bluuebunny/crossref_metadata_2025 huggingface dataset:
Structured noise in computed tomography: Effects of periodic error sources
Authors: Parker Dennis L. , Couch John L. , Peschmann Kristian R. , Smith Vernon
Published: August 2003

The artifact in computed tomography (CT) images due to cyclic projection errors, such as errors due to periodic fluctuations in x‐ray intensity, is derived and verified by computer simulation. Depending upon the relative phase of the error between projections, the artifact is shown to be described by a Bessel function (or functions) of the radial argument which is sinusoidally modulated as a function of angle. Because of the nature of Bessel functions, the artifact is essentially zero up to some minimum radius. When the effects of sampling are neglected, a single fundamental artifact is shown to occur. In fourth‐generation scanners, the fundamental artifact (neglecting sampling) will occur at a detector fan angle of about about 39° (depending on the ratio of the axis‐to‐detector, source‐to‐axis distances). The radius of appearance of this fundamental artifact is independent of the frequency of the periodic error signal and will only be visible in fourth‐generation CT scanners with detector fan angles greater than about 39°. The effects of sampling are derived and illustrated by simulation for first‐, third‐, and fourth‐generation CT‐scanner geometries. It is shown that the effect of sampling is to cause an infinite number of such artifacts to be superimposed in the final image. The radius of appearance of all but the fundamental artifact are shown to be dependent on the frequency of the periodic signal. It is shown that by judicious choice of the sampling parameters relative to the frequency of the periodic error, the artifact can be effectively eliminated.
Optimization of ionizing radiation usage in medical imaging by means of image enhancement techniques
Authors: Ram Giora
Published: August 2003

This paper focuses attention on the fact that images considered unsatisfactory for medical analysis may be rendered usable following various image enhancement techniques. In those cases where this form of image processing can sufficiently improve otherwise unusable images, the necessity of repetitive administration of radionuclides to patients may be avoided with a concomitant reduction in ionizing radiation dosages. Application of these techniques in a clinical situation reduced the dose in thallium studies by 50%. Similar results may be obtainable with other nuclear medicine procedures.
Lung correction factors for 45‐MV x‐ray therapy
Authors: McGinley Patton H. , Sanders Michael
Published: August 2003

The degree of dose perturbation produced by lung‐equivalent material exposed in a 45‐MV x‐ray beam was determined as a function of beam size, chest wall thickness, and lung thickness. It was found that the dose levels in the distal portion of the lung were increased above that measured in a water phantom. However, a significant portion of the lung received less dose than that observed at the same depth in a water phantom. An examination of the dose levels beyond lung and in the chest wall was also made.
Hyperthermia considerations for a conducting cylinder heated by an oscillating electric field applied parallel to the cylinder axis
Authors: Brezovich Ivan A. , Young John H. , Atkinson William J. , Wang Mann‐Tchao
Published: August 2003

An exact solution is given for the electric field intensity throughout a long conducting cylinder when the oscillating field is applied parallel to the cylinder axis. Implications of importance for clinical hyperthermia are that frequencies up to 20 MHz can be used without significant losses due to depth penetration.
Automated range compensation for proton therapy
Authors: Wagner Miles S.
Published: August 2003

A system has been developed to produce complex three‐dimensional Lucite compensators to adjust proton depth of penetration within treatment fields. Range adjustments are based on depth prescription contours laid on serial CT scans which contain detailed information on patient contours and inhomogeneities traversed by the beam. The automated system for range compensator production is described, with the constraints arising from proton scattering, fabrication time, and required resolution. Agreement between desired and obtained dose distributions is shown for a typical treatment site. The system's use for automated production of contoured patient apertures is also discussed.
Simulation studies of 4‐MV x‐ray spectral reconstruction by numerical analysis of transmission data
Authors: Huang Pin‐Hua , Kase Kenneth R. , Bjärngard Bengt E.
Published: August 2003

The use of transmission measurements with combinations of attenuating materials has been investigated as a method of determining the x‐ray energy spectrum from a 4‐MV linear accelerator. Simulation studies have been made with three 4‐MV x‐ray spectra of slightly different shapes. From each of these spectra, the narrow beam transmission curve was calculated, using lead to attenuate the beam for the first several points. Aluminum was then added to attenuate the beam to 0.001 of its initial intensity. A computer program using an iterative least‐squares technique has been developed to analyze the transmission data and determine the spectrum by applying some physically reasonable sensible constraints. The calculated transmission values agreed with the simulated data within the estimated experimental uncertainties, and it is concluded that the technique is reliable for the spectral reconstruction and is sensitive to small spectral changes.
Measurements of diagnostic x‐ray backscatter by a novel ion chamber method
Authors: Stanton L. , Brattelli S. D. , Day J. L. , Stanton R. E. , Villafana T.
Published: August 2003

There is a major gap in backscatter information for diagnostic x‐ray beams. Such information is increasingly needed for dose measurements and calculations, as well as for designing devices and techniques. We have therefore carried out measurements on both low Z materials and metals, using an ion chamber method designed specifically for the purpose. Lucite and two D.R. White tissue substitutes were studied extensively (BR 12 “average breast” and MS 11 “water”). Measured percent backscatter (BS) was greatest for Lucite and least for MS 11, with BR 12 in between. Backscatter buildup is rapid: 50% of full backscatter is achieved with 6 mm thickness for all three materials using mammographic beams and with about 12 mm using general diagnostic beams. A simple relationship between BS and field area permits close estimates of BS values for fields for which measured data is not available. Among metals tested, copper exhibited greatest backscatter (38% BS maximum), aluminum least, and lead in between—information of potential importance in cassette design and similar applications.
A model for calculating electron beam scattering in treatment planning
Authors: Werner Barry L. , Khan Faiz M. , Deibel Firmin C.
Published: August 2003

The Fermi‐Eyges theory of electron scattering overestimates the scattering of electron beams used in radiation therapy. The reason for this overestimate is the neglect of the loss of electrons which are scattered into highly oblique paths and removed from the beam at relatively shallow depths. A modification of Eyges’ solution to Fermi's equation is presented to take this loss of electrons into account. Equations for the calculation of isodose distributions for any medium using pencil beams are developed. Experimental confirmation is presented for electron beams of 13 and 18 MeV in homogeneous water, polystyrene, Lucite, and aluminum phantoms.
NMR rheotomography: Feasibility and clinical potential
Authors: Grant John P. , Back Carlo
Published: August 2003

An investigation has been undertaken of the effect of flow on NMR images. We term the new technique of flow analysis examined here, NMR rheotomography. Images were acquired through use of a spin–echo technique. They were of doped water passing through a glass U‐tube, simulating a small vein, which fitted into the magnetic field gradient and radiofrequency coils of an NMR imaging apparatus. For the case of the inlet arm of the U‐tube, the flow images displayed an intensity distribution which compared favorably to a simple physical model based on laminar flow. The intensity distribution observed for the outlet arm was explained through consideration of the perturbation to flow introduced by the U‐bend. Generally, the results of the feasibility study indicate that (a) the NMR spin–echo image is modified by flow in a predictable manner, (b) display of the velocity profile is possible, (c) through use of a U‐tube some separation can be demonstrated within a single image of the twin factors, proton incursion into the image “slice” and proton dephasing, which generally combine to modify the flow image intensity, and (d) discrimination between different modes of flow may be possible by NMR CT. The clinical potential suggested by the results is discussed; NMR rheotomography may prove to be particularly useful for the noninvasive diagnosis of structurally‐originating cardiovascular defects.
A xenon ionization detector for digital radiography
Authors: Drost D. J. , Fenster A.
Published: August 2003

Xenon gas x‐ray detectors have been used successfully in CT scanners; however, they have been found to be unsuitable for digital radiography. We have designed and built a new type of xenon x‐ray detector array and tested its suitability for digital radiography. The detector consists of two parallel plates separated by a 0.5‐mm gap, filled with xenon gas at a pressure of about 30 atm. One of the plates is the high‐voltage electrode, while the other is a circuit board etched to form an array of metal collector strips focused on the x‐ray source. Since there are no metal septa separating the individual detector elements, the dose efficiency of the detector is high, but image degradation will occur due to cross‐talk between detector elements. Measurements of the cross‐talk show that about an 18% reduction in contrast will occur, when a low contrast object, subtending one detector element, is imaged. We have also measured a detector MTF of 14% at 2 lp/mm, a signal of 10 pC for a 1‐mR x‐ray exposure at the detector entrance, a 6% nonlinearity in the detector signal over about 3 orders of magnitude in x‐ray exposure, and a charge collection time (time response) of about 0.1 ms. From these results it is concluded that this new detector design is feasible for digital radiography.
“Nonisolated‐sensor” solid polystyrene absorbed dose measurements
Authors: Zeitz Louis , Laughlin John S.
Published: August 2003

A “nonisolated‐sensor” solid polystyrene calorimeter was constructed to test the role of thermal diffusion in limiting the length of irradiation time during which temperature measurements with nonisolated sensors could be made sufficiently free of drift for determining dose with radiation fields such as gamma rays, x rays, and high‐energy electrons. From measured ratios of dose at 5.0 and 0.5 cm in polystyrene and comparisons to dose measurements with a polystyrene parallel‐plate (pancake) ion chamber, it was shown that thermal diffusion is sufficiently small in polystyrene to permit accurate measurements for irradiation periods of less than 20 min. Comparison of the absorbed dose measurements and depth dose ratios with pancake ion chambers and calorimeter showed, that within the precision and accuracy of the two measuring systems, there is close agreement. The nonisolated‐sensor solid polystyrene calorimeter has the interesting features of (i) simplicity of construction, (ii) simplicity of operation without vacuum or feedback for temperature control, (iii) capability of simultaneous measurements at several depths and off‐axis positions, (iv) the very small thermal defect correction with polystyrene, and (v) operation with the calorimeter in any orientation.
The physics of proton NMR
Authors: Dixon Robert L. , Ekstrand Kenneth E.
Published: August 2003

The physics of pulse NMR which is pertinent to an understanding of proton NMR imaging has been condensed and directed toward the medical physicist. The basic physical principles of spin manipulations using rf pulses are presented, and the relation between the quantum mechanical and the classical descriptions is covered in a rigorous fashion. The physics of relaxation is described and the relaxation times T1 and T2 are explained in some detail. Application of these spin manipulation techniques is illustrated by showing how they may be used in creating an image.
Resolution and noise in xeromammography
Authors: Fatouros Panos P.
Published: August 2003

The resolution and noise characteristics of the xeromammographic image are analyzed by means of a multistage model which considers the exposure, toner deposition, and toner transfer steps. A frequency‐dependent theory of xeromammographic noise is developed and comparison is made with experimental results. Central to this theory is the concept of a toner electrode formed in the immediate vicinity of the Se layer. Comparison is also made between the imaging capabilities of xeromammography and screen/film systems. The paper concludes by addressing the question of normalization of the transfer function in an electrostatic system.
Scatter dose decrement values for rectangular fields
Authors: Bjärngard Bengt E. , Brown Lisa H. , Svensson Göran K.
Published: August 2003

The scatter dose decrement value (SDV) has been studied by calculational methods for 60Co γ and 4‐ and 8‐MV x‐ray beams of rectangular cross section. In a principal plane and inside the field, the SDV is nearly independent of field size, energy, and depth when the position of the point considered is expressed as the fractional distance to the field edge. From this, it follows that the scatter dose profiles are quite similar in planes parallel to a principal plane. A second corollary is that the SDV for an arbitrary point approximately equals the product of the two SDV values for the projected points in the principal planes. Outside the field, the SDV loses this independence of the various beam conditions, and as a consequence thereof, the “product rule” leads to errors. Mathematical expressions have been derived for the SDV inside and outside small fields. The errors resulting when these small‐field formulas are used for large fields have been studied. Expressed as fractions of the total dose on the centerline, these errors are of the order of ±1% inside the field and ±2% outside.
Calculation of scattering cross sections for increased accuracy in diagnostic radiology. I. Energy broadening of Compton‐scattered photons
Authors: Carlsson Gudrun Alm , Carlsson Carl A. , Berggren Karl‐Fredrik , Ribberfors Roland
Published: August 2003

In this work, scattering cross sections differential with respect to both the scattering angle and the energy of the scattered photon are derived in the relativistic impulse approximation for the light elements H, Be, and Al, and photon energies between 30 and 200 keV. The energy broadening of the scattered photons reflects the momentum distribution of the target electrons. It increases with both increasing atomic number of the scatterer and with scattering angle. Even in light elements, the energy broadening is comparable with the intrinsic energy resolution of modern Ge spectrometers. In reconstructing primary photon energy spectra by means of a Ge spectrometer and Compton scattering techniques, i.e., by measuring the photons incoherently scattered at a given angle, the energy resolution is markedly impaired compared to direct measurements in the primary beam. This is usually explained as an effect of the nonzero acceptance angle of the detector. It is shown, however, that the fundamental energy broadening of the scattered photons is alone sufficient as an explanation. The Compton scattering technique is valuable in determining energy spectra in clinical situations. Aspects of its optimal performance are discussed. The commonly used scattering angle of 90° seems adequate. At small scattering angles, the incoherent‐scattering cross section is badly known due to electron–electron interactions and, for photon energies <100 keV, coherent scattering contributes appreciably to the total scattering even in media of low atomic number. In cases where coherent scattering dominates and where the energy degradation of the incoherently scattered photons is small compared to the energy resolution of the spectrometer, the reconstruction is simplified. The double‐differential cross sections derived can be used to simplify calculations of the Compton component of the mass–energy absorption coefficient.
An electronic device for digitizing radiotherapy films for the construction of tissue compensators
Authors: Renner W. D. , O'Connor T. P. , Bermudez N. M.
Published: August 2003

An electronic device was designed that measures film optical density and may be attached to the sonic pen of an x,y graphics terminal. Therapy portal films may be digitized by moving the assembly across the film by hand. Data is measured at a rate of 40 data points per second; hence, a large film can be digitized in about 5 min. Supporting computer software constructs a matrix array of optical densities covering the area of the film, converts optical density to dose, and plots tissue compensators. The concept of designing compensators from port films is reviewed. Phantom studies were performed to show that the compensators so designed are satisfactory for clinical application.
Analysis of Anger camera flood field uniformity based on order statistics
Authors: Wooten W. W. , Graham L. S. , Plourde R. S.
Published: August 2003

Various mathematical techniques have been used to express the uniformity of a flood field image from an Anger scintillation camera. We have defined uniformity in terms of the parameters of a collection of Poisson distributions representing a flood field. A method for estimating uniformity and for constructing a confidence set for uniformity has been derived using order statistics. The method is illustrated using the 5th order statistic.
A dosimetry review system for cooperative group research
Authors: Reinstein Lawrence E. , McShan Daniel , Glicksman Arvin S.
Published: August 2003

The validity of conclusions drawn from multi‐institutional radiotherapy studies is dependent upon the degree to which participating hospitals adhere to study requirements. A major effort undertaken by the Quality Assurance Review Center (QARC) assesses whether or not patient data which are deemed evaluable actually conform to the radiotherapy requirements of the research protocol. This paper presents the methods and results of this effort which has been ongoing for the past five years. The Dosimetry Review System (DRS) is a set of computer programs which make use of verified radiation beam data to evaluate the daily dose, total dose, dose uniformity, and TDF for protocol treatment. These programs can be adapted to facilitate and document the routine chart‐checking procedures at any large radiotherapy department. The DRS data base includes radiotherapy parameters of 600 teletherapy units at more than 250 institutions in the United States and abroad. The design of the data base, the computerized review process, and the calculational algorithms are discussed.
The effects of misregistration of the projections on spatial resolution of CT scanners
Authors: Kijewski Marie Foley , Judy Philip F.
Published: August 2003

Misregistration of the projections in 360° computed tomographic (CT) scanners has been found to blur the image without generating artifacts. The effects of this error were investigated by analytical methods and by reconstruction of real and simulated data. The point‐spread function which results from shifting each projection by a constant distance ε consists of a two‐dimensional impulse function surrounding a region of negative density. The locus of the impulse function is a circle for parallel‐beam geometry and a sixth‐order curve for fanbeam geometry. The anisotropy and position dependence of the point‐spread function in fanbeam geometry have been characterized. The line‐spread function due to the error in parallel‐beam geometry consists of two delta functions located at ±ε. In fanbeam geometry, the line‐spread function consists of two delta functions separated by approximately 2ε, with the locations of the impulses dependent on the position and orientation of the line. This error, combined with other sources of blurring, results in a system edge‐response function which contains a flat region at one‐half the maximum density.
The technical characteristics of matched filtering in digital subtraction angiography
Authors: Riederer S. J. , Hall A. L. , Maier J. K. , Pelc N. J. , Enzmann D. R.
Published: August 2003

The technical characteristics of a new digital fluorographic image processing method called matched filtering are presented. This technique, a type of extensive temporal integration, takes a weighted sum of images acquired during passage of a contrast bolus through some area of interest. The weight of each image is governed by the magnitude of the contrast bolus in that image. An essential requirement of the matched filter is that its integral be zero. It is shown for equal exposure rates and typical bolus characteristics that matched filtering provides a factor of two higher signal‐to‐noise ratio (SNR) than conventional methods for bolus transit times of 10 s or higher. Equilvalently, matched filtering can yield images with quality comparable to conventional digital subtraction angiography (DSA) at a factor of four less patient exposure. The SNR obtained with matched filtering is shown to be within 30% of an ideal bound. Comparisons of matched filtering to standard recursive methods and simple integration are made. Experimental canine studies are presented which compare matched filtering with conventional DSA.
Equipment for the clinical application of local microwave hyperthermia
Authors: Southcott B. M. , Dunscombe P. B. , Gammampila K. , Stacey A. J.
Published: August 2003

The desirable features of equipment intended for the clinical application of local microwave hyperthermia are identified and the design of a machine incorporating these features is described. An assessment of the technical aspects of the performance of the equipment is given.
Planning proton therapy of the eye
Authors: Goitein Michael , Miller Thomas
Published: August 2003

We describe a program for planning treatments of the eye with charged particle beams. Many of its features apply to treatment planning programs in general. These include the three‐dimensional definition of the tumor volume and of normal structures, the possibility of delivering the treatment beam from any direction in space, the provision of arbitrary viewpoints including a “beam's eye” point of view, the design and fabrication of the field shaping aperture, the specification of the necessary beam quality (range and modulation), the calculation and display of isodose contours on any plane in space and on relevant surfaces, the identification of the extent to which normal structures are included or excluded from the beam, and the simulation of the desired alignment film with which patient alignment can be verified.
A new look at displacement factor and point of measurement corrections in ionization chamber dosimetry
Authors: Awschalom Miguel , Rosenberg Ivan , Ten Haken Randall K.
Published: August 2003

A new technique is presented for determination of the effective point of measurement when cavity ionization chambers are used to measure the absorbed dose due to ionizing radiation in a dense medium. An algorithm is derived relating the effective point of measurement to the displacement correction factor. This algorithm relates variations of the displacement factor to the radiation field gradient. The technique is applied to derive the magnitudes of the corrections for several chambers in a p(66)Be(49) neutron therapy beam.
Product representations of teletherapy dose distributions
Authors: Jette David , Pagnamenta Antonio , Jayaraman Subramania , Lanzl Lawrence H. , Rozenfeld Martin
Published: August 2003

Product representations are frequently used for teletherapy dose distributions. For example, the dose in a central plane is often written as the product of two factors, one dependent on the depth and the other on the transverse variable. We have answered the following question: given a (two‐dimensional) set of data, how closely is it possible to represent these data by a product of two such factors, and what factors would give a best‐fit representation? We thus have developed a quantitative test with which to judge any proposed product representation, for a given set of data. As an example, we have applied our method in analyzing the accuracy of a model proposed by van de Geijn for representing central‐plane Cobalt‐60 dose data through a product representation on decrement lines intersecting the source.
Gamma camera MTFs from edge response function measurements
Authors: Logan K. William , Hickey Keith A. , Bull Stanley R.
Published: August 2003

An experimental procedure using edge response functions (ERF) has been devised to rapidly provide modulation transfer function (MTF) values for gamma camera imaging. Both camera intrinsic and system MTFs are generated. This procedure uses a simple test tool to generate the ERF which is then processed by a computer program using a cubic splines differentiation technique and a discrete Fourier transform algorithm to produce the MTF values. An analytic test of the computer algorithms as well as an experimental test using collimator data from the Bureau of Radiological Health is presented to confirm the accuracy of the procedure.
An examination of errors in characteristic curve measurements of radiographic screen/film systems
Authors: Wagner Louis K. , Barnes Gary T. , Bencomo Jose Antonio , Haus Arthur G.
Published: August 2003

The precision and accuracy achieved in the measurement of characteristic curves for radiographic screen/film systems is quantitatively investigated for three techniques: inverse square, kVp bootstrap, and step‐wedge bootstrap. Precision of all techniques is generally better than ±1.5% while the agreement among all intensity‐scale techniques is better than 2% over the useful exposure latitude. However, the accuracy of the sensitometry will depend on several factors, including linearity and energy dependence of the calibration instrument, that may introduce larger errors. Comparisons of time‐scale and intensity‐scale methods are made and a means of measuring reciprocity law failure is demonstrated.
Comments on “Noninvasive thermometry with a clinical x‐ray CT scanner”
Authors: Zamenhof Robert G. , Sternick Edward S. , Curran Bruce M.
Published: August 2003

Data which agree with those of Fallone et al. are presented. The issue of translating invitro results to the invivo situation is also discussed.
Saturation curves of parallel‐plate ionization chambers
Authors: Fallone B. G. , Podgorsak E. B.
Published: August 2003

A new analytical expression is presented to describe the full saturation curve of parallel‐plate ionization chambers. In contrast to the presently known expressions, which hold only for the near saturation region, this empirically determined expression is in excellent agreement with measurements in the whole collection efficiency range from 0 to 1 for x‐ray sources with effective energies from 20 to 150 keV and cobalt‐60 gamma rays. The dependence of the ion collection efficiency and the extrapolated electric field, which is a parameter in the new saturation curve expression, on electric field, dose, dose rate, beam quality, and chamber volume, is discussed. The effect of photoemission from the chamber polarizing electrode for low‐energy x‐ray beams on the saturation current is demonstrated. A universal ionization chamber constant is derived experimentally. It is shown that all parameters of the saturation curve equation and thus the saturation curve itself, can be calculated from one single measurement of ionization current at a given electric field and air gap thickness.
A new approach to CT pixel‐based photon dose calculations in heterogeneous media
Authors: Wong John W. , Henkelman R. Mark
Published: August 2003

The effects of small cavities on dose in water and the dose in a homogeneous nonunit density medium illustrate that inhomogeneities do not act independently in photon dose perturbation, and serve as two constraints which should be satisfied by approximate methods of computed tomography (CT) pixel‐based dose calculations. Current methods at best satisfy only one of the two constraints and show inadequacies in some intermediate geometries. We have developed an approximate method that satisfies both these constraints and treats much of the synergistic effect of multiple inhomogeneities correctly. The method calculates primary and first‐scatter doses by first‐order ray tracing with the first‐scatter contribution augmented by a component of second scatter that behaves like first scatter. Multiple‐scatter dose perturbation values extracted from small cavity experiments are used in a function which approximates the small residual multiple‐scatter dose. For a wide range of geometries tested, our method agrees very well with measurements. The average deviation is less than 2% with a maximum of 3%. In comparison, calculations based on existing methods can have errors larger than 10%.
Some theoretical derivations relating to the tissue dosimetry of brachytherapy nuclides, with particular reference to iodine‐125
Authors: Dale R. G.
Published: August 2003

Using a Monte Carlo computer technique, tables of parameters have been derived which are of use in the dosimetry of brachytherapy nuclides in a variety of tissues and organs. From the results, it has been possible to derive relationships linking the composition of a tissue with the dose received at any location around an implanted source. Other factors, such as the relative importance of scattered radiation, spectral degradation, and integral dose, are also discussed. In particular, attention is drawn to possible dosimetric problems arising from the clinical use of 125I.
Quantitative determination of tolerance doses for preoperative and postoperative radiotherapy of bones
Authors: Datta Ratna , Saha Subrata
Published: August 2003

A method has been developed for the quantitative determination of the tolerance doses for preoperative and postoperative radiotherapy of bones in New Zealand white rabbits. The midshaft osteotomy was carried out on both ulnae of each rabbit. Localized radiation of 2000, 3000, and 4000 rad (20, 30, and 40 Gy) was given in daily fractions of 500 rad to different groups of rabbits. The diaphyseal area of one forearm of each rabbit was irradiated and the other forearm was used as a control. After healing, the mechanical strength of each ulna was measured. The end point is defined as “strength reduction dose‐63” (SRD63), i.e., the dose which would be expected to reduce the mechanical strength of the irradiated, fractured, and healed bone compared with the contralateral unirradiated diaphysis by 63%. The SRD63's for preoperative and postoperative radiotherapy were 4350 rad (43.5 Gy) and 6200 rad (62 Gy), respectively, with a 500 rad (5 Gy)/fraction schedule. Through the use of the nominal standard dose (NSD) formula at 300 rad (3 Gy)/fraction and five fraction per week, these SRD63's are equivalent to 5700 rad (57 Gy) and 8100 rad (81 Gy), respectively.
A study of problems with inventory control of I‐125 seeds
Authors: McMurry H. L. , Chaney E. L. , Kirsch M.
Published: August 2003

A stringent inventory control protocol was implemented to determine the fate of I‐125 seeds used for interstitial implants. Results show where emphasis is needed to limit seed loss.
Surface doses for acrylic versus lead acrylic blocking trays for Co‐60, 8‐MV, and 17‐MV photons
Authors: Bova Francis J. , Hill Lawrence W.
Published: August 2003

Clear acrylic trays are commonly used on teletherapy units to support freehand and custom‐molded blocks for photon beam irradiation. While these trays have many desirable physical characteristics, they have the disadvantage of degrading the buildup region by contribution of low‐energy electrons to the patient's surface. Recently, clear leaded acrylic has been introduced and suggested as a replacement for acrylic. The effect of the lead acrylic on the buildup region was investigated for cobalt‐60, 8‐MV, and 17‐MV x‐ray beams. The lead acrylic was found to decrease the surface dose compared to acrylic. Except for cobalt‐60, the lead acrylic results in a higher dose than an open wire tray.
A Monte Carlo model for absorbed dose calculations in computed tomography
Authors: Beck John W. , Dunn William L. , O'Foghludha Fearghus
Published: August 2003

A Monte Carlo program has been devised that estimates the total absorbed energy and mean dose in defined regions within phantoms exposed to rotating x‐ray sources. The calculations deal with fanlike beams of rectangular cross section projected onto elliptic cylindrical phantoms, which may be inhomogeneous. The effects of coherent scattering, which may be significant in a narrow‐beam geometry, can be studied. The code can score the exit flux, allowing study of the relationship between dose and image quality. The model is described, the code is verified, and typical results are presented.
Single‐ and double‐plane iridium‐192 interstitial implants: Implantation guidelines and dosimetry
Authors: Kwan David K. , Kagan A. Robert , Olch Arthur J. , Chan Paul Y. M. , Hintz Brace L. , Wollin Myron
Published: August 2003

Computerized dosimetric studies of single‐ and double‐plane iridium‐192 (Ir‐192) planar implants were performed. With respect to dose homogeneity, we found that the optimal source and ribbon separation for single‐plane implants was 1.0 cm. For double‐plane implants, the preferred ribbon and plane separation was 1.5 cm, maintaining a 1‐cm separation for the sources. Using these separations, standard dose rate curves for single‐ and double‐plane Ir‐192 implants were generated by computer calculations. These standard curves are useful for quickly and fairly accurately estimating the dose from any size planar implant, without requiring more time‐consuming individual computer dosimetry. We believe that the curves will prove to be of practical clinical value to physicists and radiotherapists.
UV‐induced second readout of LiF thermoluminescent dosimeters in the therapeutic dose range
Authors: Zwicker R. D. , Wu A. , Sternick E. S.
Published: August 2003

A previously developed technique for reading out LiF thermoluminescent dosimeters (TLD) a second and subsequent time by means of ultraviolet (UV)‐induced repopulation of dosimetry traps was studied to determine the feasibility of maintaining a second readout capability in a radiotherapy clinical setting. It was found that with grouping of the TLDs according to second readout sensitivity, the UV‐induced readout attained a precision comparable to that of the initial readout. However, the UV‐induced TL response retained a strong previous dose memory following a standard high‐temperature anneal, and routine calibration before each reuse is recommended.
A note on designing tissue compensators for parallel opposed fields
Authors: Renner Wendel D. , O'Connor Thomas P. , Bermudez Nini M.
Published: August 2003

Missing tissue compensators are typically made to correct for the tissue defect separately for each of two parallel opposed radiation fields. Arguments and experimental evidence are provided to show that a more uniform dose distribution is achieved throughout the irradiated volume if the compensator is designed so that each opposed field delivers an equal dose to a surface defining midmass between the opposed body surfaces. An expedient method to approximate this result is to simply divide equally between the two parallel opposed fields the total amount of compensation otherwise required.
IAEA/WHO 60Co teletherapy dosimetry service using mailed LiF dosimeters. A survey of results obtained during 1975–1982
Authors: Boyd A. W. , Eisenlohr H. H.
Published: August 2003

During 1975–1982 the International Atomic Energy Agency (IAEA) in co‐operation with the World Health Organization (WHO) carried out 603 absorbed dose determinations for 60Co gamma‐ray beams for 278 radiotherapy institutes in 60 countries. The participants were asked to irradiate capsules containing LiF powder to 2 Gy in 5 cm of water. The percentage of the determinations in which the deviation between the institutes quoted dose and the IAEA measured dose was within ±5% was 62%. In 17% of the determinations, the deviation was more than ±10%. For around 70% of the institutes the deviation decreased when further measurements were carried out.
Corrected f factors for photons from 10 keV to 2 MeV
Authors: Jaeger Stanley S. , Harnisch Burdell D.
Published: August 2003

Section 4 of ICRU Report No. 30 contains information on determining the absorbed dose from exposure. Table 4.1 lists the f factor for relating absorbed dose to exposure for photons from 10 keV to 2 MeV under conditions of charged particle equilibrium for water, bone, and muscle. Upon inspection, one notices that although the water values have not changed significantly, the muscle values differ by as much as 6% from previous tables in ICRU Report Nos. 17 and 24. A recomputation of the data indicates that errors exist in the published values. Corrected f factors for photons from 10 keV to 2 MeV are calculated in this communication.
Scatter/primary ratios for x‐ray spectra modified to enhance iodine contrast in screen–film mammography
Authors: Fritz Steven L. , Chang C. H. J. , Livingston William H.
Published: August 2003

Contrast mammography to detect the uptake of iodine‐containing contrast material may be enhanced by spectral modification of the x‐ray beam. Luminance scatter‐to‐primary ratios were measured for three candidate x‐ray tube anode/filter combinations (Mo/Mo, W/Ce, and Ce/Ce). Results show that scattered radiation is significant for all tubes, is lowest for the Mo/Mo system and is essentially the same for the tungsten and cerium anode systems.
A Wiener filter for nuclear medicine images
Authors: King Michael A. , Doherty Paul W. , Schwinger Ronald B. , Penney Bill C.
Published: August 2003

To improve the quality of digital nuclear medicine images, we have developed a new implementation of the Wiener restoration filter. The Wiener filter uses as its optimality criterion the minimization of the mean‐square error between the undistorted image of the object and the filtered image. In order to form this filter, the object and noise power spectrums are needed. The noise power spectrum for the count‐dependent Poisson noise of nuclear medicine images is shown to have a constant average magnitude equal to the total count in the image. The object power spectrum is taken to be the image power spectrum minus the total count, except in the noise dominated region of the image power spectrum where a least‐squares‐fitted exponential is used. Processing time is kept to a clinically acceptable time frame through use of an array processor. Pronounced noise suppression and detail enhancement are noted with use of this filter with clinical images.
Improved applicator–patient coupling in microwave‐induced hyperthermia
Authors: Nussbaum Gilbert H. , Goodman Richard A. , Bruce Arthur A.
Published: August 2003

The effect on the efficiency of power transfer and microwave leakage of different applicator–load coupling schemes is examined. For a 915‐mHz applicator and musclelike phantom separated by 4 cm, it is found that by filling the air gap with dielectric powder or deionized water, the efficiency of power transfer from applicator to load can be raised to levels comparable to that obtained for direct applicator–load contact. For these coupling conditions, it is also found that microwave leakage intensities in the immediate vicinity of the applicator–phantom interface can be reduced to direct contact levels. Employment of such materials and techniques in our clinic, for coupling applicators to patient surfaces in the administration of local hyperthermia to head and neck tumors, has facilitated the reduction of average microwave leakage intensities from more than 15 MW/cm2 to less than 3 MW/cm2 in most cases.
Ionization chamber response to a sudden change of ambient temperature in air, water, and polystyrene phantom
Authors: Kubo Hideo
Published: August 2003

We have studied the time course of current collected with an ionization chamber and electrometer when the chamber was suddenly inserted in an air, water, or polystyrene medium whose temperature was typically 20 °C above or below room temperature. The results were analyzed in terms of a temperature time constant τ—the time required for a 63% change of the ionization current. It was found that for a Farmer‐type chamber, τ for the in‐air measurements ranges from 5–10 min, several times longer than that for the in‐water measurements (2–3 min). These τ values were confirmed with in‐cavity temperature measurements carried out with a small thermocouple.
An equation for calculating the contribution to osmotic potential of the separate solutes of water solutions
Authors: Cochrane T. T.
Published: August 2003

An equation was developed to calculate osmotic potential by formulating the several molecular pressures in a simple osmotic system. Its predictability was verified for many organic and inorganic solutes and their mixtures over concentration ranges well in excess of those found in body fluids. As the contribution to osmotic potential of the separate solute components in a solution can be calculated using the equation, it would be useful in the diagnoses and therapy of osmotic pressure related trauma and disease conditions.
Exposure uniformity considerations in slit radiography
Authors: King Michael A. , Barnes Gary T.
Published: August 2003

Slit radiography is a highly efficient means of suppressing scatter. However, when employed with a pulsating x‐ray source, a grid line type of artifact results if the movement of the slit is not properly coupled to the periodicity of the source. Taking the exposure of the film to be the convolution of the slit transmittance and the radiation intensity, the conditions for a uniform exposure have been derived for the realistic configuration of a multiple‐slit array and a slit transmittance that includes the focal spot and slit geometry. Expressions for the amplitude and spatial frequency of the artifact when the conditions are not met are derived. Methods of suppressing the artifact when its vanishing conditions are not met are also discussed.
Tumor significant dose
Authors: Supe S. J. , Nagalaxmi K. V. , Meenaksi Leela
Published: August 2003

In the practice of radiotherapy, various concepts like NSD, CRE, TDF, and BIR are being used to evaluate the biological effectiveness of the treatment schedules on the normal tissues. This has been accepted as the tolerance of the normal tissue is the limiting factor in the treatment of cancers. At present when various schedules are tried, attention is therefore paid to the biological damage of the normal tissues only and it is expected that the damage to the cancerous tissues would be extensive enough to control the cancer. Attempt is made in the present work to evaluate the concent of tumor significant dose (TSD) which will represent the damage to the cancerous tissue. Strandquist in the analysis of a large number of cases of squamous cell carcinoma found that for the 5 fraction/week treatment, the total dose required to bring about the same damage for the cancerous tissue is proportional to T−0.22, where T is the overall time over which the dose is delivered. Using this finding the TSD was defined as D⋅N−p⋅T−q, where D is the total dose, N the number of fractions, T the overall time p and q are the exponents to be suitably chosen. The values of p and q are adjusted such that p+q≤0.24, and p varies from 0.0 to 0.24 and q varies from 0.0 to 0.22. Cases of cancer of cervix uteri treated between 1978 and 1980 in the V. N. Cancer Centre, Kuppuswamy Naidu Memorial Hospital, Coimbatore, India were analyzed on the basis of these formulations. These data, coupled with the clinical experience, were used for choice of a formula for the TSD. Further, the dose schedules used in the British Institute of Radiology fractionation studies were also used to propose that the tumor significant dose is represented by D⋅N−0.18⋅T−0.06.
Temperature distributions in hyperthermia by electromagnetic induction: A theoretical model for the thorax
Authors: Brezovich Ivan A. , Young John H. , Wang Mann‐T.
Published: August 2003

Steady‐state temperature solutions to the bioheat equation are presented for magnetic induction heating of a thoracic model consisting of a spherical tumor embedded in lung tissue which is layered by muscle and fatty tissue. Analytical solutions are presented for each of the tissue regions along with their numerical evaluations over a range of physical characteristics, including surface cooling effects. A strong dependence of tumor temperature on size and blood perfusion rate is shown to exist and can be used to optimize treatment parameters. Tendencies of the chest muscles and overlaying fatty tissue to overheat, particularly in the case of an obese patient, are discussed along with the alleviating influence of surface cooling. Healthy lung tissue, on the other hand, is shown to be safe from any significant damage in such a heating situation. Transient times required for tumors to achieve thermal equilibrium are computed and shown to depend strongly on tumor size and, to a lesser extent, on blood perfusion rate. Finally, the overall results obtained from the model are compared with available clinical data and are found to be in line with those observations.
The use of neutron and gamma ray spectral measurements and calculations to obtain dosimetric information for DT neutrons
Authors: Hertel N. E. , Murphie W. E.
Published: August 2003

Neutron and gamma ray energy spectra were measured using an NE‐213 scintillator at depths of 7.2, 15.2, and 22.2 cm in a tissue‐equivalent phantom which was uniformly irradiated on one face by deuterium–tritium (DT) neutrons. Coupled neutron–gamma ray multigroup discrete‐ordinates calculations were performed using semi‐infinite slab geometry. These calculations were used to supplement the measured spectra below 1 MeV. Similar calculations were performed to study the perturbation in the phantom due to the detector. The measured and calculated spectra were used to determine the kerma distributions for neutrons and gamma rays at each location. The gamma radiation was determined to contribute more than 10% of the total dose at each depth. The calculated kerma also reveals that a knowledge of the gamma ray spectra below 1 MeV is desirable.
Dose corrections for field obliquity for 45‐MV x‐ray therapy
Authors: McGinley Patton H. , Clanton Anna , Downes Beverly , Nuskind Jeffrey
Published: August 2003

The degree of dose perturbation produced by a 25.7‐cm‐diam circular water phantom was determined for a 45‐MV x‐ray beam by direct measurement. Data obtained in a circular and a cubical water phantom was utilized to test three accepted techniques (isodose shift, TAR method, and effective SSD method) for the correction of isodose levels to account for patient curvature. In general, the effective SSD method yielded the most accurate results for all depth including the buildup region. An isodose shift factor of 0.8 was found for the 45‐MV x‐ray beam.
Computed tomography with a linear accelerator with radiotherapy applications
Authors: Swindell William , Simpson Robert G. , Oleson James R. , Chen Ching‐Tai , Grubbs Elmer A.
Published: August 2003

An earlier paper [Simpson et al., Med. Phys. 9, 574 (1982)] described a computed tomography CT scanner that was constructed by adding a detector array to a 4‐MV isocentric linear accelerator. Since the previous article, the detector array has been improved and we now demonstrate better than 3‐mm spatial resolution and better than 1% relative electron density discrimination. A series of pictures from volunteer patients is included. Normal anatomy is visualized with bone, muscle, fat, and air being clearly delineated.