bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantitative scatter measurement in digital radiography using a photostimulable phosphor imaging system
Authors: Floyd Carey E. , Lo Joseph Y. , Chotas Harrell G. , Ravin Carl E.
Published: March 2003

X‐ray scatter fractions measured with two detectors are compared: a photostimulable phosphor system (PSP) and a conventional film–screen technique. For both detection methods, a beam‐stop technique was used to estimate the scatter fraction in polystyrene phantoms. These scatter fraction measurements are compared to previously reported film‐based measurements. Scatter fractions obtained with the PSP were in good agreement both with measurements using film as well as with most previously reported measurements. For the PSP measurements, repeatability was better than 1%. It was found that the PSP provides a precise x‐ray detector for quantitative scatter measurement in digital radiography.
Comparison of imaging properties of a computed radiography system and screen–film systems
Authors: Sanada Shigeru , Doi Kunio , Xu Xin‐Wei , Yin Fang‐Fang , Giger Maryellen L. , MacMahon Heber
Published: March 2003

To compare the diagnostic quality of images obtained with a computed radiography (CR) system based on storage phosphor technology with that obtained with conventional screen–film systems, a dual‐image recording technique was devised. With this technique, a CR imaging plate is placed behind a screen–film system in a conventional cassette. This makes it possible to obtain two images simultaneously, one from each system, in a clinical examination with the same patient positioning, the same degree of patient motion, the same geometric unsharpness, and no additional exposure. The modulation transfer functions (MTFs) of the CR system with and without the dual‐image recording technique were greater at low frequencies, but lower at high frequencies, that the MTFs of the screen–film systems used. The noise Wiener spectra of the CR images at the plane of the imaging plate were greater than those of the screen–film systems, but were comparable to those of the screen–film systems at the plane of the printed film due to the reduction in image size. Clinical chest images obtained with the dual‐image recording technique appeared comparable, probably because of the image size reduction and the use of mild unsharp mask processing.
X‐ray imaging using amorphous selenium: A photoinduced discharge readout method for digital mammography
Authors: Rowlands J. A. , Hunter D. M. , Araj N.
Published: March 2003

A new digital image readout method for electrostatic charge images on photoconductive plates is described. The method can be used to read out images on selenium plates similar to those used in xeromammography. The readout method, called the air‐gap photoinduced discharge method (PID), discharges the latent image pixel by pixel and measures the charge. The PID readout method, like electrometer methods, is linear. However, the PID method permits much better resolution than scanning electrometers while maintaining quantum limited performance at high radiation exposure levels. Thus the air‐gap PID method appears to be uniquely superior for high‐resolution digital imaging tasks such as mammography.
Thermoluminescent dosimetry for 103Pd seeds (model 200) in solid water phantom
Authors: Chiu‐Tsao Sou‐Tung , Anderson Lowell L.
Published: March 2003

Dose measurements using LiF thermoluminescent dosimeters (TLD) have been performed for single 103Pd seeds (model 200) at the center of a solid water phantom. TLD cubes 1 mm on an edge were used for measurements from 1 mm to 1 cm at 1‐mm intervals. The cubes were centered along transverse and longitudinal axes and along radial lines from seed center at 10° increments. TLD chips of dimension 3.1×3.1×0.89 mm were used at distances of 2, 2.5, 3, and 4 cm at l5° angular intervals. Data are presented as the product of distance squared and dose rate per unit source strength, plotted versus distance and angle. At 1 cm from seed center along the transverse axis this product was found to be 0.88 cGy cm2 mCi−1 h−1. A dose‐rate table in polar coordinates has been formulated for use with multiseed dose distribution calculations. Comparison with data of Meigooni et al. [Endocuriether./Hyperthermia Oncol. 6, 107–117 (1990)] shows general agreement for distances of 2 cm or greater. A comparison of our transverse axis data with Russell's calculated values (Theragenics Internal Report, 4 November 1984) for an ideal point source of 103Pd shows very good agreement except at distances less than 0.5 cm, where differences are attributable to the extended source effect in the actual seed.
Accelerated helium‐ion beams for radiotherapy and stereotactic radiosurgery
Authors: Ludewigt Bernhard A. , Chu William T. , Phillips Mark H. , Renner Timothy R.
Published: March 2003

A new beam line for radiotherapy and radiosurgery with accelerated helium‐ion beams has been set up at the Bevalac. The new treatment room has been equipped with a very precise patient positioner in order to utilize the superior dose localization properties of light‐ion beams. The beam spreading and shaping system is described, the trade‐offs involved in positioning the beam modifying devices are discussed, and the physical properties of the generated radiation fields are reported. The Bragg peak modulation by axial beam stacking employing a variable range shifter is explained and the control system including beam monitoring and dosimetry is presented.
Pencil‐beam redefinition algorithm for electron dose distributions
Authors: Shiu Almon S. , Hogstrom Kenneth R.
Published: March 2003

A pencil‐beam redefinition algorithm has been developed for the calculation of electron‐beam dose distributions on a three‐dimensional grid utilizing 3‐D inhomogeneity correction. The concept of redefinition was first used for both fixed and arced electron beams by Hogstrom et al. but was limited to a single redefinition. The success of those works stimulated the development of the pencil‐beam redefinition algorithm, the aim of which is to solve the dosimetry problems presented by deep inhomogeneities through development of a model that redefines the pencil beams continuously with depth. This type of algorithm was developed independently by Storchi and Huizenga who termed it the “moments method.” Such a pencil beam within the patient is characterized by a complex angular distribution, which is approximated by a Gaussian distribution having the same first three moments as the actual distribution. Three physical quantities required for dose calculation and subsequent radiation transport—namely planar fluence, mean direction, and root‐mean‐square spread about the mean direction—are obtained from these moments. The primary difference between the moments method and the redefinition algorithm is that the latter subdivides the pencil beams into multiple energy bins. The algorithm then becomes a macroscopic method for transporting the complete phase space of the beam and allows the calculation of physical quantities such as fluence, dose, and energy distribution. Comparison of calculated dose distributions with measured dose distributions for a homogeneous water phantom, and for phantoms with inhomogeneities deep relative to the surface, show agreement superior to that achieved with the pencil‐beam algorithm of Hogstrom et al. in the penumbral region and beneath the edges of air and bone inhomogeneities. The accuracy of the redefinition algorithm is within 4% and appears sufficient for clinical use, and the algorithm is structured for further expansion of the physical model if required for site‐specific treatment planning problems. Key words: redefinition algorithm, pencil beam, 3‐D inhomogeneity correction, electron dose calculations
Electron dose calculation using multiple‐scattering theory: Localized inhomogeneities—A new theory
Authors: Jette David
Published: March 2003

In this fourth article in a series on the calculation of electron dose using multiple‐scattering theory, we deal with localized inhomogeneities by solving the Fermi equation for scattering power which is an arbitrary function of position. In fact, we go further, by solving the second‐order multiple‐scattering equation which supersedes the (first‐order) Fermi equation, again for scattering power which is an arbitrary function of position. Thus, we are no longer restricted to a horizontally layered medium, as is the case with the Fermi–Eyges theory. Our general solution is in the form of a perturbation series which evidently converges rapidly enough that only its first two or three terms need be taken for accurate dose calculation. Regarding the energy directly deposited by the primary electrons, the formulas developed in this article give very good agreement with Monte Carlo calculations for the thick half‐slab configuration, as will be seen in the next article in this series. Moreover, our first‐rank, second‐order formulas, when expressed in Fourier‐transformed space, are simple enough to be implemented in a treatment planning system providing full three‐dimensional electron dose calculation for arbitrary configurations of inhomogeneities.
Treatment plan optimization using linear programming
Authors: Rosen Isaac I. , Lane Richard G. , Morrill Steven M. , Belli James A.
Published: March 2003

Linear programming is a versatile mathematical tool for optimizing radiation therapy treatment plans. For planning purposes, dose constraint points, possible treatment beams, and an objective function are defined. Dose constraint points are specified in and about the target volume and normal structures with minimum and maximum dose values assigned to each point. A linear objective function is designed that defines the goal of optimization. A list of potential treatment beams is defined by energy, angle, and wedge selection. Then, linear programming calculates the relative weights of all the potential beams such that the objective function is optimized and doses to all constraint points are within the prescribed limits. Historically, linear programming has been used to improve conventional treatment techniques. It can also be used to create sophisticated, complex treatment plans suitable for delivery by computer‐controlled therapy techniques.
Surface dose rate calibration of Sr‐90 plane ophthalmic applicators
Authors: Goetsch Steven J. , Sunderland Kari S.
Published: March 2003

Calibration of an imported strontium‐90 ophthalmic applicator at the U.S. National Bureau of Standards (now the National Institute of Standards and Technology) has disclosed a significant discrepancy in dose rate calibration (32%–35%) with that quoted by the manufacturer. The University of Wisconsin has investigated this discrepancy and found that both laboratories use similar techniques and a version of the Bragg–Gray equation to yield dose rate estimates. Experimental results indicate a strong relationship between the size of the collecting electrode used in the extrapolation chamber and the resulting estimate of absorbed dose rate. Calibration of these applicators is reviewed and suggestions for improvement and further research are proposed.
Multimodality image integration for stereotactic surgical planning
Authors: Henri C. J. , Collins D. L. , Peters T. M.
Published: March 2003

A method is presented for integrating stereotactic projection and tomographic image data to give composite 3‐D images (stereo pairs) of cerebral anatomy and vasculature. The technique serves to combine complementary information from each modality and allows the imaged volume to be viewed directly. The procedure is largely automated and requires no additional apparatus or information beyond that which is ordinarily employed during stereotactic surgical planning. The two types of data are combined by superimposing the projection angiogram (DSA) onto a translucent volume rendered CT or MR image. Since the rendering algorithm employs an orthographic projection technique, the tomographic volume must first be reshaped and oriented to yield a perspective view that matches the DSA projection. During this process, the data undergo various interpolations which consequently affect the accuracy of target identification based on the resulting images. The integrity of the matching procedure was assessed using simulated data sets. Also, calculations were performed to estimate the resolution of measurements made from digitized stereoscopic images. The resulting sub‐pixel accuracy of the matched images suggests that the technique has potential for stereotactic applications. Preliminary results are presented illustrating combined CT‐DSA and MR‐DSA data sets.
Theory and design of “shortened” multiantenna microwave applicators with controllable SAR patterns
Authors: Leybovich Leonid B. , Nussbaum Gilbert H. , Straube William L. , Emami Bahman N.
Published: March 2003

A “shortened” multiantenna hyperthermia applicator has been designed and tested at the Mallinckrodt Institute of Radiology at Washington University School of Medicine. By shortening the distance from antenna to aperture, an applicator is obtained that produces an SAR pattern that is essentially the same as produced by a monopole antenna. By placing several properly spaced probe antennas into the same “shortened” applicator, an applicator is obtained that produces a SAR distribution that is essentially a composite of small overlapping SAR patterns produced by weakly interacting incoherently driven antennas. Such a design significantly improves the applicator's lateral heating efficiency and allows the independent control of temperatures in certain tumor areas by changing the input power to the respective antennas.
Activity quantitation in SPECT: A study of prereconstruction Metz filtering and use of the scatter degradation factor
Authors: King M. A. , Coleman M. , Penney B. C. , Glick S. J.
Published: March 2003

A study of activity quantitation with prereconstruction Metz filtering and use of the scatter degradation factor (SDF) to numerically correct for scatter was conducted. The ratio of the count rate per unit activity for source locations within a 30×23‐cm water‐filled tub phantom to the count rate per unit activity for Tc‐99m point sources of known activity imaged in air was used to judge the accuracy of activity determination. The investigation was conducted for certain locations within the tub when it was uniformly filled with Tc‐99m activity, and for the same locations at the center of 5, 4, 3, and 2‐cm diam, hot spheres imaged in a cold background. The source locations were the center, and one‐fourth, one‐half, and three‐fourths the major axis. Various methods of combining the conjugate views for use with prereconstruction attenuation correction (arithmetic and geometric mean), and extent to which the Metz filter followed the inverse filter before rolling off to suppress noise were investigated. Without Metz filtering, attenuation correction was performed using a transmission curve that included buildup. With Metz filtering, the good‐geometry attenuation coefficient was used and the combined views were scaled by the SDF calculated for the average body thickness. Depending on the size of the sphere and the extent to which the inverse filter was followed, Metz filtering combined with use of the SDF improved the accuracy of activity quantitation.
Luminance range compression for video film digitizers
Authors: Bednarek Daniel R. , Rudin Stephen , Wong Roland
Published: March 2003

Video cameras are used in many film digitization and teleradiology systems. However, the density range of medical radiographs often exceeds the dynamic range of the camera, and all diagnostic information in the original image may not be captured. Information in both the high and low density areas of the film can be captured in a single video frame if the transmitted luminance range of the radiograph is reduced. This can be accomplished by spatially modulating the back illumination of the film such that areas of lesser density receive less illumination while areas of greater density receive greater illumination. In this work, the use of a video monitor is shown to be an effective means to provide spatially modulated light for compressing the transmitted luminance range and thereby expanding the apparent dynamic range of the video camera. A simple computer‐interfaced video feedback system that determines the appropriate compression mask and a scheme for linearization of system response are described. This system provides an interactive means for control of the degree of range compression.
Semiempirical model for generating tungsten target x‐ray spectra
Authors: Tucker Douglas M. , Barnes Gary T. , Chakraborty Dev P.
Published: March 2003

A semiempirical model for generating tungsten target x‐ray spectra is presented. This model extends earlier work in two significant areas. First, both bremsstrahlung and characteristic x‐ray production are assumed to occur at varying depths within the target. Second, optimal parameters for the model were determined from experimental spectra utilizing nonlinear least‐squares techniques. As a result, good agreement is obtained between calculated and measured x‐ray tube spectra and output for different target angles and a wide range of x‐ray tube potentials. Such is not the case with previously published models.
Method for estimating the intensity of scattered radiation using a scatter generation model
Authors: Honda Michitaka , Kikuchi Katsuya , Komatsu Ken‐ichi
Published: March 2003

An analytical formula for estimating the intensity of scattered radiation in an x‐ray image under various exposure conditions has been developed. The formula was derived using measured data of scatter and primary intensity for various exposure conditions. To simplify the formula, a scatter generation model was constructed mathematically which assumes that the scattered fluence in a material depends on three processes: (1) scattering of the primary photons; (2) scattering of previously scattered photons; and (3) attenuation of the scattered photons. Using this model, the dependence of scatter‐to‐primary ratio on phantom thickness and the tube voltage was expressed by a simple equation. Parameters included in the model were determined from the analysis of measured data. Based on empirical data, it was assumed that the dependence of scatter‐to‐primary ratio on air gap and field size is not affected by variations of phantom thickness and tube voltage. The final formula, which does not include the term of phantom thickness, gives an estimate of the intensity of the scattered radiation from exposure conditions. The scatter intensity estimated using the formula was compared with measured data for various phantom thicknesses, tube voltages, air gaps, and field sizes; the results show that the intensity of scattered radiation can be estimated within about ±10% using predetermined parameters.
Clinical implementation of stereotaxic brain implant optimization
Authors: Rosenow Ulf F. , Wojcicka Jadwiga B.
Published: March 2003

This optimization method for stereotaxic brain implants is based on seed/strand configurations of the basic type developed for the National Cancer Institute (NCI) atlas of regular brain implants. Irregular target volume shapes are determined from delineation in a stack of contrast enhanced computed tomography scans. The neurosurgeon may then select up to ten directions, or entry points, of surgical approach of which the program finds the optimal one under the criterion of smallest target volume diameter. Target volume cross sections are then reconstructed in 5‐mm‐spaced planes perpendicular to the implantation direction defined by the entry point and the target volume center. This information is used to define a closed line in an implant cross section along which peripheral seed strands are positioned and which has now an irregular shape. Optimization points are defined opposite peripheral seeds on the target volume surface to which the treatment dose rate is prescribed. Three different optimization algorithms are available: linear least‐squares programming, quadratic programming with constraints, and a simplex method. The optimization routine is implemented into a commercial treatment planning system. It generates coordinate and source strength information of the optimized seed configurations for further dose rate distribution calculation with the treatment planning system, and also the coordinate settings for the stereotaxic Brown–Roberts–Wells (BRW) implantation device.
Evaluation of neutron dose equivalent levels at the maze entrance of medical accelerator treatment rooms
Authors: McGinley Patton H. , Butker Elizabeth K.
Published: March 2003

This paper evaluates the accuracy of Kersey's method of calculation of the dose level due to photoneutrons at the maze entrance of medical accelerators. In this study measurements and calculations of the neutron dose equivalent were made for 13 medical accelerator facilities. The group of accelerators was composed of four different models from two manufacturers. The maze length for the treatment rooms varied from 3.0 to 8.54 m and 10 of the mazes had a single 90‐deg turn with the remaining having two 90‐deg turns. Moderated activation detectors and a portable neutron remmeter were used for measurements in the treatment room and maze, respectively. It was found that the maximum disagreement between the measured and calculated values was a factor of 2.3 with the calculated value exceeding the measured value. The majority of the measured values were within 25% of the calculated levels. It was concluded that Kersey's method is suitable for use in designing medical accelerator mazes.
A feasibility study of invivo 14‐MeV neutron activation analysis using the associated particle technique
Authors: Garrett R. , Mitra S.
Published: March 2003

The feasibility of using the time correlated associated particle technique for in vivo 14‐MeV neutron activation analysis has been investigated. Gamma rays following neutron inelastic scattering with nitrogen, carbon, and oxygen have been measured with a 12.5×10‐cm NaI(Tl) detector. The results have been scaled to a proposed facility comprising four such detectors past which the subject would be scanned. Based on counting statistics, the precision of estimation of these elements has been determined to be 2.1%, 1.0%, and 1.1%, respectively for experimental measurements on a sample containing physiological concentrations of the major body elements. The average body dose level would be restricted to 0.3 mSv.
Coronary blood flow measurement using an angiographic first pass distribution technique: A feasibility study
Authors: Hangiandreou Nicholas J. , Folts John D. , Peppler Walter W. , Mistretta Charles A.
Published: March 2003

Due to the well‐documented problems associated with visual interpretation of coronary angiograms, more physiologic means of assessing coronary artery stenosis are being investigated. One physiologic parameter that has been suggested is coronary flow reserve (CFR). A digital subtraction angiographic technique based on first pass distribution analysis (FPA) is proposed as a means of measuring CFR and absolute coronary flow. The theory of the FPA method is first outlined, and the implementation of a preliminary version of the FPA algorithm is described. Experiments verifying the utility of this algorithm for measuring absolute flow through a flow phantom, and through the canine circumflex artery are reported. It was determined that the preliminary FPA algorithm is capable of measuring canine coronary flow ratios (R) with accuracy and precision characteristics meeting or exceeding those reported for the parametric imaging technique (RFPA=0.933⋅Rtrue, SEE=0.16, r=0.984). Accurate absolute flow (Q) measurements were obtained in all of the phantom experiments (QFPA=1.054⋅Qtrue, r=0.993), and in one of the three dogs that were studied (QFPA=0.977⋅Qtrue, r=0.935). The difficulty encountered in the other two dog experiments is attributed to the effects of system temporal lag, and would likely be corrected through the use of improved cameras. The feasibility of the general FPA method for measuring relative flow is established, and the potential for routine, absolute flow measurement is demonstrated.
Demonstration of three‐dimensional deterministic radiation transport theory dose distribution analysis for boron neutron capture therapy
Authors: Nigg David W. , Randolph Peter D. , Wheeler Floyd J.
Published: March 2003

The Monte Carlo stochastic simulation technique has traditionally been the only well‐recognized method for computing three‐dimensional radiation dose distributions in connection with boron neutron capture therapy (BNCT) research. A deterministic approach to this problem would offer some advantages over the Monte Carlo method. This paper describes an application of a deterministic method to analytically simulate BNCT treatment of a canine head phantom using the epithermal neutron beam at the Brookhaven medical research reactor (BMRR). Calculations were performed with the TORT code from Oak Ridge National Laboratory (ORNL), an implementation of the discrete ordinates, or Sn method. Calculations were from first principles and used no empirical correction factors. The phantom surface was modeled by flat facets of approximately 1 cm2. The phantom interior was homogeneous. Energy‐dependent neutron and photon scalar fluxes were calculated on a 32×16×22 mesh structure with 96 discrete directions in angular phase space. The calculation took 670 min on an Apollo DN10000 workstation. The results were subsequently integrated over energy to obtain full three‐dimensional dose distributions. Isodose contours and depth‐dose curves were plotted for several separate dose components of interest. Phantom measurements were made by measuring neutron activation (and therefore neutron flux) as a function of depth in copper–gold alloy wires that were inserted through catheters placed in holes drilled in the phantom. Measurements agreed with calculations to within about 15%. The calculations took about an order of magnitude longer than comparable Monte Carlo calculations but provided various conveniences, as well as a useful check.
A decoupled coil detector array for fast image acquisition in magnetic resonance imaging
Authors: Kwiat D. , Einav S. , Navon G.
Published: March 2003

A method for magnetic resonance imaging (MRI) is investigated here, whereby an object is put under a homogeneous magnetic field, and the image is obtained by applying inverse source procedures to the data collected in an array of coil detectors surrounding the object. The induced current in each coil due to the precession of the magnetic dipole in each voxel depends on the characteristics of both the magnetic dipole frequency and strength, together with its distance from the coil, the coil direction in space, and the electrical properties of the coils. By calculating the induced current signals over an array of coil detectors, a relationship is established between the set of signals and the structure of the body under investigation. The linear relation can then be represented in matrix notation, and inversion of this matrix will produce an image of the body. Important problems which must be considered in the proposed method are signal‐to‐noise ratio (SNR) and coupling between adjacent coils. Solutions to these problems will provide a new method for obtaining an instantaneous image by NMR, with no need for gradient switching for encoding. A general algorithm for decoupling of the coils is presented and fast sampling of the signal, instead of filtering, is used in order to reduce both noise and numerical roundoff errors at the same time. Sensitivity considerations are made with respect to the number of coils that is required and its connection with coil radius and SNR. A computer simulation demonstrates the feasibility of this new modality. Based on the solutions presented here for the problems involved in the use of a large number of coils for a simultaneous recording of the signal, an improved method of multicoil recording is suggested, whereby it is combined with the conventional zeugmatographic method with read and phase gradients, to result in a novel method of magnetic resonance imaging. In the combined method, there are no phase‐encoding gradients. Only a single slice‐selecting gradient, to be followed by a single read‐gradient. Instead of phase‐encoding gradients, use is made of an equivalent number of coils. The number of coils now is reduced significantly. This method suggests a single slice image taken within a single echo time, and where a 128×128 resolution is possible with only 128 coils. The applicability of the method is based on a successful decoupling procedure for the detectors (coils and cables) and the availability of highly accurate, high‐gain, low‐noise amplifiers with a broad dynamic range.
Intensifying effect of metallic screens on the sensitivity of x‐ray films for 400‐kV bremsstrahlung photons
Authors: Navon E. , Dick C. E. , Barnea G.
Published: March 2003

Measurements are carried out to determine the relative photographic effect produced by electrons emanating from metallic screens on a typical radiographic film. The electrons are produced in metal foils of aluminum, copper, and lead by the interaction of photons in a 400‐kV bremsstrahlung beam. Intensification factors of up to 1.65, 2.05, and 5.90 for aluminum, copper, and lead screens, respectively, are determined as a function of the foil thickness. The equilibrium thickness screens are determined to be 20 mg/cm2 for aluminum and 30 mg/cm2 for copper and lead. These results are compared with the absorbed dose in the film emulsions, calculated by Monte Carlo methods. The results of the present work are compared with those for 60Co and 137Cs photon beams. The dependence of the equilibrium thickness and the intensification factor on photon energy and the atomic number of the screen material is summarized and explained.
Quantitative imaging of I‐124 using positron emission tomography with applications to radioimmunodiagnosis and radioimmunotherapy
Authors: Pentlow K. S. , Graham M. C. , Lambrecht R. M. , Cheung N.‐K.V. , Larson S. M.
Published: March 2003

Positron emission tomography (PET) is potentially useful for the quantitative imaging of radiolabeled antibodies, leading in turn to improved dosimetry in radioimmunotherapy. Iodine‐124 is a positron‐emitting nuclide with appropriate chemical properties and half‐life (4.2 days) for such studies since the radiolabeling of antibodies with iodine is well understood and the half‐life permits measurements over several days. Unfortunately, I‐124 has a complex decay scheme with many high‐energy gamma rays and a positron abundance of only 25%. It has therefore been largely ignored as a PET‐imaging nuclide. However, measurements made with phantoms and animals under realistic conditions using a BGO‐based PET scanner have shown that satisfactory imaging and quantitation can be achieved. Investigations of spatial resolution, the linearity of regional observed count rate versus activity in the presence of other activity, and the visualization and quantitation of activity in spheres with different surrounding background activities were carried out with phantoms up to 22 cm in diameter. Compared with F‐18, spatial resolution was only slightly degraded (13.5 mm FWHM vs 12 mm FWHM) while linearity was the same over a 10:1 activity range (0.015 to 0.15 MBq/ml for I‐124). The visualization and quantitation of spheres was also slightly degraded when using similar imaging times. Increasing the imaging time for I‐124 reduced the difference. To verify that the technique would work in vivo, measurements were made of human neuroblastoma tumors in rats which had been injected with I‐124 labeled 3F8 antibody. Although the number of samples was small, good agreement was achieved between image‐based measurements and direct measurements of excised 4‐g tumors. Thus quantitative imaging of I‐124 labeled antibodies appears to be possible under realistic conditions.
Effect of tissue inhomogeneity on dose distribution of continuous activity of low‐energy electrons in bone marrow cavities with different topologies
Authors: Kwok Cheuk S. , Bialobzyski Philip J. , Yu Siu K.
Published: March 2003

Monte Carlo calculations have previously been performed by Eckerman to evaluate the absorbed fractions of continuous sources of monoenergetic electrons in marrow cavities of human bone. The difference in scattering power of electrons in cortical bone (CB) and the red marrow (RM) was neglected. In the present work the Integrated Tiger Series and Electron–Gamma–Shower Monte Carlo codes were used to investigate the effect of topology of the bone and bone marrow interface on backscatter dose increase to the marrow. Planar, cylindrical, and spherical geometries were included. For the planar geometry, a maximum dose increase of 9±1 (S.E. of the mean)% was obtained in the region within 12 mg/cm2 from the interface due to a semi‐infinite source of electrons with energy greater than 0.5 MeV. An increase of 7±1% was observed experimentally in the same region due to a semi‐infinite source of32 P. This was in good agreement with Monte Carlo calculation. Averaged over the region of RM embedding electron sources between two planar CB/RM interfaces 1000 μm apart, a dose enhancement of 10±2% was predicted for electron energies from 1 to 1.75 MeV. For the cylindrical interface with 500‐μm radius of curvature, the maximum dose increase averaged over the whole cylinder due to an isotropic distribution of monoenergetic electrons inside the cylinder was 12±1%. This occurred at 0.75 MeV. For the spherical interface with 500‐μm radius of curvature, the maximum dose increase in the region within 20 μm (2.1 mg/cm2) from the interface due to an isotropic distribution of monoenergetic electrons inside the sphere was as high as 21±1%. This occurred at about 0.5 MeV. The dose increase, averaged over the whole sphere, was 12±0.6%.
Automated data collection and analysis system for MOSFET radiation detectors
Authors: Gladstone D. J. , Chin L. M.
Published: March 2003

Metal oxide semiconductor field effect transistors (MOSFET) have been used as radiation dosimeters. Because of their small detector size, minimal power requirements, and signal integration characteristics, they offer unique possibilities as real‐time dose monitors in radiotherapy. An automated data collection and analysis system for use with MOSFET radiation dosimeters has been designed and built. The objective was to design a system which can acquire and process the MOSFET signals in real time, in any radiation field encountered in radiotherapy. In particular, major problems have been solved arising from the intrinsic drifts of the MOSFET signal during low dose rate measurements. These signal drifts are significant when the MOSFET detector is used in applications such as on‐line monitoring of radiation dose delivery in brachytherapy or radioimmunotherapy. The data collection and analysis system includes a portable IBM‐compatible personal computer fitted with digital‐to‐analog and analog‐to‐digital converter boards. A single‐chip programmable current supply is used to power the MOSFET dosimeters. Intrinsic and extrinsic drifts in signal due to ion diffusion and electron tunneling are corrected by deconvolution of the collected data in real time or after data collection. The data acquisition system and signal‐processing methodologies are described.
Obtaining S values for rectangular–solid tumors inside rectangular–solid host organs
Authors: Stinchcomb Thomas G. , Durham James S. , Fisher Darrell R.
Published: March 2003

A method is described for obtaining S values between a tumor and its host organ for use with the MIRD formalism. It applies the point‐source specific absorbed fractions for an infinite water medium, tabulated by Berger, to a rectangular solid of arbitrary dimensions which contains a rectangular tumor of arbitrary dimensions. Contributions from pairs of source and target volume elements are summed for the S values between the tumor and itself, between the remaining healthy host organ and itself, and between the tumor and the remaining healthy host organ, with the reciprocity theorem assumed for the last. This method labeled MTUMOR, is interfaced with the widely used MIRDOSE program which incorporates the MIRD formalism. An example is calculated.
SPECT volume quantitation: Influence of spatial resolution, source size and shape, and voxel size
Authors: King Michael A. , Long David T. , Brill A. Bertrand
Published: March 2003

A number of factors influence the accuracy of estimation of source volume with single‐photon emission computed tomography (SPECT) imaging. This study investigated the role of a number of factors including system spatial resolution (which includes the influence of low‐pass filters applied to suppress noise), source size and shape, and voxel size in determining volume. A rectangular parallelepiped (bar), a right cylinder, and a sphere were mathematically modeled as being imaged with a SPECT system by calculating the three‐dimensional (3‐D) convolution of them with symmetric Gaussian functions of 20 different full widths at half maximums (FWHM's). The resulting activity profiles were analyzed to determine the location of the edges as a function of the source size relative to the FWHM of the system. The edge definition criteria studied were (1) the location of the 50% count threshold and (2) the maximum in the local gradient. In addition, the threshold which yielded the correct edge location was also determined. A nonstationary computer simulation of SPECT imaging, based on the serial model of the system transfer function, was used to test the predictions of the mathematical model and investigate the influence of (1) voxel size and sampling with a discrete array of voxels; (2) attenuation; (3) scatter; (4) variable spatial resolution; (5) low‐pass filtering; and (6) noise. The mathematical model predicted that both the 50% threshold and the maximum in the local gradient methods of estimating edge location would show either an under‐ or overestimate of source volume depending on both the ratio of source diameter to system FWHM and the source shape. The predictions were found to be in good agreement with the measured volumes of simulated spherical sources. The use of finite‐size voxels was determined to yield a discrete set of possible volumes, where the possible magnitudes were dependent on voxel size and centering of the object within the array of voxels. Decreasing voxel size was found to improve the accuracy of volume quantitation in the absence of noise.
Gradient moment nulling for steady‐state free precession MR imaging of cerebrospinal fluid
Authors: Wood Michael L. , Zur Yuval , Neuringer Leo J.
Published: March 2003

Steady‐state free precession (SSFP) pulse sequences can produce magnetic resonance (MR) images rapidly, in which cerebrospinal fluid (CSF) is several times more intense than the other tissues. However, motion in the presence of magnetic field gradients reduces the intensity of CSF drastically, unless the time integral of the gradient waveform between each radio‐frequency (rf) pulse vanishes. The consequences of motion on SSFP are explored here in detail theoretically and experimentally. The principle of gradient moment nulling is applied with the objective of giving CSF in SSFP images uniformly high intensity everywhere, in spite of motion. Theoretical analysis of the phase of the transverse magnetization from a group of isochromats, with a trajectory described by a Taylor series, reveals how motion along each direction disrupts SSFP and also causes ghost artifacts. Images of CSF in the cervical spine are found to have less extensive flow voids and weaker ghosts from pulsation if the first moment calculated from the rf pulse to the center of the gradient echo vanishes for both the frequency encoding and slice selection gradient waveforms. However, first‐order moment nulling of the phase encoding gradient waveform is unnecessary for SSFP imaging of CSF.
Measurement of the replacement correction factor for parallel‐plate chambers in electron fields
Authors: Reft Chester S. , Kuchnir Franca T.
Published: March 2003

When parallel‐plate chambers are used for dosimetry in electron fields, the AAPM dosimetry protocol recommends a value of 1.0 for the replacement correction factor, Prepl,pp,E, until further data become available. Here, Prepl,pp,E for five commercially available parallel‐plate chambers was measured as a function of electron energy from a nominal value of 5.5 to 22 MeV by comparison with a cylindrical chamber whose Prepl,cyl,E was obtained from data in the protocol. Since this method is based on the concept of a constant value for Ngas,pp, the energy and modality dependence of Ngap,pp is also investigated for these chambers for Co‐60, 4‐, 6‐, 24‐MV photons and for 22‐MeV electrons. It is found that for three of the chambers Prepl,pp,E is independent of energy, consistent with unity within one or two standard deviations (s.d.). For the fourth chamber Prepl,pp,E is similarly consistent with one above 10 MeV, but decreases at lower energies, while for the fifth one it shows a systematic drop with decreasing energy.
Determination of x‐ray spectra and of the scattered component up to 300 kV
Authors: Laitano R. F. , Pani R. , Pellegrini R.
Published: March 2003

Several x‐ray spectra, including those of the ISO reference radiations, were measured by 2‐hp Ge detectors. Measurements were carried out in different experimental conditions with regard to detector size, beam collimation, and SDD. A stripping procedure to improve the spectrum analysis was developed on the basis of a detailed evaluation (by means of a Monte Carlo method) of the detector's spurious effects. These effects include K‐photon escape, Compton photon escape, electron escape, and collimation effect. The stripping procedure also allows us to determine directly the spectra of possible scattered radiation reaching the detector in addition to the primary beam. When the primary beam is heavily filtered, the leakage radiation from the x‐ray tube housing scattered onto the detector may not be negligible even when the x‐ray tube is provided with appreciable shielding. Possible practical consequences of these effects are discussed. The results obtained on the ISO x‐ray spectra are in agreement with previous determinations. The advantage of the present procedure is its more immediate applicability to Ge detectors of any size and with different beam collimation conditions.
Investigation of an FFT‐based correlation technique for verification of radiation treatment setup
Authors: Jones S. M. , Boyer A. L.
Published: March 2003

Electronic portal imaging devices that capture an image of a patient's treatment field electronically by means of a computer data acquisition system operating in real time are becoming available. This paper reports on a study of a field verification correlation algorithm that can compare each treatment portal image to an image of the correct treatment field positioning. The algorithm requires no human intervention or analysis of the images but rather uses fast Fourier transforms to produce a correlation distribution. The position and amplitude of the correlation distribution maximum were tested as objective measures of translational and rotational differences of subject positions between pairs of images. The concept was tested by using a prototype algorithm to obtain the correlation distributions for images of an Alderson Rando™ head phantom. Images of the phantom setup with various errors were compared with an image of the phantom in the initial, correct treatment position. Translations, in‐plane and out‐of‐plane rotations, and combinations of translations and rotations were studied. The algorithm accurately measured translations. The value of the correlation distribution maximum was found to be a reasonable candidate for an alignment parameter for which tolerable error thresholds might be established.
Semianalytical expressions for ( and for electrom beams
Authors: Wielopolski Lucian , Pai Sujatha , Mlyn Marc
Published: March 2003

The tables of the mean restricted collision masss stopping power ratios for water, polystyrene and acrylic relative to air given in the AAPMTG‐21 protocol have been fitted to an expression with 20 coefficients using the depth in the phantom and the mean incident electron energy as two independent variables. Using these expressions, the calculatd values agree with the tabulated values with in of the cases and within in of the cases. For each of the four cylindrical chamber inner diameters, given in the protocol, the electron fluence correction has been fitted to an expression with four coefficients using the mean electon energy at depth z as an independent variable.
A restricted angular scattering model for electron penetration in dense media
Authors: McLellan J. , Sandison G. A. , Papiez L. , Huda W.
Published: March 2003

A restricted angular scattering model for electron penetration in dense media is presented. In the model, the Fermi–Eyges transport equation is modified through the addition of an extra term which may be interpreted as representing an apparent force opposing the scattering of electrons into wider angles. The introduction of this extra term allows the modeling of the measured saturation in the mean square angular spread of electrons with depth. The restricted scattering model retains the Gaussian features of the Fermi–Eyges model and, therefore, may be readily incorporated into existing dose computation algorithms. Good agreement is obtained with measured angular electron distribution data for a point monodirectional beam over a wide range of incident electron energies (5–20 MeV) and scattering media (atomic numbers of 6 to 82). Also, a comparison of the restricted scattering model predictions with measurements of the lateral pencil beam spread shows an improvement over the predictions of Fermi–Eyges model close to the end of the electron range. Broad beam profiles were generated using both the Fermi–Eyges and restricted scattering models. A comparison of predicted and measured beam profiles shows that the restricted scattering model is a significant improvement over the Fermi–Eyges model for the prediction of beam penumbra shape in homogeneous media.
A sensitivity study of micro‐TLDs for in vivo dosimetry of radioimmunotherapy
Authors: Heidorn Douglas B. , Ten Haken Randall K. , Roberson Peter L. , Buchsbaum Donald J.
Published: March 2003

The sensitivity and precision of teflon‐imbedded CaSO4:Dy microthermoluminescent dosimeters (micro‐TLDs) were determined. The micro‐TLDs were sectioned from miniature TLDs (200 μm×400 μm×5 mm) that were fabricated using standard techniques. In order to measure absorbed dose, the miniature TLDs can be implanted directly into tissues (e.g., tumor xenografts) that have received injections of radiolabeled monoclonal antibodies. Micro‐TLDs recovered from tissue sections cut with a microtome can be read out to determine local absorbed dose. The precision of dose estimation was quantified for uniformly irradiated 32‐, 96‐, and 192‐μm TLD chips; coefficients of variation ranged from 22% to 41%, depending on chip size. The coefficients of variation were reduced to less than 12% using individual relative sensitivity factors for each micro‐TLD. The spatial resolution of the micro‐TLDs was studied by placing miniature TLDs across the sharp penumbral region of a linear accelerator x‐ray field. TLDs were sectioned into 32‐μm chips which were read out to determine the relative absorbed dose. The sharpness of the penumbra was readily quantified by the micro‐TLDs.