bluuebunny/crossref_metadata_2025 huggingface dataset:
Radiation parameters of 6 to 20 MeV scanning electron beams from the Saturne linear accelerator
Authors: Pfalzner P. M. , Clarke H. C.
Published: August 2003

Depth doses of the scanning electron beams from the Saturne Therac–20 linear accelerator at nominal energies of 6,9,13,17, and 20 MeV were measured in polystyrene using a thin window parallel plate ionization chamber. Central axis depth dose curves are derived and are analyzed according to the method of Brahme and Svensson.2 For each of the five electron energies, values are obtained for the most probable energy at the absorber surface , the practical range Rp, the 50% range R50, the therapeutic range R85, the electron dose gradients, total collision energy losses, and other radiation parameters, and these are compared to corresponding values for electron beams from a 22 MeV medical microtron and a 20 MeV betatron.
Dose calibrator response to brachytherapy sources: A Monte Carlo and analytic evaluation
Authors: Williamson Jeffrey F. , Morin Richard L. , Khan Faiz M.
Published: August 2003

It is well known that the dose calibrator response/unit exposure rate depends significantly upon source energy. However, investigation of 137Cs, 192Ir, and 226Ra brachytherapy sources by empirical, analytical, and Monte Carlo techniques shows that source filtration significantly affects the calibrator reading to exposure rate conversion factor. The results demonstrate that for each clinically used filtration thickness an exposure calibrated standard source is required to establish the response of the well chamber. An interesting consequence of this analysis is that the Sievert point dose algorithm for clinical sources overestimates the dose on the order of 3% at distances of approximately 3.5 cm from the source.
The application of multiple scattering theory to therapeutic electron dosimetry
Authors: Jette David , Pagnamenta Antonio , Lanzl Lawrence H. , Rozenfeld Martin
Published: August 2003

Fermi–Eyges multiple scattering theory for electrons is explained, and a general three‐dimensional formalism is developed for its application to problems of therapeutic electron dosimetry. The formalism is illustrated by a number of elementary examples: a rectangular beam, an isotropic point source, and a scanning line source.
Absorbed dose determination for interstitial 125I boost therapy
Authors: Waterman Frank M. , Strubler Kenneth A.
Published: August 2003

Iodine‐125 implants are being used to boost external beam treatments of unresectable pancreas and lung tumors. Calculations of the 125I activity required to achieve a specific average peripheral dose are presented as a function of the average tumor dimension for spherical, ellipsoidal, and cylindrical implants. Both uniform and random seed spacings are investigated. The results indicate that the average peripheral dose is relatively insensitive to the seed distribution as well as to the seed activity. The average tumor dose is typically 20% greater than the average peripheral dose.
A detailed experimental and theoretical comparison of the angular and energy dependencies of grid transmission
Authors: Bernstein H. , Muntz E. P. , Schreckendgust J. , Klein D. J. , Lee K.
Published: August 2003

Grid transmission characteristics have been predicted, with good agreement demonstrated between experiment and theory. Differences between the present work and an earlier theoretical analysis have been noted. It is shown that comparison between experiment and theory can lead to a sensitive method for determining grid parameters. Generally, the derived grid parameters deviate somewhat from manufacturer supplied data. Use of the manufacturer's nominal parameters can lead to large errors in predicting grid transmission.
On competitive failure modes and the usefulness of a “survival curve point of view”
Authors: Wolbarst Anthony B.
Published: August 2003

A number of medical phenomena may be discussed in terms of the probability of something “surviving” as a function of time, dose, distance, etc. Employing elementary results of engineering reliability theory, we examine the different shapes of survival curves which can arise when several modes of failure compete for the members of a homogeneous or heterogeneous population. A variety of examples of medical interest illustrate the approach.
Characteristics of Mevatron 77 15‐MV photon beam
Authors: Paul J. M. , Koch Richard F. , Khan F. R. , Devi B. S.
Published: August 2003

The characteristics of 15‐MV photon beam of Mevatron 77 have been examined with respect to clinical parameters. Some of the characteristics of this 15‐MV photon beam are different from those of similar machines used in radiotherapy. The tissue–maximum ratio values have been determined experimentally for SAD 100 cm and percentage depth dose values have been determined from tissue–maximum ratio data. It is found that the experimentally determined PDD values for SSD 80, 100, and 120 cm are within ±1% of the calculated data. The scatter–maximum ratio data have been calculated from the experimentally determined zero area attenuation coefficient and tissue–maximum ratio data and are presented as function of depth and radii of circular fields. The relative dose factors have been determined both for square and rectangular fields. The relative dose factor for rectangular fields depends on the two pairs of jaws differently and the maximum difference is about 1.5%. The flatness and symmetry are within the specifications set by the manufacturer.
Regional silver content of radiographic film determined by x‐ray fluorescence compared with optical densitometry
Authors: Oldendorf William H. , Astrahan Melvin A.
Published: August 2003

The regional silver content of radiographic film measured by x‐ray fluorescence is compared to light absorption measured by a densitometer. Silver content analysis appears to permit a greater dynamic range of useful exposure levels than does light absorption densitometry. This improvement in latitude, however, is not considered great enough to warrant development of a complex system for scanning silver distribution in radiographic applications.
Feasibility of noninvasive analysis of lead in the human tibia by soft x‐ray fluorescence
Authors: Wielopolski L. , Rosen J. F. , Slatkin D. N. , Vartsky D. , Ellis K. J. , Cohn S. H.
Published: August 2003

A postmortem study was conducted to assess the feasibility of measuring bone lead concentrations noninvasively in vivo. Characteristic L x rays were induced with an external source of 125I in the superficial tibial cortex of the intact legs of six adults who had no history of occupational exposure to lead. Tibial lead concentrations in the same bones subsequently determined by flameless atomic absorption spectroscopy varied from 15 to 35 μg Pb/g wet weight. The upper limit for the modern normal range of lead in the bone is about 25 mg Pb/g wet tissue. The linear correlation coefficient (r) between the measurements made with x‐ray fluorescence and lead concentration by absorption spectroscopy was 0.90. Radiation doses of 10 mGy (1 rad) to 1 cm2 of skin, with associated doses to the marrow of adjacent bone of about 0.6 mGy (60 mrad), yielded net lead fluorescence signals ranging from one to seven times the standard deviation of background.
Broad beam three‐dimensional irradiation for proton radiotherapy
Authors: Kanai Tatsuaki , Kawachi Kiyomitsu , Matsuzawa Hideo , Inada Tetsuo
Published: August 2003

A three‐dimensional irradiation system using scatterers for lateral spreading is proposed. This system, which is applicable to proton beams, is easily achieved by ordinary techniques using a movable multileaf collimator, a variable thickness water column, and a computer for their control. Target volumes of convex shape can be irradiated in a three‐dimensional way by this method.
An automatic method for localizing radioactive seeds in implant dosimetry
Authors: Jackson Douglas D.
Published: August 2003

A method for locating radioactive seeds in interstitial implants has been developed that requires three radiographic views. Spatial coordinates for the seeds are computed from the randomly digitized seed images on each of three radiographs, and information about the tube and film placement for each of the radiographs. Further, the ability to accurately (greater than 98% of the seeds within ±2.5 mm) locate the seeds does not require the use of a specialized radiographic technique; the radiographs need only represent three different views of the implant. Also discussed is the seed image matching technique that enables ambiguous seed matches to be resolved.
Problems encountered with a radiation field analyzer
Authors: Haskard Donald L. , Tooze Mervyn J.
Published: August 2003

Isodose measurements of 4‐MV beams obtained with a Therados radiation field analyzer were found to vary significantly with the types of detector used, viz., a Physikalisch–Technische Werkstatten (PTW) ion chamber with positive and negative collecting potentials and a Therados diode detector. Suitable means of minimizing the ion chamber polarity effect are described.
Evaluation of optically projected x‐ray images from an elastomer‐based ionographic system
Authors: Jani Shirish K. , Fatouros Panos P. , Walton Philip W.
Published: August 2003

In ionographic imaging, the ions produced in a high‐pressure, high‐Z gas are normally collected on an insulating foil. If a deformable dielectric gel is used as a collecting electrode, then the electrostatic image can be visualized by optically projecting the get deformation onto a screen. In the present work, we have evaluated the imaging performance of such an ionographic system in terms of its sensitivity and resolution capabilities. X‐ray images of a sharp lead edge formed on a thin silicone elastomer were optically projected and recorded on x‐ray films. The edge profiles were obtained at different values of x‐ray exposure, elastomer thickness, gas pressure, and collecting voltage across the chamber. These profiles were processed to obtain the sensitivity and resolution of the system at different operating conditions. Images of some test objects are shown using this system in order to demonstrate its clinical potential.
Evaluation of lead acrylic as a filter for contaminant electrons in megavoltage photon beams
Authors: Huang D. , Williams S. , Chaney E. , Long F.
Published: August 2003

Electron contamination of megavoltage photon beams increases the dose at the entrance surface and throughout the buildup region. Measurements on Co‐60, 4‐ and 6‐MV photon beams show that lead acrylic is an effective filter for removing contaminant electrons while also overcoming a number of disadvantages preventing routine use of previously proposed techniques.
Shaped field electron dosimetry for a Philips SL75/10 linear accelerator
Authors: Nair Ravi P. , Nair T. K. M. , Wrede Don E.
Published: August 2003

Both small and irregular fields are frequently the treatment of choice in many clinical applications of electron therapy. The fields are often shaped by lead or low melting point alloy placed at the end of the cone or on the patient's surface. The dosimetry for electrons of energies of 4, 6, 8, and 10 MeV is examined with particular emphasis on very small fields for treatment such as the lip, nose, and eye and irregular fields of various area/perimeter ratios. The paper discusses the dosimetry correction due to field shaping as a function of the location of the shield.
Investigation of buildup dose from electron contamination of clinical photon beams
Authors: Petti P. L. , Goodman M. S. , Gabriel T. A. , Mohan R.
Published: August 2003

The contribution made by contaminating electrons present in a clinical photon beam to the buildup dose in a polystyrene phantom has been calculated and compared to measurements. A Monte Carlo technique was employed. The calculation was divided into two parts. First, the accelerator treatment head was simulated in detail using the EGS–PEGS electromagnetic shower code. Then, information obtained from these calculations was used to compute dose curves in a polystyrene phantom. Two cases were considered, one in which both electrons and photons were incident upon the phantom, and another in which electrons were eliminated from the incident beam. Results of these calculations agree with recent experimental findings. A decrease in buildup dose as well as a shift in dmax was observed when electrons were eliminated from the beam.
Fraction of ionization from electrons arising in the wall of an ionization chamber
Authors: Lempert G. D. , Nath R. , Schulz R. J.
Published: August 2003

The accuracy of high‐energy x‐ray dosimetry can be improved by taking account of differences between the compositions of the chamber wall and the buildup cap or dosimetry phantom. The fraction of the ionization due to secondary electrons arising in the chamber wall has been determined as a function of wall thickness for 60Co gamma rays and x rays in the range of 2–25 MV for Farmer‐type chambers. Secondary electrons arising in the accelerator head were removed from the x‐ray beams by a magnetic field placed just in front of the ionization chamber. For 60Co gamma rays, the fraction increases from 40% to 100% as the wall thickness increases from 0.05 to 0.55 g cm−2. For a 0.05 g cm−2 wall, fraction decreases from 60% to 10% as the x‐ray energy is increased from 2 to 25 MV. Limited data obtained with different chambers suggest that the fraction is independent of chamber wall composition when the thickness is expressed in g cm−2.
Transportation of short‐lived positron emitters from a medical cyclotron to a remote imaging suite
Authors: Correia J. A. , Bucelewicz W. H. , Strauss H. W. , Alpert N. M. , Brownell G. L. , Taveras J. M. , Ferrari V.
Published: August 2003

This paper describes a system for the transport of compounds labeled with short‐lived positron emitting isotopes from a clinical cyclotron to a remote imaging suite. The system consists of a pneumatic transport line for the sending of batch lots of radioactive material and a pressurized gas line for the continuous transmission of radioactive gases. Experimental performance of both systems has been measured and a simple model for the pressurized gas line is compared to experimental results. The radiation dosimetry and safety aspects of the systems are also discussed.
Monte Carlo estimates of specific absorbed fractions for an I‐125 point source in water
Authors: Burns G. S. , Raeside D. E.
Published: August 2003

Monte Carlo estimates of eight specific absorbed fractions associated with an I‐125 point source in water are presented for distances ranging from 1–10 cm.
Measurement of activity yields for 12C(γ, n)11C, 14N(γ, n)13N, and 16O(γ, n)15O reactions as a function of electron beam energy and angle from the electron beam using thick target produced bremsstrahlung
Authors: Piltingsrud Harley V.
Published: August 2003

The calculation of activity yields from practical photonuclear target systems designed to produce short‐lived positron emitting radionuclides for nuclear medicine purposes requires certain basic information. These include a knowledge of the photon source (bremsstrahlung energy spectrum and intensity as a function of angle from the electron beam) and the γ, n activation cross section of the secondary target element. A lack of adequate information concerning these parameters motivated the present study in which activity yields for the reactions 12C(γ, n)11C, 14N(γ, n)13N, and 16O(γ, n)15O were measured as a function of energy of and angle from the electron beam between 16 and 30 MeV and 0° and 30.5°, respectively. The data indicate highly complex relationships between the activity yield and the experimental variables. Also indicated are possible applications of the data to indicate the energy of an electron beam producing a given bremsstrahlung field in which activation measurements are made.
Repair of the energy slit on an AECL Therac‐20 accelerator
Authors: Pipman Jacob , Carpenter Otis
Published: August 2003

Instabilities in the beam symmetry of our AECL Therac‐20 accelerator were traced back to a minute water leak in the energy defining slit.
Radiographic information theory: Correction for x‐ray spectral distribution
Authors: Brodie I. , Gutcheck Robert A.
Published: August 2003

A more complete computational method is developed to account for the effect of the spectral distribution of the incident x‐ray fluence on the minimum exposure required to record a specified information set in a diagnostic radiograph. It is shown that an earlier, less rigorous, but simpler computational technique does not introduce serious errors provided that both a good estimate of the mean energy per photon can be made and the detector does not contain an absorption edge in the spectral range. Also shown is that to a first approximation, it is immaterial whether the detecting surface counts the number of photons incident from each pixel or measures the energy incident on each pixel. A previous result is confirmed that, for mammography, the present methods of processing data from the detector utilize only a few percent of the incident information, suggesting that techniques can be developed for obtaining mammograms at substantially lower doses than those presently used. When used with film–screen combinations, x‐ray tubes with tungsten anodes should require substantially lower exposures than devices using molybdenum anodes, when both are operated at their optimal voltage.
Electron contamination in 60Co gamma‐ray beams
Authors: Attix F. H. , Lopez F. , Owolabi S. , Paliwal B. R.
Published: August 2003

All radiotherapy photon beams are accompanied to some extent by secondary electrons which originate in interactions with source hardware, collimator, shadow tray, and/or the air through which the beam passes. Skin sparing, the shape of the dose buildup curve, and the depth of the dose maximum are all influenced by this electron “contamination.” The present study of a 60Co source employs a flat ion chamber to measure dose buildup curves in polystyrene at source distances of 72 to 200 cm, with an open beam or a filter of Lucite, Cu, Pb‐loaded acrylic, or Ba‐ or Pb‐loaded nonbrowning glass placed 57 cm from the source, using 5×5, 20×20, and 35×35‐cm2 beams as defined at 80 cm SSD. The effect of electron generation in the air was studied by placing a He‐gas‐filled plastic bag in the beam. A value of about 12% is estimated for the lowest relative dose obtainable with a polystyrene phantom in a “clear” 60Co γ‐ray beam of 1‐cm diameter.
A computerized TLD system
Authors: Pla C. , Podgorsak E. B.
Published: August 2003

A computerized thermoluminescent (TL) readout technique is presented which considerably improves the precision of dose readout and facilitates the dose information management and storage. The technique is relatively simple and it involves an interface between a commercially available thermoluminescent dosimetry (TLD) analyzer and a minicomputer. Curve fitting, subtraction of unwanted thermogram peaks, background subtraction, studies of TL decay kinetics, and storage of large number of measured TL data are easily performed with the technique.
Signal‐to‐noise ratio considerations in radiographic imaging
Authors: Chakraborty D. P. , Barnes G. T.
Published: August 2003

The methodology employed to calculate radiographic signal‐to‐noise ratio (SNR) for the commonly used disk‐shaped test object is reviewed. Although the “matched” aperture yields the maximum SNR, its shape is difficult to achieve experimentally. On the other hand, a circular aperture having the same size as the object is much simpler to realize. We have performed a numerical analysis of the SNRs obtained with matched and circular apertures for two screen/film systems (a mammographic and a general purpose combination) for a range of test‐object sizes. We find that for object sizes greater than 0.5 mm in diameter, there is a less than 4% difference between the SNRs obtained with the two apertures. The shapes of some of the matched apertures are also presented. We conclude that the SNR determined with the circular aperture is a simpler and more useful determinant of system performance for the screen/film combinations studied.
Models in radiotherapy: Volume effects
Authors: Schultheiss Timothy E. , Orton Colin G. , Peck R. A.
Published: August 2003

A model for the dependence of normal tissue radiation dose response functions on volume variations and dose inhomogeneities is derived using probability theory. Power law volume correction factors and the complication probability factor are shown to be special cases arising from approximations applied to this model. Both require the assumption of small probabilities of complication. Power law volume corrections are shown to require a homogeneous dose distribution. The general model is tissue specific and can be used to calculate probabilities of complication for individual organs or isoprobability doses for radiation injury. The model is applicable to both homogeneous and inhomogeneous dose distributions and has been used in computer determination of optimal treatment parameters. Experimental data are presented which are consistent with the general model alone and which demonstrate the limits of applicability of previous models.
An electronically collimated gamma camera for single photon emission computed tomography. Part I: Theoretical considerations and design criteria
Authors: Singh Manbir
Published: August 2003

The detection and imaging characteristics of a new type of gamma camera for single photon emission computed tomography have been investigated. Unlike conventional gamma cameras which use mechanical collimation, the new gamma camera utilizes electronic collimation which is obtained from a sequential interaction of gamma radiation with a dual position‐and‐energy sensitive detection system. Coincident counting between the two detectors provides localization of activity upon a multitude of conical surfaces throughout the object, wherefrom the three‐dimensional activity distribution can be reconstructed. Not only does electronic collimation provide simultaneous multiple views of the object, but a large gain in sensitivity is also indicated over a conventionally collimated gamma camera under conditions of similar spatial resolution. Detector optimization studies have been performed to design a prototype system comprising a 33×33 array of high‐purity germanium detectors coupled to an uncollimated conventional scintillation camera. The cumulative signal‐to‐noise ratio in projection images obtained with this system is expected to be about a factor of 4 higher (sensitivity about a factor of 15 higher) than that obtained in a corresponding projection image with a conventional gamma camera for imaging a uniformly distributed Tc‐99m source in a 20‐cm‐diam ×20‐cm‐tall cylinder. A similar gain is expected in the tomographic images.
An electronically collimated gamma camera for single photon emission computed tomography. Part II: Image reconstruction and preliminary experimental measurements
Authors: Singh Manbir , Doria David
Published: August 2003

Iterative algorithms have been investigated for reconstructing images from data acquired with a new type of gamma camera based upon an electronic method of collimating gamma radiation. The camera is composed of two detection systems which record a sequential interaction of the emitted gamma radiation. Coincident counting in accordance with Compton scattering kinematics leads to a localization of activity upon a multitude of conical surfaces throughout the object. A two‐stage reconstruction procedure in which conical line projection images as seen by each position sensing element of the first detector are reconstructed in the first stage, and tomographic images are reconstructed in the second stage, has been developed. Computer simulation studies of both stages and first‐stage reconstruction studies with preliminary experimental data are reported. Experimental data were obtained with one detection element of a prototype germanium detector. A microcomputer based circuit was developed to record coincident counts between the germanium detector and an uncollimated conventional scintillation camera. Point sources of Tc‐99m and Cs‐137 were used to perform preliminary measurements of sensitivity and point spread function characteristics of electronic collimation.
Activation of the major constituents of tissue and air by a fast neutron radiation therapy beam
Authors: Ten Haken Randall K. , Awschalom Miguel , Rosenberg Ivan
Published: August 2003

The production of 11C, 13N, 15O from C, N, O, and of 39Cl and 41Ar from Ar by a  p(66)Be(49) clinical neutron therapy beam has been measured. The results of these measurements were used to estimate the production of other radionuclides, then to estimate airborne radioactivity in a typical neutron therapy room and radioactivity induced in body tissues during treatment. Only under special circumstances would airborne radioactivity necessitate a waiting period before entering a typical treatment room. The additional dose to a treatment volume due to decay products from radioactivity induced within that volume would amount to a few thousandths of the given dose and the additional body dose outside the treated volume would be a few millionths of the given dose.
A scanning system for chest radiography with regional exposure control: Theoretical considerations
Authors: Plewes D. B.
Published: August 2003

Conventional chest radiography is limited by the presence of scattered radiation and the small useful exposure range of radiographic film. A computer‐assisted scanning system to minimize these two effects is outlined. The system uses a small beam of radiation swept over the patient's chest in a raster pattern to expose a conventional film cassette, while a slit collimator scanning between the patient and the film serves to reject scattered photons. A microcomputer measures beam attenuation by the patient with a detector placed behind the film which in turn automatically adjusts the x‐ray tube output to minimize excursions in film exposure as the beam scans. A formalism which relates the patient transmission and film exposure distribution is developed and a system transfer function is given. It is shown that such a system operates as a spatial filter which attenuates film contrast for structures of spatial frequency less than the inverse scanning beam width. By manipulating the software parameters of the feedback network, it is possible to alter this filter and produce radiographs with low spatial frequency enhancement, attenuation, or contrast inversion.
Model for calculating depth dose distributions for broad electron beams
Authors: Werner Barry L. , Khan Faiz M. , Deibel Firmin C.
Published: August 2003

Central axis electron beam depth dose distributions can be transformed by replacing dose by fluence and depth by a measure of angular dispersion. This transformation was applied to a set of broad beam central axis depth dose distributions calculated by Monte Carlo code for beams with initial energies ranging from 1 to 60 MeV in homogeneous media of water, aluminum, and copper. The resulting fluence distributions belong to a family of curves that can be parametrized by a single‐valued function of initial beam energy and medium and can be used to calculate fluence distributions for accelerators. Fluence curves can be easily transformed to depth dose curves.
An efficient computer algorithm for interactive calculation of scintillation crystal response to gamma rays
Authors: Siler William , Korbly Letitia
Published: August 2003

Quantitative tests of random sampling versus Monte Carlo algorithms in calculation of scintillation crystal response to gamma rays show that considerable improvement in computational efficiency can be realized by using Monte Carlo methods.
Computed tomography from ordinary radiographs for teleradiology
Authors: Rangayyan Rangaraj M. , Gordon Richard
Published: August 2003

Computed tomography (CT) can be achieved inexpensively using ordinary x‐ray equipment available at most primary health care centers. We present here the techniques and initial results of experiments with an overhead x‐ray unit and film as means for collecting projection data for CT. Our algorithms include standard ART (algebraic reconstruction technique) and modifications we have derived to prevent streaking artifacts due to the use of a small number of views, and to correct geometric distortion due to limited angular coverage. Our methods enable remote computed tomography via teleradiology.
Buildup factors and dose around a 137Cs source in the presence of inhomogeneities
Authors: Prasad Satish C. , Bassano Daniel A. , Kubsad Shrikant S.
Published: August 2003

The effect of inhomogeneities on dose near a gamma‐ray source has been investigated. Experimental measurements were made with a 137Cs source in a polystyrene phantom at a distance of 5 cm from the source. Inhomogeneities consisted of 2‐cm‐thick slabs interposed between the source and the plane of measurement. Dose correction factors (DCF) for 2‐cm‐thick aluminum, bone, lung, and air have been determined. Our results show that for 137Cs source the dose correction factors are of the order of 3% to 8%. A theoretical model for calculation of dose correction factor in brachytherapy in the presence of inhomogeneities has been developed. The model calculates DCF using buildup factors for the water‐equivalent path between the source and the point of calculation. Good agreement was found between calculations and experimental measurements.
Data compression in digital angiography using the Fourier transform
Authors: Höhne K. H. , Obermöller U. , Riemer M. , Witte G. , Böhm M.
Published: August 2003

While digital techniques in radiology develop rapidly, problems arise with archival storage and communication of image data. This paper reports on experiments concerning data reduction of digital image sequences of the heart and the brain. The time‐intensity curves corresponding to every picture element are subjected to the Fourier transform and reconstructed from a number of coefficients smaller than the original number of images. The reconstruction error is assessed by visual inspection and by determining the mean‐square deviation of the original and the reconstructed curve. It is shown that compression factors between 5 and 10 may be achieved without loss of diagnostic information. It is furthermore demonstrated that storage of the images in the form of Fourier coefficients leads to advantages in fast retrieval, enhancement of morphology, and possibility of further quantitative analysis.
Cumulated activities determined from biodistribution data in pregnant rats ranging from 13 to 21 days gestation. I. Tc‐99m pertechnetate
Authors: Wegst Audrey V. , Goin James E. , Robinson Ralph G.
Published: August 2003

Cumulated activity estimates for Tc‐99m pertechnetate were determined using biodistribution data from pregnant and nonpregnant rats. The pregnant rats were studied at 13, 15, 17, 19, and 21 days gestation. The results indicate that maternal organ cumulated activities are not a simple function of gestational age. The organs into which Tc‐99m pertechnetate enters through passive diffusion follow the pattern established by the blood, generally resulting in an increase from the 13th through the 17th day with a decrease on the 19th and 21st day. The organs dominated by active transport follow unique and different patterns. The fetal cumulated activity estimates increased exponentially with gestational age and the placental estimates increased linearly.
Evaluation of fetal dose from megavoltage irradiation of the knee and neonate followup
Authors: Nair Ravi P. , Nair T. K. M. , El‐Akkad Salah
Published: August 2003

A 24‐yr‐old female patient who was to undergo radiation therapy management for a recurrent low‐grade fibrosarcoma on her right knee was found to be 9 weeks pregnant. The patient and her relatives insisted on carrying the pregnancy to maturity, despite undergoing irradiation of her right knee for local control of her disease and to take the teratological risk, if any, that it entails. This paper discusses the measurement of scattered dose in water, fetal dose estimation in an Alderson–Rando human phantom and possible ways of minimizing it.
An overview of errors in line source dosimetry for gamma‐ray brachytherapy
Authors: Jayaraman Subramania , Lanzl Lawrence H. , Agarwal Suresh K.
Published: August 2003

The generally used approach for routine brachytherapy dosimetry depends on a value of source strength provided by the source supplier, the theoretical concept of exposure rate constants for different nuclides, and the applicability of inverse square law to point sources. Corrections for filtration of the radiation within the capsule of the source and attenuation in tissue medium are effected based on attenuation coefficients and data published in the literature. Therefore there is no unique or ideal way of selecting the required data and there could be a spread in the dose values derived by different users. The errors inherent in the current practice of dosimetry of linear sources in brachytherapy are discussed. If the brachytherapy sources are specified in terms of exposure rate at a distance from the source by the source suppliers, the overall uncertainty in the dosimetry at regions of clinical interest around the source could be limited to about ±6%.
Reconstruction of 4‐MV bremsstrahlung spectra from measured transmission data
Authors: Huang Pin‐Hua , Kase Kenneth R. , Bjärngard Bengt E.
Published: August 2003

Transmission data for 4‐MV bremsstrahlung beams have been measured with a combination of lead and aluminum attenuators. From these data, the original energy spectra have been reconstructed using an iterative least‐squares technique, previously evaluated by simulation studies. The spectra on the central axis for three similar 4‐MV linear accelerators indicated no significant differences. When studying the spectra at 5° and 9° off the central axis, that at 9° showed the expected increase of low‐energy photons. All these spectra showed a maximum photon energy of 4.5±0.2 MeV. When the magnetron power was reduced, the spectrum on the central axis shifted to lower energies and the maximum photon energy decreased to 3.5±0.2 MeV. The result of this experimental study confirms the conclusions from the previous simulation, that the numerical technique for analysis of transmission data can accurately represent 4‐MV bremsstrahlung spectra and detect differences in energy distribution with changes in machine tuning and position in the radiation field for a 4‐MV bremsstrahlung beam.
Air activation produced by high‐energy medical accelerators
Authors: McGinley Patton H. , White Thomas A.
Published: August 2003

The activity of 15O and 13N per unit volume of air produced by a 25 and a 45‐MeV medical accelerator was determined by direct measurement. The accelerators were operated in such a fashion as to produce maximum activation of the treatment room air. Levels of the order of 1% or less of the maximum permissible concentration in air for 15O and 13N were found immediately after accelerator shutdown. Three different techniques for calibrations of the air detector were investigated.
Peripheral dose from megavolt beams
Authors: Fraass Benedick A. , van de Geijn Jan
Published: August 2003

The peripheral dose (PD), defined as the dose outside of therapeutic radiation beams, has been investigated for 60Co, 4‐, 6‐, and 10‐MV x‐ray machines. The measurements have been carried out down to dose levels of about 0.1% of the peak dose in the beam, since that dose level may be of clinical importance in some situations. The PD measurements for the various machines are qualitatively similar, which allows the identification of a simple basic data set which can characterize the PD for any particular machine. The PD has been separated into two components: in‐phantom scatter dose and transmission (leakage) dose. Knowledge of the two components is important clinically when shielding is considered.
On the significance of very small angle scattered radiation to radiographic imaging at low energies
Authors: Muntz E. P. , Fewell T. , Jennings R. , Bernstein H.
Published: August 2003

We have studied the angular distribution of scattered radiation at low energies for angles between 2° and 15° from the outward normal to the exit surface of several phantoms, with 1° resolution. A cryogenically cooled germanium detector was used to measure the spectra of the scattered radiation. The differential scattering fluences, or numbers of photons per unit solid angle per unit surface area, exhibit distinct peaks at angles in the vicinity of 5°, with the angular position being only slightly energy dependent but very material dependent. The scattered spectra show large changes as a function of angle, in some cases actually becoming harder than the exit unscattered beam. The significance of this behavior relative to the imaging of targets in mammography examinations is discussed.
Surface dose for megavoltage photon beams outside the treatment field
Authors: Starkschall G. , St. George F. J. , Zellmer D. L.
Published: August 2003

Measurements made on photon beams from four different radiotherapy machines have demonstrated that skin dose several centimeters outside the boundary of a treatment field may be as much as 20% of the central axis maximum dose. This surface dose has been measured for an AECL Theratron 80, Siemens Mevatron VI, Varian Clinac 20, and CGR Sagittaire for distances up to 12 cm outside the field boundary and for depths up to the depth of maximum central axis dose. This dose has also been measured as a function of field size and of source‐to‐skin distance. For the lower energy photon beams, this radiation is significantly attenuated in the first 2—3 mm of tissue, while for higher energy beams, a buildup phenomenon with a dmax of 2–3 mm is observed. The magnitude of this radiation is approximately linearly dependent upon field dimension for all energies.
Recent progress in x‐ray stereoscopes
Authors: Sen Zhang , King Paul H. , Xiaodong Pang
Published: August 2003

An improved reconstructed stereoscopic x‐ray image display system, based on the principle of binocular parallax, is described. Pulse‐synchronized operation of two triode x‐ray tubes and one plumbicon TV camera is employed to separate the left and right images for presentation to the two eyes, respectively. The principle of binocular perception, quantitative characteristics of the stereoscopic depth, the overcoming of the inertia problem of the single‐camera scheme, and a way to achieve low x‐ray dosage and enhanced contrast of image are presented. Experimental results and applications are discussed.
An extreme value paradigm for the effect of size of target volume on end results in radiation oncology
Authors: Herbert Donald E.
Published: August 2003

In clinical radiation oncology, it is commonly reported that complications of normal tissue occur more readily at larger field sizes for a given dose and recurrence of disease is observed more frequently from the larger tumors for a given dose. Cognate phenomena have long been observed in the study of the strength of materials. That is, the larger specimens will fracture under less applied stress, breakdown under less applied voltage, corrode in a shorter time, etc. The statistical theory of extreme values has provided both a rational explanation and a technique for exploitation of these “size effects” on the likelihood of specimen failure. This theory describes the relation which exists between the parameters (in particular, the location parameter) of the frequency distributions of the extreme values [smallest x(1) and largest ] in a sample from a population of observations xi and the sample size n. It is shown in the present paper that the clinical failure phenomena are not inconsistent with the statistical theory of extreme values. The paper presents heuristic comparisons of the predictions of this theory with the received clinical observations of the effect of the size of the volume of irradiated tissues on the likelihood of occurrence of the misadventures of clinical radiation oncology: recurrence of disease and complication of normal tissue. The concordance of observations and predictions is acceptable. The quality and quantity of the currently available data have precluded the construction of any apodictic representations.
Calibration procedure in dual‐energy scanning using the basis function technique
Authors: Wong C. K. , Huang H. K.
Published: August 2003

We present a technique to simplify the calibration procedure of the dual‐energy scanning, using aluminum (AL) and plastic (PL) as basis materials. In essence, this method determines the “basis functions” of the basis materials at the chosen energies. This technique replaces the two‐dimensional calibration procedure, which is tedious, by two simple one‐dimensional calibration steps. In addition, this technique also provides an alternative approach for solving the dual‐energy problem.
Accurate T2 NMR images
Authors: Schneiders Nicholas J. , Post Hans , Brunner Peter , Ford Joseph , Bryan R. Nick , Willcott M. Robert
Published: August 2003

We present a method for producing accurate calculated T2 nuclear magnetic resonance (NMR) images. A modified Carr–Purcell–Meiboom–Gill pulse sequence is used to obtain a series of images with progressive T2 dependence. This image series is then analyzed pixel by pixel to generate a T2 and initial signal strength image. Tests performed using four samples of known T2 indicate accuracies of better than 9%.
Experimental and theoretical energy and angular dependencies of scattered radiation in the mammography energy range
Authors: Klein D. J. , Chan Heang‐Ping , Muntz E. P. , Doi K. , Lee K. , Chopelas P. , Bernstein H. , Lee J.
Published: August 2003

Predicted scatter characteristics from a Monte Carlo code have been compared to an experiment for a 4.0‐cm‐thick acrylic resin (Plexiglas) phantom and 27.3‐keV radiation. The results show generally good agreement, except that in the scattered spectra the predictions appear to underestimate the proportion of photons in the low‐energy tail of the scattered radiation. The angular dependency of the energy‐integrated scattered radiation fluence is in excellent agreement with the predictions.
The dosimetry of a single “hockey stick” portal for treatment of tumors of the cranio‐spinal axis
Authors: Glasgow Glenn P. , Marks James E.
Published: August 2003

Conventional treatment of tumors of the cranio‐spinal axis portal usually involves multiple‐field, moving junction treatments to avoid overlapping fields over the spinal cord. To avoid these problems, we irradiate the cranio‐spinal axis using a single “hockey stick” portal and the 25‐MV x‐ray beam from a Varian Clinac‐35® linear accelerator. Patients are positioned prone on the floor 229 cm from the radiation source and the collimators are rotated 45° so the maximum diagonal dimension of the field 116 cm at 229 cm is coincident with the cranio‐spinal axis. The head is alternately rotated to treat the right‐hand side one day and the left‐hand side the next day. Thermoluminescent dosimetry in an anatomical phantom reveals that, relative to the 100% dose delivered at 4‐cm depth on the central axis of the blocked field, the midline posterior fossa dose is about 100%, with a maximum dose of about 105% to the extreme posterior portion of the skull. The midline neck dose is about 95% and the dose to the inferior portion of the spinal cord is about 105%. The doses to other critical organs are also presented.
Temperature rise during photoradiation therapy of malignant tumors
Authors: Svaasand Lars O. , Doiron Daniel R. , Dougherty Thomas J.
Published: August 2003

This report discusses the optical and thermal distribution during photoradiation therapy of malignant tumors. Emphasis is put on the therapeutic procedure with the light dose delivered through an inserted optical fiber. Theoretical predictions and experimental results indicate that the temperature rise during the procedure may give rise to hyperthermal cell kill. The report discusses the extent of the regions with hyperthermal bioeffects in terms of tissue parameters as optical absorption and scattering, thermal conductivity, specific heat, blood flow, and optical dose parameters as optical power and exposure time.
Fluorescence bronchoscopy for localization of carcinoma in situ
Authors: Profio A. Edward , Doiron Daniel R. , Balchum Oscar J. , Huth Gerald C.
Published: August 2003

A fluorescence bronchoscope system has been developed for imaging lung tumors by fluorescence of a previously injected, tumor‐specific agent hematoporphyrin derivative. Carcinoma in situ has been localized, but there are too many false positives and negatives. A new system has been implemented which allows rapid switching between viewing of fluorescence, and viewing of the same area under white light illumination as in conventional bronchoscopy. The excitation source is a violet krypton ion laser coupled to a fused quartz fiber light conductor, with a diverging microlens to spread the light uniformly. A third‐generation, microchannel plate image intensifier amplifies the weak fluorescence for viewing and video display, recording, and analysis. A movable mirror and periscope bypasses the intensifier for normal color viewing and video display and recording, with the laser shutter closed and the white light shutter open. This facilitates accurate localization, comparison of the color and fluorescence images, and precise sampling during biopsy. The improved system should reduce the false positive rate due to biopsy sampling error, and together with the video analyzer should reduce indeterminate results.
Radiation dose enhancement in tumors with iodine
Authors: Mello Renato Santos , Callisen Hannes , Winter James , Kagan A. Robert , Norman Amos
Published: August 2003

The loading of tissue with iodine can result in the enhancement of the radiation dose absorbed from low‐energy x‐ray or gamma ray sources. We have explored the potential of this phenomenon for radiation therapy. We have demonstrated the effect of iodine concentration and radiation quality on this dose enhancement in lymphocytes, we have calculated the effect of such enhancement on depth dose distributions in the brain, we have estimated the iodine content in two human brain tumors during computerized tomography (CT) scans, we have studied the dispersion of the iodine contrast media after direct injection into rabbit tumors, and we have demonstrated that the combination of x‐ray and contrast media injection is far more effective than either agent alone in causing the regression of mouse tumors. These results suggest that there may be a therapeutic advantage from loading tumors with iodine and treating them with low‐energy photons.
Kermas for various substances averaged over the energy spectra of fast neutron therapy beams: A study in uncertainties
Authors: Awschalom M. , Rosenberg I. , Mravca A.
Published: August 2003

Kermas for various substances averaged over the energy spectra of fast neutron therapy beams, as well as ratios of average kermas relative to muscle, were calculated in an attempt to estimate the uncertainties introduced in these quantities by the poor knowledge of the elemental kerma functions, actual neutron energy spectra, and composition of tissues and other materials. Average kermas have uncertainties of the order of 7%–25%, while for ratios of average kermas the uncertainties are of the order of 2%–5% for materials of clinical interest. It is concluded that the ratio of average kerma of muscle to A‐150 tissue‐equivalent plastic should be 0.93±0.03 for the new p+Be clinical neutron beams.
Quantum noise in detectors
Authors: Rimkus Daniel , Baily Norman A.
Published: August 2003

The variance in the number of x‐ray photons absorbed by a detector is derived from theoretical considerations. The distributions in the number of x‐ray photons produced by the x‐ray tube, transmitted through the patient, and absorbed by the detector are described. These distributions are compounded to yield a distribution in the number of x‐ray photons absorbed by a detector. The standard deviation (quantum noise) in this distribution is very well approximated by the commonly used and experimentally verified quantity √N̄ where N̄ is the average number of x‐ray photons absorbed by the detector.