bluuebunny/crossref_metadata_2025 huggingface dataset:
Estimation of the diameter of and iodine concentration within blood vessels using digital radiography devices
Authors: Kruger Robert A.
Published: August 2003

A variety of digital radiographic and fluoroscopic devices have been developed which can isolate small concentrations of iodine within the cardiovascular system. Using these devices, time dependent subtraction images have been formed which only display opacified vasculature. Theory is presented and simple methods have been developed for determining vessel diameters and iodine concentration from such subtraction images. The methods have been verified using plexiglass and aluminum vessel phantoms imaged with a computerized radiography device. Using this device the diameter of a 5 mm diameter vessel could be determined to within 6% (0.28 mm) even though the pixel width in the digitized image corresponded to 1.34 mm. In the same vessel, it is estimated that an iodine concentration of 46 mg/cm3 could be determined with 10% accuracy.
Generalized image combinations in dual KVP digital radiography
Authors: Lehmann L. A. , Alvarez R. E. , Macovski A. , Brody W. R. , Pelc N. J. , Riederer S. J. , Hall A. L.
Published: August 2003

Dual energy basis decomposition techniques apply to single projection radiographic imaging. The high and low energy images are non‐linearly transformed to generate two energy‐independent images characterizing the integrated Compton/photoelectric attenuation components. Characteristic linear combinations of these two basis images identify unknown materials, cancel known materials, and generate synthesized monoenergetic images. The problems of intervening materials and material displacement are solved in general for a wide class of clinical imaging tasks. The basis projection angle indentifies one from a family of energy selective imaging tasks, and such performance measures as the contrast enhancement factor (CEF) and signal to noise ratio (SNR) are expressed as functions of this angle. Algorithms for the decomposition of high and low energy measurements are compared and experimental images are included.
Neutron dose equivalent next to the target shield of a neutron therapy facility using an LET counter
Authors: Stinchcomb Thomas G. , Kuchnir Franca T.
Published: August 2003

The use of a spherical tissue‐equivalent proportional counter for measurements of the lineal energy (y) and derivations of the linear energy transfer (LET) for fast neutrons has the advantage of giving distributions of dose and dose equivalent as functions of either LET or y. A measurement next to the target shielding of the neutron therapy facility at the University of Chicago Hospitals and Clinics (UCHC) is described, and the data processing is outlined. The distributions are presented and compared to those from measurements in the neutron beam. The average quality factors are presented.
Phase insensitive ultrasonic attenuation coefficient determination of fresh bovine liver over an extended frequency range
Authors: Pohlhammer J. D. , Edwards C. A. , O'Brien W. D.
Published: August 2003

The ultrasonic attenuation coefficient of fresh bovine liver was determined by the phase insensitive techniques of the radiation force balance at 1.37, 4.15, 6.90, and 9.65 MHz, and the scanning laser acoustic microscope (SLAM) at 100 MHz. A least squares fit of the ultrasonic attenuation coefficient (in Np/cm) vs ultrasonic frequency (in MHz) to the 1–10 MHz data yields A = 0.043 f1.266 (r**2 = 0.895) and to the 1–100 MHz data yields A = 0.043 f1.270 (r**2 = 0.954). The following observations can be made: the greatest frequency range (2 decades) over which ultrasonic frequency has been determined for the same specimens. (2) This is the first time it has been shown that the frequency dependence of attenuation remains essentially unchanged over this large frequency range. (3) The frequency dependence is slightly greater than has been observed from the various literature compilations. (4) The attenuation coefficient magnitudes are the lowest values yet determined for fresh liver. (5) The attenuation magnitudes are from 1.3 to 2.2 times greater than the ultrasonic absorption values in the same tissue.
p(42)Be neutron therapy beams: Dose rate and penetration as a function of target thickness and beam filtration
Authors: Rosenberg I. , Awschalom M. , Kuo T. Y. , Tom J. L.
Published: August 2003

It is shown that, in the production of p(42)Be neutron beams for clinical use, the use of semithick targets leads to more desirable beam characteristics when appropriate backstop materials are used. Furthermore, an algebraic representation of beam penetration and of dose per unit charge on target, including hardening by polyethylene filters, provides a method for target optimization. Key words: neutron, target, optimization, clinical, power, depth‐dose
Rotating laminar emission camera with GE‐Detector: An analysis
Authors: Mauderli Walter , Fitzgerald Lawrence T. , Urie Marcia M. , Tosswill Christopher H.
Published: August 2003

Design criteria for a germanium detector emission camera with laminar collimator‐detector geometry are reported. In this design, parallel plates above a grooved germanium slab form detector channels which accumulate data in multiple projections through 180°. Activity distribution is determined through mathematical reconstruction from the projections. The laminar design has greater efficiency than a hole‐collimated device due to a favorable open area ratio and due to collimation in only one dimension. The relative sensitivity at the center of the detector strip increases with detector length and distance from collimator face. Spatial resolution depends upon the design geometry (septal penetration and scatter within the crystal are of such small magnitude that degradation of the point spread function is minimal). A 30 channel prototype device (ROLEC) shows good correlation with theoretically determined PSF and signal–to–noise ratio (SNR). Measuring times projected for a clinical sized device (300 mm diam) are about 4.6 times that of the Anger camera (with same SNR) and high resolution collimator. Key words: emission camera, laminar camera, germanium camera
Analytic representation of electron central‐axis depth dose data
Authors: Jette David , Lanzl Lawrence H. , Rozenfeld Martin , Pagnamenta Antonio
Published: August 2003

We have examined a number of analytic representations of electron central‐axis depth dose data current in the literature, testing them against sets of standard depth dose data. One of them, a two‐parameter model of Shabason and Hendee, is recommended in situations in which good accuracy (∼2%) is desired, with the values of the parameters determined by an approximation formula which we have developed elsewhere. For higher accuracy, we have developed a polynomial model which gives, typically, a standard deviation of the fitting polynomial from the data points of 1%, and a maximum deviation of 2%. Fitting polynomials obtained with this method possess the property of having zero slope at the position of actual maximum dose, and generally a fifth‐order polynomial (requiring four nonzero coefficients) provided the most acceptable fit. The four parameters involved are determined through inversion of a 4 × 4 matrix, and we have tabulated these four coefficients for the standard data sets. The polynomial model is designed for interpolation in the range between the 100% dose depth and the 10% dose depth, and another fitting curve of the same type can be adjoined to cover depths less than the 100% dose depth. Key words: electron teletherapy, central‐axis depth dose, polynomial model, interpolation
Field separation of adjoining therapy fields
Authors: Garavaglia Guido
Published: August 2003

The question of optimal portal separation between two contiguous fields is of importance in radiotherapy. An analytical linear model based on experimental data has been developed for a Co–60 unit (Siemens Gammatron S 65 K). It allows the computation of the separation distance for any combination of field sizes not necessarily having the same source‐surface‐distance, defined either with penumbra trimmers or focused shaping blocks.   Key words: dose homogeneity, field junction, gap
Systematic method of formulating liquid phantoms with a given elemental composition and density
Authors: Lam Gabriel K. Y.
Published: August 2003

A general method of formulating tissue equivalent liquid mixtures of a given chemical composition and density using the technique of linear programming is described. It is used to generate mixtures with equivalent atomic composition as ICRP Standard Man and mammalian muscle (NBS Handbook 85) using eight compounds to cover the range of densities from 1.0 to 1.13. Use of the method to handle other parameters of a mixture is also described. Key words: T.E. liquid, elemental composition, density
Confirmation of a speculation concerning average tissue–air ratio determinations for rotational Co‐60 radiation therapy treatment planning
Authors: Liu N. H. , Miller M. P. , Raeside D. E. , Wizenberg M. J.
Published: August 2003

The question of the number of radii which are necessary to accurately determine the average tissue–air ratio (TAR) to be used in 60Co rotational radiation therapy treatment planning was studied using actual patient contours. It was found that 12 radii adequately determine the average TAR for clinical purposes. Key words: TAR, 60Co, rotational therapy
Use of a Victoreen 500 electrometer to determine ionization chamber collection efficiencies
Authors: Almond Peter R.
Published: August 2003

An investigation has been made of the Victoreen 500 electrometer's capability to predict saturation corrections for ionization chamber measurements. This electrometer has been provided with a switch that reduces the polarizing voltage on the chamber to 40% of its normal value. It can be demonstrated theoretically that ion chamber measurements at two separate voltages should be sufficient to determine the saturation correction, for both pulsed beams and continuous radiation. Tests were made with the Victoreen 500 which indicated that this is the case. Saturation corrections of up to 10% have been demonstrated for both pulsed and continuous beams and these can be predicted using the Victoreen 500 electrometer to within 1%. Key words: ionization chambers, collection efficiency, pulsed beams, electrometers, dosimetry
Radiographic information theory and application to mammography
Authors: Brodie Ivor , Gutcheck Robert A.
Published: August 2003

A theoretical estimate is made for the lowest exposure necessary to record the smallest feature of interest, using various radiographic detecting surfaces and allowing for the probability of making errors to be within certain specified bounds. These calculated exposures are compared with the actual exposures given in clinical situations in order that the smallest feature of interest can be observed by the practitioner with the same probability of error. A measure of the viewing efficiency of a radiographic process is given by the ratio of these exposures. The application of these concepts to mammography for three different recording media—film, film/screen, and xeroradiography—shows that the minimum entrance exposure necessary for recording information by each receptor varies with the energy of the x‐ray beam, and that the optimal photon energy lies in the 21‐ to 25‐keV region. All three methods with their present modes of processing use at most only a few percent of the information they actually intercept. This argues, for example, that if some more efficient method of reading xerographic plates were found, entrance exposures as low as 9 mR per exposure would suffice for a mammogram.
The Wisconsin kVp test cassette with orthochromatic film
Authors: Simpkin Douglas J.
Published: August 2003

The use of orthochromatic x‐ray film in a Wisconsin kVp Test Cassette calibrated with RP film has been evaluated. It is found that orthochromatic film usage in the test cassette will lead to overestimates of the x‐ray tube peak potential for 3φ and 1φ radiographic beams and 3φ mammographic beams. The magnitude of this error ranges from 0.5 to 3.5 kVp, depending on the cassette type, cassette region, and x‐ray tube potential waveform.
Changes in the dose‐profile of a 10 MV x‐ray beam within and beyond low density material
Authors: Kornelsen R. O. , Young M. E. J.
Published: August 2003

The degradation of the profile of 10 MV x‐ray beams and reduction in central axis dose for small fields due to loss of lateral electronic equilibrium in low density materials has been measured. The magnitude of the effect for different field sizes, depths and densities is reported.
Magnetic analysis of the radiation components of a 10 MV photon beam
Authors: Ling C. Clifton , Schell Michael C. , Rustgi Surendra N.
Published: August 2003

For megavoltage x‐ray beams, the percent depth dose increases considerably with field size in the buildup region, with a concomitant shift in the position of the maximum dose (dmax) to a shallower depth. Various authors disagree as to the cause of this effect. The radiation components contributing to absorbed dose in the buildup region of 10‐MV photon field were analyzed as a function of field size by placing an electromagnet next to the Clinac 18 treatment head. The percent depth dose curves in the buildup region, obtained with a parallel plate chamber downstream from the magnetic field at 85 cm SSD, exhibited no dmax shift and a much reduced dependence on field size, in clear distinction with similar data taken with zero magnetic field. Confirmatory data were obtained at 100 and 120 cm SSD. These results clearly show that scattered electrons are the primary cause for the dmax shift and the dose increase in the buildup region with increasing field size.
Unwanted radiation produced by leakage neutrons from medical electron accelerators
Authors: Ing H. , Shore R. A.
Published: August 2003

Monte Carlo calculations have been made to determine the energy delivered to a phantom by neutrons escaping from the head of a Varian Clinac 35 medical accelerator at an SSD of 1 m. The energy was sorted into two regions: inside and outside a volume defined by a circular beam of area 100 and 600 cm2. For the two beam sizes, the energies outside the treatment volume were 12 and 8.7 g‐rad (per photon rad) respectively. Room scattering increased these values by about 20%. These energies are smaller than those delivered by scattered photons by more than ten times.
Dose descriptors for computed tomography
Authors: Spokas John J.
Published: August 2003

A weakness in the dose descriptor, the computed tomography dosimetry index, is discussed and an alternate descriptor is proposed. The new descriptor, the equivalent rectangular width, conveniently expresses the spatial spread of dose and is simply derived from customary dose measurements. A measure of performance, which expresses the relative size of the volume being imaged with respect to the volume receiving the dose, is suggested for computed tomography.
A comparison of computed and measured heel effect for various target angles
Authors: Fritz Steven L. , Livingston William H.
Published: August 2003

Two models for thick target emission spectra, one using constant depth of Bremsstrahlung and one using continuous slowing‐down of electrons and multiple thin targets, were used to predict filtered emission spectra at various angles with respect to the central axis. Integration of these spectra and comparison against measured heel effect gave excellent agreement for tungsten targets with take‐off angles of 7° and 10° at 60 and 100 kVp when the angular anisotropy of Bremsstrahlung was taken into account. Results for a 17.5° target at 60 kVp were poor, possibly indicating a need for a better model of Bremsstrahlung angular dependence.
The effect of geometric errors in the reconstruction of iridium‐192 seed implants
Authors: Rosen Isaac I. , Khan Kutub M. , Lane Richard G. , Kelsey Charles A.
Published: August 2003

In the treatment of tumors using interstitial implants of radioactive seeds, the accuracy of computed dose distributions depends upon the accuracy with which the three‐dimensional source geometries are reconstructed from radiographs of the implants. The effect of geometric reconstruction errors in iridium–192 seed implants were studied, using tumor dose as the measure. Tumor dose was defined as the average dose around the periphery of the treatment volume. Three ideal mathematical implants and five actual patient implants were used. The implants were distorted by randomly moving a specified number of seeds a specified distance. Tumor doses were directly calculated for the ideal implants. For the actual implants, isodose distributions were plotted and were read by a radiotherapist. For both types of implants, percentage errors in the tumor doses were calculated for the distorted reconstructions relative to the correct reconstructions. It was found that the tumor dose was accurate to within 5% if all the seeds were reconstructed to within 0.5 cm of their actual positions. Furthermore, up to 5% of the seeds could be mismatched between films, or otherwise incorrectly reconstructed, with position errors as large as 20 cm, and not change the tumor dose by more than 5%.
Optimal short scan convolution reconstruction for fan beam CT
Authors: Parker Dennis L.
Published: August 2003

The problem of using a divergent fan beam convolution reconstruction algorithm in conjunction with a minimal complete (180° plus the fan angle) data set is reviewed. It is shown that by proper weighting of the initial data set, image quality essentially equivalent to the quality of reconstructions from 360° data sets is obtained. The constraints on the weights are that the sum of the two weights corresponding to the same line‐integral must equal one, in regions of no data the weights must equal zero, and the weights themselves as well as the gradient of the weights must be continuous over the full 360°. After weighting the initial data with weights that satisfy these constraints, image reconstruction can be conveniently achieved by using the standard (hardwired if available) convolver and backprojector of the specific scanner.
The photon‐fluence scaling theorem for Compton‐scattered radiation
Authors: Pruitt John S. , Loevinger Robert
Published: August 2003

This paper concerns a method of scaling photon fluence from one scattering material to another when the photon energies are such that the dominant mode of interaction is Compton scattering. The theorem establishes a one‐to‐one correspondence between points in the two scattering media where the spectra of primary and scattered photons have the same distribution in energy and angle, and where the fluence ratio equals the square of the electron density ratio. Experimental tests were made with cobalt‐60 gamma radiation using ionization‐chamber measurements in graphite, acrylic plastic, polystyrene, and water phantoms. The experimental results are consistent with the equality of photon spectral shapes and angular distributions at corresponding points. The fluence ratios may differ by a few percent from the predicted values, depending on distance from the source.
A rotate–translate CT scanner providing cross‐sectional data suitable for planning the dosimetry of radiotherapy treatment
Authors: Leach M. O. , Webb S. , Bentley R. E.
Published: August 2003

An isotope scanner (J & P Engineering Multipoise scanner, Mk. III) has been converted to provide a simple transmission CT scanning device, using a 137Cs γ‐ray source. The performance of the scanner has been evaluated by imaging a variety of phantoms and an anaesthetised rabbit. The relationship between the measured linear attenuation coefficient and the known electron density was found to be linear, for a range of materials with densities between those of bone and air. For reconstructed pixels of size 5×5 mm2 the percentage standard deviation of linear attenuation coefficient is typically 2.4% for bone and 3.6% for muscle. The spatial resolution of the device was measured and the performance of the scanner with the maximum design source strength was predicted. In the reconstruction of a cross section of the rabbit and of a human thorax phantom, air–muscle, lung–muscle, and muscle–bone interfaces are clearly visible. From experience gained with this scanner the role of simple CT scanning devices in radiotherapy treatment planning is considered. The resolution in linear attenuation coefficient and the spatial resolution available from the scanner are considered sufficient for radiotherapy treatment planning.
The problem of obliquely incident beams in electron‐beam treatment planning
Authors: Ekstrand Kenneth E. , Dixon Robert L.
Published: August 2003

Oblique incidence of an electron beam can alter the central axis depth dose. The incident beam can be considered to be an integration of many pencil beams or slit beams. Depending on the depth in the phantom, neighboring pencil beams may have a greater or lesser contribution to the dose at a point on the central axis compared to the contribution under normal incidence. The effect has been studied experimentally and theoretically. For 6‐ and 9‐MeV electron beams, oblique incidence is found to produce an increased dose at shallow depths and a decreased dose at normal treatment depths.
Reconsideration of the power‐law (Batho) equation for inhomogeneity corrections
Authors: Wong John W. , Henkelman R. Mark
Published: August 2003

The power‐law (Batho) equation for inhomogeneity corrections to the dose calculated in a layered medium has been examined to elucidate the implicit approximations made in its derivation and hence to discover its limitations. Relationships based on primary and first scatter dose calculations are established between the Batho correction and the true correction from which several conclusions can be drawn. For dose corrections within water in a two‐layer medium, the Batho method underestimates the correction when the electron density (ρ) of the overlaying inhomogeneity relative to water is less than 1, and overestimates it when this density is greater than 1. The Batho method is excellent for small fields and ρ<1, but is poor for large fields and ρ>1. When the power‐law equation is extended to multilayer media, by assuming that the correction factor for each layer multiplies independently, the method gives less accurate results. The largest errors occur inside an inhomogeneity directly underneath a top layer of unit density, since the contribution from such a layer is inherently ignored. All of these conclusions are demonstrated in the paper by experimental measurements. Finally, relationships are shown between the Batho correction and both the correction factor proposed by MacDonald et al. and the differential scatter air ratio correction.
Silicon measurement in a lung phantom by neutron inelastic scattering
Authors: Ettinger K. V. , Morgan W. D. , Miola U. J. , Vartsky D. , Ellis K. J. , Wielopolski L. , Cohn S. H.
Published: August 2003

A study was made to assess the feasibility of determining the silicon level in human lungs in vivo by measuring the gamma rays arising from the neutron inelastic scattering reaction 28Si (n, n′γ) 28Si. Neutron energies in the range 5–8 MeV represent the best compromise between the conflicting requirements of high energy for good detection statistics and low energy to minimize the dose to the subject. The sensitivity of measurement was enhanced by pulsing the neutron beam and counting only during the period of bombardment. This effectively reduced the background counts emanating from thermal neutron reactions in the phantom and from the fast neutron reaction 31P(n,α)28Al. In measurements with an anthropomorphic phantom, no interference peaks from other prompt inelastic scattering reactions were observed. With one Ge(Li) detector of 19% relative efficiency, a detection limit of 0.6 g of silicon per 10 mSv was obtained. On this basis, it is estimated that six Ge(Li) detectors of 25% efficiency each would be capable of measuring 0.15 g of silicon in the lungs, the average level found in nonoccupationally exposed adults.
Design constraints in computed tomography: A theoretical review
Authors: Parker Dennis L. , Couch John L. , Peschmann Kristian R. , Smith Vernon , Jimbo Massao , Wang Edmund C.
Published: August 2003

The mathematical coupling of various types of measurement errors to image artifacts in conventional computed tomography geometries is derived. Primarily treated are errors which occur at a fixed radius, simple harmonic error fluctuations, and random errors. The results can be used to establish a quantitative relationship between desired image quality and design tolerances on various components of the computed tomography scanner.
Calculation of electric fields in conductive media
Authors: Doss James D.
Published: August 2003

A method is presented, based upon finite‐difference forms of Laplace's equation, for the iterative calculation of three‐dimensional electric field distributions in electrically conductive media. The method, while generally applicable to any conductive media, will be presented with emphasis on its use for the prediction of power density in tissue when radio‐frequency hyperthermia is utilized in the treatment of cancer. A computer code which performs these calculations has been written in BASIC so that it may be adapted to relatively inexpensive desktop computers for use in treatment planning. Example calculations of the distribution of electric potential, gradient, and power density with specific electrode configurations are presented. Applications and limitations of the technique are discussed.
The effects of scatter in x‐ray computed tomography
Authors: Joseph Peter M. , Spital Robin D.
Published: August 2003

The effects of detection of scattered radiation in x‐ray transmission CT are studied both theoretically and experimentally. It is shown that scatter induces nonlinear errors in the measurement of attenuation values which can lead to cupping, streaks, and CT number inaccuracies. It is shown that scatter effects predominate over beam spectrum hardening effects for large body parts, and that the artifact propensity is a direct function of the scatter‐to‐primary ratio. The presence of scatter induced streaks were demonstrated experimentally on both a third‐ and a fourth‐generation CT scanner using an appropriate water‐equivalent phantom. A simple model with constant scatter background leads to a correction algorithm which was tested on several phantoms and one human pelvis. The algorithm worked well on the smaller phantoms but was less successful for the larger objects. Nevertheless, it still gave substantial improvement in the pelvic scan. We demonstrated that, at least in the pelvis, scatter is a more significant source of error than beam hardening and that improved scatter correction algorithms are needed. The consequences for the quantitative interpretation of CT numbers for clinical diagnoses are discussed.
Angular response of miniature ultrasonic hydrophones
Authors: Shombert David G. , Smith Stephen W. , Harris Gerald R.
Published: August 2003

The voltage response of ceramic and polyvinylidene fluoride (PVDF) hydrophones was measured in the receive mode for angles of incidence ranging from 0°–90°. The measurements were performed at 2.5, 3.5, 5.0, and 8.0 MHz; these frequencies are typical of those used in medical diagnosis. The results are compared to three theoretical models based on diffraction theory; correlation between the measured response and theoretical models is evident for some PVDF hydrophones but not for others, and not for any ceramic hydrophone. The effective radius, as defined in the AIUM–NEMA standard for diagnostic ultrasound, is calculated and compared to the test criteria established in that standard. All of the ceramic hydrophones and two of the five PVDF hydrophones failed to meet the criteria.
Noninvasive thermometry with a clinical x‐ray CT scanner
Authors: Fallone B. G. , Moran P. R. , Podgorsak E. B.
Published: August 2003

A CT scanner yields CT numbers which are proportional to the fractional difference in effective local electron density of the subject material with respect to that of calibration material. A homogeneous water‐equivalent material is used as a calibration phantom under isothermal conditions. Any temperature variation (spatial or temporal) in the subject material subsequently scanned, will generate a CT‐number shift in the CT image because of density changes due to thermal expansion. The potential use of the thermally generated CT‐number shift in noninvasive thermometry during cancer hyperthermia was studied in vitro in samples of water and muscle tissue. The reproducibility of the area‐averaged CT‐number measurement on our EMI‐7070 scanner was found to depend strongly on the time interval between successive counterclockwise scans and on the size of the region of interest used for area averaging. A linear relationship was found between the CT number and water density in the water temperature range from 10 to 55 °C. In the hyperthermia temperature range (36–50 °C), the relationship between the CT number and temperature itself is linear, with a CT‐number thermal shift of about 0.4 and 0.45 HU/°C for water and muscle tissue, respectively. The achievable temperature discrimination is a fraction of °C at spatial resolutions of the order of a centimeter.
Radiation leakage from electron applicator assembly on a linear accelerator
Authors: Schneider Andrew J.
Published: August 2003

Radiation leakage levels at and near the surface of our linear accelerator were measured for the available electron energies and found to be unacceptably high at several locations. Leakage levels were quantitated for several field sizes. The clinical problems which could arise due to the leakage are illustrated and a solution to the problem is suggested.
Radiographic mottle: A comprehensive theory
Authors: Barnes Gary T.
Published: August 2003

A comprehensive theory of radiographic density fluctuations is developed. The theory incorporates film granularity, quantum mottle, the absorbed x‐ray photon energy distribution, fluctuations in phosphor light photon yield, and phosphor coating weight variations. The resulting expressions allow one to calculate the density fluctuations or, alternatively, the Wiener spectrum that will be obtained with a radiographic screen/film system from the physical parameters of the system. Reasonable agreement is obtained between experimental results and calculated values for three typical screen/film systems. An expression is also derived for the detective quantum efficiency (DQE) of screen/film systems, and the results of DQE calculations are presented for a commonly used screen/film combination as a function of density and of object size.
Theoretical temperature distributions for solenoidal‐type hyperthermia systems
Authors: Strohbehn John W.
Published: August 2003

One type of system proposed for producing hyperthermia for cancer therapy of deep‐seated tumors consists of a cylindrical conducting coil (solenoid) in which the patient (or a limb of the patient) is placed. The current in the conducting coil creates an alternating magnetic field inside the patient, which induces eddy currents in the tissue. The eddy currents deposit power and hence produce heating. In this paper, steady‐state temperature profiles are calculated analytically, assuming a homogeneous one‐dimensional model which includes blood perfusion. Numerical methods are used to calculate the temperature distributions as a function of time for this homogeneous model and to calculate the temperature profiles when there are radial variations in tissue parameters including blood flow. Based on these computer simulations, it would appear that in most cases a solenoid‐type hyperthermia system will not be able to provide deep‐seated heating in the abdomen or thorax, but should be able to raise temperatures to therapeutic levels to about 6 cm depth in the abdomen and in the muscle layer in the thorax.
Some physical considerations in whole skin electron beam therapy
Authors: Holt J. G. , Perry D. J.
Published: August 2003

The short range of low‐energy electrons has made them suitable for the treatment of skin lesions, especially when extensive areas must be irradiated with special considerations to save the normal underlying tissue. This report covers some salient features of total body electron irradiation—the construction of the large fields required, x‐ray contamination levels, and multiple‐field techniques. While the investigation is essentially experimental, we also indicate the results of calculations. We conclude most generally that treatment planning with whole skin irradiations can be as precise as with smaller fields.
Properties of thermal waves in vascular media; application to blood flow measurements
Authors: Svaasand Lars O.
Published: August 2003

This paper discusses a principle for the determination of the blood perfusion rate. The method is based upon measurement of the phase‐shift between periodic heat flow and the corresponding temperature rise.
Unwanted photon and neutron radiation resulting from collimated photon beams interacting with the body of radiotherapy patients
Authors: Ing H. , Nelson W. R. , Shore R. A.
Published: August 2003

Monte Carlo calculations have been made to determine the energies delivered by photons and neutrons to the human body irradiated by collimated photon beams. The beams were monoenergetic and ranged from 100 keV to 40 MeV. The energy deposition in the body was sorted into two regions: inside and outside the irradiated volume. Most of the results obtained were for a beam size of 100 cm2 although some calculations were also made for 600 cm2 beams. The effect of beam size on energy deposition in the two regions was investigated for 60Co gamma rays. Graphs are presented which give the integral doses delivered by neutrons and photons to the two regions for therapy beams of various energies. These graphs can be used to calculate the integral doses which are delivered inside and outside the treatment volume for photon spectra from most medical accelerators. Calculations of energy deposition were also made for the spectra from two particular accelerators. These were done using Monte Carlo as well as by simply “folding” the spectra into the results for monoenergetic photons. The results obtained by both methods were in good agreement and indicated that the integral doses deposited outside the treatment volume by neutrons are more than two orders of magnitude smaller than those deposited by scattered photons.
Prediction of electron beam output factors
Authors: Mills Michael D. , Hogstrom Kenneth R. , Almond Peter R.
Published: August 2003

A method to predict square and rectangular field output factors from the measurement of selected fields of electron beams on the Therac 20 Saturne has been developed. A two parameter fit of the square field output factor data, based on the functional dependence as predicted by a pencil beam calculational model, has proven clinically acceptable. The pencil beam distributions are given by the Fermi–Eyges theory of multiple Coulomb scattering. For a rectangular field, the output factor can be calculated from the square root of the product of the two square field output factors with sides equal to those of the rectangular field. If however, there is a significant asymmetry between the X and Y collimator systems, then rectangular field output factors should be predicted from the product of the X and Y one‐dimensional output factors. One‐dimensional output factors are defined as output factors of rectangular fields where one side remains constant and equal to the side of the square reference field. Measured data indicate either of the two methods of determining rectangular field output factors to be clinically acceptable for the Therac 20, the use of one‐dimensional output factors demonstrating greater accuracy. Data show agreement to within approximately 1.5% at electron energies of 6, 9, 13, and 17 MeV.
Determination of bromine in blood serum by 125I excited x‐ray fluorescence
Authors: Rapaport M. S. , Mantel M. , Shenberg C.
Published: August 2003

A radioisotope excited XRF method based on the use of five 10‐mCi 125I point sources arranged in a newly designed configuration is applied to the bromine determination in very small blood serum samples (⩽50 μL). The possibility of determination of 0.05 μg Br in blood serum during 100 s counting time with a standard deviation of ±10% is described. The simplicity and low cost of the present method are major advantages over the other nondestructive methods and render it suitable for medical laboratories.
A note on equivalent circles, squares, and rectangles
Authors: Bjärngard Bengt E. , Siddon Robert L.
Published: August 2003

The scatter dose in the center of a circular beam of photons can be represented by a serial expansion, the first term of which is proportional to the radius. If this term only is used in a scatter integration, the expression becomes proportional to the average radius of the field contour, whatever its shape. For a square, the ratio between its side and the average diameter is s/d = 0.891, the relation between the equivalent circular and square fields for small fields. For rectangles, is given by the area‐to‐perimeter ratio multiplied by a function that increases slowly with the elongation ratio. The error term resulting from the use of only the linear term to describe scatter remains small under a variety of conditions.
The dosimetric properties of an applicator system for intraoperative electron‐beam therapy utilizing a Clinac–18 accelerator
Authors: McCullough Edwin C. , Anderson Joseph A.
Published: August 2003

A prototype electron applicator system providing circular and rectangular fields for use in intraoperative electron beam therapy with a Varian Clinac 18 linear accelerator has been fabricated. The dosimetric properties of this system for a variety of electron‐beam energies, applicator sizes, and x‐ray collimator settings was documented. Significant findings include: (a) surface dose values are in excess of 90% for electron energies of 12 MeV and above; (b) for the 18‐MeV beam, the deepest depth where the central axis dose is 90% of its maximum value is in excess of 50 mm for circular applicators whose diameters are in excess of 5 cm; and (c) the treatment time to deliver 1000 rads “given dose” (at a given dose rate of 300 MU/min) is on the order of 3–4 min. Cross‐field behavior is acceptable for the intended application and x‐ray contamination is less than 4% for any applicator/electron energy combination. A system for irregular field blocking and TLD verification dosimetry has been developed.
Considerations in selecting a radiotherapy computer system
Authors: Karzmark C. J. , Rust D. C.
Published: August 2003

Considerations used to select minicomputer software and hardware appropriate for radiotherapy patients’ records storage and retrieval are discussed. (AIP)
Tissue phantom ratios for a Clinac 4/100
Authors: Biggs Peter J. , Doppke Karen P. , Leong Joseph C. , Russell Michael D.
Published: August 2003

Tissue phantom ratios (TPR), based on a normalization depth of 5 cm, have been measured in water for field sizes from 5×5 cm2 to approximately 40×40 cm2 and for depths from 1 to 40 cm for a Varian Clinac 4/100. These TPR's have been compared with those calculated from percent depth doses measured at the same time, and the two sets of data generally agree to better than 1%, with an average ratio of measured to calculated TPR of 0.999±0.013. Beam profiles have been measured for open and wedged fields, with particular concern for the often observed “horns,” or the increase in dose at the corners of the field. The maximum dose at a depth of 1 cm, along the diagonal of the field for this machine, is approximately 5% higher than at the same depth on the central axis, whereas along the principal plane the maximum dose is only about 3% higher.
A Laplace transform pair model for spectral reconstruction
Authors: Archer Benjamin R. , Wagner Louis K.
Published: August 2003

A four‐parameter Laplace transform pair model, which accurately reconstructs an experimental bremsstrahlung spectrum from attenuation data, is presented. Computed spectral values with both aluminum and copper attenuators generally agree with experimental 70‐kVp data to better than 2%. Reconstructed spectra at other kVp's also show good agreement with published data.
Acoustic backscattering from ultrasonically tissuelike media
Authors: Insana Michael F. , Zagzebski James A. , Madsen Ernest L.
Published: August 2003

The acoustic backscattering coefficients of a tissue‐mimicking (TM) material have been measured using a modified Sigelmann–Reid technique in order to assess the similarity of its acoustic properties to those of soft tissues. A simple reference scatter material was used to probe the strengths and the limitations of the measurement technique. Backscatter coefficients measured from the TM material exhibit a frequency dependence of the form fm in the range 1.0–8.0 MHz where 3.5≤m≤3.8. The backscatter coefficient is also found to be approximately proportional to the particle concentration in the TM material up to concentrations that yield an attenuation coefficient of 0.9 db/cm/MHz. Comparisons of backscatter coefficients measured from the TM material are made with published values for liver, myocardium, and blood.
Scatter in 240‐kVp mobile chest radiography
Authors: Wagner Louis K. , Cohen Gerald
Published: August 2003

The effects of scatter radiation on signal‐to‐noise ratio and optical density contrast are quantitatively compared for three tissue interfaces at 85, 110, and 240 kVp in mobile chest techniques. It is shown that scatter in the mediastinal portion of the radiograph is virtually independent of energy, while it substantially increases with energy in the lung fields.
Compton scatter effects in CT reconstructions
Authors: Glover G. H.
Published: August 2003

Compton scatter of x‐ray quanta is the dominant attenuation mechanism in medical diagnostic imaging. In this paper, it is shown that the scatter‐to‐primary ratio determines the nature and intensity of scatter artifacts in computed tomography (CT) reconstructions and that this ratio, while significantly lower than in radiographic and fluoroscopic examinations, can still be significant in CT. It is found that high spatial‐frequency artifacts can arise even though the detected scatter intensity has little or no high‐frequency modulation. Reconstructions from x‐ray data are presented which show “cupping” as well as dark streaks connecting high‐attenuation regions. Correction of the data from measurements of scatter eliminates these artifacts. It is, moreover, observed that the intensity of the artifacts is often diminished when a beam‐shaping attenuator is employed. Calculations of scatter intensity are developed from a model which includes single‐event and two‐event scatter. This analysis is in good agreement with measurements on round water phantoms. Extension to other detector geometries shows, not unexpectedly, that detectors with poorer collimation yield larger scatter artifacts.
The development of improved ultrasound heaters suitable for superficial tissue heating
Authors: Munro P. , Hill R. P. , Hunt J. W.
Published: August 2003

The acoustical fields generated by several ultrasound heaters have been measured to determine their suitability for heating superficial lesions in cancer patients. Three different acoustical sensors were used in the study, and one sensor, consisting of a thermocouple embedded in a sound‐absorbing plastic, proved to be the most practical device for routine use. The method employed to mount the piezoelectric crystal in the heater was found to have a profound effect on the acoustical field generated by the heater. Clamping the crystal close to its edge resulted in a field with a prominent acoustical maxima on the crystal axis. A flexible attachment at the very edge of the crystal resulted in a much more uniform field which could be further improved by rapidly sweeping the frequency of the signal used to excite the piezoelectric crystal. A heater in which the rear electrode of the piezoelectric crystal is sectioned into a series of concentric rings has also been developed. This heater can deposit more acoustical energy at the edges of a treatment volume than at the center, and the diameter of the ultrasound beam can also be adjusted. The results demonstrate that (i) the acoustical fields of ultrasound heaters must be accurately measured before using the heaters clinically, and that (ii) by careful design, both uniform or controlled nonuniform acoustical fields can be generated.
Mailed thermoluminescent dosimetry reviews in radiation therapy
Authors: Wochos John F. , DeWerd Larry A. , Hilko Robert , Meyer Jeff A. , Stovall Marilyn , Spearman David , Thomason Cynthia , Dubuque Gregory L.
Published: August 2003

The six Centers for Radiological Physics performed periodic thermoluminescent dosimetry (TLD) reviews for photon beams at 276 facilities across the country. The purpose of the reviews and the techniques in use are briefly described. Results from 2413 mailed reviews of megavoltage units indicate that, in 92% of the reviews, a specified dose was delivered within ±5% of the TLD‐measured dose. A comparison is made to other mailed TLD review systems.
Computer‐controlled direct TMR measurement
Authors: Reinstein Lawrence E. , McShan Daniel L.
Published: August 2003

It is common practice to derive tissue maximum ratios (TMRs) indirectly by calculation from percent depth doses (PDD) data which are more convenient to measure using currently available automated scanners. A system has been developed, however, for the completely automatic direct measurement of TMR, using an ionization chamber which is rigidly supported at the isocenter of a teletherapy machine. The chamber is immersed in a water phantom which is moved up and down by computer control of the motorized treatment couch. Ionization current is sampled by the computer which simultaneously regulates both the radiation field size and chamber depth. This system provides a means of rapidly measuring and processing complete sets of TMR and output factor values for both square and elongated field shapes. The results of such measurements performed on the Clinac 18 accelerator are described in this paper.
A contrast‐detail analysis of diagnostic ultrasound imaging
Authors: Smith Stephen W. , Lopez Hector
Published: August 2003

For diagnostic ultrasound imaging, as in computed tomography, a feature of prime importance is the detection of focal lesions of varying size and contrast (echo amplitude) from surrounding tissue. This study describes a new tissue‐simulating phantom which has been used to measure the threshold detection of varying contrast, simulated lesions. The phantom consists of a block of tissue‐mimicking gelatin which contains a row of conical targets at a depth of 7 cm. Each cone contains a different tissue‐mimicking material so that the echo amplitude of the cones relative to the background material covers a dynamic range of 20 dB. Cross‐sectional B‐scans, perpendicular to the lengths of the cones, result in images of disks of constant diameter but varying contrast. Parallel cross‐sectional scans yield “lesions” varying in diameter from 20 to 1 mm. Relative contrast of the cones vs background tissue is obtained by varying scattering particle sizes from 90 to 300 μm. Ultrasound B‐scans of the phantom were examined by medical physicist observers to determine threshold detection of lesions as a function of size and contrast. The results indicate that detection of high contrast targets is limited by the imaging system's spatial resolution. Detection of low contrast targets is limited by the image speckle, i.e., coherent noise.