Dosimetry Problems Research Articles

A resource facility for kinetic analysis: modeling using the SAAM computer programs.

Kinetic analysis and integrated system modeling have contributed significantly to understanding the physiology and pathophysiology of metabolic systems in humans and animals. Many experimental biologists are aware of the usefulness of these techniques and recognize that kinetic modeling requires special expertise. The Resource Facility for Kinetic Analysis (RFKA) provides this expertise through: (1) development and application of modeling technology for biomedical problems, and (2) development of computer-based kinetic modeling methodologies concentrating on the computer program Simulation, Analysis, and Modeling (SAAM) and its conversational version, CONversational SAAM (CONSAM). The RFKA offers consultation to the biomedical community in the use of modeling to analyze kinetic data and trains individuals in using this technology for biomedical research. Early versions of SAAM were widely applied in solving dosimetry problems; many users, however, are not familiar with recent improvements to the software. The purpose of this paper is to acquaint biomedical researchers in the dosimetry field with RFKA, which, together with the joint National Cancer Institute-National Heart, Lung and Blood Institute project, is overseeing SAAM development and applications. In addition, RFKA provides many service activities to the SAAM user community that are relevant to solving dosimetry problems.

ESR dosimetry and dating in aragonitic mollusks

Much current research in ESR involves mollusks. As well as being useful for ESR dating, mollusks often present interesting problems in dosimetry. A number of molluskan species have been dated successfully by ESR. This work will discuss results on a previously unstudied genus, Mercenaria, using samples approx. 100 ka old, from Norfolk, Va (U.S.A.). Extensive comparison dating is available for the deposits, using, for example, uranium series disequilibrium and amino acid racemization. In addition, the work compares several proposed methodologies for determining the accumulated radiation dosage by ESR.

The next decade in external dosimetry.

In recent years, a number of external dosimetry problems have been solved. However, changes in standards and legal concepts relating to the application of dosimetry results will require further enhancements in measurement techniques and philosophy in the next 10 y. The introduction of effective dose equivalent and the legal use of probability of causation will require that much greater attention be given to determination of weighted organ dose from external exposure. An imminent change--an increase in the fast neutron quality factor--will require a new round of technology development in a field that has just received a decade of close scrutiny. For the future, we must take advantage of developments in microelectronics. The use of random access memory (RAM) and metal-on-silicon (MOS) devices as detector elements, particularly for neutron dosimetry, has exciting possibilities that are just beginning to be explored. Advances in microcircuitry are leading, and will continue to lead, in the development of a new generation of small, rugged and "smart" radiation survey instruments that will make the most of detector data. It has become possible with very compact instruments to obtain energy spectra, linear-energy-transfer (LET) spectra, and quality factors in addition to the usual integrated dosimetric quantities: exposure, absorbed dose, and dose equivalent. These instruments will be reliable and easy to use. The user will be able to select the level of sophistication that is required for any specific application. Moreover, since the processing algorithms can be changed, changes in conversion factors can be accommodated with relative ease. During the next decade, the use of computers will continue to grow in value to the health physicist. Personal computers and codes designed for dosimetry applications will become prominent, providing the health physicist with the ability to perform sophisticated data reduction, spectra unfolding and even radiation modeling and transport calculations on the desk top. In the far term, the use of computers could extend to the development of sophisticated tracking systems that would follow and record the workers' movements throughout a radiation area. These data, together with information from area monitors, air samplers and personnel dosimeters, could be used to develop truly integrated dose estimates, including reconstruction of organ doses.

Biological effects of non-ionizing radiations: cellular properties and interactions.

The Lauriston Taylor lectures honor the founder of the National Committee on Radiation Protection and Measurement, soon to be followed by the corresponding international organization. These standard setting bodies had a vast influence on proper recognition of radiation hazards. The 10th Taylor lecture is the first to deal with nonionizing radiations and may be, therefore, of particular interest to the bioengineer. During early history biophysics and bioengineering were primarily concerned with ionizing radiation bioeffects and electrophysiology. The nonionizing part of the radiation field and electrophysiology are closely related. Biomedical observation, biophysical and bioengineering efforts in the nonionizing radiation field are defined and complement each other. Topics concentrate on the relevant biophysical and bioengineering efforts of the author and his colleagues. They include: electrical properties of biological systems; established electrical field interactions (excitation, macromolecular responses and cellular responses); problems of dosimetry (macroscopic and microscopic considerations); conclusions about relative merits of various research approaches.

An arrangement for irradiating cultured mammalian cells with aluminium characteristic ultrasoft X-rays

Ultrasoft X-rays are useful for testing the validity of mechanistic models of biological damage caused by radiation. Described here is the construction and operation of a cold-cathode transmission-target discharge tube for irradiating mammalian cells in vitro with aluminium characteristic X-rays (1.487 keV). Particular attention is given to the problems of sample preparation and dosimetry for this shallowly penetrating radiation. The proportion of contaminating bremsstrahlung radiation is measured to establish the optimum operating conditions. Preliminary data from experiments using V79 Chinese hamster cells show that aluminium characteristic X-rays are about twice as effective at inactivating the cells as 250 kVp X-rays.

Dosimetry of pulsed mixed radiations

The problem of dosimetry in a pulsed mixed radiation field around a specially-designed electron linear accelerator which can deliver pulsed electrons of 50 nC and pulse width of 20 ps, are described. The quick response of the ionization chamber to short pulsed radiation is observed and the effect of the response to the dosimetry is also studied. In a mixed field it might be convenient from the stand-point of the dosimetry to define a quantity that can well express the characteristics of the mixed field. The average G-value and the average quality factor are considered to be parameters suitable for such a quantity.

Etched Track Techniques in Radiation Dosimetry

Abstract Conventional detectors used in radiation protection dosimetry (for a given amount of energy deposited in their macroscopic volumes) are most sensitive to sparse radiations (electrons, X or gamma) than to fast neutrons or high LET particles, i.e. those particles characterised by high biological effectiveness. By contrast, damage track detectors are completely insensitive to sparse radiations and can be very sensitive to high LET particles (typically alpha particles and neutron induced recoils). To facilitate the applications of these new detecting methods in radiation protection dosimetry, techniques have been developed which exploit the high energy deposition in the vicinity of the track to initiate amplification or avalanche type processes, which can be easily detected. The discovery that CR-39 plastic is sensitive to protons with a wide range of energy shows promise for the solution of the complex problem of personal neutron dosimetry.

The dosimetry of bone irradiated by fast neutrons

The previous work on the dosimetry of bone is briefly reviewed. A dosimetric theory for the response of detectors irradiated by fast neutrons is applied to the problem of bone dosimetry. In the theory the detector of cavity shape is characterized by distributions of chord lengths along which the neutron-produced charged particles travel and deposit energy. Cavities of different convex geometries can be treated. A simplified version of the theory uses a single mean chord length to characterise the cavity. The absorbed dose to individual marrow cavities in trabecular bone is calculated over a large range of marrow cavity size for monoenergetic neutrons ranging from 0.5 to 7.0 MeV and for 252Cf neutrons. The influence of cavity shape is explored by considering spheres and cylinders of different elongation. The difference in adsorbed dose is not great. Also the simplified model using a single mean chord length gives results in close agreement with the results obtained with chord length distributions.

A New Approach to the Problems of Extremity Dosimetry

A New Approach to the Problems of Extremity Dosimetry

The new NACP- and ICRU-dosimetry protocols for dosimetry of high-energy photon and electron radiation

In 1980 the NACP (Nordic Association of Clinical Physics) published new recommendations for the absorbed dose determination in electron and photon beams having maximum energies between 1 and 50 MeV and in addition a supplement in 1981 specially devoted to problems in dosimetry using low-energy electrons, with /7o < 15 MeV [8,9]. These protocols as well as the ionization chamber calibration procedure based on the very recent ICRU electron dosimetry Report 35 [4] will be discussed. Also, some background, not appearing in these reports, will be given. tors, and define the conditions (i.e. irradiation geometry and beam qualities) for which they are valid. It is often not understood that it is necessary to use a consistent set of numerical data both for the application of cavity theory at the Standards Laboratory to determine exposure or kerma and at the hospital for the conversion factors (cf. page 4 in ICRU Report 35). In order to stress this point the complete calibration chain must be analysed. The exposure for 6~ gamma rays, Xc, is determined at the Standards Laboratory from absolute measurements of J , ir, the electric charge (of one sign) per unit mass of air by using the relationship (see e.g. ref. 5).

Obliquity correction for electron beams.

Uneven air gaps, beam obliquity, or sloping contours create complex dosimetry problems in electron beam treatment planning. We find that the depth dose distribution in an obliquely incident beam can be calculated from the data for a normally incident beam by using inverse square law and obliquity factors. The obliquity factors have been determined for various energy beams in the range of 6-22 MeV and can be used for manual treatment planning.

Dosimetry comparison and characterisation of an Al K ultrasoft X-ray beam from an MRC cold-cathode source

Ultrasoft X-rays of 0.3-5 keV have provided a unique tool for the investigation of intracellular mechanisms of radiation action in biological organisms, including mammalian cells. However, their use presents unique practical problems in dosimetry and experimental design. Detailed interpretation of the biological results requires reliable dosimetry and well characterised monoenergetic beams. This paper presents a comparison between two fundamentally different dosimetric techniques, namely the ionisation current in an extrapolation chamber and photon counts in a proportional counter. Agreement within 7% was obtained when these two methods were applied to an Al K X-ray beam (1.5 keV) from an MRC cold-cathode transmission target discharge tube as previously used in many biological experiments. Photographic film was calibrated as a relative dosimetric technique and used for investigation of the intensity uniformity of the radiation field. These techniques provide a comprehensive characterisation of the beam in the position of the biological cells, including photon flux (or absorbed dose rate), spectral purity (showing <<1% bremsstrahlung relative to characteristic Al X-rays) and uniformity over the irradiation area (within about 5% for mammalian cell irradiations).

Partial kerma factors for neutron interactions with 12C at 20 < En < 65 MeV

New measurements of elastic and inelastic scattering of 20–26 MeV neutrons from 12C are presented and analyzed in terms of a deformed optical model potential. Results of these analyses have been compared with other recent differential and total neutron scattering measurements and with proton scattering data in order to develop a consistent representation of the energy dependence of the n- 12C interaction over a broad energy range. Applications of the data and the model to problems in neutron dosimetry are discussed.

Neutron spectrum unfolding by the Monte Carlo method

Bayes' formalism is applied to neutron dosimetry problems. It is shown that this formalism and a special Monte Carlo algorithm (importance sampling random walk) can be used for parameter estimation in cases where the least-squares method fails. Three examples are discussed. The essential advantages of this method are that it makes possible the evaluation of confidence limits in neutron dose problems and the determination of the (unfolded) neutron spectrum from a set of a few reaction rates.

Experimental Methods for Determining Latchup Paths in Integrated Circuits

Methods of determining latchup paths in integrated circuits are discussed and applied to several device technologies. Localized laser irradiation was used to find latchup-sensitive regions with a special experimental configuration that overcomes the dosimetry problems inherent in small area beams. Two infrared imaging methods were used to find current paths after latchup was initiated with the laser. Circuit interaction in one device type caused the power supply current to decrease after latchup, which shows that measurement of power supply current is not always a reliable way to detect latchup in integrated circuits.

Application of a finite-difference technique to the human radiofrequency dosimetry problem.

A powerful finite-difference numerical technique has been applied to the human radiofrequency dosimetry problem. The method possesses inherent advantages over the method-of-moments approach in that its implementation requires much less computer memory. Consequently, it has the capability to calculate specific absorption rates (SARs) at higher frequencies and provides greater spatial resolution. The method is illustrated by the calculation of the time-domain and frequency-domain SAR responses at selected locations in the chest. The model for the human body is comprised of rectangular cells with dimensions of 4X4X6 cm and dielectric properties that simulate average tissue (2/3 muscle). Additionally, the upper torso (chest) is configured by both homogeneous and inhomogeneous models in which this region is subdivided into 20,736 cells with dimensions of 1X1X1 cm. The homogeneous model of the chest consists of cells with average tissue properties, and the calculated results are compared with measurements acquired from a homogeneous phantom model when the exposure frequency is 350 MHz. For the inhomogeneous chest model the lungs and surrounding region (ribs, spine, sternum, fat, and muscle) are modeled with as much spatial resolution as allowed by the 1X1X1 cm cells. Computed results from the inhomogeneous chest model are compared with the homogeneous model.

Damage Track Detectors for Neutron Dosimetry: II. Characteristics of Different Detection Systems

The application of solid state nuclear track detectors to personnel neutron dosimetry is reviewed. Four methods of neutron detection are considered; (1) detection using (n,f) reactions, (2) thermal neutron detection via (n,a) reactions in external radiators, (3) fast neutron detection using heavy recoils and (n,a) reactions occurring mostly within the track detector, and (4) neutron detector via proton recoils and (n,p) reactions. The main features of each of these detection methods are discussed. Finally the nature of neutron dosimetry problems and their possible solution using multielement dosemeters are outlined.

The dosimetry of bone incorporating alpha-emitting radionuclides.

The previous work on the dosimetry of alpha-emitting radionuclides incorporated in bone is briefly reviewed. The application of cavity ionisation theory to problems of bone dosimetry is propounded and recent developments of the cavity theory for alpha particle fields are applied to bone dosimetry problems. The mean marrow dose over a large range of bone cavity size calculated by a simple theory using a mean chord length to characterise a cavity is compared with results of a more elaborate theory employing the chord length distribution for a sphere. The difference is not great. The influence of the shape of the cavity is explored by considering cylindrical cavities of different elongation. Data are presented for both volume-seeking and surface-seeking radioactive nuclides. The endosteal dose to a 10 mu layer is calculated as a function of cavity size for both volume-seeking and surface-seeking radioactive nuclides. The endosteal dose is also calculated for a surface seeker as a function of endosteal layer thickness. Finally, the results of these calculations are shown to be generally in good agreement with those of the calculations of earlier workers. It is concluded that a simple and reliable method of calculating the mean marrow dose and endosteal dose for both volume- and surface-seeking alpha emitters has been established.

The application of multiple scattering theory to therapeutic electron dosimetry.

Fermi–Eyges multiple scattering theory for electrons is explained, and a general three‐dimensional formalism is developed for its application to problems of therapeutic electron dosimetry. The formalism is illustrated by a number of elementary examples: a rectangular beam, an isotropic point source, and a scanning line source.

Microwave Cytotoxicity: Lack of in Vitro Evidence for Nonthermal Effects at High Power Levels

A unique cylindrical microwave cavity chamber for the exposure of mammalian cells was designed and built. The cavity was used to determine whether or not microwaves (896 or 434-460 MHz) are capable of affecting cellular survival via nonthermal mechanisms other than those resulting from equivalent thermal exposures. Chinese hamster ovary (HA-1) cells or radiation-induced fibrosarcoma (RIF) mouse cells were grown directly on gold-plated copper disks to assure optimum heat dissipation and accurate thermal dosimetry. The temperature was controlled precisely (+/-0.1/sup o/C and was measured continuously during microwave exposures. Microwave power levels of 135 W/cm/sup 3/ of absorbed power maintained for 30 min caused no discernible decrease in cellular survival of proliferating cells compared to that measured in appropriate heat controls over a temperature range of 12 to 46/sup o/C. In addition, RIF mouse cells were exposed similarly in Hanks' balanaced salt solution (HBSS). Again, no additional decrease in survival beyond that due to heating was observed for microwave exposure in full medium; however, a significant decrease in survival was noted when cells were treated in HBSS which was at pH 6.9-7.2. This phenomenon may have implications in tumors with significant portions of the population at low pH or with lowmore » nutrient concentrations. Since these absorbed power levels are at least two orders of magnitude greater than those that will be necessary to hear and maintain tumors at hyperthermic treatment temperatures for cancer therapy, these results suggest that cellular destruction in proliferating cells can be predicted by the heat effect and that any microwave-specific nonthermal effects encountered in vivo will likely be due to problems of thermal dosimetry of physiological factors related to this mode of heat distribution.« less