addition, geometric means (GMs) of observed Kds were compared with the recommended values in the IAEA Technical Report Series 422 (TRS-422). The results showed that GMs of Kds for most of the elements agreed well with the recommended values, but GMs of Kds for Mn, Fe, and Cd were more than 10 times lower than the recommended values. The obtained Kd values could be important to investigate the behavior, transport, and fate of artificial radionuclide and to assess the radiological doses in estuarine areas.

Risks Associated with Low Doses and Low Dose Rates of Ionizing Radiation: Why Linearity May Be (Almost) the Best We Can Do

Deterministic and stochastic effects associated with high-dose ionizing radiation (x-ray) exposure have been known for almost as long as ionizing radiation itself (1–3). At lower doses, radiation risks are primarily stochastic effects, in particular, somatic effects (cancer) rather than the deterministic effects characteristic of higher-dose exposure (4–6). In contrast to deterministic effects, for stochastic effects, scientific committees generally assume that at sufficiently low doses there is a positive linear component to the dose response—that is, that there is no threshold (4–6). This does not preclude there being higher-order (eg, quadratic) powers of dose in the dose response that may be of importance at higher doses. It is on this basis that models linear (or linear-quadratic) in dose are often used to extrapolate the experience of the Japanese atomic bomb survivors (who were typically exposed at a high dose rate to moderate doses [average, 0.1 Sv]) to estimate risks from low doses and low dose rates (4–6). Most population-based cancer risk estimates are based primarily on the Japanese atomic bomb survivor Life Span Study (LSS) cohort data (4–6). However, evidence of excess risks comes from a large number of other studies as well. In the parallel editorial (7), evidence is presented for possible real (or at least “practical”) thresholds or “hormetic” (beneficial) effects of low doses of ionizing radiation. As we summarize here, and in contrast to the arguments of Tubiana et al (7), we judge that there is little epidemiologic or biologic evidence for these for cancer. The arguments are of three forms: (a) assessment of the degree of curvature in the cancer dose response within the Japanese atomic bomb survivors and other exposed groups (in particular, departure from linear or linear-quadratic curvature), (b) consistency of risks between the Japanese and other moderate- and low-dose cohorts, and (c) assessment of biologic data on mechanisms. Most of the information on radiation-induced cancer risk comes from (a) the Japanese atomic bomb survivors, (b) medically exposed populations, (c) occupationally exposed groups, and (d) environmentally exposed groups (6). In the higher-dose radiation therapy studies, where doses received are very much higher than in the LSS, sometimes in the range at which cell sterilization occurs, excess cancer risks per unit dose tend to be less than in comparable subsets of the LSS (8,9). However, as we show, risks in moderate- and low-dose medically and occupationally exposed groups are generally consistent with those in the LSS.

Influence of crop types and soil properties on radionuclide soil-to-plant transfer factors in tropical and subtropical environments

This paper presents a descriptive statistical analysis of radionuclide soil-to-plant transfer factors ( Fv ) for tropical and subtropical environments. These values were collected from previous databases and standard publications with the objective of contributing to the IAEA Technical Report Series: Handbook of parameter values for the prediction of radionuclide transfer to humans in terrestrial and freshwater environments. More than 2200 Fv values of different radionuclides were gathered and arranged into specific databases, detailing relevant information regarding the environments where this parameter was calculated. This study explores the dependence of Fv values to crop types, and soil properties. The wide variability and uncertainty observed in calculated Fv values were considerably reduced when the data was independently grouped into clusters containing the same radionuclide/plant group/soil type combinations. For each cluster the principal statistical quantities were determined. Using these quantities, the Fv distributions of each data set was explored. Fv probability distribution is discussed to clarify the use of this empirical parameter in radioecological and radiological assessment models.