bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of basic imaging properties in digital radiography. 11. Multiple slit‐beam imaging technique with image intensifier–TV digital system
Authors: Kume Yuichiro , Doi Kunio
Published: March 2003

We are developing a digital x‐ray imaging system using a multiple slit assembly (MSA) and an image intensifier (II)–TV digital system. The advantage of this approach is that the scatter from an object and the veiling glare in the II–TV system can be reduced significantly while the x‐ray utilization is maintained much better than that with a single slit‐beam technique. The quality of reconstructed images is related to many parameters such as the slit width, the lead spacer, the number of image frames, and the reconstruction algorithm. In this study, reduction of scatter and veiling glare was measured quantitatively, and image artifacts were analyzed. It was found that the fraction of scatter and veiling glare can be reduced to approximately 0.01–0.1 by use of the MSA imaging technique, and that the magnitude of the fractions is strongly dependent upon the slit width and the lead spacer of the MSA used. The artifacts are caused by inaccuracies in the slit width, lead spacer, and scan motion, and by undersampling of image data. The overlap scanning technique was effective in reducing the magnitude of these artifacts in the reconstructed image.
Characteristics of an ethylene–polyethylene high‐pressure ionization chamber and its potential for deriving radiation dose and quality information in neutron‐gamma radiation fields
Authors: Makrigiorgos Gerassimos
Published: March 2003

A recently developed method for measuring dose and quality parameters in mixed neutron‐gamma radiation fields is extended for neutron energy regions relevant to current neutron therapy. It is theoretically shown that if a polyethylene high‐pressure ionization chamber filled with a gas mixture of 95% ethylene and 5% carbon dioxide is used at suitable gas pressures, it may overcome the limitations found for a similar tissue‐equivalent chamber and measure both the gamma ray absorbed dose fraction and the mean incident neutron energy for neutrons between 0.1 and at least 30 MeV, if certain conditions exist. The simultaneous use of the polyethylene high‐pressure ionization chamber as a conventional neutron dosimeter also allows determination of both the neutron and gamma ray absorbed doses. Estimated accuracies are 15% for the mean incident neutron energy and 15%–30% for the doses determination. The present method may complement currently available techniques as it presents certain advantages in situations where the neutron spectrum is poorly known. If coupled with other dosimeters, the accuracy of the method can be improved.
Two‐dimensional dose distribution around a commercial 125I seed
Authors: Burns G. S. , Raeside D. E.
Published: March 2003

The Monte Carlo method was used to investigate the dose distribution around a 3M Company model 6711 125I seed immersed in a water phantom. Dose rate per unit activity data are presented as a matrix of 63 points surrounding the seed. Relative dose data are presented graphically for two mutually perpendicular directions and compared with the corresponding data for the only other 125I seed currently available, the 3M Company model 6702 125I seed. The 6711 relative dose distribution decreases more rapidly with distance from the seed than does the 6702 relative dose distribution. Uncertainties in the 6711 seed dose distribution produced by end‐weld thickness variations were investigated and found to be substantial at certain points.
A dose homogeneity index for evaluating 192Ir interstitial breast implants
Authors: Wu Andrew , Ulin K. , Sternick E. S.
Published: March 2003

To evaluate and optimize dose homogeneity of 192Ir interstitial breast implants, we define a quantity, the dose homogeneity index (DHI), as follows: DHI=[V(TDR) −V(HDR)]/V(TDR), where V(TDR) denotes the total treatment volume enclosed by the prescribed treatment dose rate (TDR) and V(HDR) denotes the volume enclosed by high‐dose rate (HDR), which is 1.5×TDR or greater. We have used the DHI to examine and compare 192Ir double‐plane implants of various sizes planned by the Memorial system or the Tufts system. Criteria have been suggested for the number of planes required for implants in a given treatment volume. Anderson's volume‐dose histogram with inverse square suppression is adopted for illustration.
Solutions of two paramagnetic ions for use in nuclear magnetic resonance phantoms
Authors: Schneiders Nicholas J.
Published: March 2003

The introduction of paramagnetic ions to affect relaxation times has been used in a variety of nuclear magnetic resonance (NMR) applications. All such relaxants used in NMR phantoms to date have consisted of a single paramagnetic ion. The disadvantage of this is that only one relaxation time can be adjusted as desired, either T1 or T2. This study demonstrates that, by properly choosing two paramagnetic ions, it is possible to adjust both T1 and T2 independently over a wide range of values. Specifically, solutions of MnCl2 and NiCl2 were prepared that simultaneously matched target T1 and T2 values to within approximately 6%.
Slit design considerations for rotating‐aperture, scanning‐beam radiography
Authors: Bednarek Daniel R. , Rudinger George , Rudin Stephen
Published: March 2003

The rotating‐aperture wheel (RAW) scanning‐beam device is uniquely applicable for scatter elimination in short‐time, rapid‐sequence, and real‐time radiographic imaging because of the continuous rotary motion of its slit pattern. This rotary motion places special restrictions on the slit pattern design. Although simple sector‐shaped slits provide uniform primary transmission, they entail an unacceptable degree of slit widening on small‐diameter wheels. The use of multiple slit zones with slits of different angular width has reduced the extent of this widening on a prototype RAW; however, interzone boundary artifacts caused by differential primary x‐ray cutoff are apparent on some clinical images. This problem is eliminated with a unique spiral‐shaped aperture pattern which consists of slits of constant width and constant spacing. Each slit is radially continuous and provides uniform primary transmission without interzone artifacts. This spiral pattern satisfies all requirements and appears to be the pattern of choice for rotating‐aperture scanning‐beam radiography.
Reconstruction for fan beam with an angular‐dependent displaced center‐of‐rotation
Authors: Crawford Carl R. , Gullberg Grant T. , Tsui Benjamin M. W.
Published: March 2003

A convolutional backprojection algorithm is derived for a fan beam geometry that has an angular‐dependent displacement in its center‐of‐rotation from the midline of the fan beam. In both x‐ray computed tomography and single photon emission computed tomography, misalignment can occur when the mechanical center‐of‐rotation is not colinear with midline of the fan beam. In some cases the shift in the center‐of‐rotation is constant for every angle, whereas, in other cases it varies with angular position. Standard reconstruction algorithms, which directly filter and backproject the fan beam data without rebinning into parallel beam geometry, have been derived for a geometry having its center‐of‐rotation at the midline of the fan beam. However, in the case of any misalignment of the center‐of‐rotation, if these conventional reconstruction algorithms are used to reconstruct the fan beam projections, structured artifacts and a loss of resolution will result. Simulations are performed that illustrate these artifacts and demonstrate how the new algorithm corrects for this misalignment. A method for estimating the parameters of the fan beam geometry, including the angular‐dependent shift in the center‐of‐rotation, is also described.
A simple isocenter checking procedure for radiotherapy treatment machines using the optical pointer
Authors: Hudson F. R.
Published: March 2003

Techniques are described for simple and convenient checks on the position and size of the isocenter of radiotherapy treatment machines by measuring the displacement of the optical pointer on a flat scale on the surface of the treatment couch.
Characteristics of the high‐energy photon beam of a 25‐MeV accelerator
Authors: Luxton Gary , Astrahan Melvin A.
Published: March 2003

The CGR Saturne 25 is an isocentrically mounted standing wave medical linear accelerator that produces dual‐energy photon beams and a scanned electron beam with six selectable energies between 4 and 25 MeV. The highest energy photon beam is nominally referred to as 23 MV. For this beam the mean energy of the accelerated electron beam on the 1.3 radiation length (4 mm) tungsten x‐ray target is found to be approximately 21 MeV, with the energy acceptance stated to be ±5%. The electron beam traverses a 270° bending magnet upstream of the x‐ray production target. The resulting bremsstrahlung beam passes through a combination steel and lead flattening filter, 4‐cm maximum thickness. Dosimetric data for the 23‐MV beam are presented with respect to rectangular field output factor, depth of maximum dose as a function of field size, surface and buildup dose, central axis percent depth dose, tissue‐phantom ratios, beam profile, applicability of inverse square, and block transmission. Some data are also presented on the effect of different flattening filter designs on apparent beam energy.
Dose computations for asymmetric fields defined by independent jaws
Authors: Chui Chen‐Shou , Mohan Radhe , Fontenla Doracy
Published: March 2003

Asymmetric fields defined by independent jaws can be used to split a beam or to match adjacent fields. We have extended a method originally developed for symmetric fields to calculate the dose for asymmetric fields. The dose to a point is computed as the product of the tissue maximum ratio (TMR), the off center ratio (OCR), and the inverse square factor. The TMR is computed from the measured central axis depth doses for symmetric fields. The OCR is obtained by multiplying the primary OCR (POCR) and the boundary factors (BF's) for the four jaws. The POCR's and BF's were derived from measured beam profiles, which include the effect of off‐axis beam quality variations. Using this method, the beam profiles and isodose distributions for asymmetric fields of a 6‐MV accelerator were calculated and compared with the measured data. The agreement is within experimental errors both in the penumbra region and along the central ray of the asymmetric field.
Electron dose calculation using multiple‐scattering theory. A. Gaussian multiple‐scattering theory
Authors: Jette David
Published: March 2003

This article is the first in a series on the calculation of electron dose using multiple‐scattering theory. In it we develop a unified theory, which we term Gaussian multiple‐scattering theory, starting from a number of contributions already in the literature: the Fermi–Eyges multiple‐scattering theory, the Yang path length distribution, the second‐order multiple‐scattering theory of Jette [Med. Phys. 12, 178 (1985)], and the diffusion theory of Bethe et al. [Proc. Am. Philos. Soc. 78, 573 (1938)]. After examining in detail the ramifications and limitations of Gaussian multiple‐scattering theory, we derive basic formulas generalizing the Fermi–Eyges theory, for use in subsequent articles. We also find explicit, accurate expressions for incorporating the scattering power into the theory.
An iron metabolism study in humans by means of stable tracers
Authors: Cantone M. C. , Molho N. , Pirola L. , Gambarini G. , Hansen Ch. , Roth P. , Werner E.
Published: March 2003

An investigation of iron metabolism in a female patient volunteer by administration of stable iron isotopes as tracers was performed. The applied methodology had already been tested in rabbits in comparison with radioactive tracer technique. The subject under study was given 58Fe solution intravenously and about 45 min later 57Fe solution orally. Ten blood samples were drawn at different times within 522 min from injection. Single iron isotopes content in plasma samples was determined by proton nuclear activation. A Compton suppressor system was utilized to improve the detector limits. The characteristic parameters of iron plasma clearance and of iron intestinal absorption were determined.
Theoretical evaluation of dose distributions in water about models 6711 and 6702 125I seeds
Authors: Williamson Jeffrey F. , Quintero Francisco J.
Published: March 2003

The distribution of absorbed dose about models 6711 and 6702 125I seeds in water has been calculated from first principles using the Monte Carlo method. Dose is calculated as a function of angle with respect to the transverse seed bisector for distances from the seed center ranging from 0.1 to 7.5 cm. The computed results are compared to measured data. A truncated Fourier series is used to describe the Monte Carlo data in terms of a small number of coefficients, facilitating accurate and efficient dose calculations for clinical treatment planning.
Access control systems for radiotherapy treatment rooms
Authors: Aldrich J. E. , Berkey John
Published: March 2003

The role of the time‐delay or start‐up switch as a safety feature in radiotherapy treatment rooms is discussed. A simple optical system which can be retrofitted to any treatment room is described.
A multiray model for calculating electron pencil beam distribution
Authors: Yu C. X. , Ge W. S. , Wong J. W.
Published: March 2003

Based on the Fermi–Eyges theory, a set of recursion relations was derived for calculating electron distributions in the layered geometry. The electron distribution at a specific depth was obtained by convolving the upstream electron distribution with a kernel determined by the scattering parameters of the layer. Modifications were made to overcome some inherent limitations of the Fermi–Eyges theory. For each point in the medium, the most probable, or mean, path traversed by the electrons in reaching the point was derived. The skewness of the mean paths and the related energy degradation were included in a multiray model for pencil beam calculations. The resultant electron planar fluence distributions are no longer Gaussian as predicted by the original theory. The effects of edges or localized inhomogeneities are also included. Comparisons between our calculations and Monte Carlo simulations show good agreement.
Monte Carlo evaluation of specific dose constants in water for 125I seeds
Authors: Williamson Jeffrey F.
Published: March 2003

To clinically utilize relative three‐dimensional dose distribution data for 125I seeds in water, the specific dose constant must be known. This constant is the ratio of absolute dose rate in medium, 1 cm from the source on its transverse bisector, to source strength. We have used the Monte Carlo method to calculate specific dose constants in water for three types of 125I seeds (models 6711, 6701, and 6702). Our photon transport code realistically models the complex internal structure of these interstitial sources as well as the exposure standardization experiments conducted at the National Bureau of Standards which form the basis of 125I source strength specification. In addition, relative attenuation factors for the three seed types are presented. Our results indicate that published data overestimate the specific dose constant by 10% to 14%.
Experimental verification of cesium brachytherapy line source emission using a semiconductor detector
Authors: Metcalfe Peter E.
Published: March 2003

Described is an experimental verification technique for cesium brachytherapy line source emission. The dose rate levels produced by a line source algorithm are compared with measurements taken around J‐series stainless‐steel sheathed cesium sources with a p‐type semiconductor diode detector. Further study of isodensity contours is undertaken using a film dosimetry technique. The errors involved in using these techniques are assessed.
A Monte Carlo study of multiple scatter effects in Compton scatter densitometry
Authors: Speller Robert D. , Horrocks Julie A.
Published: March 2003

The contribution of multiple scatter to the measured signal in x‐ and γ‐ray Compton scatter densitometry has been investigated theoretically by the use of Monte Carlo techniques to follow individual photon life histories. A three component phantom was employed in the computer model to simulate the patient at three examination sites; the radius/ulna, the femoral neck, and the lumbar spine. Monoenergetic radiation beams of 60‐ and 100‐keV photons and polyenergetic x‐ray spectra of 100 and 140 kVp were used. Scattered events were detected over 360° and classified according to their origin and frequency of scatter. The single scatter in bone to multiple scatter ratio was studied as an indication of the signal‐to‐noise ratio and this was found to vary with phantom size but was independent of photon energy. Correction factors to be used in a clinical densitometer to account for the inclusion of multiple scatter events were computed. These were found to be 0.65–0.58 at the optimum scattering angles for the phantoms considered.
An analytical model of the scattered radiation distribution in diagnostic radiology
Authors: Boone John M. , Seibert J. Anthony
Published: March 2003

A simple scatter model is used to analytically derive the point spread function (PSF) for scattered radiation in diagnostic radiology. The resulting equation is a function of four physical parameters; object thickness, object‐to‐detector distance (air gap), and the linear attenuation coefficients for both primary and scatter radiation. Though the model is based upon single scattering, it is shown that by reducing the scatter attenuation coefficient the analytic model compares well to the multiple scattering PSF determined using Monte Carlo analysis.
Energy and rate dependence of diagnostic x‐ray exposure meters
Authors: Wagner Louis K. , Cerra Frank , Conway Burton , Fewell Thomas R. , Ohlhaber Thomas R.
Published: March 2003

Variations in x‐ray exposure measurements among a variety of contemporary diagnostic exposure meters are investigated. Variations may result from systematic errors due to calibration, beam‐quality dependence and exposure‐rate dependence. It is concluded that the majority of general purpose diagnostic meters will agree to within 10% of each other if exposure rates are below 1.3 mC kg−1 s−1 of air (5 R s−1) and beam qualities are typical for general purpose radiology, excluding mammography. For exposure rates comparable to those in barium enema radiography the variations can range up to 25% or more. Variations up to 40% were observed among general purpose exposure meters at mammographic beam qualities. In the mammographic range, mammographic (thin window) exposure meters varied by no more than 2%.
Determination of the relative angle between orthogonal films for radioactive implants
Authors: Amols Howard I. , Martel Mary
Published: March 2003

Dose calculations for radioactive seed implants require knowledge of the three‐dimensional source coordinates. These are usually determined from a pair of orthogonal radiographs. However, occasionally localization films are taken with portable, and/or nonisocentric x‐ray units, and no assurances can be made as to whether or not the films were truly exposed in an orthogonal geometry. A three‐dimensional magnification ring is described (consisting of three mutually orthogonal rings) which permits the treatment planner to accurately establish the exact source rotation angle used when exposing the films. This angle can in turn be used when reconstructing source coordinates, to insure accuracy in treatment planning.
Laplace reconstruction of experimental diagnostic x‐ray spectra
Authors: Archer Benjamin R. , Fewell Thomas R. , Wagner Louis K.
Published: March 2003

This paper displays the results of a blind study used to determine the capability of a Laplace transform pair model to accurately reconstruct diagnostic x‐ray spectra from experimental attenuation data. Spectra reconstructed from attenuation measurements are compared to experimental spectra obtained on the same unit using an intrinsic germanium spectrometer system. The results show that when pure attenuation materials are used, good agreement is obtained between the experimental and computed spectra. If an alloy attenuator like 1100 aluminum is used, the proportion of contaminants must be included in the Laplace formulation for accurate reconstruction.
Calculation of dose profiles in homogeneous phantoms for irregular, partially attenuated, photon beams
Authors: Pla Conrado , Podgorsak Ervin B. , El‐Khatib Ellen
Published: March 2003

Measured and calculated dose profiles under partial attenuators which cover only part of the radiation beam are presented. The study was performed for x‐ray beams generated with a 4‐MV linear accelerator at a source–surface distance of 120 cm in a water phantom for lead attenuators of arbitrary shape but constant thickness. Dose correction factors, which are used to multiply the open beam data to predict doses under partial attenuators, depend strongly on attenuator parameters, such as its thickness, lateral dimensions, and distance from phantom or patient surface, in addition to depending on depths in the phantom. The dose correction factors are calculated with Clarkson sector integration techniques, and the results, in spite of the simplifying assumptions used in the algorithm, generally agree with measured data to within 3%. The calculational method therefore may be applied to general clinical situations in which partial attenuators are used.
The density matrix formalism of nuclear relaxation: A review
Authors: Harpen Michael D.
Published: March 2003

This is a review of the density matrix formalism of quantum statistical mechanics as it relates to nuclear relaxation. The single spin and coupled exchanging two spin systems are treated explicitly. We show the circumstances under which these models reduce to the more familiar expressions used to describe proton relaxation in tissue. The effect of radiofrequency (rf) pulses on the density matrix is presented as well as the density matrix description of the Carr–Purcell pulse technique and conditions under which even and odd echo trains will superpose or are independent of rf pulse rate.
A new method of computing spin‐lattice relaxation maps in magnetic resonance imaging using fast scanning protocols
Authors: Hinson William H. , Sobol Wladyslaw T.
Published: March 2003

A new algorithm to compute spin‐lattice relaxation (T1) maps in magnetic resonance imaging (MRI) by using fast imaging protocols and monitoring the magnetization evolution towards a steady state is proposed. This algorithm uses a general least‐squares fit to multiple point experimental data and is thus much more precise than the standard two‐point fit. Since this imaging protocol is designed to consume time comparable to that of standard clinical protocols, it has an advantage in comparison to traditional multiple point protocols, which require considerably longer scanning times. In addition to T1 maps the protocol can generate final images suitable for clinical diagnosis. Thus it is possible to generate relaxation data without considerably lengthening the total required MRI study time. The results of phantom testing of this protocol are reported.
X‐ray scatter removal by deconvolution
Authors: Seibert J. A. , Boone J. M.
Published: March 2003

The distribution of scattered x rays detected in a two‐dimensional projection radiograph at diagnostic x‐ray energies is measured as a function of field size and object thickness at a fixed x‐ray potential and air gap. An image intensifier–TV based imaging system is used for image acquisition, manipulation, and analysis. A scatter point spread function (PSF) with an assumed linear, spatially invariant response is modeled as a modified Gaussian distribution, and is characterized by two parameters describing the width of the distribution and the fraction of scattered events detected. The PSF parameters are determined from analysis of images obtained with radio‐opaque lead disks centrally placed on the source side of a homogeneous phantom. Analytical methods are used to convert the PSF into the frequency domain. Numerical inversion provides an inverse filter that operates on frequency transformed, scatter degraded images. Resultant inverse transformed images demonstrate the nonarbitrary removal of scatter, increased radiographic contrast, and improved quantitative accuracy. The use of the deconvolution method appears to be clinically applicable to a variety of digital projection images.
Localization of inter‐rib spaces for lung texture analysis and computer‐aided diagnosis in digital chest images
Authors: Powell Gregory F. , Doi Kunio , Katsuragawa Shigehiko
Published: March 2003

An automated method for sampling lung textures in digital posterior/anterior chest images is being developed for use in computer‐aided diagnosis of interstitial pulmonary diseases. In our present approach, two vertical profiles in the periphery of both lungs are fitted with a shift‐variant sinusoidal function from which we estimate locations of posterior ribs and inter‐rib spaces. Regions of interest (ROI's) for sampling lung textures are then automatically centered on the calculated locations of inter‐rib spaces. In tests with 66 chest images, the overall success rate in placing 6.4 mm×6.4 mm ROI's within inter‐rib spaces with this method was 71%, with an average of 18 ROI's selected in 4–5 s/image by a VAX11/750 computer. When four additional alternative ROI's were selected on the sides of each original ROI, the success rate in having at least one ROI correctly located in an inter‐rib space increased to 94%. Since we are still developing a fully automated sampling method, the present approach has been incorporated into a semiautomated method that is currently being used to sample lung textures from a large number of clinical cases.
Beam profile generator for asymmetric fields
Authors: Loshek David D. , Keller Kristi A.
Published: March 2003

A boundary factor technique for predicting beam profiles has been described by Chui and Mohan [Med. Phys. 13, 409 (1986)]. Boundary factors are calculated as the ratio of the intensity measured in the central plane of a collimated field to the intensity measured in the same location in a 40×40 cm field. However, significant discrepancies arise if these factors are applied to the 40×40 cm intensity function at off‐axis points to predict the beam profile for independently collimated fields. These discrepancies are primarily due to the assumption that the 40×40 cm profile approximates an unperturbed intensity function that would exist in the absence of the collimators or scattering media. Two techniques to reduce the residual perturbation are presented. The resulting refined boundary factors allow further factoring so as to permit the calculation of beam profiles for any field size and offset from three discrete functions.
Measurement of the dose equivalent of leakage radiation through an isocentric gantry used for neutron therapy
Authors: Horton J. L. , Stafford P. M. , Kliauga P.
Published: March 2003

The leakage radiation through the shielding on an isocentric gantry of a neutron therapy machine was measured with a Rossi‐type proportional counter. The dose equivalent of the leakage radiation was determined at two positions: (1) in the plane of the patient and (2) in the plane of the target. The dose equivalent of the leakage radiation is approximately the same as the leakage of a high‐energy x‐ray linac.
Effect of gold shielding on the dosimetry of an 125I seed at close range
Authors: Wu Andrew , Sternick E. S. , Muise D. J.
Published: March 2003

Radioactive 125I plaques with gold shields have been used for the treatment of choroidal melanoma. The effect of the gold shield on the dosimetry of a single 125I seed (model 6711) has been investigated in this paper. Increases in dose at close range due to the presence of the shield are observed. Such enhancement is in agreement with Williamson's Monte Carlo calculations.
Determination of diagnostic x‐ray spectra with characteristic radiation using attenuation analysis
Authors: Archer Benjamin R. , Wagner Louis K.
Published: March 2003

An analytical method to compute x‐ray spectra from attenuation data utilizing the Laplace transformation has been extended to include characteristic radiation. It is based on an a priori technique of determining the ratio of characteristic radiation exposure to the total radiation exposure in diagnostic spectra. The technique is shown to produce characteristic intensities in good agreement with experimentally determined values.
A convolution method for constructing primary beam profiles in the presence of beam modifiers
Authors: Starkschall George
Published: March 2003

Empirical functions that describe primary beam profiles for radiotherapy treatment planning systems generally account for finite source size only on beams unmodified by blocks, wedges, or compensating filters. To incorporate the effects of extended sources on such modified beams and to treat the effect of an extended source consistent with the manner in which the unmodified beam is treated, the unmodified beam profile can be written as a convolution of an unknown source function with a collimator transmission profile. Using Fourier transforms, one can then solve for the source function. This source function is then convolved with a beam transmission function that has been modified by blocks, wedges, or compensating filters to obtain a primary beam profile. A number of examples are presented that demonstrate the calculations of the effects of beam modifiers on primary beam profiles.
A mathematical child phantom for the calculation of dose to the organs at risk
Authors: Francois P. , Beurtheret C. , Dutreix A. , De Vathaire F.
Published: March 2003

In order to calculate the doses received by the organs of 530 children treated by radiation for cancer between 1945 and 1969 at the G. Roussy Institute, we have developed a computer program for organ location calculation. To calculate the location of each child's organs of interest at the time of the treatment, only two parameters are necessary; sex and height or sex and age when the height at the time of the treatment is unknown. The algorithm is based on the metric studies of growth known as auxology. Each organ is located by one point representing its center. The model has been checked on 100 healthy children.
Component evaluation of event size spectra for a clinical 14‐MeV neutron beam
Authors: Schmidt Rainer , Hess Axel
Published: March 2003

Microdosimetric investigations were performed in a solid TE phantom at the DT‐neutron generator at Hamburg–Eppendorf. Event size spectra were measured at different depths on the axis of a 10×10 cm2 field and at different lateral positions at a constant depth. Additionally, the microdosimetric spectrum of a 60Co source was determined. From radiobiological measurements the relative biological effectiveness (RBE) of crypt stem cells of mice was estimated as a function of lineal energy. The measured microdosimetric spectra are folded with this RBE function so that RBE values at different positions in the phantom were obtained. The predicted change of the RBE inside and outside the useful beam of a 10×10 cm2 field is shown. Contributions to the RBE dose from the various charged particle components are analyzed separately.
An empirical formula for calculating the output factors of electron beams from a Therac 20 linear accelerator
Authors: Chen Fan‐Shih
Published: March 2003

A polynomial formula, deduced from the data published by Mills et al. [Med. Phys. 12, 473 (1985)], in predicting the relative electron beam output factors, is presented in this report. This formula contains four parameters. By choosing four measured output factors, from four field sizes normalized at the field size of (10,10), the values of these parameters can be determined. A comparison of the factors predicted with this formula and the values measured by Mills et al. shows that the differences between the field sizes of (4,4) to (30,30) are 0.5% or less in 31 out of 35 field sizes. All the 35 field sizes are within 1% for an electron beam of 20 MeV. With 6‐MeV electron beams, the differences are 0.5% or less in 26 out of 35 field sizes, and 1% or less in 31 out of 35 field sizes. Those having differences greater than 1% have either a small field size (5 cm) or a large field size (20 cm). Considering that this formula requires only four accurately measured relative output factors, one can predict the factors of any field within an acceptable accuracy. The calculation is easy with a scientific hand calculator. This formula provides major improvement over the other methods which require many mesurements to be taken in order to interpolate with acceptable accuracy.
Verification of total body photon irradiation dosimetry techniques
Authors: Kirby Thomas H. , Hanson William F. , Cates Douglas A.
Published: March 2003

A method of verifying the dosimetry of patients undergoing total body irradiation (TBI) with photon beams having energies from cobalt‐60 to 25 MV is presented. A simple set of spot checks at the TBI axis has been used to verify data used for TBI dosimetry. Calculations to verify dose delivered to TBI patients are done in the same manner as those irradiated at standard treatment distances. A simple method of effective field size determination for various anatomical locations in a typical adult is presented. Measurements in an Alderson phantom with thermoluminescent dosimeters and an ion chamber at several anatomical locations indicate that this calculational method can predict the dose along the patient axis to within 4% for 60Co and 18‐MV photon beams, provided the dosimetry data are appropriate (as determined by the spot checks). Results of intercomparisons of TBI beam calibration, off‐axis and depth‐dose data at various institutions visited by the Radiological Physics Center are also presented.
A model of heat production and transport in a water calorimeter
Authors: Nath Ravinder , Rothman Arthur
Published: March 2003

The heat diffusion equation for a water calorimeter under isothermal and adiabatic boundary conditions has been solved analytically for a general source function. Based upon this model an interactive computer program has been developed and employed to predict the temporal variation of the temperature distribution in a water calorimeter irradiated with 250 kV, 4‐, 6‐, and 25‐MV x rays and 7‐, 13‐, and 32‐MeV electrons. The model requires central‐axis depth dose curves as inputs and allows for any number of alternate heating and cooling periods. It is found that the shape of the cooling curve following an irradiation period depends upon the location of the point of measurement, the choice of boundary conditions, and the thermal history of the calorimeter.
The energy response of agar‐alanine phantom dosimeter to gamma radiation
Authors: Ciesielski B. , Wielopolski L. , Reinstein L. E.
Published: March 2003

Calculations of the energy response of an electron paramagnetic resonance (EPR) signal induced by gamma radiation in an agar‐alanine phantom dosimeter are presented. Theoretically calculated slopes of the EPR signal calibration lines are comparable with those obtained experimentally for low‐(50 kVp), medium‐(662 keV), and high‐(15 MVp) energy photons. The sensitivity of the phantom dosimeter (EPR signal amplitude/Gray) varies less than 2% within the 150‐ to 20‐MeV energy range. For energies above 150 keV, the influence of variations in the size of alanine crystals is negligible.
Reference dose rates for single‐ and double‐plane 192Ir implants
Authors: Saw Cheng B. , Suntharalingam Nagalingam
Published: March 2003

The proper selection of the reference dose rate is critical in the irradiation of a tumor or tumor bed using interstitial implant. The selected reference dose rate should result in the delivery of highly homogeneous dose throughout the target volume, adequately cover the target volume, and minimize irradiation of the surrounding normal tissues. In this paper, the influence of the reference dose rate on the adequacy of the irradiation of idealized target volumes using single‐ and double‐plane 192Ir implants was studied in terms of three volumetric irradiation indices. The results show that maximum relative dose homogeneity can be attained if the proper reference dose rate is chosen. This isodose rate contour exhibits a width larger than the thickness of the target volume in the central plane. The lowest dose rate within the idealized target volume is not recommended as the reference dose rate to avoid a large volume of the surrounding tissues from receiving dose rates equal to or greater than this dose rate, and also the inhomogeneous irradiation of the target volume.
Backscatter measurements from a single seed of 125I for ophthalmic plaque dosimetry
Authors: Luxton Gary , Astrahan Melvin A. , Petrovich Zbigniew
Published: March 2003

To determine the dosimetric effect of a gold plaque applicator used in 125I ophthalmic irradiation, relative dose rates at points 2–18 mm transverse to the axis of a single seed of 125I were measured in an acrylic phantom under three different measurement conditions. The detectors were 1‐mm diameter×3‐mm length LiF thermoluminescent dosimeters (TLD's). Conditions corresponded to the following: (i) full scatter, (ii) the presence of an ophthalmic gold plaque, and (iii) no scatter material on the side of the seed opposite to the TLD's. The dose rate with the gold plaque is less than that with full scatter phantom. There is no significant decrease in dose rate at 2.2 mm from the seed. Dose rate is significantly reduced at greater distances. The does rate decrease ranges from 4% at 5 mm to 10% at 18 mm. The 125I seed in the gold plaque gives 3%–5% higher dose rate than in the absence of backscatter material.
An analytical equation of electron beams percentage depth ionization curve along the central axis
Authors: Chen Fan‐Shih
Published: March 2003

An analytical equation is proposed in this article. This equation contains four parameters. One of them is the depth of maximum ionization (dm) which can be determined from experiments. The other three parameters can be calculated from the measured percentage depth ionization curve. The values calculated with this equation fit very well with measured data in the buildup region with a difference of 2% or less, and in the falloff region with an error of 2 mm or less in terms of depth. The electron beam energy ranged from 6 to 20 MeV from a Therac 20 Saturne Linear Accelerator. This equation can not be applied beyond the practical range Rp.
Testing the count rate performance of the scintillation camera by exponential attenuation: Decaying source; Multiple filters
Authors: Adams Ralph , Mena Ismael
Published: March 2003

An algorithm and two fortran programs have been developed to evaluate the count rate performance of scintillation cameras from count rates reduced exponentially, either by a decaying source or by filtration. The first method is used with short‐lived radionuclides such as 191mIr or 191mAu. The second implements a National Electrical Manufacturers’ Association (NEMA) protocol in which the count rate from a source of 191mTc is attenuated by a varying number of copper filters stacked over it. The count rate at each data point is corrected for deadtime loss after assigning an arbitrary deadtime (τ). A second‐order polynomial equation is fitted to the logarithms of net count rate values: ln(R)=A+BT+CT2 where R is the net corrected count rate (cps), and T is the elapsed time (or the filter thickness in the NEMA method). Depending on C, τ is incremented or decremented iteratively, and the count rate corrections and curve fittings are repeated until C approaches zero, indicating a correct value of the deadtime (τ). The program then plots the measured count rate versus the corrected count rate values.
Image feature analysis and computer‐aided diagnosis in digital radiography. 3. Automated detection of nodules in peripheral lung fields
Authors: Giger Maryellen Lissak , Doi Kunio , MacMahon Heber
Published: March 2003

We are investigating the characteristic features of lung nodules and the surrounding normal anatomic background in order to develop an algorithm of computer vision for use as an aid in the detection of nodules in digital chest radiographs. Our technique involves an attempt to eliminate the background anatomic structures in the lung fields by means of a difference image approach. Then, feature‐extraction techniques, such as tests for circularity, size, and their variation with threshold level, are applied so that suspected nodules can be isolated. Preliminary results of this automated detection scheme yielded high true‐positive rates and low false‐positive rates in the peripheral lung regions of the chest. This detection scheme, which can assist the final diagnosis by the clinician, has the potential to improve the early detection of lung carcinomas.
Contrast in diaphanography of the breast
Authors: Navarro Glenis A. , Profio A. Edward
Published: March 2003

Diaphanography is an imaging technique used in diagnosis of breast disease including cancer. The breast is illuminated with low intensity light and the transmission pattern of red and near‐infrared radiation is detected, amplified, reconstructed and displayed in a monitor. The instrumentation for diaphanography has evolved empirically, mostly through clinical practice, without a very clear understanding of the scientific basis of the technique. This research is concerned with investigating theoretically the dependence of the contrast produced by a lesion in a diaphanography image on the size, depth at which a tumor is located, photon energy, and photon angular flux distribution. Contrast calculations using the dot computer code in a two‐dimensional geometry showed that decreasing the size of a tumor by 50% decreases the contrast by a factor of 3 and 4 for 695‐ and 853‐nm photons, respectively. Decreasing the size of the normal tissue where a tumor is imbedded by 25% (from 4 to 3 cm) does not change the contrast very much (less than 20%) for both 695‐ and 853‐nm photons. The contrast for 950‐ and 695‐nm photons is comparable while the values for 853‐nm photons are smaller by a factor of 5 for similar cases. The contrast was also found to be dependent on the angle at which the diffuse light is detected after it transverses the host tissue, maximum contrast was found for 695‐ and 853‐nm photons at about 55°. For a detection angle of 77° the contrast observed is 3× and 12× smaller for 695‐ and 853‐nm photons, respectively. For smaller angles such as 18° the contrast was found to be a factor of 2 and 4 smaller for 695‐ and 853‐nm photons, respectively. It was also found that a tumor perturbs the photon flux density over very short distances in normal tissue (the effect is very localized). The flux recuperates at a distance of about two diffusion lengths. The condition that the lesion must be located next to the skin surface where a detector or camera is placed overrides any other effect.
Parallel‐plate ionization chamber response in cobalt‐60 irradiated transition zones
Authors: Kooy Hanne M. , Simpson Larry D. , McFaul James A.
Published: March 2003

The authors study the acceptance of a Capintec parallel‐plate ionization chamber. The Capintec chamber is used for dose measurements in a lead and polystyrene slab phantom irradiated with cobalt‐60 γ rays. The authors define an enhancement ratio to quantify the dose measurements. The enhancement ratio equals the ratio of dose measured with the lead slab present to dose measured under equilibrium conditions in polystyrene at equal primary beam attenuation. The measured enhancement ratio at the exit side of the lead/polystyrene interface is 25% lower than the Monte Carlo predicted enhancement ratio. The authors propose that geometric acceptance limitations of the Capintec chamber to large‐angle, low‐energy electrons are the cause for this difference. A Monte Carlo simulation of the Capintec chamber acceptance confirms the hypothesis.
The effect of angular spread on the intensity distribution of arbitrarily shaped electron beams
Authors: Mohan Radhe , Chui Chen‐Shou , Fontenla Doracy , Han Kerry , Ballon Douglas
Published: March 2003

Knowledge of the relative intensity distribution at the patient's surface is essential for pencil beam calculations of three‐dimensional dose distributions for arbitrarily shaped electron beams. To calculate the relative intensity distribution, the spatial spread resulting from angular spread is convolved with a two‐dimensional step function whose shape corresponds to the applicator aperture. Two different approaches to obtain angular spread or the equivalent spatial spread are investigated. In the first method, the pencil beam angular spread is assumed to be Gaussian in shape. The angular spread constants (σθ) are then obtained from the slopes of measured intensity profiles. In the second method, the angular spread, in the form of an array of numerical values, is obtained by the deconvolution of measured intensity profiles. After obtaining the angular spread, the calculation for convolution is done in a number of parallel planes normal to the central axis at various distances from the electron collimator. Intensity at any arbitrary point in space is computed by interpolating between intensity distributions in adjacent planes on either side of the point. The effects of variations in angular spread as a function of field size for two treatment machines, one with a scanned electron beam and the other with a scattering foil, have been studied. The consequences of assuming angular spread to be of Gaussian shape are also examined. The electron intensity calculation techniques described in this paper apply primarily to methods of dose calculations that employ pencil beams generated using Monte Carlo simulations.
Correction for intensity falloff in surface coil magnetic resonance imaging
Authors: Brey William W. , Narayana Ponnada A.
Published: March 2003

A method has been developed to compensate for sensitivity variation in surface coil images. An algorithm to derive the surface coil profile by acquiring a crude body coil image of the region under study is presented and tested using a homogeneous phantom. Practical application is demonstrated on images of a tomato and rabbit acquired with a 2 T 33‐cm bore magnetic resonance imager/spectrometer.
Investigations on the near surface dose for three 10‐MV x‐ray beam accelerators with emphasis on the reduction of electron contamination
Authors: Rao B. Mallikarjuna , Prasad S. Guru , Parthasaradhi K. , Lee Young , Ruparel Raj , Garces R.
Published: March 2003

A study of three 10‐MV x‐ray clinical accelerators with emphasis on the reduction of electron contamination was conducted. This study, which was performed with different types of trays and filters, suggests that, at 100‐cm source–surface distance (SSD), Pb can be used as an effective filter material up to 30×30 cm2; however, due to its transparency, a Clear‐Pb tray is useful for field sizes up to a 20×20 cm2. Percent depth doses for a few selected depths and field sizes at this nominal SSD were examined. No significant differences, with the exception of the location of Dmax, amongst the three accelerators were noticed.
Lead shielding thickness for dose reduction of 6‐MeV electrons for different square fields
Authors: Prasad S. Guru , Parthasaradhi K. , Arbetter S. , Lee Y. , Garces R.
Published: March 2003

The relative percent dose reduction by lead(Pb) of 6‐MeV electrons produced by Clinac 1800 for 6×6, 10×10, 15×15, 20×20, and 25×25 cm2 cones both with and without buildup is measured. The thickness of Pb required to attenuate the intensity of the primary electron beam to 95% and 98% depends upon the cone size and upon the depth in phantom at which transmission measurements are made.