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Biomedical subjects

H G Menzel

Publications and source records attributed to H G Menzel.

18 recordsLinked to original sources
PubMed2006

The ICRU (International Commission on Radiation Units and Measurements): its contribution to dosimetry in diagnostic and interventional radiology.

The ICRU (International Commission on Radiation Units and Measurements was created to develop a coherent system of quantities and units, universally accepted in all fields where ionizing radiation is used. Although the accuracy of dose or kerma may be low for most radiological applications, the quantity which is measured must be clearly specified. Radiological dosimetry instruments are generally calibrated free-in-air in terms of air kerma. However, to estimate the probability of harm at low dose, the mean absorbed dose for organs is used. In contrast, at high doses, the likelihood of harm is related to the absorbed dose at the site receiving the highest dose. Therefore, to assess the risk of deterministic and stochastic effects, a detailed knowledge of absorbed dose distribution, organ doses, patient age and gender is required. For interventional radiology, where the avoidance of deterministic effects becomes important, dose conversion coefficients are generally not yet developed.

Calibration↗
PubMed2004

Dose equivalent measurements in a strongly pulsed high-energy radiation field.

The stray radiation field outside the shielding of high-energy accelerators comprises neutrons, photons and charged particles with a wide range of energies. Often, accelerators operate by accelerating and ejecting short pulses of particles, creating an analogue, pulsed radiation field. The pulses can be as short as 10 micros with high instantaneous fluence rates and dose rates. Measurements of average dose equivalent (rate) for radiation protection purposes in these fields present a challenge for instrumentation. The performance of three instruments (i.e. a recombination chamber, the Sievert Instrument and a HANDI-TEPC) measuring total dose equivalent is compared in a high-energy reference radiation field (CERF) and a strongly pulsed, high-energy radiation field at the CERN proton synchrotron (PS).

Body Burden↗
PubMed2002

Biological weighting of absorbed dose in radiation therapy.

Absorbed dose is a quantity which is scientifically rigorously defined and used to quantify the exposure of biological objects, including humans, to ionising radiation. There is, however, no unique relationship between absorbed dose and induced biological effects. The effects induced by a given absorbed dose to a given biological object depend also on radiation quality and temporal distribution of the irradiation. In radiation therapy, empirical approaches are still used today to account for these dependencies in practice. In hadron therapy (neutrons, protons, ions), radiation quality is accounted for with a diversity of (almost hospital specific) methods. The necessity to account for temporal aspects is well known in external beam therapy and in high dose rate brachytherapy. The paper reviews the approaches for weighting the absorbed dose in radiation therapy, and focusses on the clinical aspects of these approaches, in particular the accuracy requirements.

Absorption↗
PubMed2000

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.

Aircraft↗
PubMed1999

Risk assessment for cancer induction after low- and high-LET therapeutic irradiation.

The risk of induction of a second primary cancer after a therapeutic irradiation with conventional photon beams is well recognized and documented. However, in general, it is totally overwhelmed by the benefit of the treatment. The same is true to a large extent for the combinations of radiation and drug therapy. After fast neutron therapy, the risk of induction of a second cancer is greater than after photon therapy. Neutron RBE increases with decreasing dose and there is a wide evidence that neutron RBE is greater for cancer induction (and for other late effects relevant in radiation protection) than for cell killing. Animal data on RBE for tumor induction are reviewed, as well as other biological effects such as life shortening, malignant cell transformation in vitro, chromosome aberrations, genetic effects. These effects can be related, directly or indirectly, to cancer induction to the extent that they express a "genomic" lesion. Almost no reliable human epidemiological data are available so far. For fission neutrons a RBE for cancer induction of about 20 relative to photons seems to be a reasonable assumption. For fast neutrons, due to the difference in energy spectrum, a RBE of 10 can be assumed. After proton beam therapy (low-LET radiation), the risk of secondary cancer induction, relative to photons, can be divided by a factor of 3, due to the reduction of integral dose (as an average). The RBE of heavy-ions for cancer induction can be assumed to be similar to fission neutrons, i.e. about 20 relative to photons. However, after heavy-ion beam therapy, the risk should be divided by 3, as after proton therapy due to the excellent physical selectivity of the irradiation. Therefore a risk 5 to 10 times higher than photons could be assumed. This range is probably a pessimistic estimate for carbon ions since most of the normal tissues, at the level of the initial plateau, are irradiated with low-LET radiation.

Alpha Particles↗
PubMed1998

Specification of radiation quality in fast neutron therapy: microdosimetric and radiobiological approach.

Specification of radiation quality is an important issue in fast neutron therapy since the biological effectiveness of the beams varies to a large extent with neutron energy. It must meet specific criteria, mainly derived from the accuracy requirement for absorbed dose delivery. A first approach to this problem consists in identifying physical parameters that can be related to Relative Biological Effectiveness (RBE) and which describe the beam production technique (e.g. neutron-producing reaction, p + Be or d + Be, energy of the incident particle). A second is based on microdosimetry, which provides a description of the secondary radiation components to which the biological consequences of irradiations are more directly correlated. A third approach consists in experimental RBE determinations in reference conditions: intestinal crypt regeneration in mice after irradiation to the whole body with single doses is proposed as a standard biological system for radiobiological calibrations of clinical fast neutron beams. Dosimetric, microdosimetric and radiobiological intercomparisons are encouraged since they provide a homogeneous set of data which facilitate the exchange of clinical information. They also constitute a basis for the clinical RBE approach and an overall check of the irradiation procedure. Therefore they should be recommended in every non-conventional radiation therapy facility.

Animals↗
PubMed1997

Dosimetry for occupational exposure to cosmic radiation.

In the course of their work, aircraft crew and frequent flyers are exposed to elevated levels of cosmic radiation of galactic and solar origin and secondary radiation produced in the atmosphere, aircraft structure, etc. This has been recognised for some time and estimates of the exposure of aircraft crew have been made previously and included in, for example, UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation) publications. The recent increased interest has been brought about by several factors--the consideration that the relative biological effectiveness of the neutron component as being underestimated; the trend towards higher cruising altitudes for subsonic commercial aircraft and business jet aircraft; and, most importantly, the recommendations of the International Commission on Radiological Protection (ICRP) in Publication 60, and the revision of the Euratom Basic Safety Standards Directive (BSS). In 1992, the European Dosimetry Group (EURADOS) established a Working Group to consider the exposure to cosmic radiation of aircraft crew, and the scientific and technical problems associated with radiation protection dosimetry for this occupational group. The Working Group was composed of fifteen scientists (plus a corresponding member) involved in this field of study and with knowledge of radiation measurement at aviation altitudes. This paper is based on the findings of this Working Group. Where arrangements are made to take account of the exposure of aircraft crew to cosmic radiation, dose estimation procedures will not be necessary for persons for whom total annual doses are not liable to exceed 1 mSv, and therefore, in general, for crew on aircraft not routinely flying above 8 km. Where estimates of effective dose and, in the case of female staff who are pregnant, equivalent dose to the embryo or fetus, are required (for regulatory or other purposes), it was concluded that the preferred procedure was to determine route doses and fold these with data on staff rostering.

Aircraft↗
PubMed1996

Present status, trends and needs in fast neutron therapy.

Fast neutrons were introduced in cancer therapy, in the 1970s, on the basis of radiobiological arguments. After 30 years, these arguments are still valid and have not been refuted by more recent experimental data. Although neutron therapy has been applied routinely for about 25 years, there is still no general agreement concerning its value and its place among the other radiation therapy techniques. In order to be able to draw objective conclusions from the available clinical results and mainly to compare the results from the different centres in a relevant way, a consensus has to be reached on several issues: 1) a protocol for dose measurement in a homogeneous phantom in reference conditions; 2) dose computation at the level of the target volume(s) and the normal tissues at risk; 3) method of dose specification for reporting; and 4) specification of radiation quality in neutron therapy and the related RBE problems. The International Commission on Radiation Units and Measurements (ICRU) has published recommendations on Clinical Neutron Dosimetry (ICRU Report 45, 1989) which are now universally applied. As far as dose specification for reporting is concerned, ICRU recommendations for photons (ICRU Report 50, 1993) can be extended and adapted for fast neutrons. However, special care is required to take into account the tissue compositions. In fast neutron therapy, specification of radiation quality raises a particular problem because the neutron RBE, relative to gamma rays, is higher than unity (it ranges from about 2 to 5) and furthermore significantly varies with neutron beam energy. In addition, the RBE also varies with dose and biological system. In these conditions, besides the classical concept of RBE introduced jointly by the ICRP and the ICRU in 1963, the concepts of "reference RBE" and "clinical RBE" are proposed here for application in fast neutron therapy. Microdosimetry provides an adequate method to describe radiation quality, at the point of interest in the irradiated medium and in the actual irradiation conditions. From the analysis of microdosimetric spectra, a RBE value of a particular neutron beam, for a given biological system, can be predicted provided that the biological weighing function for that biological system has been obtained. In any case, correlation of the microdosimetric description of a given beam and the experimental RBE values for that beam improves the confidence in both sets of data.

Cancer Care Facilities↗
PubMed1994

The clinical RBE and microdosimetric characterization of radiation quality in fast neutron therapy.

High-LET radiation therapy using fast neutrons is being applied regularly at several centres worldwide and in the future, other types of radiation qualities, such as protons and heavier ions and boron neutron capture therapy (BNCT) are likely to be used. The neutron beams used are of considerably varying energy and thus considerable variations in the relative biological effectiveness (RBE) have been found. At present, no generally accepted method exists for the quantitative specification of these differences in radiation quality for clinical purposes. This is in clear discrepancy with the accuracy requirements in clinical dosimetry. An approach is presented which is based on a single parameter radiation quality characterization determined in combined microdosimetric and radiobiological experiments. It is shown that the method can meet the accuracy requirements of clinical dosimetry and that it is applicable within a concept of formalized procedure of clinical practice and experience ('clinical RBE').

Energy Transfer↗
PubMed1993

RBE in fast neutron therapy and in boron neutron capture therapy. A useful concept or a misuse?

In high-LET radiation therapy, radiation quality and radiation quality differences have to be taken into account and specified. In fast neutron therapy, an operational approach has been adopted which is based on the concept of "clinical RBE". The paper discusses the quantities of RBE (relative biological effectiveness), reference RBE and clinical RBE and their relationship and significance in radiation therapy. In particular, the difference between the well defined RBE in radiation biology and the clinical RBE which is based on the judgement of radiotherapists is elucidated and emphasized. The clinical RBE is based on the reference RBE and implicitly includes differences in physical selectivity of the irradiation beams and clinical experience. The particular aspects of radiation quality in boron neutron capture therapy (BNCT) are due to the poor penetration of the primary beam, the inhomogeneity of the spatial distribution of 10B nuclides in the irradiated tissue and the short range of the alpha-particles emitted after neutron capture in 10B. The related problems in accounting for radiation quality in BNCT and in the applicability of the clinical RBE concept are discussed.

Boron Neutron Capture Therapy↗
PubMed1990

Microdosimetric specification of radiation quality in neutron radiation therapy.

The neutron beams used by various radiotherapy centres are of widely differing energies, and differences of up to 50 per cent in the relative biological effectiveness (RBE) between different beams have been found in radiobiological experiments. Moreover, at some facilities RBE variations have been observed with increasing depth in a phantom. In spite of this evidence, there is no quantitative and uniquely accepted specification of radiation quality used in practice. The urgency of an adequate solution of this problem is illustrated by the fact that in radiation therapy the usual accuracy requirement for the quantity of radiation, i.e. the absorbed dose to be delivered to the tumour, is 3.5 per cent (1 SD). In this paper a pragmatic solution for the specification of radiation quality for fast neutron therapy is proposed. It is based on empirical RBE versus lineal energy response or weighting functions. These were established by using existing radiobiological data and microdosimetric spectra measured under identical irradiation conditions at several European neutron irradiation units.

Energy Transfer↗
PubMed1987

Dosimetry of low-energy neutrons using low-pressure proportional counters.

Measurements in nearly monoenergetic beams of 144, 24.5, and 2 keV neutrons and of thermal neutrons have been performed with low-pressure proportional counters. The suitability of a tissue-equivalent proportional counter (TEPC) for dosimetry of low-energy neutrons has been investigated. In contrast to higher neutron energies, the modification of the primary radiation field by the detector wall and the contribution of secondaries produced in the gas are significant. These effects have been investigated by additional measurements with a carbon-walled proportional counter. The various physical processes of neutron interaction with wall and gas of the TEPC have been analyzed, and absorbed dose, kerma, and kerma contributions from the various processes are presented. In addition, dose contributions from contaminating neutrons and photons have been obtained for the calibration fields used. The results have been related to neutron fluence. The comparison with tabulated kerma factors shows excellent agreement, indicating the suitability of the TEPC method for dosimetry of low-energy neutrons.

Energy Transfer↗
PubMed1985

Proportional counter dosimetry and microdosimetry for radiotherapy with multiple pion beams.

At the Swiss Institute for Nuclear Research (SIN) cancer patients are irradiated with negatively charged pi mesons using a 60-beam medical pion generator, the Piotron. A low-pressure tissue-equivalent proportional counter was used to measure absorbed dose and microdosimetric spectra. A method was developed to allow discrimination of events from different beam components, i.e., beam contamination (electrons and muons), pions in flight, and stopping pions. Measurements were performed along the axis and at lateral distances off one of these identical pion beams. The marked changes of total microdosimetric spectra with depth in phantom detected in earlier measurements are mainly due to large variations in the dose contributions of the beam components and much less to changes in the shapes of the individual microdosimetric spectra. The single beam measurements were used to calculate three-dimensional distributions of absorbed dose and of dose mean lineal energy, yD, for dynamic patient irradiations. Within the whole target volume yD remains nearly constant when irradiated with all 60 beams, whereas considerable changes were found for irradiations with 31 beams coming from a semicircle. Both size and shape of target volumes influence yD, the maximum values ranging from 30 to 45 keV/micron.

Elementary Particles↗
PubMed1979

Energy deposition spectra of negative pions and their application to radiation therapy.

Treatment planning for pion radiation therapy must take into account changes in radiation quality within the patient. At the biomedical channel piE3 of SIN (Swiss Institute for Nuclear Research) microdosimetric measurements have been performed to investigate radiation quality within pion irradiated phantoms. Results are presented in terms of microdosimetric spectra and derived quantities. As expected marked differences are observed between dose peak and plateau for "narrow" pion beams. The influence of simulated site diameter on measured spectra has been found to be more pronounced in the plateau region than in the peak. Investigation of the influence of peak width on radiation quality revealed a dilution of the high-LET dose fraction for broader peaks.

Elementary Particles↗