Harmen Bijwaard

Harmen Bijwaard
Inholland University of Applied Sciences / National Institute for Public Health and the Environment (RIVM) · Medical Technology Group / Centre for External Safety

PhD

About

78
Publications
13,646
Reads
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5,232
Citations
Citations since 2017
18 Research Items
1410 Citations
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Introduction
I currently combine a position as chair of the medical technology group of Inholland University of applied sciences with a project coordinatorship at RIVM regarding medical radiation applications See also: http://www.linkedin.com/in/harmenbijwaard And: http://www.geo.uu.nl/~bijwaard/resume/cv.html
Additional affiliations
September 2000 - December 2012
National Institute for Public Health and the Environment (RIVM)
Position
  • Senior Researcher
July 1994 - October 1999
Utrecht University
Position
  • PhD Student

Publications

Publications (78)
Article
Full-text available
Recent global travel time tomography studies by Zhou [1996] and van der Hilst et al. [1997] have been performed with cell parameterizations of the order of those frequently used in regional tomography studies (i.e., with cell sizes of 1°-2°). These new global models constitute a considerable improvement over previous results that were obtained with...
Article
Full-text available
Tomographic imaging of the mantle under Tibet, India and the adjacent Indian Ocean reveals several zones of relatively high P-wave velocities at various depths. Under the Hindu Kush region in northeastern Afghanistan and southern Tajikistan, a regional northward-dipping slab is seen in the entire upper 600 km of the mantle and is apparently still a...
Article
Mammography screening is an accepted procedure for early detection of breast tumors among asymptomatic women. Since this procedure involves the use of X rays, it is itself potentially carcinogenic. Although there is general consensus about the benefit of screening for older women, screening practices differ between countries. In this paper radiatio...
Article
Full-text available
Cenozoic rifting and volcanism in Europe have been associated with either passive or active mantle upwellings. Tomographic images show a low velocity structure between 660- and 2000-kilometer depth, which we propose to represent a lower mantle upwelling under central Europe that may feed smaller upper-mantle plumes. The position of the rift zones i...
Article
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A stochastic two-stage cancer model is used to analyse the relation between lung cancer and cigarette smoking. The model contains the main rate-limiting stages of carcinogenesis, which include initiation, promotion (clonal expansion of initiated cells), malignant transformation and a lag time for tumour formation. Various data sets were used to tes...
Article
Introduction: The Netherlands does not have a national guideline for performing radiographic examinations on pregnant patients. Radiographic examination is a generic term for all examinations performed using ionizing radiation, including but not limited to radiographs, fluoroscopy and computed tomography. A pilot study amongst radiographers (Medic...
Article
Since the first Oxford Survey of Childhood Cancer's results were published, people have become more aware of the risks associated with prenatal exposure from diagnostic x rays. As a result, it has since been the subject of many studies. In this review, the results of recent epidemiological studies are summarized. The current international guideline...
Conference Paper
Purpose Contemporary approaches to optimization often involve physical phantoms which represent human anatomy. Images are analysed using mathematical techniques. Inferences are then made to predict whether abnormalities would be visible in human images. Such approaches have limitations – e.g. abnormalities are not included, and phantoms are simple...
Article
Introduction: In the Netherlands, Diagnostic Reference Levels (DRLs) have not been based on a national survey as proposed by ICRP. Instead, local exposure data, expert judgment and the international scientific literature were used as sources. This study investigated whether the current DRLs are reasonable for Dutch radiological practice. Methods: A...
Article
The development of eHealth is dramatically changing the way healthcare is provided and organized. eHealth applications are used not only by healthcare professionals but also by patients specifically to self-manage their health condition. The development of eHealth applications requires a new methodological approach, departing from the more conventi...
Article
Purpose In the era of conventional radiology films that were rejected for various reasons, were collected and later analyzed for educational purposes. Rejections should be avoided to save time, money, but also to minimize patient exposure to radiation. Nowadays, in digital radiological imaging rejected images can be deleted easily or they can be st...
Article
A survey was conducted among 20 Dutch hospitals about radiation protection for interventional fluoroscopy. This was a follow-up of a previous study in 2007 that led to several recommendations for radiation protection for interventional fluoroscopy. The results indicate that most recommendations have been followed. However, radiation-induced complic...
Article
Full-text available
Introduction Recent research has identified the issue of ‘dose creep’ in diagnostic radiography and claims it is due to the introduction of CR and DR technology. More recently radiographers have reported that they do not regularly manipulate exposure factors for different sized patients and rely on pre-set exposures. The aim of the study was to ide...
Article
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Atherosclerosis is the development of lipid-laden plaques in arteries and is nowadays considered as an inflammatory disease. It has been shown that high doses of ionizing radiation, as used in radiotherapy, can increase the risk of development or progression of atherosclerosis. To elucidate the effects of radiation on atherosclerosis, we propose a...
Article
Introduction In the Netherlands, hospitals have difficulty in implementing the formal procedure of comparing radiation dose values to Diagnostic Reference Levels (DRLs). Methods To support the hospitals, train radiography students, and carry out a nationwide dose survey, diagnostic radiography students performed 125 DRL comparisons for nine differ...
Article
A survey about radiation protection in pediatric radiology was conducted among 22 general and seven children's hospitals in the Netherlands. Questions concerned, for example, child protocols used for CT, fluoroscopy and x-ray imaging, number of images and scans made, radiation doses and measures taken to reduce these, special tools used for childre...
Article
Introduction In the Netherlands Diagnostic Reference Levels (DRLs) have been set for 11 radiological examinations in 2012. The values of these DRLs were chosen on the basis of available scientific literature and expert judgment. Purpose The purpose of this study was to determine the level of adaptation of the current DRLs by Dutch hospitals and to...
Poster
Asses the exposure factor tube voltage (kVp) to obtain better image quality at similar effective dose or lower effective dose at similar image quality compared to the standard setting of 77 kVp and 20 mAs for lumbar spine imaging on a Samsung XGEO-GC80 xray system.
Article
Full-text available
Background: Physical inactivity is a growing public health concern. Use of mobile applications (apps) may be a powerful tool to encourage physical activity and a healthy lifestyle. For instance, apps may be used in the preparation of a running event. However, there is little evidence for the relationship between app use and change in physical acti...
Article
Epidemiological miner cohort data used to estimate lung cancer risks related to occupational radon exposure often lack cohort-wide information on exposure to tobacco smoke, a potential confounder and important effect modifier. We have developed a method to project data on smoking habits from a case-control study onto an entire cohort by means of a...
Article
Diagnostic reference levels (DRLs) for medical x-ray procedures are being implemented currently in the Netherlands. By order of the Dutch Healthcare Inspectorate, a survey has been conducted among 20 Dutch hospitals to investigate the level of implementation of the Dutch DRLs in current radiological practice. It turns out that hospitals are either...
Poster
Assessment of dose levels tested to Diagnostic Reference Levels (DRLs) in Dutch hospitals by students radiography of Inholland University of Applied Sciences.
Article
Exposures to ionizing radiation from medical examinations are on the rise. An important cause for this has been the advent and ever-increasing use of computed tomography (CT) scans for diagnostic purposes. It is often implied that population aging contributes significantly to this rise. Here, the trends in population statistics are compared to the...
Article
Full-text available
From studies of the atomic bomb survivors, it is well known that ionizing radiation causes several forms of leukemia. However, since the specific mechanism behind this process remains largely unknown, it is difficult to extrapolate carcinogenic effects at acute high-dose exposures to risk estimates for the chronic low-dose exposures that are import...
Article
Breast cancer incidence in a tuberculosis fluoroscopy cohort has been modelled with a two-stage carcinogenesis model. The relatively simple model, in which hormonal influences only affect the number of sensitive target cells, fits the data very well. Under the assumption that individual hormonal differences average out, and with a relative biologic...
Article
Full-text available
A biologically based two-stage carcinogenesis model is applied to epidemiological data for lung cancer mortality in a large uranium miner cohort of the WISMUT company (Germany). To date, this is the largest uranium miner cohort analyzed by a mechanistic model, comprising 35,084 workers among whom 461 died from lung cancer in the follow-up period 19...
Article
A mechanistic two-stage carcinogenesis model has been applied to model lung-cancer mortality in the largest uranium-miner cohort available. Models with and without smoking action both fit the data well. As smoking information is largely missing from the cohort data, a method has been devised to project this information from a case-control study ont...
Article
Full-text available
The European Radiobiology Archives (ERA), together with corresponding Japanese and American databases, hold data from nearly all experimental animal radiation biology studies carried out between 1960 and 1998, involving more than 300,000 animals. The Federal Office for Radiation Protection, together with the University of Cambridge have undertaken...
Article
Two-mutation model fits to bone cancer mortality data from mice, rats and beagle dogs injected with (239)Pu or (226)Ra show that (1) it is possible to fit the radiation-related parameters for animals from different strains of the same species together; (2) for every species the same significant parameters are found in the models for (239)Pu and in...
Article
Full-text available
Recently, the observed promotion in the clonal expansion of a two-stage cancer model was attributed to a small excess replacement probability for the initiated cells. The proposed mechanism of excess replacement was evaluated for single intermediate cells surrounded by normal cells. This paper investigates this mechanism further using the same biol...
Article
Two-mutation carcinogenesis models of mice and rats injected with 239Pu and 226Ra have been derived extending previous modellings of beagle dogs injected with 239Pu and 226Ra and radium dial painters. In all cases statistically significant parameters could be derived fitting data from several research groups jointly. This also lead to similarly par...
Article
Full-text available
A two-mutation carcinogenesis model with clonal expansion of pre-malignant cells is used to describe lung cancer mortality data from studies on French and Czech miners with relatively low exposures to radon. The aim was to derive radon-induced lung cancer risk estimates applicable to different populations using a model description consistent with b...
Article
Data from beagle experiments and radium dial painters were used to derive two-mutation carcinogenesis models for bone cancer induced by the bone-seeking radionuclides radium, strontium and plutonium. For all data, the model fits indicate that at low doses both mutation rates depend linearly and equally strongly on dose rate. For the high-LET alpha-...
Article
Exposure to cosmic radiation in space poses an increased risk for radiation-induced cancer later in life. Modelling is essential to quantify these excess risks from low and protracted exposures to a mixture of radiation types, since they cannot be determined directly in epidemiological studies. Multistage carcinogenesis models provide a mechanistic...
Article
The continental margin of the Korean Peninsula is little known in its crustal structure, although various opening models of the southwestern part of the East Sea (Japan Sea) have been presented. Accordingly, continental rifting and subsequent seafloor spreading processes in the East Sea have not been adequately addressed. The crustal and sedimentar...
Article
Despite the various opening models of the southwestern part of the East Sea (Japan Sea) between the Korean Peninsula and the Japan Arc, the continental margin of the Korean Peninsula remains unknown in crustal structure. As a result, continental rifting and subsequent seafloor spreading processes to explain the opening of the East Sea have not been...
Article
It is argued that the `cellular' dose-response relationships of model parameters cannot be determined from mechanistic model fits to experimental or epidemiologic cancer data. Baseline population cancer incidence data show conclusions about intermediate cell kinetics to be especially questionable. Here we recommend that mechanistic models should be...
Article
Implications of risk estimates, as required for practical radiation protection purposes, were explored through a preliminary re-analysis of leukaemia in the Japanese atomic bomb survivors using a biologically based cancer model. The calculations for the risks posed for contracting leukaemia pointed to important differences between low-dose-rate ('c...
Article
A two-mutation carcinogenesis model has been applied to model osteosarcoma incidence in two data sets of beagles injected with 226Ra. Taking age-specific retention into account, the following results have been obtained: (1) a consistent and well-fitting solution for all age and dose groups, (2) mutation rates that are linearly dependent on dose rat...
Article
The ISC Bulletin is the most widely used data set for traveltime tomography since it comprises the largest collection of arrival times. The large number of stations and events gives the best ray path coverage of the Earth’s mantle currently available, but the data also contain a considerable amount of noise. The effects of noise are supposedly redu...
Article
A two-mutation carcinogenesis model, formulated in terms of biologically motivated equations for mutation and expansion steps, has been applied in a mechanistic modelling of the lung cancer incidence in two large data sets of rats exposed to radon, both separately and jointly. Results indicate that (1) the equations employed are able to provide an...
Article
Full-text available
&#118--&#118We develop algorithms for the construction of irregular cell (block) models for parameterization of tomographic inverse problems. The forward problem is defined on a regular basic grid of non-overlapping cells. The basic cells are used as building blocks for construction of non-overlapping irregular cells. The construction algorithms ar...
Article
Full-text available
Recent tomographic results are used to trace the South China Sea and Philippine Sea subducting slabs, south and northeast of Taiwan along the Manila and Ryukyu trenches, respectively. In particular, the 3-D plates interaction beneath Taiwan is discussed based on a close-up view of the tomographic sections together with earthquake hypocenters distri...
Article
Studies of the geodynamic evolution of Southeast Asia have resulted in a number of tectonic reconstructions that exhibit a broad consensus as well as significant differences. In this contribution we apply a method to further test these surface reconstructions, using independent seismic tomography results. Our kinematic modelling procedure comprises...
Article
Full-text available
The cause and geodynamic impact of flat subduction are investigated. First, the 1500 km long Peru flat slab segment is examined. Earthquake hypocenter data image two morphologic highs in the subducting Nazca Plate which correlate with the positions of subducted oceanic plateaus. Travel time tomographic images confirm the three-dimensional slab geom...
Article
New regional seismological data acquired in Colombia during 1993 to 1996 and tectonic field data from the Eastern Cordillera (EC) permit a reexamination of the complex geodynamics of northwestern South America. The effect of the accretion of the Baudó-Panama oceanic arc, which began 12 Myr ago, is highlighted in connection with mountain building in...
Article
Full-text available
Recent advances in global imaging have lead to tomographic mantle models with regional scale details. To improve these models further, we have extended the usual linearized approach to traveltime tomography to non-linear tomography. Here ‘non-linear’ means that seismic ray bending due to inferred velocity heterogeneity is taken into account in an i...
Article
Full-text available
The cause and geodynamic impact of flat subduction are investigated. In particular the 1500 km long Peru flat slab segment is examined using relocated earthquake hypocenters and travel-time tomography. Two morphologic highs in the subducting Nazca Plate are imaged, beneath N. Peru (2-5°S) and S. Peru (12-15°S) at depths of 100 km and 80 km, respect...
Article
We have developed a ray tracing algorithm that traces first- and later-arriving global seismic phases precisely (traveltime errors of the order of 0.1 s), and with great computational efficiency (15 rays s- 1). To achieve this, we have extended and adapted two existing ray tracing techniques: a graph method and a perturbation method. The two result...
Article
Full-text available
Iceland is known to be a centre of both hotspot and Mid-Atlantic Ridge activity. A plume origin for the hotspot has been suggested by observational, laboratory and numerical investigations as well as by several seismological studies. The latter have, however, not yielded a detailed image of the entire mantle volume below Iceland. We present tomogra...
Article
Full-text available
Recent results from seismic tomography demonstrate that subducted oceanic lithosphere can be observed globally as slabs of relatively high seismic velocity in the upper as well as lower mantle(1,2). The Asian mantle is no exception, with high-velocity slabs being observed downwards from the west Pacific subduction zones under the Kurile Islands, Ja...
Article
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The SE Asian region is characterised by the active subduction of Cenozoic marginal basins. A new tomographic model interpreted in the light of geological data, provides details on the geometry of the oceanic lithospheric slabs subducted along the eastern margin of Sundaland. We present first evidences for a relatively continuous active margin which...
Article
Full-text available
In the last decades CT has become a routine procedure that takes only a few seconds to generate three-dimensional (moving) images of internal organs showing details of half a millimetre. This has several big advantages, but it can also have disadvantages. The radiation dose for the patient could increase. In this report recent advances in CT techno...
Article
Full-text available
More and more radiology departments change from conventional to digital imaging techniques. This change can have a beneficial or an adverse effect on the resulting image quality and patient dose. In this report the consequences of a change to digital radiology for patient safety are investigated for the Health Care Inspectorate. Apart from that, th...
Article
Full-text available
Most radiology departments of Dutch hospitals hold unused possibilities for lowering the radiation dose to children. This was found in an investigation commissioned to the RIVM by the Dutch Health Care Inspectorate. Since children are more sensitive to the long-term harmful effects of ionizing radiation than adults, it is important to give radiatio...
Article
Full-text available
The inventory of current initiatives for the Quality Assurance (QA) and Quality Control (QC) of X-ray equipment reported was undertaken in response to a need for improvement in the QA of radiology departments expressed by the Dutch Health Care Inspectorate. Work on building the inventory started with a literature study and was further developed wit...
Article
Full-text available
In the absence of Dutch guidelines for the quality control of modern (digital) X-ray equipment, crucial equipment parameters have been identified for commissioning and performance testing. Commissioning and performance testing are an essential part of the quality assurance of X-ray equipment. This quality assurance should contribute to an adequate...
Article
Full-text available
The radium concentration was measured in 25 samples of harbour sludge taken from the Rijnmond area (Rotterdam harbours and the Nieuwe Waterweg) in 2002. High radium levels were found near the former discharge points of the phosphate ore processing plants, confirming the results of previous campaigns. The results of these previous campaigns (1994-20...
Article
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In the last few years, the emissions of radioactive substances to air and water through the operations of Dutch enterprises have decreased substantially, mostly due to the closure of two ore- and raw material-processing industries. Nevertheless, the processing industries are still responsible for the largest industrial contribution to the average r...
Article
Full-text available
Three measures may optimize the radiation dose that patients receive during interventional radiology procedures. The first is by using modern equipment that is appropriate for interventional radiology procedures, while the second involves paying extra attention to radiation protection in courses in the field of interventional radiology. A final mea...
Article
Full-text available
The British handbook on quality assurance of CT and other x-ray equipment may, with some adaptations, also be used in the Netherlands. This is the main conclusion of a literature study by RIVM on quality assurance of such equipment. Images from CT scanners and other x-ray equipment must have sufficient quality to enable a correct diagnosis. They ar...

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Project (1)
Project
Researching the value of apps and digital interventions for an active lifestyle