bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermocouples—The Arizona experience with in‐house manufactured probes
Authors: Anhalt D. , Hynynen K.
Published: March 2003

The performance of several different types of multisensor thermocouple probes have been tested to determine the feasibility of each type for use in the hyperthermia clinic. All of the probes tested were manufactured in‐house, and a detailed description of the construction process will be presented. The overall performance of the probes in terms of robustness, calibration, conduction errors, and response time will be described. In particular, this study describes our experience with in‐house manufactured thermocouples over the past several years. The results indicate that when strict quality assurance guidelines are followed, in‐house manufactured thermocouples perform satisfactorily—thereby providing an alternative to purchasing probes and measurement systems from commercial vendors if the proper resources are available.
Biological effects of the Auger emitter iodine‐125: A review. Report No. 1 of AAPM Nuclear Medicine Task Group No. 6
Authors: Sastry Kandula S. R.
Published: March 2003

The biological implications of Auger electron cascades following inner shell ionization of atoms have been of interest for over 25 years. By virtue of their decay via orbital electron capture and/or internal conversion, several biomedical radionuclides emit numerous low‐energy electrons spontaneously. The biological effects of such radionuclides incorporated into tissues cannot be predicted a priori because of the highly localized patterns of energy deposition by the electrons. Results of extensive research using Iodine‐125 as a model Auger electron emitter are now available. This article presents an up‐to‐date review of the physical and radiobiological data on this Auger emitter. Valuable concepts concerning the action of internal Auger emitters are identified phenomenologically, and questions that need to be answered are indicated. The present understanding provides a scientific basis toward estimation of risk associated with Auger emitters used in diagnosis, and suggests potential applications to therapy.
Polarity effect in plane‐parallel ionization chambers using air or a dielectric liquid as ionization medium
Authors: Wickman Göran , Holmström Thord
Published: March 2003

A plane‐parallel ionization chamber having a sensitive volume of 2 mm3 and using the dielectric liquid tetramethylsilane as the sensitive medium instead of air is described. In the design of the chamber special attention was given to the factors that can cause unwanted currents in the cable, stem, or the chamber dielectric material. The chamber has been tested with respect to the polarity effect in regions of radiation fields where ordinary plane‐parallel ionization chambers will often fail. These regions are the build‐up region in photon fields, and the region close to the practical range for electrons where nonelectronic equilibrium is significant. Experimental results show that, despite the extremely small ionization volume in the liquid ionization chamber, the polarity effect never exceeds a few tenths of a percent in field positions where well‐known commercially available chambers with much less spatial resolution designed for measurements in radiation therapy fields can show polarity effects of 5% to 30%. The origin of spurious currents and how they must be minimized in the design of either a liquid‐ or gas‐filled ionization chamber is discussed.
Broad line quantitative chemical shift spectroscopy
Authors: Sobol W. T. , Elster A. D. , Hinson W. H. , Chwals W. J.
Published: March 2003

Proton NMR spectroscopy was applied to quantitate the measurement of total body water/fat distributions in vivo. A special MR protocol was developed to excite a thick slab of tissue and display the magnitude NMR spectrum of the collected response signal. Very short echo time TE (8 ms) and long repetition time TR (4000 ms) were used to minimize relaxation damping of the signal intensities. The spectrum was then decomposed into individual lines and proton densities of different species were calculated. Proton density information was converted into weight percentage data using stoichiometrical and physiological information. The technique was validated using phantoms that contained different mixtures of water/maize oil. A high‐resolution NMR spectrum of maize oil samples was used to determine the stoichiometric information. The test results showed good agreement with the known composition of the phantom within the whole range of water content (0–100%). This method is very fast since no phase encoding of data is required. Preliminary results for monkeys show promising potential in clinical applications.
A ρ‐θ technique for treatment verification in radiotherapy and its clinical applications
Authors: Ding George X. , Shalev Shlomo , Gluchev Georgi
Published: March 2003

A new technique based on a ρ‐θ coordinate system for determining differences in patient position between portal and simulator images is presented. Unlike the conventional point matching method, which requires the fiducial points to be labeled in pairs before the registration, the ρ‐θ technique avoids this manual procedure. It accomplishes the treatment verification in two major steps; image alignment and field displacement analysis. For the same number of fiducial points in the simulator and portal images, it first finds the corresponding paired points if the points are not distributed symmetrically about their centroid. This is followed by alignment of these paired points using the least squares matching method to find the optimal two‐dimensional rigid body transformation parameters (shift, rotation, and scaling factor). The transformation parameters are then used to transform the portal field edge into the simulator image, so that the portal field can be compared with the prescribed field on the simulator image. A number of parameters were explored to describe the field displacement errors, including treatment field size, under/over irradiated size, the shift in center of gravity of the field, the field edge shift, and rotation of the field. The ρ‐θ technique as implemented is both fast and accurate. Experiments on the registration of radiological phantom portal images acquired with an on‐line portal imaging system mounted on a linear accelerator indicate an accuracy on the order of 1 mm in detecting the shift of the field's center of gravity and approximately 1° in detecting the field rotation. The results of a clinical trial are also presented. The technique appears well suited as an integral part of an automated on‐line portal imaging treatment verification system.
Monte Carlo optimization of metal/phosphor screens at megavoltage energies
Authors: Radcliffe T. , Barnea G. , Wowk B. , Rajapakshe R. , Shalev S.
Published: March 2003

The physics of imaging with metal/phosphor (Gd2O2S:Tb on brass) screens at megavoltage energies has been investigated using Monte Carlo simulation. It has been found that pair production is a significant contributor to energy deposition for Bremsstrahlung beams with energies greater than 6 MV. The effects of different thicknesses of phosphor and metal have been studied, and it is shown that the metal plays a significant role in establishing electronic equilibrium in the phosphor. The transport of optical photons through the phosphor has been modeled, and was found that only 10% to 20% of the light created in the phosphor escapes from the surface, with much of the loss being due to total internal reflection at the surface. Calculated results have been compared with experimental measurements of screen brightness for different phosphor and metal thicknesses. The SNR of a video electronic portal imaging device (VEPID) has been calculated as a function of x‐ray and optical photon detection efficiency. The non‐Poisson distribution of energy deposition in the phosphor is an important contributor to the SNR. The results of this paper should serve as a useful guide to the engineering design of future electronic portal imaging systems.
Evaluation of electron‐beam uniformity during commissioning of a linear accelerator
Authors: Mandelzweig Y. , Feygelman V.
Published: March 2003

Electron‐beam profiles measured during acceptance testing and commissioning of a linear accelerator were analyzed according to manufacturer's specifications and more stringent AAPM TG‐25 recommendations. The difference between specifications of the AAPM report and those experienced commercially is discussed. Although all the electron beams met the manufacturer's specifications, the uniformity parameters for some of them were outside the limits suggested by the AAPM report. Profiles acquired at depths larger than dmax were extremely valuable for evaluation and adjustment of the beams. The following suggestions for practical machine commissioning are made: Profiles taken deeper than at dmax are extremely useful indicators of the beam nonuniformity; acquisition of these profiles should be a part of the routine acceptance testing procedure; and beam uniformity should be evaluated against AAPM recommendations, and this should be included in the purchase specifications.
Automated selection of regions of interest for quantitative analysis of lung textures in digital chest radiographs
Authors: Chen Xuan , Doi Kunio , Katsuragawa Shigehiko , MacMahon Heber
Published: March 2003

In order to implement a computerized scheme for quantitative analysis of interstitial lung disease in chest radiographs in clinical situations, a fully automated method of selecting many square regions of interest (ROIs) in peripheral lung areas are developed. First, the peripheral lung regions are identified, based on the automated detection of lung apices, ribcage edges, and diaphragm. Then a large number of ROIs are selected sequentially by filling in the identified peripheral regions. Finally, those ROIs containing sharp edges are removed based on an edge gradient analysis, for which a gradient‐weighted edge orientation histogram is employed. Approximately 200–400 ROIs were automatically selected for each case with this method. The evaluation of using ROC analysis indicated that the automated ROI selection method was effective in quantitative analysis of lung textures in digital chest radiographs.
An improved method for rebinning kernels from cylindrical to Cartesian coordinates
Authors: Rathee S. , McClean B. A. , Field C.
Published: March 2003

This paper describes the errors in rebinning photon dose point spread functions and pencil beam kernels (PBKs) from cylindrical to Cartesian coordinates. An area overlap method, which assumes that the fractional energy deposited per unit volume remains constant within cylindrical voxels, provides large deviations (up to 20%) in rebinned Cartesian voxels while conserving the total energy. A modified area overlap method is presented that allows the fractional energy deposited per unit volume within cylindrical voxels to vary according to an interpolating function. This method rebins the kernels accurately in each Cartesian voxel while conserving the total energy. The dose distributions were computed for a partially blocked beam of uniform fluence using the Cartesian coordinate kernel and the kernels rebinned by both methods. The kernel rebinned by the modified area overlap method provided errors less than 1.7%, while the kernel rebinned by the area overlap method gave errors up to 4.4%.
Patient dose and image quality in five standard x‐ray examinations
Authors: Havukainen R. , Pirinen M.
Published: March 2003

Patient doses and image quality in five standard x‐ray examination projections (22–36 measurements per each projection) have been measured, using homogeneous phantoms. The means and range of variation for the entrance skin air kerma values were: abdomen AP 5.2 mGy (1.1–21 mGy), chest PA 0.27 mGy (0.035–0.84 mGy), lumbar spine AP 8.4 mGy (2.9–28 mGy), skull LAT 3.1 mGy (1.1–7.7 mGy), and thoracic spine AP 7.9 mGy (1.3–22 mGy). Considerable variation was found in image quality parameters: film optical densities, image contrasts, and resolutions as well as in exposure values, tube voltages, exposure times, and in half‐value thicknesses. The study indicated the need to standardize medical x‐ray examination techniques in different x‐ray departments. The measuring method can be used for comparing the patient dose and image quality of an individual x‐ray unit to the doses and image quality in general use. The results can be used as the reference values for quality control of x‐ray equipment.
Evaluation of mammographic viewbox luminance, illuminance, and color
Authors: Haus Arthur G. , Gray Joel E. , Daly Timothy R.
Published: March 2003

Twenty‐three viewboxes were evaluated in six mammography facilities. Luminance and illuminance measurements were made with a recently calibrated photometer. Color temperatures were measured with a Minolta color meter. The average luminance for the 23 viewboxes was 2920 nit (lumen/Sr/m2), the lowest value was 1610 nit, and the highest value was 3630 nit. The average illuminance was 40 lux (lumen/m2), with 6 lux as the lowest value, and 97 lux as the highest. The average color temperature was 8400 K with the lowest value of 4900 K, and the highest of 10 900 K.
The evaluation of a clinical thermometer for measuring developer temperature in automatic film processors
Authors: Wilson William B. , Haus Arthur G. , Nierman Carol , Lillie Ronald , Batz Thomas , Moore Robert
Published: March 2003

In medical imaging, the temperature of the developer solution in the film processor affects film speed (radiation dose), film contrast, and film base plus fog. The National Council on Radiation Protection and Measurement (NCRP) Report 99 on Quality Assurance, and the American College of Radiology (ACR) Mammography Quality Control Manual for Radiologic Technologists, indicate that the developer temperature should be within ±0.5 °F (±0.3 °C) of that recommended by the manufacturer for the specific film/developer combination being used. The accuracy and repeatability of the thermometer is most important. This paper describes the requirements of a thermometer for measuring the temperature of the developer solution and suggests an inexpensive but accurate device for doing so.
Two‐dimensional pulsatile hemodynamic analysis in the magnetic resonance angiography interpretation of a stenosed carotid arterial bifurcation
Authors: Tasciyan Talin A. , Banerjee Rupak , Cho Young I. , Kim Richard
Published: March 2003

A two‐dimensional pulsatile hemodynamic analysis based on the finite‐element technique was performed on a minimally stenosed carotid artery to identify the possible explanation for the differences in the x‐ray and magnetic resonance carotid angiograms of a patient. The magnetic resonance angiogram was obtained by applying the maximum intensity projection algorithm to axial slices, acquired using the time‐of‐flight principle. The differences in the x‐ray and magnetic resonance depictions were interpreted based on velocity profile, wall shear stress, and streamline data provided by the hemodynamic analysis. The specific contribution of the stenosis was further isolated from that of the bifurcation by comparing the flow patterns within the stenotic artery with those of its normal counterpart. The Doppler spectral velocity wave form of the patient constituted the basis for the pulsatile flow velocity specification. The analysis took into consideration the non‐Newtonian viscosity of blood. The numerical procedure was validated through different convergence criteria and through shear stress comparisons. The importance of hemodynamic analyses in relation to magnetic resonance angiography was further discussed along with possible shortcomings of the technique.
An unbiased signal‐to‐noise ratio measure for magnetic resonance images
Authors: McGibney G. , Smith M. R.
Published: March 2003

Estimating the true signal‐to‐noise ratio (SNR) of magnetic resonance (MR) images with low signal is confounded by the magnitude presentation of the data. This paper suggests a simple solution to this problem. A common method of measuring SNR compares the mean signal to the standard deviation of the noise. This SNR measure was found to be satisfactory for high but not low signal‐to‐noise image regions because of noise bias. These inconsistencies are removed by introducing unbiased definitions of the signal and noise levels in terms of their root‐mean‐square values. The approaches are compared by evaluating the SNR values for MR medical images.
Dosimetry considerations of bone‐seeking radionuclides for marrow ablation
Authors: Bayouth J. E. , Macey D. J.
Published: March 2003

Marrow ablation by radionuclide therapy for patients requiring bone marrow transplantation is possible by injecting bone‐seeking radiopharmaceuticals. For each radionuclide under consideration, one should determine the (1) amount of activity required to deliver a given radiation dose to the marrow, (2) waiting period before reinfusion to limit the radiation dose to the transplant marrow to an acceptable level, and (3) dose to other critical organs. In an attempt to answer these questions, dose estimates for several radionuclides of interest (32P, 90Y, 153Sm, 166Ho, 186Re, and 188Re) have been calculated. All doses are derived following the MIRD methodology. Biodistribution data of 153Sm‐labeled phosphates in the rat are used to estimate uptake of similar radiopharmaceuticals in humans. Typically the skeleton retains 50% of the injected activity and 50% is excreted rapidly through the urine, permitting delivery of ablation doses to the marrow, with tolerable doses to other organs. Skeletal retention data measured from a diagnostic dose can be used to calculate the activity required to deliver a desired marrow ablation dose consistent with toxicity limits set by other critical organs.
Compensation for attenuation, scatter, and detector response in SPECT reconstruction via iterative FBP methods
Authors: Liang Zhengrong
Published: March 2003

Iterative filtered backprojection (FBP) reconstruction is a fast method for single photon emission computed tomography (SPECT) that can provide simultaneous compensation for nonuniform attenuation, scatter, and distance‐dependent detector response. The iterative FBP method was applied to the reconstruction of SPECT images of a chest phantom consisting of nonuniform attenuating media. One hundred twenty projections containing 20 million counts were reconstructed on an image array of 128×128×64. The accuracy of reconstruction was significantly improved, in terms of concentration ratio, object shape, and noise reduction. Results of this experimental study indicate that iterative FBP can effectively reconstruct SPECT images, while other iterative methods, such as maximum a posteriori probability (MAP), will spend at least ten times more computing effort in the reconstruction on the same computer. The disadvantage of iterative FBP is its inability to model the noise properties of data collection accurately, as compared to the MAP methods.
Effect of energy resolution on scatter fraction in scintigraphic imaging: Monte Carlo study
Authors: Kojima Akihiro , Matsumoto Masanori , Takahashi Mutsumasa , Uehara Shuzo
Published: March 2003

The effect of energy resolution in detector systems on scatter fractions in scintigraphic imaging through Monte Carlo simulation is investigated. A 10‐cm Tc‐99m line source within a cylindrical water phantom 20 cm in diameter and 20 cm in length was modeled and energy spectra were calculated at three different line source positions. The energy resolution was changed from 8% to 16% FWHM at 140 keV and a symmetrical energy window width was varied from 8% to 23% on the photopeak of 140 keV in energy spectra corresponding to each energy resolution. The relationship between the scatter fraction and the symmetrical energy window width, and the relationship between the scatter fraction and the primary counts were presented for all energy resolutions investigated. Furthermore, the effect of the asymmetrical energy window on reducing the scatter fraction was also studied and compared with the narrow symmetrical energy window. The results quantitatively showed that improved energy resolution can considerably decrease the scatter fraction with a narrow symmetrical energy window or an asymmetrical energy window without significant primary count‐loss compared to that obtained with lower quality energy resolution. The asymmetrical energy window could reduce scatter fraction as compared with the narrow symmetrical energy window when the same number of primary counts was required for both energy windows. Knowing the relationship between the scatter fraction and the primary counts is important in scintigraphic imaging to select the optimum energy window corresponding to the energy resolution.
Dead time of an anger camera in dual‐energy‐window‐acquisition mode
Authors: Zasadny Kenneth R. , Koral Kenneth F. , Swailem Fayez M.
Published: March 2003

Two side‐by‐side energy windows are sometimes employed in quantitative single photon emission computed tomography (SPECT) studies. The count‐rate losses at high activities for a GE400AT camera were measured in such a dual‐window‐acquisition mode by imaging a decaying source composed of a hot sphere within a warm cylinder. The data in each window was either kept separate or combined for purposes of dead‐time correction and the paralyzable model was assumed. In addition, correction factors were derived from a “monitor” source at the edge of the camera. Finally, energy spectra for only the monitor‐source region of interest and for the entire camera were obtained under both low‐ and high‐count conditions and compared. With 99mTc (1) the spectral measurements show no peak shift but reveal pulse‐pileup spectral degradation. (2) The monitor‐source corrections do not agree well with those from the model, presumably because of the differential effects of such degradation. For this camera the preferred correction method for patients is one using the model and two, effective, phantom‐derived dead times for the separate data from the two windows. The two effective dead times are needed to compensate for pulse pileup adding more counts to the lower‐energy window than to the higher‐energy one at high rates. For 99mTc, the effective dead time to correct data in the 93–123 keV window is 7.0±0.14 μs and for that in the 124–154 keV window 5.95±0.10 μs, and for 131I, for data in the 260–332 keV window 18.8 μs and for that in the 333–405 keV window 14.3 μs.
Energy distributions from a racetrack microtron measured with a magnetic spectrometer
Authors: Sorcini B. B. , Rosander S.
Published: March 2003

Energy spectra of accelerated electron beams from a racetrack microtron were measured using a magnetic spectrometer. The spectrometer utilized a 90° dipole magnet. A ray‐tracing program was developed to determine the slit positions of the spectrometer based on a detailed map of the magnetic field measured at field strengths corresponding to about 20 and 50 MeV. The total a priori uncertainty (previously often called systematic or class B uncertainty) of the measured most probable energy Ep is 0.22% (one approximate standard deviation) and the a posteriori uncertainty (previously often called random or class A uncertainty) is 0.04% (1σ). The estimated energy resolution (ΔE/E) of the spectrometer is 4×10−4. Spectral energy distributions of the electron beam were measured at a Ep=21.1 and 51.6 MeV, and the obtained full width at half‐maximum of the energy distributions were 53 and 34 keV, respectively. All the measurements were performed in vacuum to minimize the influence of electron energy loss and scatter.
A technique for the evaluation of a missing tissue compensator system
Authors: Chu T. , Lee K. , Dunscombe P.
Published: March 2003

A two dimensional approach to the evaluation of a missing tissue compensator system has been developed and implemented. Quantitative descriptors of the dose area histograms generated by scanning films irradiated under a variety of compensated and uncompensated conditions are proposed. The method has been found to be useful during the acceptance testing of a commercial compensator system and the results of this exercise are presented.
Characteristics of a spoiled 6‐MV beam from a dual‐energy linear accelerator
Authors: Lee Plato C. , Thomason Cynthia , Glasgow Glenn P.
Published: March 2003

A beam spoiler for a 6‐MV x‐ray beam was designed and spoiled beam dosimetry performed. The spoiled beam quality was similar to that of the unspoiled beam. The percentage depth doses at 5 mm were at least 90% for all field sizes except 4×4 cm, while the surface dose at 0 mm varied from 22.5% for a 4×4‐cm field to 85.8% for a 22×22‐cm field. The spoiled beam showed degraded beam flatness for small field size at superficial depths; the beam flatness at 6 mm for a 4×4‐cm field was ±9.0%. The beam flatness improved as the field size increased, e.g., at same depth, the beam flatness was ±2.5% for a 22×22‐cm field. The penumbra width (90%−10%) of the spoiled beam was greater than that of the unspoiled beam for all field sizes and at all depths; e.g., at 0‐mm depth, for a 22×22‐cm field, the penumbra width was 3.8 cm for the unspoiled beam and 7.2 cm for the spoiled beam. Beyond dmax the difference in the penumbra widths between the spoiled and unspoiled beam was about 3–4 mm for all field sizes and at all depths. The peripheral dose was larger for the spoiled beam.
Dose‐volume histogram computations for small intracranial volumes
Authors: Kooy Hanne M. , Nedzi Lucien A. , Alexander Eben , Loeffler Jay S. , Ledoux Robert J.
Published: March 2003

A sampling formalism is presented to accurately compute the absolute volumes and integral dose‐volume histograms of small volumes treated in stereotactic radiosurgery. The presence of small volumes and sharp dose gradients places special constraints on the computational formalism and the accuracy required to compute the dose‐volume relationships. We use a spatially nonuniform random sampling method to allow an efficient and accurate computation of the dose‐volume histograms for an arbitrary number of volumes. The computation of absolute volume vs dose allows intercomparison of dose delivered to target and dose‐critical volumes and allows a quantitative trade‐off analysis often critical to an optimal treatment of the lesion.
Buildup region of high‐energy x‐ray beams in radiosurgery
Authors: Sixel Katharina E. , Podgorsak Ervin B.
Published: March 2003

The depths of dose maxima of radiosurgical x‐ray beams increase with the field diameter in the range from 10–30 mm. Furthermore, the degree of the increase is proportional to the photon beam energy. This behavior is in contrast to that of large radiotherapeutic fields, where the depths of dose maxima decrease with increasing field size. The surface doses, depths of dose maxima, and collimator scatter factors for radiosurgical beams with energies between 6 and 18 MV are presented. It is shown that the change in dmax for radiosurgical beams is a result of photon scatter in the phantom rather than in the collimator. Monte Carlo simulations of the radiosurgical beams are used to separate the total dose into two components: the primary dose and the scattered dose. Calculations indicate that buildup region characteristics are governed by the primary dose deposition in the medium. The scattered dose has a minimal effect on the total dose deposited in media by radiosurgical beams.
A simple test phantom for stereotactic computed tomography
Authors: Ekstrand Kenneth E. , Olds Warren W. , Branch Charles L.
Published: March 2003

An easy‐to‐use phantom has been constructed for checking the accuracy of a stereotactic computed tomography localization system. This phantom has been used on a commercially available stereotactic radiosurgery system. With this system, the phantom reference point, whose location is established by means of a precision measuring implement, can be localized by a computed tomography (CT) scanner with a standard deviation of measurement that is less than 0.3 mm in three orthogonal axes.
Filter wheel equalization in DSA: Simulation results
Authors: Boone John M. , Gardiner Geoffrey A. , Levin David C.
Published: March 2003

Digital subtraction angiography (DSA) is a valuable and frequently used diagnostic technique which allows the evaluation of vascular anatomy and pathology. In order to improve the utility and diagnostic performance of DSA, a filter wheel system is presented which can provide mechanically simple, rapidly adaptable, and clinically practical radiographic equalization to DSA images. The filter wheel equalization system consists of a series of computer‐driven filter wheels, mounted between the x‐ray tube and collimator. Each wheel has an annular area of attenuator material which intersects the x‐ray beam and carries a rotationally varying compensation pattern on it. Rotation of the filter wheel modulates the attenuator pattern in the x‐ray field under computer control, in a manner designed to increase the x‐ray exposure to underexposed areas in the image. A system with eight wheels has 1019 possible equalization patterns. The compensation patterns are removed in the subtracted DSA images. Computer simulation techniques were used to evaluate various design scenarios for the filter wheel system, using a data base of 191 clinical DSA mask images. For a practical implementation of the filter wheel system, an improvement in the signal to noise ratio of 23%, averaged over the image, was found.
A high‐resolution XRII‐based quantitative volume CT scanner
Authors: Holdsworth D. W. , Drangova M. , Fenster A.
Published: March 2003

A laboratory volume CT scanner has been developed, with high spatial resolution in all three dimensions, which can be used for quantitative analysis of excised tissue samples in vitro. The system incorporates an x‐ray image intensifier, optically coupled to a time‐delay integration (TDI) CCD to obtain low‐noise and low‐scatter projections of the sample volume. A water bath surrounds the sample to equalize the exposure to the image intensifier, thereby reducing the dynamic range of the input signal. The scanner operates in two modes, producing either a single, transverse image through the sample or a three‐dimensional image of the sample volume. Spatial resolution is adjustable over the range of 1.2 to 2.8 mm−1. System response is linear over the range −1000 to 3500 Houndsfield units (HU), with an average precision of ±80 HU. The precision of geometric measurements in the transverse plane allows circumference measurements to within ±0.1 mm. Finally, applications of this technique of nondestructive analysis in biomedical research are discussed.
Tumor dosimetry in radioimmunotherapy: Methods of calculation for beta particles
Authors: Leichner Peter K. , Kwok Cheuk S.
Published: March 2003

Calculational methods of beta‐particle dosimetry in radioimmunotherapy (RIT) are reviewed for clinical and experimental studies and computer modeling of tumors. In clinical studies, absorbed‐dose estimates are usually based on the in‐vivo quantitation of the activity in tumors from gamma camera images. Because of the limited spatial resolution of gamma cameras, clinical dosimetry is necessarily limited to the macroscopic level (macrodosimetry) and the MIRD formalism for absorbed‐dose calculations is appropriate. In experimental RIT, tumor dimensions are often comparable to or smaller than the beta‐particle range of commonly used radionuclides (for example, 131I, 67Cu, 186Re, 188Re, 90Y) and deviations from the equilibrium dose must be taken into account in absorbed‐dose calculations. Additionally, if small tumors are growing rapidly at the time of RIT, the effects of tumor growth will need to be included in absorbed‐dose estimates. In computer modeling of absorbed‐dose distributions, analytical, numerical, and Monte Carlo methods have been used to investigate the consequences of uniform and nonuniform activity distributions and the effects of inhomogeneous media. Measurements and calculations of the local absorbed dose at the multicellular level have shown that variations in this dose are large. Knowledge of the absorbed dose is essential for any form of radiotherapy. Therefore, it is important that clinical, experimental, and theoretical investigations continue to provide information on tumor dosimetry that is necessary for a better understanding of the radiobiological effects of RIT.
Multicellular dosimetry for beta‐emitting radionuclides: Autoradiography, thermoluminescent dosimetry and three‐dimensional dose calculations
Authors: Yorke E. D. , Williams L. E. , Demidecki A. J. , Heidorn D. B. , Roberson P. L. , Wessels B. W.
Published: March 2003

Inhomogeneities in activity distributions over distances from 10 to 104 μm are observed in many tumors treated with radiolabeled antibodies. Resulting nonuniformities in absorbed dose may have consequences for the efficacy of radioimmunotherapy. Activity variations may be directly studied with quantitative autoradiography (ARG). Converting these data to absorbed dose distributions requires additional information about pharmacokinetics, the use of a point source function and consideration of the complete three‐dimensional activity distribution, as obtained from sequential autoradiographic slices. Thermoluminescent dosimetry with specially prepared CaSO4:Dy dosimeters implanted into tissue can directly measure absorbed dose in selected regions. The conditions under which thermoluminescent dosimeters (TLD) are used differ markedly from “normal” use conditions in external beam radiotherapy. Therefore special calibration and quality assurance precautions are needed to assure the precision of this technique. Procedures and pitfalls in the use of both techniques in radioimmunotherapy are described.
An overview of imaging techniques and physical aspects of treatment planning in radioimmunotherapy
Authors: Leichner Peter K. , Koral Kenneth F. , Jaszczak Ronald J. , Green Alan J. , Chen George T. Y. , Roeske John C.
Published: March 2003

Planar and tomographic imaging techniques and methods of treatment planning in clinical radioimmunotherapy are reviewed. In clinical trials, the data needed for dosimetry and treatment planning are, in most cases, obtained from noninvasive imaging procedures. The required data include tumor and normal organ volumes, the activity of radiolabeled antibodies taken up in these volumes, and the pharmacokinetics of the administered activity of radiolabeled antibodies. Therefore, the topics addressed in this review include: (1) Volume determinations of tumors and normal organs from x‐ray‐computed tomography and magnetic resonance imaging, (2) quantitation of the activity of radiolabeled antibodies in tumors and normal organs from planar gamma camera views, (3) quantitative single‐photon emission computed tomography and positron emission tomography, (4) correlative image analysis, and (5) treatment planning in clinical radioimmunotherapy.
Dosimetry of solid tumors
Authors: Meredith Ruby F. , Johnson Timothy K. , Plott Gene , Macey Daniel J. , Vessella Robert L. , Wilson Latresia A. , Breitz Hazel B. , Williams Lawrence E.
Published: March 2003

Dosimetry data arising from a decade of radioimmunotherapy are summarized along with techniques utilized to arrive at the reported dose estimates. Generality of the MIRD methodology allows it to serve as a vehicle for the calculation of solid tumor dosimetry although several limitations exist. Nonstandard geometries of solid tumors will ultimately necessitate determination of absorbed fractions for the individual tumors. Several approaches currently under investigation are described. For reasons of practicality, solid tumor dosimetry estimates continue to use the assumption of homogeneous activity distribution in a source organ, accounting for either all radiation or only nonpenetrating radiation. As computation tools become available for incorporating inhomogeneous cellular level data, the currently used “average dose” as an index of tumor sterilization will likely be replaced with a statistical distribution based on the number of viable cells in the tumor volume. Estimates of a tumor control dose would be based upon a linear extension of dose coupled with a threshold dose for cell sterilization.
Dosimetry of intraperitoneally administered radiolabeled antibodies
Authors: Roeske John C. , Chen George T. Y. , Brill A. Bertrand
Published: March 2003

Intraperitoneal and intracavitary radioimmunotherapy differ from other approaches of radioimmunotherapy in that high activity and dose gradients exist near the solution/tumor interface. Dose to tumor and normal tissue at the interface is a function of depth and is due to three major components: (1) the activity concentration of the administered radiolabeled antibody solution as a function of time within the compartment; (2) the spatial distribution of antibody/radionuclide complex as a function of depth and time as the biomolecules bind to and permeate tumor/normal tissues; and (3) the physical characteristics of the radionuclide in relation to depth of antibody penetration. In this review, the biological and physical aspects of intraperitoneally administered radiolabeled antibodies are discussed, and the state of experimental and calculational studies for this site is described. Areas requiring future investigation are examined, and recommendations are made regarding the type of measurements and calculations which are required for accurate dosimetry.
Radiobiology of radiolabeled antibody therapy as applied to tumor dosimetry
Authors: Langmuir V. K. , Fowler J. F. , Knox S. J. , Wessels B. W. , Sutherland R. M. , Wong J. Y. C.
Published: March 2003

This paper reviews the radiobiological aspects of radioimmunotherapy (RIT) with radiolabeled antibodies, including comparisons between RIT and external beam irradiation. The effectiveness of cell killing by radiation decreases with the dose rate and the rate of decrease is determined by the size of the shoulder on the radiation survival curve. Tumors with poor repair capabilities exhibit less of a dose rate effect than tumors with good repair capabilities. Continued tumor cell proliferation during treatment occurs at very low dose rates and can contribute to the reduced effectiveness of low dose rate radiation. Toxicity to normal tissues will determine the total dose of radiolabeled antibody that can be given and this will be influenced by the choice of both the radionuclide and the antibody. The reported enhanced effectiveness of RIT may be due to multiple factors including selective targeting of cells responsible for tumor volume doubling, tumor surface binding rather than homogeneous binding throughout the tumor volume, targeting of the tumor vasculature, or block of cell cycle progression in G2. During RIT, there is less time for reoxygenation of hypoxic tumor cells than during a course of conventional external beam radiotherapy. It has not yet been determined whether this will have a detrimental effect on RIT. Probably the most important factor in the success of RIT is dose heterogeneity. Any viable portion of a tumor that is not targeted and does not receive a significant radiation dose will potentially lead to treatment failure, no matter how high the dose received by the remainder of the tumor. Comparisons between RIT and external beam radiation have shown a wide range of relative efficacy. Tumors most likely to respond to RIT are tumors with poor repair capabilities, tumors that are susceptible to blockage in radiosensitive phases of the cell cycle, tumors that reoxygenate rapidly, and tumors that express the relevant antigen homogeneously. From a radiobiological perspective, it appears that RIT alone is unlikely to cure many tumors and that combination with other treatment modalities will be essential.
Probability of radiation‐induced complications for normal tissues with parallel architecture subject to non‐uniform irradiation
Authors: Jackson A. , Kutcher G. J. , Yorke E. D.
Published: March 2003

A biologically based model is developed to predict radiation‐induced normal tissue complication probability (NTCP) in inhomogeneously irradiated organs such as the lung or the kidney. The organ is assumed to be composed of independent functional subunits (FSUs) organized with a parallel architecture and it is assumed that the complication is produced only if a sufficiently large number of FSUs (the “functional reserve”) are destroyed. A general expression for NTCP is derived, as well as simple expressions for the mean and standard deviation of the radiation damage to the FSUs. It is demonstrated that these results for inhomogeneous irradiation reproduce those of the serial and tumor control models when the functional reserve consists of one or all of the FSUs, respectively. When the number of FSUs is large, the dose response for organs with identical characteristics is very steep. Since clinical dose‐response curves may arise from populations with varying functional reserves and radiosensitivities, we derive expressions for the NTCP for inhomogeneously irradiated organs that incorporate such variations.
A preliminary phantom study on a proposed model for quantification of renal planar scintigraphy
Authors: Kojima Akihiro , Takaki Yoshikazu , Matsumoto Masanori , Tomiguchi Seiji , Hara Masafumi , Shimomura Osamu , Koga Yukinori , Takahashi Mutsumasa
Published: March 2003

A method for estimation of the absolute renal activity within background activity in renal planar scintigraphy will be presented. This method corrects for oversubtraction of background activity with consideration of background activity of the kidney volume, and employs the depth‐independent buildup factor (DIBF) method for the correction of attenuation and scatter of photons. This method requires the depth and thickness of the organ and the thickness of background for a background activity correction. The transmission factor (TF) for a volume source is derived from integrating TF for a thin source over the thickness of the organ for the DIBF method. To validate this method, phantom studies with various uniform background activity concentrations were performed and the data were compared with conventional background subtraction that do not consider the organ's volume. The results showed that with the conventional background subtraction method at all depth activity was underestimated with errors of 5%–30% for organ/background concentration ratios of 5–40, while this method estimated the true count rate with errors of less than 5%. More accurate quantifications of renal functions such as renal uptake, glomerular filtration rate (GFR) and renogram may be obtained by this proposed method on the planar images.
A method for selective removal of out‐of‐plane structures in digital tomosynthesis
Authors: Kolitsi Z. , Panayiotakis G. , Pallikarakis N.
Published: March 2003

The quality of the reconstructed images in Digital Tomosynthesis is often limited by the presence of artifacts due to blur from planes other than the fulcrum plane. A technique has been developed for the separation and subsequent removal of unrelated structures from the reconstructed plane. The method involves the reconstruction of the blur originating in user‐selected “noisy” planes as it appears on the plane of interest. This is achieved by projecting the reconstructed images of the selected plane on the image formation plane for all viewing angles, and subsequently, synthesizing its blurred image on the plane of interest. There are no restrictions as to the identity of the planes to be removed. Reproduction of the noise is performed using the tomosynthesis algorithm itself, thus the technique can be modified to suit any reconstruction algorithm. The proposed technique was implemented on the Multiple Projection Algorithm and was experimentally evaluated using a radiotherapy simulator unit.
Development of a high quality film duplication system using a laser digitizer: Comparison with computed radiography
Authors: Yoshimura Hitoshi , Xu Xin‐Wei , Doi Kunio , MacMahon Heber , Hoffmann Kenneth R. , Giger Maryellen L. , Montner Steven M.
Published: March 2003

A high quality film‐duplication system was developed in order to improve the image quality of duplicated radiographs and to recover improperly exposed films. The system consists of a laser film digitizer, a laser film printer, a workstation, and a magneto‐optical disk. Radiographs are digitized by the laser digitizer, processed by the computer for image enhancement, and then printed on a film by the laser printer. A nonlinear density‐correction technique is employed in recovering improperly exposed radiographs using the H&D curve of the screen‐film system. Using the new duplication system in our department, the average recovery rate was over 80% for chest and abdominal films rejected due to over‐ or underexposure. The basic imaging properties of the duplication system were compared with those of a Computed Radiography (CR) system and a conventional screen‐film system. For low spatial frequencies, the MTF of the CR system is superior to that of the digital duplication system; however, for high spatial frequencies, the MTF of the duplication system is superior. The noise in the duplication system is about half of that in the CR system.
The general solution to the Bloch equation with constant rf and relaxation terms: Application to saturation and slice selection
Authors: Mulkern Robert V. , Williams Michael L.
Published: March 2003

The general solution to the Bloch equation in the rotating frame which includes the effects of relaxation during a constant amplitude, off‐resonance rf field has been developed. The solution is used to monitor the transient approach to steady‐state saturation levels during off‐resonance irradiation applied continuously or in pulses to systems with arbitrary relaxation rates. The time course of the magnetization during amplitude modulated rf pulses is followed with the general solution and the transverse relaxation time dependence of typical slice profiles is examined. The calculations serve to illustrate the generality of the solution. A thorough discussion of various computational concerns is provided.
Y2O2S:Eu phosphor screens evaluation
Authors: Giakoumakis G. E. , Nomicos C. D. , Skountzos P. , Koutroubas S. , Zisos A. , Yiakoumakis E. N. , Katsarioti M. C. , Kaliakatsos J. A. , Rovithi M. , Panayiotakis G. S. , Evangelou E. K.
Published: March 2003

The x‐ray luminescence of Y2O2S:Eu phosphor screens is studied both in transmission and in reflection mode observation. Detailed experimental data concerning the dependence of the absolute efficiency on the tube voltage and the screen's thickness are presented and comparisons to another rare earth phosphor material (Y2O2S:Tb) are given. With the help of theoretical calculations based on the Hamaker–Ludwig model all the experimental data are explained and the intrinsic efficiency and scattering coefficients of the phosphor are estimated.
How accurately can EGS4/PRESTA calculate ion‐chamber response?
Authors: Rogers D. W. O.
Published: March 2003

Ion‐chamber responses are calculated for graphite, PMMA, and aluminum‐walled ion chambers free‐in‐air in 60Co beams and 200‐keV beams for a graphite chamber. The EGS4 Monte Carlo system is used with various electron step‐size algorithms, in particular the PRESTA algorithm, the much simpler ESTEPE constraint on the energy loss per step, and in combination. Contrary to previous reports, it is found that there are variations in the calculated ion chamber response of up to 3% in 60Co beams and up to 8% in the 200‐keV beam. It is recommended that all ion chamber calculations be done with the PRESTA algorithm plus an additional constraint on the energy losses per step of 1% (or less for higher‐Z materials). The systematic uncertainty in the calculations for 60Co beams is found to be 1% (1σ) and somewhat higher in 200‐keV beams because of sensitivity to transport parameters such as AE and ECUT.