European measurements of aircraft crew exposure to cosmic radiation

For more than 5 y, the European Commission has supported research into scientific and technical aspects of cosmic-ray dosimetry at flight altitudes in civil radiation. This has been in response to legislation to regard exposure of aircraft crew as occupational, following the recommendations of the International Commission on Radiological Protection in Publication 60. The response to increased public interest and concern, and in anticipation of European and national current work, within a total of three multi-national, multi-partner research contracts, is based on a comprehensive approach including measurements with dosimetric and spectrometric instruments during flights, at high-mountain altitudes, and in a high-energy radiation reference field at CERN, as well as cosmic-ray transport calculations. The work involves scientists in the fields of neutron physics, cosmic-ray physics, and general dosimetry. A detailed set of measurements has been obtained by employing a wide range of detectors on several routes, both on subsonic and supersonic aircraft. Many of the measurements were made simultaneously by several instruments allowing the intercomparison of results. This paper presents a brief overview of results obtained. It demonstrates that the knowledge about radiation fields and on exposure data has been substantially consolidated and that the available data provide an adequate basis for dose assessments of aircraft crew, which will be legally required in the European Union after 13 May 2000.     

A technical basis for the continued use of exposure as an acceptable operational quantity in radiation protection

Within the tabulated values of the new [to U.S. Department of Energy (DOE)] radiation weighting factors, it can be seen that a doubling of the neutron factor occurs for the 0.1 to 2 MeV neutron energy range. Hence, with the effective replacement of the quality factor by these new radiation weighting factors (for the protection quantities), it has been widely understood that the new changes will most definitely impact neutron dosimetry. However, it is less well understood that the new changes could also affect photon (and beta) dosimetry, i.e., photon reference fields, instrument design, and instrument calibrations. This paper discusses the ramifications, and ultimately concludes that the use of exposure for workplace measurements complies with both current and amended DOE requirements.     

Nuclear accident dosimetry intercomparison studies

Twenty-two nuclear accident dosimetry intercomparison studies utilizing the fast-pulse Health Physics Research Reactor at the Oak Ridge National Laboratory have been conducted since 1965. These studies have provided a total of 62 different organizations a forum for discussion of criticality accident dosimetry, an opportunity to test their neutron and gamma-ray dosimetry systems under a variety of simulated criticality accident conditions, and the experience of comparing results with reference dose values as well as with the measured results obtained by others making measurements under identical conditions. Sixty-nine nuclear accidents (27 with unmoderated neutron energy spectra and 42 with eight different shielded spectra) have been simulated in the studies. Neutron doses were in the 0.2-8.5 Gy range and gamma doses in the 0.1-2.0 Gy range. A total of 2,289 dose measurements (1,311 neutron, 978 gamma) were made during the intercomparisons. The primary methods of neutron dosimetry were activation foils, thermoluminescent dosimeters, and blood sodium activation. The main methods of gamma dose measurement were thermoluminescent dosimeters, radiophotoluminescent glass, and film. About 68% of the neutron measurements met the accuracy guidelines (+/- 25%) and about 52% of the gamma measurements met the accuracy criterion (+/- 20%) for accident dosimetry.     

Characterization of a new commercial single crystal diamond detector for photon- and proton-beam dosimetry

A synthetic single crystal diamond detector (SCDD) is commercially available and is characterized for radiation dosimetry in various radiation beams in this study. The characteristics of the commercial SCDD model 60019 (PTW) with 6- and 15-MV photon beams, and 208-MeV proton beams, were investigated and compared with the pre-characterized detectors: Semiflex (model 31010) and PinPoint (model 31006) ionization chambers (PTW), the EDGE diode detector (Sun Nuclear Corp) and the SFD Stereotactic Dosimetry Diode Detector (IBA). To evaluate the effects of the pre-irradiation, the diamond detector, which had not been irradiated on the day, was set up in the water tank, and the response to 100 MU was measured every 20 s. The depth–dose and profiles data were collected for various field sizes and depths. For all radiation types and field sizes, the depth–dose data of the diamond chamber showed identical curves to those of the ionization chambers. The profile of the diamond detector was very similar to those of the EDGE and SFD detectors, although the Semiflex and PinPoint chambers showed volume-averaging effects in the penumbrae region. The temperature dependency was within 0.7% in the range of 4–41°C. A dose of 900 cGy and 1200 cGy was needed to stabilize the chamber to the level within 0.5% and 0.2%, respectively. The PTW type 60019 SCDD detector showed suitable characteristics for radiation dosimetry, for relative dose, depth–dose and profile measurements for a wide range of field sizes. However, at least 1000 cGy of pre-irradiation will be needed for accurate measurements.     

Extremity dose: its definition, standards and regulatory limits, radiobiological significance, measurement and practical considerations

This paper reviews several inter-related aspects of partial-body exposures to ionizing radiation, with particular emphasis on hands. The topics featured in this review are: the definition of extremity, the radiobiological significance of extremity dose and its influence on dose standards, current and future dose standards and regulatory limits, monitoring requirements along with the availability and selection of suitable dosimeters, the question of dose averaging and dosimeter placement and practical considerations for the implementation of an extremity dosimetry program. The review is purposely kept general in nature and readers with a specific interest in a particular aspect are encouraged to read the original papers. This review is written from the perspective of a practicing health physicist who may wish to read the available literature on this topic and incorporate some of the information into an existing or planned extremity dosimetry program.     

Characteristics of the neutron field in the KEK counter hall

We have measured the neutron leakage spectra outside the shielding in the KEK counter hall using a multisphere technique supplemented by the 12C(n, 2n)11C reaction in a carbon activation detector. The neutron spectra were derived from the measurements using the LOUHI78 unfolding code. The shape of these unfolded neutron spectra matched very closely that of spectra calculated by O'Brien and McLaughlin. A comparison of the dose equivalent as derived from the spectra with that measured by a neutron dose equivalent meter confirmed that the dose equivalent meter measurements usually underestimate the dose equivalent by at least 30%.     

用于环境辐射水平监测的热释光测量系统的质量控制

目的 探讨热释光测量系统的质量控制方法,验证热释光测量系统能否准确有效的用于环境辐射水平监测。方法 采取的环境辐射监测用热释光测量系统质量控制方法包括热释光测量系统的稳定性检验、热释光探测器的分散性筛选、测量结果不确定度评定,并与高气压电离室测量方法进行对比。结果 读出器预热及测读过程中光源系数变化范围在0.070～0.073,稳定性符合使用要求;热释光探测器的χ²值为2.088,服从正态分布;热释光测量系统满足非线性响应、变异系数和能量响应的计量要求;热释光累积剂量测量结果与高气压电离室相比偏差最大-6.58%。结论 本实验室采取的质控措施可作为同类热释光测量系统的质控措施的参考;本实验室的热释光测量系统通过了各项检验,满足环境辐射累积剂量监测的使用要求。     

Pre-litigation strategies--gathering and preserving documentary evidence.

Radiation injury claims may arise under various legal theories. In addition, plaintiffs may advance such claims within different jurisdictional venues, such as federal and state courts and workers' compensation boards. Irrespective of the jurisdiction or the legal theory underlying the claim, one element remains common to these claims--the quality and quantity of the evidence. While many different pieces of evidence may be needed to litigate a radiation injury claim, the most important evidence for the investigating health physicist is that which establishes the nature and extent of radiation exposure. Most radiation injury claims are associated with late radiation injury, often an allegation of radiation-induced cancer. Because radiation-induced cancers have a long latency period, claims may not arise for years, or even decades, after exposure. Therefore, the immediate challenge to the health physicist, who investigates an exposure, is to avoid the temptation of a "wait and see" approach to gathering evidence. Not only may evidence be short-lived in nature, but with the passage of time memories grow dim and witnesses may become unavailable. Prompt and thorough gathering of pertinent evidence likely will be a determining factor in the outcome of any radiation injury claim. Although ensuring the availability of all pertinent evidence is the key role of the investigating health physicist, he or she also can help to ensure that the evidence does not inadvertently become inadmissible in a court of law, for example, under the hearsay rule. To ensure that the necessary evidence is available in admissible form, the task of gathering evidence should be systematically approached using a pre-established process that reflects a basic understanding of the rules of evidence. Such a process is discussed here.     

Requirements for radiation oncology physics in Australia and New Zealand

This Position Paper reviews the role, standards of practice, education, training and staffing requirements for radiation oncology physics. The role and standard of practice for an expert in radiation oncology physics, as defined by the ACPSEM, are consistent with the IAEA recommendations. International standards of safe practice recommend that this physics expert be authorised by a Regulatory Authority (in consultation with the professional organization). In order to accommodate the international and AHTAC recommendations or any requirements that may be set by a Regulatory Authority, the ACPSEM has defined the criteria for a physicist-in-training, a base level physicist, an advanced level physicist and an expert radiation oncology physicist. The ACPSEM shall compile separate registers for these different radiation oncology physicist categories. What constitutes a satisfactory means of establishing the number of physicists and support physics staff that is required in radiation oncology continues to be debated. The new ACPSEM workforce formula (Formula 2000) yields similar numbers to other international professional body recommendations. The ACPSEM recommends that Australian and New Zealand radiation oncology centres should aim to employ 223 and 46 radiation oncology physics staff respectively. At least 75% of this workforce should be physicists (168 in Australia and 35 in New Zealand). An additional 41 registrar physicist positions (34 in Australia and 7 in New Zealand) should be specifically created for training purposes. These registrar positions cater for the present physicist shortfall, the future expansion of radiation oncology and the expected attrition of radiation oncology physicists in the workforce. Registrar physicists shall undertake suitable tertiary education in medical physics with an organised in-house training program. The rapid advances in the theory and methodology of the new technologies for radiation oncology also require a stringent approach to maintaining a satisfactory standard of practice in radiation oncology physics. Appropriate on-going education of radiation oncology physicists as well as the educating of registrar physicists is essential. Institutional management and the ACPSEM must both play a key role in providing a means for satisfactory staff tuition on the safe and expert use of existing and new radiotherapy equipment.     

Use of water-equivalent plastic scintillator for intravascular brachytherapy dosimetry

Beta irradiation has recently been investigated as a possible technique for the prevention of restenosis in intravascular brachytherapy after balloon dilatation or stent implantation. Present methods of beta radiation dosimetry are primarily conducted using radiochromic film. These film dosimeters exhibit limited sensitivity and their characteristics differ from those of tissue, therefore the dose measurement readings require correction factors to be applied. In this work a novel, mini-size (2 mm diameter by 5 mm long) dosimeter element fabricated from Organic Plastic Scintillator (OPS) material was employed. Scintillation photon detection is accomplished using a precision photodiode and innovative signal amplification and processing techniques, rather than traditional photomultiplier tube methods. A significant improvement in signal to noise ratio, dynamic range and stability is achieved using this set-up. In addition, use of the non-saturating organic plastic scintillator material as the detector enables the dosimeter to measure beta radiation at very close distances to the source. In this work the plastic scintillators have been used to measure beta radiation dose at distances of less than 1 mm from an Sr-90 cardiovascular brachytherapy source having an activity of about 2.1 GBq beta radiation levels for both depth-distance and longitudinal profile of the source pellet chain, both in air and in liquid water, are measured using this system. The data obtained is compared with results from Monte Carlo simulation technique (MCNP 4B). Plastic scintillator dosimeter elements, when used in conjunction with photodiode detectors may prove to be useful dosimeters for cardiovascular brachytherapy beta sources, or other applications where precise near-source field dosimetry is required. The system described is particularly useful where measurement of actual dose rate in real time, a high level of stability and repeatability, portability, and immediate access to results are prime requirements.     

Determination of neutron spectra in a MOX plant for the qualification of the BD-PND bubble detector

As a result of the introduction of the ICRP 60 recommendations and the increasing contribution of the neutron dose to the total dose of the personnel at the Belgonucleaire Mox fuel fabrication plant, the BD-PND bubble detector manufactured by Bubble Technology industries was introduced as a new, reliable personal neutron dosimeter. In the framework of the evaluation program of the bubble detector, measurements and calculations of the neutron spectra in the installations of the fuel fabrication plant were performed. The measurements were carried out with a ROSPEC neutron spectrometer, and the calculations were performed by means of the Monte Carlo code MCNP 4A. Comparison between measurements and calculations revealed good agreement. On the basis of the obtained neutron spectra, a correction factor was determined to take into account the new ICRP 60 recommendations and the difference between the calibration spectrum of the bubble detectors and the observed neutron spectra at the plant. This correction factor was applied to the calibration factor provided by Bubble Technology Industries.     

Operational health physics

A review of the operational health physics papers published in Health Physics and Operational Radiation Safety over the past fifteen years indicated seventeen general categories or areas into which the topics could be readily separated. These areas include academic research programs, use of computers in operational health physics, decontamination and decommissioning, dosimetry, emergency response, environmental health physics, industrial operations, medical health physics, new procedure development, non-ionizing radiation, radiation measurements, radioactive waste disposal, radon measurement and control, risk communication, shielding evaluation and specification, staffing levels for health physics programs, and unwanted or orphan sources. That is not to say that there are no operational papers dealing with specific areas of health physics, such as power reactor health physics, accelerator health physics, or governmental health physics. On the contrary, there have been a number of excellent operational papers from individuals in these specialty areas and they are included in the broader topics listed above. A listing and review of all the operational papers that have been published is beyond the scope of this discussion. However, a sampling of the excellent operational papers that have appeared in Health Physics and Operational Radiation Safety is presented to give the reader the flavor of the wide variety of concerns to the operational health physicist and the current areas of interest where procedures are being refined and solutions to problems are being developed.     

Operational health physics

A review of the operational health physics papers published in Health Physics and Operational Radiation Safety over the past fifteen years indicated seventeen general categories or areas into which the topics could be readily separated. These areas include academic research programs, use of computers in operational health physics, decontamination and decommissioning, dosimetry, emergency response, environmental health physics, industrial operations, medical health physics, new procedure development, non-ionizing radiation, radiation measurements, radioactive waste disposal, radon measurement and control, risk communication, shielding evaluation and specification, staffing levels for health physics programs, and unwanted or orphan sources. That is not to say that there are no operational papers dealing with specific areas of health physics, such as power reactor health physics, accelerator health physics, or governmental health physics. On the contrary, there have been a number of excellent operational papers from individuals in these specialty areas and they are included in the broader topics listed above. A listing and review of all the operational papers that have been published is beyond the scope of this discussion. However, a sampling of the excellent operational papers that have appeared in Health Physics and Operational Radiation Safety is presented to give the reader the flavor of the wide variety of concerns to the operational health physicist and the current areas of interest where procedures are being refined and solutions to problems are being developed.     

A method of obtaining neutron dose and dose equivalent from digital measurements and analysis of recoil-particle tracks

The feasibility of a digital approach to neutron dosimetry has been investigated. Such an approach uses an ionization detector capable of measuring the numbers of electrons produced within various subvolumes of a chamber gas along a charged-particle track. In addition, a computer algorithm is used to infer absorbed dose, LET, and dose equivalent given this digital track-structure information for each event. This paper describes one detector design capable of providing digital track-structure information and discusses examples of proton and C-ion tracks calculated from a Monte Carlo charged-particle transport code. The associated computer algorithm is presented next with its verification accomplished by running a variety of recoil particles through a simulated detector volume and comparing the resulting average energy deposition and dose equivalent to those unfolded by the algorithm.     

Neutron discrepancies in the DS86 Hiroshima dosimetry system.

More than a decade has passed since a complete revision was initiated of the radiation doses received by survivors of the Hiroshima and Nagasaki atomic bombings. The new dosimetry system (DS86) was completed in 1986 and adopted shortly thereafter. Overall, DS86 was noted to be a clear improvement over the old dosimetry system. However, based on limited validation measurements, troublesome inconsistencies were suggested for neutrons. Since 1986, a substantial number of additional neutron activation measurements have been made in mineral and metal samples from Hiroshima. Importantly, a large number of measurements have now been made at distances beyond 1 km. Here, inconsistencies between neutron activation measurements and DS86 calculations for Hiroshima are examined using all available measurement data, including new measurements for 36Cl which extend the measurement range to more than 1.7 km from the epicenter, and Monte Carlo modeling calculations for each sample measured. Results show that thermal neutron activation measured beyond approximately 1 km in Hiroshima (at distances most relevant for radiation-risk evaluation) is two to 10, or more, times higher than that calculated based on DS86. Similar trends observed when comparing results by several independent measurement laboratories, using different analytical methods, suggest that the DS86 calculations for low-energy neutrons are in error. Because of the importance of the Hiroshima data in radiation risk evaluation, this large discrepancy is in need of resolution.     

Prematurely condensed chromosome rings after neutron irradiation of human lymphocytes

Calibration curves for fission spectrum neutrons and other high LET radiations are scarce in cytogenetic dosimetry and particularly for Prematurely Condensed Chromosome Rings (PCC-ring). Here we analyzed the behavior of the PCC-ring frequency and PCC index after neutron irradiation in a broad dose interval from 1 to 26 Gy. PCC-rings were induced in lymphocytes with Calyculin A. 6455 PCC cells in G1, G2/M and M/A stages were analyzed. The best fitting between the frequency of PCC ring (Y) and the Dose (D) was obtained with the equation Y = (0.059 ± 0.003) D. The saturation of the PCC-ring was observed after around 4 Gy, but it was still possible to analyze cells exposed up to 26 Gy. The distribution of rings by cell follows Poisson or Neyman type distribution for all doses. This PCC-ring dose effect curve can be used in case of accidental overexposure to neutron radiation, allowing a dose assessment in a reliable way. Additionally, the PCC index seems to be well correlated with radiation dose and decrease in a dose dependent manner from 13% in non exposed sample down to 0.2%. This observation allows the possibility to perform a quick classification of victims exposed to high doses of both gamma and neutron radiations. The PCC assay can then be used for both neutron dose estimation up to 4 Gy and for the rapid classification of victims exposed to higher doses. This assay could be included in the multiparametric approach developed to optimize the medical treatment of radiation victims.     

CT所致受检者个体化器官剂量的研究进展

CT检查所引发的辐射风险备受关注,器官剂量被认为是量化受检者辐射剂量和评估风险的最有意义的技术参数。目前获取CT所致受检者器官剂量的方法主要包括：物理模体测量法、人体直接测量法、剂量转换系数法、蒙特卡罗模拟法、剂量计算软件法等。尽管不同的方法各有其特点和应用情形,但受检者器官剂量的个体化始终是辐射防护与剂量学研究所追求的目标。基于人工智能的个体化建模和GPU蒙卡仿真使得受检者器官剂量个体化计算成为可能,而基于CT探测器信号的受检者器官剂量反推则为受检者器官剂量的个体化研究提供了新的解决方案。     

F:\DOCS\DOCS--physicians and automation

While a paperless system may not be commonplace today, strides are being taken by groups such as CPRI to ensure the development of such a system. Several hospitals and clinics are moving toward or have implemented paperless or limited paper environments using patient-centered systems where charting is performed at the "bedside" of the patient through sophisticated software and hardware systems. Such systems will continue to evolve until the ATM of patient care is created. At that time, patients' access to their own information will be an acceptable phenomenon, physician use of computers will be commonplace, acceptance that adjunct knowledge bases must be coupled with the human skills of the physician, and test redundancy will be considered intolerable. These steps will contribute to the cost reductions needed to truly "reform" health care and create a value-added product for the United States.     

Dose verification of eye plaque brachytherapy using spectroscopic dosimetry

Eye plaque brachytherapy has been developed and refined for the last 80 years, demonstrating effective results in the treatment of ocular malignancies. Current dosimetry techniques for eye plaque brachytherapy (such as TLD- and film-based techniques) are time consuming and cannot be used prior to treatment in a sterile environment. The measurement of the expected dose distribution within the eye, prior to insertion within the clinical setting, would be advantageous, as any errors in source loading will lead to an erroneous dose distribution and inferior treatment outcomes. This study investigated the use of spectroscopic dosimetry techniques for real-time quality assurance of I-125 based eye plaques, immediately prior to insertion. A silicon detector based probe, operating in spectroscopy mode was constructed, containing a small (1 mm³) silicon detector, mounted within a ceramic holder, all encapsulated within a rubber sheath to prevent water infiltration of the electronics. Preliminary tests of the prototype demonstrated that the depth dose distribution through the central axis of an I-125 based eye plaque may be determined from AAPM Task Group 43 recommendations to a deviation of 6 % at 3 mm depth, 7 % at 5 mm depth, 1 % at 10 mm depth and 13 % at 20 mm depth, with the deviations attributed to the construction of the probe. A new probe design aims to reduce these discrepancies, however the concept of spectroscopic dosimetry shows great promise for use in eye plaque quality assurance in the clinical setting.     

Rational risk estimation in relation to atomic bomb radiation

This paper summarizes genetic and somatic data on persons exposed to low doses of atomic bomb radiation in Hiroshima and Nagasaki. Compared with experimental estimates, the new dosimetry system proposed in 1986 underestimates neutron doses, supporting qualitatively the conclusion by the 1965 dosimetry system that Nagasaki A-bomb emitted predominantly gamma rays whereas Hiroshima A-bomb emitted both gamma rays and fast neutrons. A theory based on two recessive mutations in hemopoietic stem cells is proposed to explain radiation leukemogenesis. The theory can explain, at least partly, the actual dose-response curve for incidences of acute leukemia in Hiroshima but cannot explain chronic leukemia in Nagasaki. Existence of a large threshold dose in the latter's dose relationship supports the hypothesis that A-bomb radiation at high doses above a threshold value was a promoter and/or progressor of leukemia. Various lines of evidence that support this hypothesis are presented. Hence, it is not warranted to assume that risk of death from cancer at a high dose, say, 1 Gy can be divided by 100 to obtain the risk at 1 cGy. Risk at low doses should be assessed by direct scrutiny of actual data at low doses in spite of their large statistical uncertainty. Actual data show that A-bomb survivors at 1-9 cGy had apparently lower incidences of tumors than unexposed persons.