Development of health-based exposure limits for radiofrequency radiation from wireless devices using a benchmark dose approach.

BACKGROUND: Epidemiological studies and research on laboratory animals link radiofrequency radiation (RFR) with impacts on the heart, brain, and other organs. Data from the large-scale animal studies conducted by the U.S. National Toxicology Program (NTP) and the Ramazzini Institute support the need for updated health-based guidelines for general population RFR exposure. OBJECTIVES: The development of RFR exposure limits expressed in whole-body Specific Absorption Rate (SAR), a metric of RFR energy absorbed by biological tissues. METHODS: Using frequentist and Bayesian averaging modeling of non-neoplastic lesion incidence data from the NTP study, we calculated the benchmark doses (BMD) that elicited a 10% response above background (BMD10) and the lower confidence limits on the BMD at 10% extra risk (BMDL10). Incidence data for individual neoplasms and combined tumor incidence were modeled for 5% and 10% response above background. RESULTS: Cardiomyopathy and increased risk of neoplasms in male rats were the most sensitive health outcomes following RFR exposures at 900 MHz frequency with Code Division Multiple Access (CDMA) and Global System for Mobile Communications (GSM) modulations. BMDL10 for all sites cardiomyopathy in male rats following 19 weeks of exposure, calculated with Bayesian model averaging, corresponded to 0.27-0.42 W/kg whole-body SAR for CDMA and 0.20-0.29 W/kg for GSM modulation. BMDL10 for right ventricle cardiomyopathy in female rats following 2 years of exposure corresponded to 2.7-5.16 W/kg whole-body SAR for CDMA and 1.91-2.18 W/kg for GSM modulation. For multi-site tumor modeling using the multistage cancer model with a 5% extra risk, BMDL5 in male rats corresponded to 0.31 W/kg for CDMA and 0.21 W/kg for GSM modulation. CONCLUSION: BMDL10 range of 0.2-0.4 W/kg for all sites cardiomyopathy in male rats was selected as a point of departure. Applying two ten-fold safety factors for interspecies and intraspecies variability, we derived a whole-body SAR limit of 2 to 4 mW/kg, an exposure level that is 20-40-fold lower than the legally permissible level of 0.08 W/kg for whole-body SAR under the current U.S. regulations. Use of an additional ten-fold children's health safety factor points to a whole-body SAR limit of 0.2-0.4 mW/kg for young children.

Long-term experience and analysis of data on diagnostic reference levels: the good, the bad, and the ugly.

OBJECTIVES: To analyze 11-year data of France for temporal trends in dose indices and dose optimization and draw lessons for those who are willing to work on creation and update of diagnostic reference levels (DRLs). METHODS: The data from about 3000 radiology departments leading to about 750,000 imaging exams between 2004 and 2015 was analyzed, and patterns of reductions in dose for those below and above the DRLs were estimated and correlated with technology change. RESULTS: Dose optimization achieved was important and significant in departments which were above or just below the DRL (p = .006) but not in those which were around half of the DRL values. The decrease in 75th percentile value of Kerma air product (KAP) for chest radiography by 27.4% between 2004 and 2015 was observed with the number of flat panel detectors increase from 6 to 43%. A good correlation between the detector type distribution and the level of patient radiation exposure is observed. Otherwise, setting DRLs for standard-sized patient excludes patients lower and higher weighted than "standard." CONCLUSIONS: The concept of DRL may become obsolete unless lessons drawn from the experience of users are taken into account. While establishing DRLs should be part of the regulations, setting up and updating values should be governed by bodies whose decision-making cycle is short, at the most 1 year. A local rather than national approach, taking into account body habitus and image quality, needs to be organized. KEY POINTS: • The technology changes faster than regulations. Requirement of DRL establishment should be part of the regulations; however, setting and updating values should be the role of professional societies. • The concept of DRL, highlighting the 75th percentile values and dedicated to standard-sized adult, misses optimization opportunities in the majority of patients who are below the 75th percentile value and outside the range of standard-sized adult. • The ugly aspects of the DRL concept include its non-applicability to individuals, no customization to clinical indications, and lack of consideration of image quality.

National Diagnostic Reference Levels for Endovascular Aneurysm Repair and Optimisation Strategies.

OBJECTIVE: The International Commission on Radiological Protection (ICRP) has highlighted the large number of medical specialties using fluoroscopy outside imaging departments without programmes of radiation protection (RP) for patients and staff. Vascular surgery is one of these specialties and endovascular aneurysm repair (EVAR) is one of the most challenging procedures requiring RP guidance and optimisation actions. The recent European Directive on Basic Safety Standards requires the use and regular update of diagnostic reference levels (DRL) for interventional procedures. The objective of the study was to know the doses of patients undergoing EVAR with mobile Xray systems and with hybrid rooms (fixed Xray systems), to obtain national DRLs and suggest optimisation actions. METHODS: The Spanish Chapter of Endovascular Surgery launched a national survey that involved hospitals for 10 autonomous communities representing the 77% of the Spanish population (46.7 million inhabitants). Patient dose values from mobile Xray systems were available from nine hospitals (sample of 165 EVAR procedures) and data from hybrid rooms, from seven hospitals, with dosimetric data from 123 procedures. The initial national DRLs have been obtained, as the third quartile of the median values from the different centres involved in the survey. RESULTS: The proposed national DRLs are 278 Gy cm2 for hybrid rooms and 87 Gy cm2 for mobile Xray systems, and for cumulative air kerma (cumulative AK) at the patient entrance reference point, 1403 mGy for hybrid rooms, and 292 mGy for mobile systems. CONCLUSION: An audit of patient doses for EVAR procedures to identify optimised imaging protocol strategies is needed. It is also appropriate to evaluate the diagnostic information required for EVAR procedures. The increase by a factor of 3.2 (for kerma area product) and 4.8 (for cumulative AK) in the DRLs needs to be justified when the procedures are performed in the hybrid rooms rather than with mobile Xray systems.

A model for in situ plan of care for a critically unstable pediatric patient following I-131 MIBG infusion.

Recent clinical trials have moved iodine-131 (I-131) metaiodobenzylguanidine (MIBG) therapy into frontline management of high-risk neuroblastoma. With this expansion, it is reasonable to anticipate the need for intensive care level resuscitations. Radiation exposure remains the greatest risk to health care professionals managing these patients. We combined shock simulation scenario data with actual radiation dosimetry data to create a care model allowing for aggressive, prolonged in situ resuscitation of a critically ill pediatric patient after I-131 MIBG administration. This model will maintain a critical care provider's radiation level below 10% of the annual occupational dose limit (5 mSv, 500 mrem) per patient managed.

Setting Guidelines for Electromagnetic Exposures and Research Needs.

Current limits for exposures to nonionizing electromagnetic fields (EMF) are set, based on relatively short-term exposures. Long-term exposures to weak EMF are not addressed in the current guidelines. Nevertheless, a large and growing amount of evidence indicates that long-term exposure to weak fields can affect biological systems and might have effects on human health. If they do, the public health issues could be important because of the very large fraction of the population worldwide that is exposed. We also discuss research that needs to be done to clarify questions about the effects of weak fields. In addition to the current short-term exposure guidelines, we propose an approach to how weak field exposure guidelines for long-term exposures might be set, in which the responsibility for limiting exposure is divided between the manufacturer, system operator, and individual being exposed. Bioelectromagnetics. © 2020 Bioelectromagnetics Society.

Dose limits for occupational exposure to ionising radiation and genotoxic carcinogens: a German perspective.

This paper summarises the view of the German Commission on Radiological Protection ("Strahlenschutzkommission", SSK) on the rationale behind the currently valid dose limits and dose constraints for workers recommended by the International Commission on Radiological Protection (ICRP). The paper includes a discussion of the reasoning behind current dose limits followed by a discussion of the detriment used by ICRP as a measure for stochastic health effects. Studies on radiation-induced cancer are reviewed because this endpoint represents the most important contribution to detriment. Recent findings on radiation-induced circulatory disease that are currently not included in detriment calculation are also reviewed. It appeared that for detriment calculations the contribution of circulatory diseases plays only a secondary role, although the uncertainties involved in their risk estimates are considerable. These discussions are complemented by a review of the procedures currently in use in Germany, or in discussion elsewhere, to define limits for genotoxic carcinogens. To put these concepts in perspective, actual occupational radiation exposures are exemplified with data from Germany, for the year 2012, and regulations in Germany are compared to the recommendations issued by ICRP. Conclusions include, among others, considerations on radiation protection concepts currently in use and recommendations of the SSK on the limitation of annual effective dose and effective dose cumulated over a whole working life.

Radiation exposure in the treatment of pediatric supracondylar humerus fractures.

PURPOSE: To determine the factors that influence radiation exposure during repair of supracondylar humerus fractures. METHODS: Medical records of almost 200 children with supracondylar fractures were retrospectively analyzed for variables correlated with fluoroscopy time and radiation dose as measures of radiation exposure. RESULTS: There was no statistically significant difference in fluoroscopy time (27 vs. 22 s p = 0.345) or direct radiation dose (0.394 vs. 0.318 mSv p = 0.290) between uniplanar and biplanar C-arm use. No statistically significant differences in fluoroscopy time or radiation dose were found for surgical technique, comorbid ipsilateral fractures, preoperative neurovascular compromise, or resident participation. There was a significant 8.3 s increase in fluoroscopy time (p = 0.022) and 0.249 mSv increase in radiation dose (p = 0.020) as the fracture type increased from II to III. An increase in one pin during CRPP resulted in a statistically significant 10.4 s increase in fluoroscopy time and a 0.205 mSv increase in radiation dose. There were significant differences between the physician with the lowest fluoroscopy time and radiation dose compared with the physicians with the two highest values for both fluoroscopy time and radiation dose (p < 0.01). CONCLUSIONS: We found no significant difference in direct radiation exposure or fluoroscopy time when comparing biplanar to uniplanar C-arm use, resident participation, preoperative neurovascular compromise, or for comorbid ipsilateral fractures. Both outcomes increased significantly as fracture type increased from II to III and as the number of pins used during CRPP increased. Both outcomes were significantly different between the surgeons performing CRPP.

Temporal evolution of activation products in a zircaloy-4 guide tube and the estimation of its external gamma dose rate for decommissioning activities.

The dismantling of structural objects during the decommissioning of nuclear facilities needs radioactive source characterisation for the planning of decommissioning strategies in compliance with the ALARA (as low as reasonably achievable) principle. The sources may arise from neutron activation of the structural components in the reactor core as well as contamination due to the radioactive release from the fuel occurred during normal operation or unplanned events in a nuclear power plant (NPP). In a pressurised heavy water reactor (PHWR), various in-core components are predominantly made of either zircaloy-2 or 4. The nuclides present as impurities in the zircaloy, playing a crucial role in the activity inventory due to neutron activation of those nuclides, which in turn determine the external gamma dose rate. The activity of the activation products depend on the neutron flux seen by the component, duration of irradiation and cooling period, half-lives of the daughter products and the amount of the impurities present in the structural components. To illustrate this, a guide tube made up of zircaloy-4 has been considered. A guide tube assembly is a part of the primary shut down system (PSS) which guides the movement of absorber elements in the upward and downward direction in the calandria. This study has identified and quantified the activity inventory in a guide tube at the end of the operation of the reactor using the ORIGEN2 code, and then estimated the associated external gamma dose rate using the FLUKA Monte Carlo code. The findings will help the management of radioactive waste, cost optimisation and collective dose budgeting during the decommissioning stage of a typical PHWR.

Proposed achievable levels of dose and impact of dose-reduction systems for thrombectomy in acute ischemic stroke: an international, multicentric, retrospective study in 1096 patients.

BACKGROUND: International dose reference levels are lacking for mechanical thrombectomy in acute ischemic stroke patients with large vessel occlusions. We studied whether radiation dose-reduction systems (RDS) could effectively reduce exposure and propose achievable levels. MATERIALS AND METHODS: We retrospectively included consecutive patients treated with thrombectomy on a biplane angiography system (BP) in five international, high-volume centers between January 2014 and May 2017. Institutional Review Board approvals were obtained. Technical, procedural, and clinical characteristics were assessed. Efficacy, safety, radiation dose, and contrast load were compared between angiography systems with and without RDS. Multivariate analyses were adjusted according to Bonferroni's correction. Proposed international achievable cutoff levels were set at the 75th percentile. RESULTS: Out of the 1096 thrombectomized patients, 520 (47%) were treated on a BP equipped with RDS. After multivariate analysis, RDS significantly reduced dose-area product (DAP) (91 vs 140 Gy cm2, relative effect 0.74 (CI 0.66; 0.83), 35% decrease, p < 0.001) and air kerma (0.46 vs 0.97 Gy, relative effect 0.63 (CI 0.56; 0.71), 53% decrease, p < 0.001) with 75th percentile levels of 148 Gy cm2 and 0.73 Gy, respectively. There was no difference in contrast load, rates of successful recanalization, complications, or clinical outcome. CONCLUSION: Radiation dose-reduction systems can reduce DAP and air kerma by a third and a half, respectively, without affecting thrombectomy efficacy or safety. The respective thresholds of 148 Gy cm2 and 0.73 Gy represent achievable levels that may serve to optimize current and future radiation exposure in the setting of acute ischemic stroke treatment. As technology evolves, we expect these values to decrease. KEY POINTS: • Internationally validated achievable levels may help caregivers and health authorities better assess and reduce radiation exposure of both ischemic stroke patients and treating staff during thrombectomy procedures. • Radiation dose-reduction systems can reduce DAP and air kerma by a third and a half, respectively, without affecting thrombectomy efficacy or safety in the setting of acute ischemic stroke due to large vessel occlusion.

Pediatric CT radiation exposure: where we were, and where we are now.

Since the turn of the last millennium, the pediatric radiology community has blazed a patient-quality and safety trail in helping to effectively address the public and the news media's concerns about the implications of ionizing radiation from CT scanners in children. As such, this article (1) reviews the potential deleterious effects of ionizing radiation, (2) discusses why limiting radiation exposure in children is so important, (3) tells the history of pediatric CT radiation exposure concerns, (4) explains the interventions that took place to address these concerns and (5) touches on the current school of thought on pediatric CT dose reduction.

"Next Day" Examination Reduces Radiation Exposure in Cervical Spine Clearance at a Level 1 Pediatric Trauma Center: Preliminary Findings.

BACKGROUND: Safe and effective clearance of the pediatric cervical spine presents a challenging problem due to a myriad of reasons, which has often led to further imaging studies such as computed tomographic (CT) scans being performed, exposing the pediatric patient to significant radiation with a potential increased cancer risk. The goal of this study is to develop an effective algorithm for cervical spine clearance that minimizes radiation exposure. METHODS: A cervical spine clearance protocol had been utilized in our institution from 2002 to 2011. In October 2012, the protocol was revised to provide indications for appropriate imaging by utilizing repeat "next day" physical examination. In 2014, the protocol was again revised with the desired goal of decreasing the use of CT scans through increased involvement of the Spine Service. A retrospective review was commenced using information from the Trauma Database from 2011 to 2014. Three groups were analyzed according to which protocol the patients were evaluated under: 2011, 2012, and 2014 protocols. RESULTS: During the study period, 762 patients underwent cervical spine clearance; 259 (2011 protocol), 360 (2012 protocol), and 143 (2014 protocol). The average age of all patients was 8.8 years, with 28% of patients younger than 5 years of age. There were no missed or delayed diagnoses of cervical spine injury. The use of CT scans decreased during the study period from 90% (2011 protocol) to 42% (2012 protocol) to 28.7% (2014 protocol). There was an increase in time to removal of the cervical collar at 13 to 24 hours from 8% (2011 protocol) to 22% (2012 protocol) to 19% (2014 protocol). This was not associated with an increase in hospital length of stay, which averaged 2.51 days (2011 protocol), 2.45 days (2012 protocol), and 2.27 days (2014 protocol). CONCLUSIONS: Repeat "next day" clinical examinations and increased involvement of the Spine Service decreased radiation exposure without compromising the diagnosis of cervical spine injury or increasing the length of stay at a Level One Pediatric Trauma Center in this pilot study. LEVEL OF EVIDENCE: Level 4-case series.

The new lens dose limit: implication for occupational radiation protection.

AIM AND OBJECTIVES: The aim of this article was to explore the implications of the new Euratom dose limit for occupational radiation protection in the context of medical occupational radiation exposures. The European Directive 2013/59/Euratom takes into account the new recommendations on reduction in the dose limit for the lens of the eye for planned occupational exposures released in 2012 by the International Commission on Radiological Protection (ICRP 118). MATERIALS AND METHODS: Different dose-monitoring procedures and devices were considered. Occupational eye lens doses reported by previous studies were analyzed, mainly considering workers involved in interventional procedures with X-rays. The current status of eye lens radiation protection and the main methods for dose reduction were investigated. RESULTS: The analysis showed that the workers, potentially exceeding the new limit, are clinical staff performing interventional procedures with a relatively high X-ray dose. Regarding radiological protection issues, the considered literature reports that the proper use of personal protective equipment may reduce the eye lens absorbed dose. CONCLUSION: The evaluation of the occupational eye lens dose is essential to establish which method of personal dose monitoring should be preferred. Furthermore, education and training about the right use of personal protective equipment are important for medical staff working with ionizing radiation.

Practical recommendations for the application of DE 59/2013.

The changes introduced with Council Directive 2013/59/Euratom will require European Member States adapt their regulations, procedures and equipment to the new high standards of radiation safety. These new requirements will have an impact, in particular, on the radiology community (including medical physics experts) and on industry. Relevant changes include new definitions, a new dose limit for the eye lens, non-medical imaging exposures, procedures in asymptomatic individuals, the use and regular review of diagnostic reference levels (including interventional procedures), dosimetric information in imaging systems and its transfer to the examination report, new requirements on responsibilities, the registry and analysis of accidental or unintended exposure and population dose evaluation (based on age and gender distribution). Furthermore, the Directive emphasises the need for justification of medical exposure (including asymptomatic individuals), introduces requirements concerning patient information and strengthens those for recording and reporting doses from radiological procedures, the use of diagnostic reference levels, the availability of dose-indicating devices and the improved role and support of the medical physics experts in imaging.

A European survey on the regulatory status for the estimation of the effective dose and the equivalent dose to the lens of the eye when radiation protection garments are used.

Following the proposal of the ICRP for the reduction of the dose limit for the lens of the eye, which has been adopted by the International Atomic Energy Agency and the European Council, concerns have been raised about the implementation of proper dose monitoring methods as defined in national regulations, and about the harmonisation between European countries. The European Radiation Dosimetry Group organised a survey at the end of 2017, through a web questionnaire, regarding national dose monitoring regulations. The questions were related to: double dosimetry, algorithms for the estimation of the effective dose, methodology for the determination of the equivalent dose to the lens of the eye and structure of the national dose registry. The results showed that more than 50% of the countries that responded to the survey have legal requirements about the number and the position of dosemeters used for estimation of the effective dose when radiation protection garments are used. However, in only five out of 26 countries are there nationally approved algorithms for the estimation of the effective dose. In 14 out of 26 countries there is a legal requirement to estimate the dose to the lens of the eye. All of the responding countries use some kind of national database for storing individual monitoring data but in only 12 out of 26 countries are the estimated effective dose values stored. The personal dose equivalent at depth 3 mm is stored in the registry of only seven out of 26 countries. From the survey, performed just before the implementation of the European Basic Safety Standards Directive, it is concluded that national occupational exposure frameworks require intensive and immediate work under the coordination of the competent authorities to bring them into line with the latest basic safety standards and achieve harmonisation between European countries.

2018 ACC/HRS/NASCI/SCAI/SCCT Expert Consensus Document on Optimal Use of Ionizing Radiation in Cardiovascular Imaging-Best Practices for Safety and Effectiveness, Part 2: Radiological Equipment Operation, Dose-Sparing Methodologies, Patient and Medical Personnel Protection.

The stimulus to create this document was the recognition that ionizing radiation-guided cardiovascular procedures are being performed with increasing frequency, leading to greater patient radiation exposure and, potentially, to greater exposure to clinical personnel. While the clinical benefit of these procedures is substantial, there is concern about the implications of medical radiation exposure. ACC leadership concluded that it is important to provide practitioners with an educational resource that assembles and interprets the current radiation knowledge base relevant to cardiovascular procedures. By applying this knowledge base, cardiovascular practitioners will be able to select procedures optimally, and minimize radiation exposure to patients and to clinical personnel. "Optimal Use of Ionizing Radiation in Cardiovascular Imaging - Best Practices for Safety and Effectiveness" is a comprehensive overview of ionizing radiation use in cardiovascular procedures and is published online. To provide the most value to our members, we divided the print version of this document into 2 focused parts. "Part I: Radiation Physics and Radiation Biology" addresses radiation physics, dosimetry and detrimental biologic effects. "Part II: Radiologic Equipment Operation, Dose-Sparing Methodologies, Patient and Medical Personnel Protection" covers the basics of operation and radiation delivery for the 3 cardiovascular imaging modalities (x-ray fluoroscopy, x-ray computed tomography, and nuclear scintigraphy). For each modality, it includes the determinants of radiation exposure and techniques to minimize exposure to both patients and to medical personnel.

2018 ACC/HRS/NASCI/SCAI/SCCT Expert Consensus Document on Optimal Use of Ionizing Radiation in Cardiovascular Imaging-Best Practices for Safety and Effectiveness, Part 1: Radiation Physics and Radiation Biology: A Report of the American College of Cardiology Task Force on Expert Consensus Decision Pathways Developed in Collaboration With Mended Hearts.

The stimulus to create this document was the recognition that ionizing radiation-guided cardiovascular procedures are being performed with increasing frequency, leading to greater patient radiation exposure and, potentially, to greater exposure for clinical personnel. Although the clinical benefit of these procedures is substantial, there is concern about the implications of medical radiation exposure. The American College of Cardiology leadership concluded that it is important to provide practitioners with an educational resource that assembles and interprets the current radiation knowledge base relevant to cardiovascular procedures. By applying this knowledge base, cardiovascular practitioners will be able to select procedures optimally, and minimize radiation exposure to patients and to clinical personnel. Optimal Use of Ionizing Radiation in Cardiovascular Imaging: Best Practices for Safety and Effectiveness is a comprehensive overview of ionizing radiation use in cardiovascular procedures and is published online. To provide the most value to our members, we divided the print version of this document into 2 focused parts. Part I: Radiation Physics and Radiation Biology addresses the issue of medical radiation exposure, the basics of radiation physics and dosimetry, and the basics of radiation biology and radiation-induced adverse effects. Part II: Radiological Equipment Operation, Dose-Sparing Methodologies, Patient and Medical Personnel Protection covers the basics of operation and radiation delivery for the 3 cardiovascular imaging modalities (x-ray fluoroscopy, x-ray computed tomography, and nuclear scintigraphy) and will be published in the next issue of the Journal.

Radiation Dose Reduction During EVAR: Results from a Prospective Multicentre Study (The REVAR Study).

OBJECTIVE: To evaluate radiation exposure in standard endovascular aneurysm repair (EVAR) using intra-operative guidance with pre-operative computed tomographic angiography (CTA) fusion and strict ALARA guidelines in a modern hybrid room. MATERIAL AND METHODS: Between February and November 2016, consecutive patients with AAA undergoing EVAR with a bifurcated device in a hybrid room under fusion imaging guidance were prospectively enrolled in six aortic centres from the United States (n = 1), Europe (n = 4), and Japan (n = 1). Demographic data including body mass index (BMI), indirect dose area product (DAP), cumulative air kerma (CAK), variables influencing dose delivery, and contrast media volume were collected. RESULTS: 85 patients (90.4% males) were included. The median age was 75 (IQR 69-81), with a median BMI of 27.4 (IQR 24.7-30.6). Median DAP and CAK were 14.7 (IQR 10.0-27.7) Gy·cm2 and 107 (IQR 68.0-189.0) mGy, respectively. The median contrast volume was 47 mL (IQR 35-70) (equivalent to 14.1g of iodine [IQR 10.5-21.0]). Median DAP per centre was 28.1 (n = 16, IQR 12.6-47.1), 15.9 (n = 11, IQR 11.9-22.5), 14.2 (n = 12, IQR 10.9-25.7), 20.2 (n = 18, IQR 7.0-39.5), 10.3 (n = 27, IQR 8.2-14.7) and 26.5 (n = 1) Gy·cm2. In multivariable analysis, collimation was the only factor that was significantly associated with DAP reduction, (coefficient = -0.014 per percentage of collimation, 95% CI -0.019 to -0.008, p < .001). CONCLUSIONS: With adherence to the ALARA principle and routine application of fusion imaging guidance for EVAR, low radiation exposure compared with the published literature can be achieved in a real world setting.

Perspectives on setting limits for RF contact currents: a commentary.

BACKGROUND: Limits for exposure to radiofrequency (RF) contact currents are specified in the two dominant RF safety standards and guidelines developed by the Institute of Electrical and Electronics Engineers (IEEE) and the International Commission on Non-Ionizing Radiation Protection (ICNIRP). These limits are intended to prevent RF burns when contacting RF energized objects caused by high local tissue current densities. We explain what contact currents are and review some history of the relevant limits with an emphasis on so-called "touch" contacts, i.e., contact between a person and a contact current source during touch via a very small contact area. RESULTS: Contact current limits were originally set on the basis of controlling the specific absorption rate resulting from the current flowing through regions of small conductive cross section within the body, such as the wrist or ankle. More recently, contact currents have been based on thresholds of perceived heating. In the latest standard from the IEEE developed for NATO, contact currents have been based on two research studies in which thresholds for perception of thermal warmth or thermal pain have been measured. Importantly, these studies maximized conductive contact between the subject and the contact current source. This factor was found to dominate the response to heating wherein high resistance contact, such as from dry skin, can result in local heating many times that from a highly conductive contact. Other factors such as electrode size and shape, frequency of the current and the physical force associated with contact are found to introduce uncertainty in threshold values when comparing data across multiple studies. CONCLUSIONS: Relying on studies in which the contact current is minimized for a given threshold does not result in conservative protection limits. Future efforts to develop limits on contact currents should include consideration of (1) the basis for the limits (perception, pain, tissue damage); (2) understanding of the practical conditions of real world exposure for contact currents such as contact resistance, size and shape of the contact electrode and applied force at the point of contact; (3) consistency of how contact currents are applied in research studies across different researchers; (4) effects of frequency.

A critical evaluation of the NCRP COMMENTARY 27 endorsement of the linear no-threshold model of radiation effects.

Regulatory policy to protect the public and the environment from radiation is universally based on the linear, no-threshold model (LNT) of radiation effects. This model has been controversial since its inception over nine decades ago, and remains so to this day, but it has proved remarkably resistant to challenge from the scientific community. The LNT model has been repeatedly endorsed by expert advisory bodies, and regulatory agencies in turn adopt policies that reflect this advice. Unfortunately, these endorsements rest on a foundation of institutional inertia and numerous logical fallacies. These include most significantly setting the LNT as the null hypothesis, and shifting the burden of proof onto LNT skeptics. Other examples include arbitrary exclusion of alternative hypotheses, ignoring criticisms of the LNT, cherry-picking evidence, and making policy judgements without foundation. This paper presents an evaluation of the National Council on Radiation Protection and Measurements' (NCRP) Commentary 27, which concluded that recent epidemiological studies are compatible with the continued use of the LNT model for radiation protection. While this report will likely provide political cover for regulators' continued reliance on the LNT, it is a missed opportunity to advance the scientific discussion of the effects of low dose, low dose-rate radiation exposure. Due to its Congressionally chartered mission, no organization is better positioned than the NCRP to move this debate forward, and recommendations for doing so in future reviews are provided.

Quality assurance in CT: implementation of the updated national diagnostic reference levels using an automated CT dose monitoring system.

AIM: To evaluate the implementation of the updated computed tomography (CT) diagnostic reference levels (DRLs) from the German Federal Office for Radiation Protection into clinical routine using an automatic CT dose monitoring system. METHODS AND MATERIALS: CT radiation exposure was analysed before and after implementing the updated national DRLs into routine clinical work in 2016. After the implementation process, institutional CT protocols were mapped to the anatomical regions for which DRLs were provided. Systematically, protocols that exceeded the thresholds were optimised and analysed in detail. The CT radiation output parameters analysed were volumetric CT dose index (CTDIvol) and dose-length product (DLP). Three radiologists evaluated subjective image quality using a three-point Likert scale. RESULTS: The study included 94,258 CT series (from 27,103 CT examinations) in adult patients performed in 2016. When averaged over all body regions with available DRL, institutional CTDIvol/DLP values were always below the DRLs (65.2±32.9%/67.3±41.5% initially; 59.4±32%/60.5±39.9% after optimisation). Values exceeding the national DRLs were found for pelvis (n=268; CTDIvol 107.7±65.7%/DLP 106.3±79.3%), lumbar spine (n=91; 160.8±74.7%/175.2±104.1%), and facial bones (n=527; 108±39%/152.7±75.7%). After optimisation, CTDIvol and DLP were 87.9±73%/87.8±80.8% for the pelvis, 67.8±33.2%/74.5±50.6% for the lumbar spine and 95.1±45.8%/133.3±74.6% for the viscerocranium. CONCLUSION: An automatic CT dose monitoring system enabled not only comprehensive monitoring of a DRL implementation process but can also help to optimise radiation exposure.