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M Zankl

Publications and source records attributed to M Zankl.

At least 37 records · Page 2Linked to original sources
PubMed2001

Construction of a computed tomographic phantom for a Japanese male adult and dose calculation system.

Computational human phantoms have been widely used to estimate organ doses and other dosimetric quantities related to the human body where direct measurements are difficult to perform. In recent years, voxel phantoms (voxel = volume element) based on computed tomographic (CT) data of real persons have been constructed which provide a realistic description of the human anatomy. A CT phantom of a Japanese male adult with an average body size was developed as the first Asian voxel phantom. The segmented phantom consists of more than 100 regions enabling the calculation of doses for various parts of the body. The bone marrow distribution was precisely modelled according to the CT values. The EGS4 Monte Carlo transport code was combined with the phantom to calculate organ doses for external exposure due to photons and electrons up to 1 TeV. The calculated organ doses were compared with respective data using MIRD-type mathematical phantoms. In some cases, significant discrepancies in doses were observed, demonstrating the necessity of sophisticated models for accurate dose calculations.

Adult↗
PubMed2001

The adult male voxel model "Golem" segmented from whole-body CT patient data.

This paper describes the construction of an adult male voxel model named "Golem" intended to be used for Monte Carlo simulations to calculate dosimetric quantities for radiation protection considerations. The model was segmented from whole-body medical image data of a living person who was 38 years old and had external dimensions close to those of the ICRP Reference Man. The segmentation process using dedicated image processing hard- and software is described and the resulting model is characterised with respect to weight and height of the total body, organ and tissue masses and red bone marrow distribution. A comparison with the respective data for ICRP Reference Man and three further voxel models is presented. Golem was found to agree reasonably well with Reference Man, so that he can be used for the assessment of "representative" body doses.

Adult↗
PubMed2001

[Calculation of conversion coefficients for radiological protection against external radiation exposure].

Calculations are essential for radiation protection practice because organ doses and effective doses cannot be measured directly. Conversion coefficients describe the numerical relationships of protection quantities and operational quantities. The latter can be measured in practical situations using suitable dosimeters. The conversion coefficients are calculated using radiation transport codes--usually based on Monte Carlo methods--that simulate the interactions of radiation with matter in computational models of the human body. A new generation of human body models, the so-called voxel models, are constructed from image data of real persons using suitable image processing systems, consequently, they represent the human anatomy more realistically than the so-called mathematical models. The numerical effects of realistic body anatomy on the calculated conversion coefficients can amount to 70% and more for external exposures.

Calibration↗
PubMed2001

Backscatter factors for mammography calculated with Monte Carlo methods.

The objective of this study is to establish a comprehensive set of backscatter factors for mammography based on the exposure model proposed by the European Protocol on Dosimetry in Mammography. The Monte Carlo calculated backscatter factors (BSFs) presented in this study are for various exposure conditions encountered in mammographic practice as well as in calibration procedures. The data demonstrate the variation of the BSF as a function of the exposure parameters, hence enabling a better match with calibration conditions and, at the same time, reviewing the BSF data already recommended by the European Protocol. Furthermore, earlier data for BSF for general diagnostic radiology are validated.

Calibration↗
PubMed2001

Impact on internal doses of photon SAFs derived with the GSF adult male voxel phantom.

This paper describes the effect on over 3,000 sets of internal dose estimates of using photon Specific Absorbed Fractions (SAFs) calculated using two different types of phantoms, specifically the MIRD-type anthropomorphic phantom originally developed by Snyder and the new adult male voxel phantom, GOLEM, developed at GSF. The SAFs based on the MIRD-type phantom are currently used by the International Commission on Radiological Protection (ICRP) in internal dose calculations, but there are suggestions of moving towards SAFs generated from voxel phantoms, thus there is an interest in the potential differences in internal doses. Overall, it is found that some tissue doses calculated using the voxel phantoms can differ significantly from those of the MIRD-type phantom; however, the effective dose appears to be quite robust to changes in photon SAFs.

Administration, Inhalation↗
PubMed2000

Comparison of internal radiation doses estimated by MIRD and voxel techniques for a "family" of phantoms.

The aim of this study was to use a new system of realistic voxel phantoms, based on computed tomography scanning of humans, to assess its ability to specify the internal dosimetry of selected human examples in comparison with the well-established MIRD system of mathematical anthropomorphic phantoms. Differences in specific absorbed fractions between the two systems were inferred by using organ dose estimates as the end point for comparison. A "family" of voxel phantoms, comprising an 8-week-old baby, a 7-year-old child and a 38-year-old adult, was used and a close match to these was made by interpolating between organ doses estimated for pairs of the series of six MIRD phantoms. Using both systems, doses were calculated for up to 22 organs for four radiopharmaceuticals with widely differing biodistribution and emission characteristics (technetium-99m pertechnetate, administered without thyroid blocking; iodine-123 iodide; indium-111 antimyosin; oxygen-15 water). Organ dose estimates under the MIRD system were derived using the software MIRDOSE 3, which incorporates specific absorbed fraction (SAF) values for the MIRD phantom series. The voxel system uses software based on the same dose calculation formula in conjunction with SAF values determined by Monte Carlo analysis at the GSF of the three voxel phantoms. Effective doses were also compared. Substantial differences in organ weights were observed between the two systems, 18% differing by more than a factor of 2. Out of a total of 238 organ dose comparisons, 5% differed by more than a factor of 2 between the systems; these included some doses to walls of the GI tract, a significant result in relation to their high tissue weighting factors. Some of the largest differences in dose were associated with organs of lower significance in terms of radiosensitivity (e.g. thymus). In this small series, voxel organ doses tended to exceed MIRD values, on average, and a 10% difference was significant when all 238 organ doses were considered as a single group. In 12 comparisons of effective dose, the mean voxel to MIRD ratio was 1.07 (range 0.72-1.32). It was shown for the majority of cases that, whereas some large differences in SAF values exist, differences in source organ and effective dose values between the MIRD and voxel methods were largely accounted for by the respective organ mass differences. The reasons for various organ dose differences with the selected radiopharmaceuticals are discussed. Taking biological variation into account, there is reasonable agreement between the two methods but some significant differences exist that warrant further investigation. More extensive comparisons involving a wide variety of voxel phantoms are required to establish whether realistic voxel phantoms should eventually replace the MIRD system.

Adult↗
PubMed2000

The influence of different technique factors on image quality of lumbar spine radiographs as evaluated by established CEC image criteria.

In this study we have investigated the image quality of lumbar spine radiographs taken after recording technical and physical parameters. Two technical parameters were altered, tube voltage (70 kV and 90 kV for the anteroposterior (AP) projection and 77 kV and 95 kV for the lateral projection) and sensitivity of the film-screen system (sensitivity class 400 and 600). In total, 85 images were included in the study. Entrance surface dose (ESD) was measured using thermoluminescent dosemeters. The mean value of ESD for the different technique groups varied between 1.9 mGy (90 kV, sensitivity class 400) and 4.6 mGy (70 kV, sensitivity class 400) for the AP projection, and between 6.4 mGy (95 kV, sensitivity class 600) and 20.4 mGy (70 kV, sensitivity class 400) for the lateral projection. Image criteria given in the "European Guidelines on Quality Criteria for Radiographic Images" were used to assess image quality. Two evaluation methods have been employed. A straightforward scoring of fulfilled image criteria, and visual grading analysis using the structures defined in the image criteria. The latter method provided a sharper distinction between groups of images taken using different radiographic techniques. The average number of fulfilled image criteria for the AP projections varied between 0.74 (90 kV, sensitivity class 400) and 0.87 (70 kV, sensitivity class 400). For the lateral projection this number varied between 0.79 (95 kV, sensitivity class 600) and 0.84 (77 kV, sensitivity class 600). This study shows that image criteria are useful tools in clinical studies of image quality.

Adolescent↗
PubMed1999

A PC program for estimating organ dose and effective dose values in computed tomography.

Dose values in CT are specified by the manufacturers for all CT systems and operating conditions in phantoms. It is not trivial, however, to derive dose values in patients from this information. Therefore, we have developed a PC-based program which calculates organ dose and effective dose values for arbitrary scan parameters and anatomical ranges. Values for primary radiation are derived from measurements or manufacturer specifications; values for scattered radiation are derived from Monte Carlo calculations tabulated for standard anthropomorphic phantoms. Based on these values, organ doses can be computed by the program for arbitrary scan protocols in conventional and in spiral CT. Effective dose values are also provided, both with ICRP 26 and ICRP 60 tissue-weighting coefficients. Results for several standard CT protocols are presented in tabular form in this paper. In addition, potential for dose reduction is demonstrated, for example, in spiral CT and in quantitative CT. Providing realistic patient dose estimates for arbitrary CT protocols is relevant both for the physician and the patient, and it is particularly useful for educational and training purposes. The program, called WinDose, is now in use at the Erlangen University hospitals (Germany) as an information tool for radiologists and patients. Further extensions are planned.

Dose-Response Relationship, Radiation↗
PubMed1999

Personal dose equivalent for photons and its variation with dosimeter position.

This work presents conversion coefficients per air kerma free-in-air for the personal dose equivalent, Hp(10), calculated according to its definition by the International Commission on Radiation Units and Measurements as a quantity in the human body. The values were calculated using Monte Carlo methods for various dosimeter positions in the trunk of a voxel model of an adult male, and they are given for various directions of incidence of broad parallel photon beams with energies between 10 keV and 10 MeV. It is shown that the numerical values of the personal dose equivalent depend on the exact position of the dosimeter, with maximum differences between 12% and 80%, depending on the beam geometry. It is further shown that the recommended calibration quantity Hp slab(10), which has been used in ICRP Publication 74 and ICRU Report 57 in the absence of data in the human body to approximate personal dose equivalent, does represent the latter quantity in a sensible way for some, but not all, beam geometries. Comparison of the values for the personal dose equivalent of this work with effective dose revealed that Hp(10) is a conservative estimate or close approximation of E for most irradiation geometries and photon energies.

Adult↗
PubMed1998

Calculation of backscatter factors for diagnostic radiology using Monte Carlo methods.

Backscatter factors were determined for x-ray beams relevant to diagnostic radiology using Monte Carlo methods. The phantom size considered most suitable for calibration of dosimeters is a cuboid of 30 x 30 cm2 front surface and 15 cm depth. This phantom size also provides a good approximation to adult patients. Three different media were studied: water, PMMA and ICRU tissue; the source geometry was a point source with varying field size and source-to-phantom distance. The variations of the backscatter factor with phantom medium and field geometry were examined. From the obtained data, a set of backscatter factors was selected and proposed for adoption as a standard set for the calibration of dosimeters to be used to measure diagnostic reference doses.

Adult↗
PubMed1998

Calculation of the effective dose and its variation from environmental gamma ray sources.

Effective dose, an indicator of the stochastic effect of radiation, has been widely used in dose evaluation in the environment. Though conversion factors have been used to obtain E from the air kerma or air absorbed dose, the variation of the conversion factors due to the change of exposure conditions has not been sufficiently investigated. This report documents an investigation of the variation of the effective dose per air kerma for environmental gamma rays depending on the exposure conditions using anthropomorphic phantoms and Monte Carlo calculations, taking into account the precise angular and energy distributions of the environmental gamma rays incident on the human body. As causes of the variation, posture of human bodies, biases of environmental source distributions, and body size were considered. The variation of effective dose in a prone position compared with that in a standing position was found to be within 30%. The bias of environmental sources causes the effective dose per air kerma to vary by 20% at maximum, but in some cases for low-energy gamma rays the variation was found to be up to 40% due to the change in the energy spectrum. The effective dose for a new born infant was estimated to be higher than that for an adult by a maximum of 80-90% for low-energy gamma rays from anthropogenic sources because of a lower shielding effect of the smaller body. The variation of the effective dose equivalent shows a similar tendency to the effective dose. Consequently, this study made it possible to estimate the uncertainties of effective dose and effective dose equivalent evaluated from air kerma or absorbed dose in air using the standard available conversion factors.

Adult↗
PubMed1997

Molecular analysis of the L1CAM gene in patients with X-linked hydrocephalus demonstrates eight novel mutations and suggests non-allelic heterogeneity of the trait.

Eight novel mutations were identified in the gene encoding L1CAM, a neural cell adhesion protein, in patients/families with X-linked hydrocephalus (XHC) providing additional evidence for extreme allelic heterogeneity of the trait. The two nonsense mutations (Gln440Ter and Gln1042Ter) result most likely in functional null-alleles and complete absence of L1CAM at the cell surface. The four missense mutations (Leu482Pro, Ser542Pro, Met741Thr, and Val752Met) as well as delSer526 may considerably alter the structure of L1CAM. Interestingly, a missense mutation in an XHC family predicting the Val768Ile change in the second fibronectin type III domain of L1CAM was found not only in the two affected cousins and their obligate carrier mothers but also in two unaffected male relatives of the patients. Several possible explanations of this finding are discussed; the most likely being that Val768Ile is a rare non-pathogenic variant. If this were indeed the case, our data suggest that the XHC in this family is not due to a mutation of the L1CAM gene, i.e., that, in addition to the extreme allelic heterogeneity of XHC, a non-allelic form of genetic heterogeneity may also exist in this trait.

Alleles↗
PubMed1997

Progressive hydrocephalus in two members of a family with autosomal dominant Noonan phenotype.

We present a family with an autosomal dominant phenotype characterized by pulmonary valve stenosis, craniofacial dysplasia with marked hypertelorism and, as a variable feature, progressive hydrocephalus. This phenotype is manifested in four patients from three subsequent generations of a family, with expression ranging from mild pulmonary stenosis combined with slight but characteristic facial dysmorphism to severe cyanotic pulmonary valve stenosis with multiple malformations lethal in early childhood. We consider this to be an unusual variant of Noonan syndrome.

Adult↗
PubMed1996

[Radiation exposure in interventional radiology as exemplified by the chemoembolization of hepatocellular carcinoma and laser angioplasty of the pelvic arteries].

PURPOSE: Estimation of radiogenic risks for patient and radiologist in chemoembolisation of hepatocellular carcinoma (HCC) and laser angioplasty of the pelvic arteries. METHODS: In 5 chemoembolisations of HCC (4 males, one female) and 6 laser angioplasties of the pelvic arteries (5 males, one female) the surface doses received by patient and operator were measured using thermoluminescent dosimeters in standardised positions. The organ doses of the patient were derived by conversion factors employed on the measured surface doses. Effective dose was determined according to the recommendations of ICRP 60. RESULTS: The risk of lethal malignant disease and genetic disorder derived from the doses in the patient was found to be of the magnitude of 10(-4)-10(-5). The thresholds for transient erythema of the skin and depression of hematopoiesis can be reached after high expositions. A theoretical maximum of 700 laser angioplasties of the pelvic arteries allowable in one year was calculated based on the dose to the operator's left hand. For chemoembolisation of HCC, the dose to the left eye lens would reach the yearly maximum after approximately 1000 procedures. Remarkable risks for malignant disease of skin and thyroid as well as detectable opacities of the eye lens can occur after frequent interventions for many years. CONCLUSIONS: Because of the lower life expectancy the patient's risk for stochastic effect can be seen as minimal. No clinically relevant deterministic effects will occur. In the case of frequent interventions, the dose absorbed by the radiologist is likely to exceed the prescribed dose limit and to cause remarkable risk for stochastic and non-stochastic effects after many years.

Aged↗
PubMed1995

An analysis of the equivalent dose calculation for the remainder tissues.

In the 1990 Recommendations of the International Commission on Radiological Protection, the risk-weighted quantity "effective dose equivalent" was replaced by a similar quantity, "effective dose." Among other alterations, the selection of the organs and tissues contributing to the risk-weighted quantity and their respective weighting factors were changed, including a modified definition of the so-called "remainder." Close consideration of this latter definition shows that it causes certain ambiguities and unexpected effects which are dealt with in the following. For several geometries of external photon irradiation, the numerical differences of two possible methods of evaluating the remainder dose from the doses to ten single organs, namely as arithmetic mean or as mass weighted average, are assessed. It is shown that deviation from these averaging procedures, as prescribed for those cases where a remainder organ receives a higher dose than an organ with a specified weighting factor, causes discontinuities in the energy dependence of the remainder dose and, consequently, also non-additivity of this quantity. These problems are discussed, and it is shown that, although the numerical consequences for the calculation of the effective dose are small, this unsatisfactory situation needs clarification. One approach might be to abolish some of the ICRP guidance relating to the appropriate tissue weighting factors for the remainder tissues and organs and to make other guidance more precise.

Adult↗
PubMed1994

Realistic computerized human phantoms.

To estimate the risk resulting from exposures to ionizing radiation, the organ and tissue doses should be assessed. A convenient method is the calculation of these doses using representations of the human body, called models or phantoms, together with computer codes simulating the transport of radiation in the body. Most commonly used are mathematical phantoms whose external and internal volumes are defined by simple geometric bodies. More recently, phantoms constructed from computed tomographic data of real persons were introduced as an improvement. These phantoms present advantages concerning the location and shape of the organs, in particular the hard bone and bone marrow, whose distribution can be assessed with high resolution. So far, three of these phantoms were constructed at the GSF, a fourth is under process. The construction technique is described, and some calculational results of organ doses due to external photon irradiation are presented.

Adult↗
PubMed1993

Effective dose--how effective for patients?

The question discussed in this paper is whether effective dose can reflect the risk to patients from radiological procedures and can be used, for example, to optimise procedures and compare risks of various methods, to define dose constraints, and to estimate the risks to individuals or populations attributed to medical exposures. This report demonstrates that the use of effective dose for patients could be misleading or even wrong due to inappropriate simplifications of the underlying biological mechanisms and inappropriateness of the weighting factors connected with the definition of effective dose for a given patient population. We show that the choice of the most meaningful quantities to express patient exposure depends strongly on the respective situation.

Bone Marrow↗