bluuebunny/crossref_metadata_2025 huggingface dataset:
A light source for testing radiological television cameras
Authors: Rowlands J. A. , Schulenburg K. S. , DeCrescenzo G.
Published: March 2003

A light source for testing and setting up radiological television systems has been designed and built using green light emitting diodes and an optical integrating sphere. It is shown to have an optical spectrum similar to the green output phosphors used in x‐ray image intensifiers (XRII's). It can be made uniform in intensity across the output port and does not show the small scale granularity characteristic of phosphors. It has a Lambertian angular distribution which, by the addition of neutral density filters, can be made to mimic the angular distribution at the output of an XRII. It can easily and accurately be modulated or switched and a luminance comparable to that of an XRII output phosphor can be achieved.
Geometrical aspects of computed tomography: Sensitivity profile and exposure profile
Authors: Gagne Robert M.
Published: March 2003

A simple model has been developed for the generation of theoretical sensitivity and exposure profiles perpendicular to the tomographic plane in computed x‐ray tomography. The model incorporates the functional dependence on scanner geometry, focal spot size and shape, and detector sensitivity. The sensitivity and exposure profiles are best depicted as the convolution of functions, when appropriately scaled, describing the focal spot intensity distribution and the transmittance of the pre‐ and postpatient collimators. Predictions of the model agree well with experimental results on both sensitivity and exposure profiles for small and large nominal slice thicknesses from five different computed tomography (CT) x‐ray systems. The CT x‐ray systems selected represent both state of the art and older scanner models. Comparisons are also made on the degree of matching of the sensitivity and exposure profiles for each scanner which can be used as a measure of geometrical efficiency in the direction perpendicular to the tomographic plane.
Linearity and contrast scale control in computed tomography
Authors: Nosil Josip , Pearce Keith I. , Stein Richard A.
Published: March 2003

The aim of this paper is to present linearity studies and quality control charts for changes in the computed tomography (CT) number of water and contrast scales for two CT scanners over one year. Linear regression relates the attenuation coefficient to CT number. The CT number for water and the contrast scale values as obtained from the fit are: CT1=(−0.13±1.3) Hounsfield units (HU), CT2=(−1.8±1.6) HU and contrast scale (CS)1=(1.80±0.03) 10−4 cm−1 HU−1, CS2=(1.82±0.02) 10−4 cm−1 HU−1 for Picker International scanner models 600SE and 1200SX, respectively. Direct measurements of CT numbers are compared with fitted results, providing a necessary preliminary steps in the development of objective CT interpretation.
The effect of differences in data base on the determination of absorbed dose in high‐energy photon beams using the American Association of Physicists in Medicine protocol
Authors: Mijnheer B. J. , Chin L. M.
Published: March 2003

Exposure rates were adjusted at the National Institute of Standards and Technology (NIST) on January 1, 1986 to take into account more recent values for some physical parameters, mainly in electron stopping power ratios. Exposure calibration factors for 60Co gamma rays NX will therefore be lowered by 1.1%. Consequently, absorbed dose determinations in high‐energy photon beams will be reduced by the same amount if the values for these physical parameters remain unchanged in the American Association of Physicists in Medicine (AAPM) protocol. If the same data base as used at NIST is applied in the AAPM protocol, then Ngas/NX values, water–air stopping power ratios, and Pwall values will be different. The overall change in absorbed dose determinations using a consistent set of data will be a reduction of 0.8% for 60Co gamma rays and 1.5% for a 20‐MV x‐ray beam compared to the values before January 1, 1986. Since the net effect is small when different sets of data are applied, the new NIST exposure calibration factors may be used in combination with the AAPM protocol without significant error.
Determination of three‐dimensional structure in biplane radiography without prior knowledge of the relationship between the two views: Theory
Authors: Metz Charles E. , Fencil Laura E.
Published: March 2003

A novel method allows the determination of three‐dimensional object structure from two projection images that are obtained at arbitrary, unknown orientations. Only minimal prior information concerning the imaging system is required. First, the image coordinates of eight or more object points that can be identified unambiguously in both views are used to determine the relative geometry of the two projections. Subsequently, the three‐dimensional coordinates of the identified object points are determined, to within a scale factor, from the image coordinates of the points and the calculated imaging system geometry. A theoretical description of the overall method is provided, along with techniques for the reduction of effects of experimental errors and numerical errors thay may arise in the course of the calculations. Methods to retrieve the absolute scale of the object are discussed also.
Basic imaging properties of a computed radiographic system with photostimulable phosphors
Authors: Fujita Hiroshi , Ueda Katsuhiko , Morishita Junji , Fujikawa Tsuyoshi , Ohtsuka Akiyoshi , Sai Tokugi
Published: March 2003

We measured the characteristic curve, modulation transfer function (MTF), and the Wiener spectrum of a commercially available computed radiographic (CR) system with photostimulable phosphor plate (imaging plate, IP). The characteristic curve (system response) obtained by an inverse‐square x‐ray sensitometry showed a wide dynamic range (order of 103 in maximum). The slit technique was employed to determine the MTF's, such as IP MTF, presampling MTF including the unsharpness of the detector (IP) and the blurring effect of the sampling aperture, and laser‐printer MTF. It was found that the MTF of the standard type of IP was comparable to that of medium‐speed screen/film systems. The noticeable degradation of resolution in our CR system, however, occurred at the stage of image data sampling: the presampling MTF was inferior to the IP MTF due to the effect of the scattering and resultant spreading of the incident laser beam and the emitted luminescence. The noise was characterized by means of digital Wiener spectrum using uniformly exposed noise data. Exposure ranges could be separated into different sections depending upon the noise sources, such as quantum mottle at low exposure and system structure noise at high exposure.
Scientific basis of breast diaphanography
Authors: Profio A. Edward , Navarro Glenis A. , Sartorius Otto W.
Published: March 2003

Diaphanography, also known as transillumination, is a breast diagnostic technique based on differences in the diffuse transmittance of visible or near‐infrared radiation. Previous papers by the authors reported on investigations of the effect of tumor size, depth at which the tumor is located, the thickness of the breast, and the effect of using photons of different wavelengths. The results from the study reported here indicate that absorption of light in hemoglobin is the basis for the luminance contrast, and shift in the infrared to red transmission ratio, in the diaphanographic image. Evidence is based on known extinction coefficients for oxyhemoglobin and deoxyhemoglobin as a function of wavelength, measurements of the transmitted spectrum in specimens, in vivo dual wavelength transillumination imaging of lesions containing different amounts of blood (bloody and clear cysts, hematomas, veins, fibroadenomas, and carcinomas), and comparison of preoperative diaphanographic images to blood vessel volumes measured by microscopic analysis of surgical specimens. Oxygenation affects the relative proportions of infrared and red light transmitted, but does not influence the diagnosis based on luminance contrast.
Simulation studies of dual‐energy x‐ray absorptiometry
Authors: Sorenson James A. , Duke Peter R. , Smith Steven W.
Published: March 2003

Computer simulations were performed to predict the performance characteristics of dual‐energy x‐ray absorptiometry. K‐edge filter techniques were analyzed in detail and compared to 153Gd sources in terms of output intensity, precision, patient dose, image contrast, beam hardening, and marrow fat effects. Similar analyses were performed for two dual‐kV techniques that have been reported in the literature. The simulations indicate that K‐edge filter techniques, or a dual‐kV technique combined with K‐edge filtering, can provide performance capabilities that equal or exceed those achievable with 153Gd systems. A (70/140) dual‐kV technique with conventional (Al or Cu) filtration also has advantages in terms of source output intensity, but is 2–3× inferior to the K‐edge techniques and 153Gd in terms of patient dose and beam‐hardening effects.
An energy sensitive cassette for dual‐energy mammography
Authors: Chakraborty Dev P. , Barnes Gary T.
Published: March 2003

A cassette for simultaneously acquiring dual‐energy mammographic images is proposed and studied utilizing a theoretical noise analysis model. The cassette consists of a sandwich of two storage phosphor plates separated by a copper filter. The front, low atomic number, plate was assumed to be comprised of SrFBr and the rear, high atomic number, plate of commercially available BaFBr (98 mg/cm2 coating weight). Assuming a constant x‐ray tube voltage of 50 kVp and a typical breast thickness, the theoretical model yielded a front SrFBr phosphor coating weight of ≊21 mg/cm2. The study indicates that a relatively large separation in the average x‐ray photon energies absorbed in the two plates can be obtained. It also indicates that both a high‐quality conventional (single energy) digital image and a tissue canceled digital image (i.e., a calcium image) can be obtained at dose levels comparable to those currently employed. The latter image could potentially improve the early detection of cancerous microcalcifications and also lends itself to computer aided diagnosis.
A water phantom controller for automated acquisition of linac beam parameters
Authors: Schmid M. G. , Morris R. L.
Published: March 2003

Three‐dimensional water phantoms are routinely used when acquiring the data necessary to commission medical linear accelerators. A new water phantom controller has been developed at our institution that is unique in several aspects. The water phantom controller is based on an IBM XT compatible computer. This has been interfaced to an Artronix three‐dimensional water phantom and a commercially available linac setup controller. Some of the unique features of the new controller are (i) its ability to perform three‐dimensional coordinate transformations on the fly (this removes the need to level and align the water tank with the beam axes and greatly reduces setup time). (ii) Its ability to communicate with a device which can control the linac operating parameters (this allows the water phantom controller to adjust, for example, the jaw size of the accelerator as it acquires data). (iii) Its ability to output the acquired data in a number of modes, including screen display, hardcopy plot, or disk file that may be transferred to a central treatment planning computer). (iv) Its ability to digitally process the acquired data. This water phantom controller may be used to gather machine data in a highly automated manner, greatly reducing the time required to gather the desired data.
Quantification techniques for dual‐energy cardiac imaging
Authors: Molloi Sabee Y. , Mistretta Charles A.
Published: March 2003

We have previously reported a motion immune dual‐energy subtraction technique in which x‐ray tube voltage and x‐ray beam filtration are switched at 30 Hz between 60 kVp (2.0‐mm Al filter) and 120 kVp (2.0‐mm Al+2.5‐mm Cu filtration). In this paper we consider the suitability of these dual‐energy images for quantitative measurements of iodine thickness and volume. Optimized iodine signal‐to‐noise ratio(S/N) was measured as a function of phantom thickness. Using a fixed mAs, the S/N of the dual‐energy images was found to decrease by sevenfold as lucite thickness increased from 10 to 25 cm. For the same increase in lucite thickness S/N for time subtraction images decreased by fivefold. Image quality in two human volunteers was subjectively judged to be good. In order to quantitate physiological parameters such as ejection fraction and left ventricular volume, energy dependent corrections for scatter and veiling glare, beam hardening, detector nonuniformity, heel effect, and uncanceled bone signals were developed. Since the dual‐energy technique does not conpletely cancel bone, a preinjection dual‐energy subtraction image was used to estimate integrated bone contributions to iodine volume measurements. In a phantom measurement simulating exercise ventriculography, the known (Vk) and videodensitometrically measured (Vm) volumes of 19 mg/cm3 solution of iodine were related by Vm=0.95 Vk+1.50 cm3 (r>0.99).
The influence of the size of the grid used for dose calculation on the accuracy of dose estimation
Authors: Niemierko Andrzej , Goitein Michael
Published: March 2003

The standard presentation of a dose distribution as an isodose map is based on interpolation between dose values calculated on a matrix of equally spaced points. We explored the question of how the spacing of the grid used for the dose matrix affects the error due to interpolating the dose at any point. We defined two types of errors: the dose error, which is the difference between the interpolated and true dose at a given point; and the position error, which is the distance between the point of interest and the nearest point which has, in fact, the dose value estimated for the point of interest. We examine the problem using both an analytical beam profile (a Fermi function) and measured 60Co, x‐ray and proton beam profiles. Our analysis showed that the interpolation errors are proportional to the curvature of the dose distribution and are relatively high in regions on either side of, but not including, the steepest part of the penumbra. Our results showed how big an interpolation error one should expect for a given size of the calculation grid. The specification of accuracy should be cast in the form of a pair of requirements, one for dose and the other for position. At a given point, only one of the two requirements needs to be satisfied. The position requirement is almost always the less demanding in clincial practice and permits the use of a larger grid spacing than if only a dose requirement is applied. As a rule of thumb, we recommended a grid size 2.5 times the largest acceptable position error when that error is in the range of from 1 to a few millimeters.
Film‐screen mammography x‐ray tube anodes: Molybdenum versus tungsten
Authors: Kimme‐Smith Carolyn , Bassett Lawrence W. , Gold Richard H. , Rothschild Peter
Published: March 2003

Gridless screen‐film mammography at 23 kVp with a W anode (inherent filtration: 0.1 mm Al, added filtration: 0.025 mm Mo) can achieve contrast identical to that achieved with gridless film‐screen mammography at 27 kVp with a Mo anode (inherent filtration: 1.0 mm Be, added filtration: 0.025‐mm Mo). However, W‐anode film‐screen mammograms obtained at 23 kVp require more radiation than Mo‐anode film‐screen mammograms obtained at 27 kVp. The lack of contrast of W‐anode film‐screen images produced at the same kVp as Mo‐anode images was verified clinically and with a low contrast test object imaged over a range of densities. A step wedge test object was then used to match contrast between Mo‐ and W‐anode gridless film‐screen images at various kVp. The low contrast test object images verified the contrast equivalence of images obtained at 23 kVp for a W anode and 27 kVp for a Mo anode. A comparison of the two kVp for different anode materials was tested clinically on ten patients. The clinical and low contrast test object experiments were reviewed by three radiologists specializing in mammography.
137Cs dosimetry table for asymmetric source
Authors: Waggener R. , Lange J. , Feldmeier J. , Eagan P. , Martin S.
Published: March 2003

A common 137Cs brachytherapy source has a 2‐cm physical length and 1.38‐cm active length. The active length is not symmetric with respect to the source center because one source end contains an eyelet. Current dose rate tables assume a symmetric source loading with respect to the source center. A computer program was written to calculate an asymmetric distribution using the manufacturers' source specifications. Corrections were made for attenuation and obliquity through the source materials. Dose rate values in cGy/h for a 137Cs source equivalent to 1 mg of 226Ra are shown as a function of the radius from the source center and angle from the source end containing the eyelet. Dose rate values in the table were confirmed by ferrous sulfate measurements using small volumes. The table values agree with published values at points more distant than a few cm and lying at an angle such that the asymmetry of the source loading has its minimum influence.
Detection of pion‐induced radioactivity by autoradiography and positron emission tomography (PET)
Authors: Shirato Hiroki , Harrison Robert , Kornelsen R. O. , Lam Gabriel K. Y. , Gaffney Cristopher C. , Goodman George B. , Grochowski Ed , Pate Brian
Published: March 2003

An autoradiographic technique incorporating a new imaging system was used to detect pion‐induced radioactivity in Plexiglass and the results were compared with aluminium activation and PET imaging. The activity distribution in the region of the pion‐stopping peak was similar in all three cases. Another large signal in the entrance region due to in‐flight interactions [12C(π−,π−n)11C] was detected by autoradiography and by PET but was not reflected in the aluminium activation measurements. This new technique is capable of defining the stopping region in phantoms with a better resolution than PET scanning and is useful as a complementary technique to other methods of pion dosimetry.
A correlated noise reduction algorithm for dual‐energy digital subtraction angiography
Authors: McCollough Cynthia H. , Van Lysel Michael S. , Peppler Walter W. , Mistretta Charles A.
Published: March 2003

It has long been recognized that the problems of motion artifacts in conventional time subtraction digital subtraction angiography (DSA) may be overcome using energy subtraction techniques. Of the variety of energy subtraction techniques investigated, non‐k‐edge dual‐energy subtraction offers the best signal‐to‐noise ratio (SNR). However, this technique achieves only 55% of the temporal DSA SNR. Noise reduction techniques that average the noisier high‐energy image produce various degrees of noise improvement while minimally affecting iodine contrast and resolution. A more significant improvement in dual‐energy DSA iodine SNR, however, results when the correlated noise that exists in material specific images is appropriately cancelled. The correlated noise reduction (CNR) algorithm presented here follows directly from the dual‐energy computed tomography work of Kalender who made explicit use of noise correlations in material specific images to reduce noise. The results are identical to those achieved using a linear version of the two‐stage filtering process described by Macovski in which the selective image is filtered to reduce high‐frequency noise and added to a weighted, high SNR, nonselective image which has been processed with a high‐frequency bandpass filter. The dual‐energy DSA CNR algorithm presented here combines selective tissue and iodine images to produce a significant increase in the iodine SNR while fully preserving iodine spatial resolution. Theoretical calculations predict a factor of 2– 4 improvement in SNR compared to conventional dual‐energy images. The improvement factor achieved is dependent upon the x‐ray beam spectra and the size of blurring kernel used in the algorithm. In the limit of large blurring kernels, the noise‐reduced dual‐energy image has an iodine SNR approaching the maximum value achievable with a linear combination of the low‐ and high‐energy images, with the additional advantage that low spatial frequency tissue signals are substantially reduced. Phantom measurements confirm the predicted increase in SNR of the CNR technique while images processed both by conventional dual‐energy and CNR methods demonstrate the noise suppression of the CNR algorithm and the tissue edge artifacts which it may introduce.
Comparison of methods to determine electron pencil beam spread in tissue‐equivalent media
Authors: Sandison G. A. , Huda W. , Savoie D. , Battista J. J.
Published: March 2003

This study has intercompared the predictions of Fermi–Eyges theory for the rms spatial spread (σ) of an electron pencil beam scattering in muscle‐, lung‐ and bone‐equivalent media with those of; two range straggling modifications to the theory, Monte Carlo simulations, and an empirical method based on broad beam penumbra. Systematic differences among the results obtained by these methods for the values of σ have been identified. Monte Carlo simulations are lower than the predictions of Fermi‐Eyges theory for σ at all depths whereas the broad beam penumbra method results are in reasonable agreement with Fermi–Eyges theory at depths less than ∼0.7 times the range of the incident electrons. All of the methods investigated have an increasing discrepancy from the predictions of Fermi–Eyges theory with depth, especially close to the end of the electron range. The two range‐straggling modifications to Fermi–Eyges theory developed for soft tissue do not agree with either measured or Monte Carlo results for σ in homogeneous scattering media of lung and bone.
On the use of effective dose in the treatment planning of high linear‐energy‐transfer radiation
Authors: Lam Gabriel K. Y.
Published: March 2003

Treatment planning for conventional radiations is based on the assumption that the effect of a combination of doses at any location in the treatment field in a multibeam plan will be equivalent to that of a single dose made up of the total sum of the doses delivered to that location. This is obviously valid for conventional low linear‐energy‐transfer (LET) radiations when the dose contributions from various beam components are associated with the same relative biological effectiveness (RBE) value of unity. However, this is not the case for the new generation of charged particle beams whose RBEs have been shown to vary significantly with depth. A concept of effective dose, defined as the mathematical product of physical dose and RBE value evaluated for an effect level, is developed for the treatment planning of these high‐LET particle radiations. Based on radiobiological results in mixed radiation experiments, it is shown that these effective doses are linearly additive like physical doses and hence, can be used directly for general treatment planning using linear algorithms already developed for the use of physical doses. This is illustrated using examples of simplified one‐dimensional plans for the TRIUMF pion beam.
Reply to the “Comments on: ‘Absorbed dose comparison among commercial ionization chambers in polystyrene and acrylic phantoms’ ”
Authors: Kubo Hideo , Cheng PoCheng
Published: March 2003

The comments of John Spokas (Ref. 3) on the performance of Exradin chambers (Ref. 1) are answered. (AIP)
Effective dose equivalents, HE, in diagnostic radiology
Authors: Huda W. , Bissessur K.
Published: March 2003

Values of the effective dose equivalent, HE, per unit entrance skin dose (+backscatter) are presented for twelve common radiological examinations. These HE data are derived from organ doses calculated for standard man using Monte Carlo techniques and are based on a specific beam size. The resultant HE data are presented as functions of x‐ray kVp, beam filtration (mm Al) and the projection (anterior–posterior (AP); posterior–anterior (PA); lateral; or oblique) used. In addition, two methods are presented which permit the computation of HE values for standard man for radiological examinations, which employ different field sizes.
Origins of flare in x‐ray image intensifiers
Authors: Luhta R. , Rowlands J. A.
Published: March 2003

The disk spread function of flare of an x‐ray image intensifier (XRII) was measured using monoenergetic x rays. The signal‐to‐noise ratio at the center of the disks and the pulse height spectrum of the flare are also measured. These measurements are correlated with the physical construction of the XRII. A simple model of the XRII is developed which is used to identify the various sources of flare.
Lesion detection in radiologic images using an autoassociative paradigm: Preliminary results
Authors: Raff Ulrich , Newman Francis D.
Published: March 2003

An area of artificial intelligence that has gained recent attention is the neural network approach to pattern recognition and classification. The use of neural networks in radiologic lesion detection is explored by employing what is known in the literature as the “novelty filter.” This filter uses a linear algebraic model, whereupon in neural network terms, images of normal patterns become “training vectors” and are stored as columns of a matrix. An image of an abnormal pattern is introduced and the abnormality or the “novelty” is extracted. A noniterative technique has been applied. In a preliminary experiment, autoassociative recall was tested using alphabetic characters as training vectors. The second experiment used sections of transverse magnetic resonance (MR) images (TR=3000 ms, TE=40 ms) of normal patients as the training vectors. A section of a transverse MR brain image with multiple sclerosis lesions was introduced to the filter and the abnormalities were extracted. In conclusion, a neural network based lesion detector may have great promise in medical pattern recognition.
Signal strength in subsecond FLASH magnetic resonance imaging: The dynamic approach to steady state
Authors: Hänicke W. , Merboldt K. D. , Chien D. , Gyngell M. L. , Bruhn H. , Frahm J.
Published: March 2003

Subsecond fast low‐angle shot (FLASH) magnetic resonance imaging (MRI) allows single shot studies of the human heart within measuring times of about 100–300 ms depending on the data matrix. In contrast to conventional FLASH MRI subsecond applications acquire data during the approach to steady state. A detailed analysis of the saturation behavior of the signal is given for the ideal case of a rectangular slice profile. In a second step, realistic slice profiles assuming Gaussian‐shaped excitation pulses were taken into account by means of a numerical solution of the Bloch equations. It turns out that the signal strength and the resulting image intensity is considerably higher than may be expected from steady‐state considerations. Correspondingly optimized flip angles depend on the number of phase‐encoding steps. Assuming long T1 relaxation times as, for example, encountered in muscle and brain tissue and repetition times of 5 ms or less, optimum flip angles are 12°–16°. The use of even higher flip angles (≥20°) causes heavily distorted slice profiles and a dynamic increase of the effective slice thickness. Flip angles of the order of the Ernst angle (6°) correspond to steady‐state conditions and lead to considerable signal losses. The theoretical results are confirmed by subsecond FLASH MRI studies of the human heart using a 2.0 T whole‐body system (Siemens Magnetom).
Coronary perfusion pressure and inflow resistance have different influence on intramyocardial flows during coronary sinus interventions
Authors: Schreiner Wolfgang , Neumann Friederike , Mohl Werner
Published: March 2003

A mathematical model is used to represent the vascular bed of the left coronary circulation by an arterial, a capillary and a venous compartment. The model is first adjusted so as to reproduce arterial hemodynamics known from measurements during normal perfusion. Additionally, measurements under coronary sinus occlusion are used to assess the venous section of the model. While the calculated phasic shapes of epicardial flows are seen to agree with measurements, intramyocardial flows, which are inaccessable to measurement, are predicted from the model. The model is run under stepwise changes of coronary perfusion pressure and coronary artery resistance for both the normal state and coronary sinus occlusion. Intramyocardial flow between capillaries and veins, being the main determinant for a possible therapeutic effect of coronary sinus interventions, is estimated.
Comparison of measured parameters from a 24–keV and a broad spectrum epithermal neutron beam for neutron capture therapy: An identification of consequential parameters
Authors: Fairchild R. G. , Saraf S. K. , Kalef‐Ezra J. , Laster B. H.
Published: March 2003

Epithermal neutron beams are under development in a number of locations in the U.S. and abroad. The increased penetration in tissue provided by these neutrons should circumvent problems associated with the rapid attenuation of thermal neutron beams encountered in previous clinical trials of neutron capture therapy (NCT). Physical and radiobiological experiments with two “intermediate energy” or “epithermal” beams have been reported. A comparison is made here between the 24‐keV iron‐filtered beam at Harwell, England, and the broad‐spectrum Al2 O3 moderated beam at the Brookhaven Medical Research Reactor (BMRR). In addition, parameters which are relevant for NCT, and which are best suited for evaluation and comparison of beams, are discussed. Particular attention is paid to the mean neutron energy which can be tolerated without significant reduction of therapeutic gain (TG), where TG is the ratio of tumor dose to maximum normal tissue dose. It is suggested that the simplest and most meaningful parameters for comparison of beam intensity and purity are the epithermal neutron fluence rate, and the fast neutron dose per epithermal neutron (4.2×10−11 rad/neutron for the broad‐spectrum beam and 29×10−11 rad/neutron for the 24‐keV beam). While the Al2 O3 beam is close to optimal, the 24‐keV beam produces a significant fast neutron dose which results in a lower TG. It is argued that if sufficient intensity is available, TG is the parameter which determines the potential usefulness of a beam for NCT. Data are presented to illustrate that with an epithermal fluence rate of ∼1.8×109 n/cm2 s, the Al2 O3 filtered beam at the BMRR is optimized and suitable for clinical application. A TG of ∼3 can be realized with currently available compounds; NCT of a brain tumor in a single exposure would take ∼30 min. Further increases in TG can only be obtained from increased boron concentration and retention within tumor cells, and from improved clearance of boron from normal tissues.
Spatial resolution measurements for passive microwave radiometry using a tissue‐equivalent phantom
Authors: Behrman Richard H. , Brodie Marlene A. , Sternick Edward S. , Grabowy Richard S. , Gemmell Lee Ann , Carr Kenneth L.
Published: March 2003

A tissue‐equivalent “hot” line source phantom is described for assessing spatial resolution in passive microwave radiometry systems. LSFs were measured for two rectangular waveguide antennas connected to a 4.7‐GHz radiometer. The normalized LSFs and corresponding modulation transfer functions were found to be independent of line source temperature, but dependent upon antenna size, orientation, and line source depth.
Propagation and reduction of error in three‐dimensional structure determined from biplane views of unknown orientation
Authors: Fencil Laura E. , Metz Charles E.
Published: March 2003

We are developing a technique for determination of the three‐dimensional (3‐D) structure of vascular objects from two radiographic projection images acquired at arbitrary and unknown relative orientations. No separate calibration steps are required with this method, which exploits an inherent redundancy of biplane imaging to extract the imaging geometry as well as the 3‐D locations of eight or more object points. The theoretical basis of this technique has been described previously. In this paper, we review the method from the perspective of linear algebra and describe an improvement, not heretofore reported, that reduces the method's sensitivity to experimental error. We then examine the feasibility and inherent accuracy of this approach by computer simulation of biplane imaging experiments. The precision with which 3‐D object structure may be retrieved, together with the dependence of precision on the actual imaging geometry and errors in various measured quantities, is studied in detail. Our simulation studies show that the method is not only feasible but potentially accurate, typically determining object‐point configurations with root‐mean‐square (RMS) error on the order of 1 to 2 mm. The method is also quite fast, requiring approximately one second of CPU time on a VAX 11/750 computer (0.6 MIPS).
Computed tomography scanning with simultaneous patient translation
Authors: Crawford Carl R. , King Kevin F.
Published: March 2003

This paper deals with methods of reducing the total time required to acquire the projection data for a set of contiguous computed tomography (CT) images. Normally during the acquisition of a set of slices, the patient is held stationary during data collection and translated to the next axial location during an interscan delay. We demonstrate using computer simulations and scans of volunteers on a modified scanner how acceptable image quality is achieved if the patient translation time is overlapped with data acquisition. If the concurrent patient translation is ignored, structured artifacts significantly degrade resulting reconstructions. We present a number of weighting schemes for use with the conventional convolution/backprojection algorithm to reduce the structured artifacts through the use of projection modulation using the data from individual and multiple slices. We compare the methods with respect to structured artifacts, noise, resolution and to patient motion. Review of preliminary results by a panel of radiologists indicates that the residual image degradation is tolerable for selected applications when it is critical to acquire more slices in a patient breathing cycle than is possible with conventional scanning.
Separation of dose‐gradient effect from beam‐hardening effect on wedge factors in photon fields
Authors: Kalend A. M. , Wu Andrew , Yoder V. , Maitz A.
Published: March 2003

It is known experimentally that a wedge transmission factor depends upon the field size and depth of measurement in particular. Dependence of the transmission upon depth has been attributed to a hardening of the incident beam through the filter, which preferentially absorbs the low‐energy photon of the bremsstrahlung component of that beam. We have attempted to separate this hardening effect from that of increased phantom scatter due to dose gradient induced by the wedge filter. Using an experimental wedge machined from cerrobend, the filter transmission at depth is measured and redefined relative to an “equally hardened” beam, obtained by filtering through a flat slab of equal thickness at the center of the wedge. Results of the Co‐60, 4‐, and 8‐MV wedged beams indicate that nearly half of the increase in the transmission at depth is due to the effect of dose‐gradient scatter in polystyrene phantom. Based on a simple relationship between primary and scattering radiation, an algebraic presentation is indeed in support of the dose gradient resulting in apparent increase in the wedge factors, at depth. Key words: wedge factor, beam hardening, Co‐60, x ray, dose gradient
Evaluation of captive bolus applicators
Authors: Chou C. K. , McDougall John A. , Chan Kwok W. , Luk Kenneth H.
Published: March 2003

Three square (L, M, MS) and one rectangular (HN) applicators with captive boluses were provided by the Clini‐Therm Corporation for evaluation. Surface cooling is achieved by attaching a mineral oil captive bolus to the built in water‐circulating tubes at the aperture of the applicators. These applicators were tested on a phantom with a 2‐cm fat slab over 10‐cm‐thick muscle. Surface and sagittal heating patterns were obtained using a thermograph. All captive‐bolus applicators have heating patterns similar to that of the regular Clini‐Therm applicators. Due to hot spots at the edges of the applicators where the E fields terminate, these modified applicators should not be placed in direct contact with patients when boluses are not used. Tests with Clini‐Therm regular water bolus instead of the captive oil bolus indicated that the orientation of water flow should be parallel to the E field to minimize perturbation of the heating patterns. Thermal conduction studies showed that the captive bolus reacts too slowly for skin temperature control. The modified captive bolus applicators did not improve the performance of the system.
Radiation leakage through electron applicators on Clinac‐1800 accelerators
Authors: Perec Alexander , Kubo Hideo
Published: March 2003

Radiation leakage through electron applicators by 6‐, 9‐, 12‐, 16‐, and 20‐MeV electron beams from Varian Clinac‐1800 has been measured with films. High levels of leakage were found under the corners of applicators and the touch‐plate mounting port holes. The radiation leakage, relative to the central‐axis dose at dmax, was found to be up to 13% on the patient plane [100‐cm source‐to‐film distance (SFD)] and up to 35% beneath the corners of applicators (96‐cm SFD). Up to 18% radiation leakage was measured beneath the touch plate near the mounting port holes (96‐cm SFD). The extent of radiation leakage in all electron beams was investigated and some simple shielding solutions to reduce the leakage are suggested.
Random sampling for evaluating treatment plans
Authors: Niemierko Andrzej , Goitein Michael
Published: March 2003

We analyze the influence of sampling technique on the accuracy of estimating irradiated volumes, dose‐volume histograms and tumor control and normal tissue complication probabilities. The sampling techniques we consider are uniform distribution of points on a regular Cartesian grid and random selection of points. For three‐dimensional treatment planning, random sampling leads to a significant reduction in estimation error and/or in the number of calculation points necessary to achieve a required accuracy. We discuss advantages and drawbacks of random sampling, as compared to sampling on a regular grid. It is suggested that, in practical situations, at least 50 times fewer randomly sampled points per organ/volume of interest are needed for fast estimation of complication probability with the same accuracy, i.e., not exceeding 5% (within 95% confidence limits) in the worst case.
Determination of surface dose rate from a 90Sr ophthalmic applicator
Authors: Ali Mohamed M. , Khan Faiz M.
Published: March 2003

Surface dose rates from two 90Sr ophthalmic applicators were measured using thin thermoluminescent dosimeter (TLD) chips. The TLD's were calibrated against the 90Sr source itself. The calibration technique is described. The results were compared to those obtained by three other techniques. The calibration in terms of roentgen equivalent betas per second provided by the manufacturer was found to be ∼30% lower when compared to our measured dose rates. The surface dose rates obtained with the TLD's calibrated against 6‐MV x rays were 18% higher. One of the two sources was sent to both the National Institute of Standards and Technology (NIST) and Amersham International for calibration. NIST and Amersham use extrapolation chambers as a Bragg–Gray cavity to determine the surface dose rate. NIST results gave values higher than ours by ∼5%. The Amersham results were ∼35% lower than ours.
Mammographic resolution: Influence of focal spot intensity distribution and geometry
Authors: Nickoloff Edward L. , Donnelly Eileen , Eve Leroy , Atherton James V. , Asch Thane
Published: March 2003

The influence of focal spot intensity distribution and geometry upon mammographic image quality were evaluated. The modulation transfer functions (MTF's) for eight different intensity distributions were determined and plotted in a manner to eliminate the effects of magnification and focal spot dimension. The results indicated that the total cross‐sectional area is important for focal spots with uniform intensity distributions and equivalent diameters. For equivalent focal spot dimensions, intensity distributions with edge bands were shown to have less spatial resolution than uniform intensity distributions. Focal spots with greater intensities towards their centers provided better resolution than either uniform intensity distributions or distributions with edge bands for equivalent sizes. The type of intensity distribution was also shown to affect the accuracy of star pattern measurements of focal spot size; this method of measurement is only precise for a uniform square intensity distribution. Errors obtained with several other intensity distributions were tabulated. The variations of the effective focal spot size with position along the anode–cathode axis were shown to be of a factor of approximately two to three. The combined effects of geometric blur and film/screen blur were presented for various heights above the cassette tray on several different mammographic systems.
Dose distribution around a 3.0‐mm type 6702 I‐125 seed
Authors: Scarbrough E. C. , Sanborn G. E. , Anderson J. A. , Nguyen P. D. , Niederkorn J. Y. , Antich P. P.
Published: March 2003

The 3M Company recently produced a special version of the type 6702 seed for use in animal studies of ocular melanoma. The seed consists of a single I‐125 impregnated ion exchange resin sphere encapsulated in a 3.0‐mm‐long titanium cylinder, as opposed to the normal 4.5‐mm cylinder containing from three to five resin spheres. Monte Carlo simulations and measurements show that the dose distribution around the 3‐mm capsule differs in places by up to 10% from that of the 4.5‐mm seed. In addition, the two seed types differ by 12% in the ratio of dose in tissue along the transverse seed axis to apparent activity. These differences must be taken into account when using these seeds.
Applying a polynomial formula to photon beam output and equivalent square field
Authors: Chen Fan‐Shih
Published: March 2003

The polynomial formula proposed by Chen [Med. Phys. 15, 348 (1988)] in calculating the electron beam output from a Therac 20 linear accelerator has been applied to generating the output factor of various machines with photon energies ranging from 100 kVp to 18 MeV. The calculated outputs are within 1% of the measured values. This formula can be very useful to the physicist in preparing an output table of photon beams or electron beams for a therapeutic unit. An equation is derived from this formula to calculate the equivalent square. The derivation shows that only under special circumstances is the equivalent square field equivalent to 2ab/(a+b); otherwise the equivalent square field depends on the formula's parameters as well as the sides of the rectangular field. These parameters, in turn, are dependent on the photon energy, the medium irradiated, and the collimator design.
Dosimetric aspects of a 3.3‐MV linear accelerator
Authors: Steidley K. David , Rosen Coleman W.
Published: March 2003

Both the design considerations and the dosimetric properties of the Siemens Model 5800 linear accelerator are discussed. This unit is of such an energy (3.3 MV) as to imitate Cobalt‐60 teletherapy depth doses. A linear relation of dmax to depth dose at low energies was found for various wave guides and targets. The energy of the unit can be characterized by its nominal accelerating potential of 2.70 MV, its d80 of 5.3 cm, its first half‐value layer of 0.8 cm lead and the measured energy of the electron beam at 3.3 MeV. The following selected commissioning aspects are reported: central axis depth dose, relative output factors, beam profiles, wedge factors, virtual source position, back scatter factors, penumbra and build‐up region.
Microdosimetric single‐event spectra for megavoltage electrons
Authors: Zellmer D. L. , Amols H. I.
Published: March 2003

Experimental techniques have been developed for obtaining single‐event microdosimetric spectra from hospital based linear accelerators. Therapeutic electrons of 12, 15, 18, and 20 MeV from Clinic 18 and 20 accelerators have been produced at ultralow dose rates. Details of the experimental methods have been described previously by the authors. Single‐event lineal energy spectra for these beams, as measured by a Rossi chamber differ significantly from cobalt‐60 both in shape and dose average lineal energy (ȳd) which, depending on electron energy, can be 20–40% lower. The spectral peaks for electrons are greatly enhanced compared to cobalt. The ȳd for electrons also differs from previously reported values for 10–15‐MV photon beams. These differences are less pronounced than for differences with cobalt. Spectral peaks and shapes correlate well with the actual electron stopping powers in tissue. The theory of dual radiation action predicts changes in relative biological effectiveness at low doses for megavoltage photon and electrons. Although at clinical doses the predicted differences are not statistically significant.
Comparison of ferrous sulfate (Fricke) and ionization dosimetry for high‐energy photon and electron beams
Authors: Kwa William , Kornelsen Richard O.
Published: March 2003

Dose measurements using Fricke and ionization methods were compared for 60 Co gamma rays, 4–25‐MV photons, and 10–25‐MeV electrons. Fricke derived doses based on a constant yield (εmG) were in good agreement with ionization derived doses based on the American Association of Physicists in Medicine Task Group 21 protocol and the National Research Council of Canada (NRC) ND calibration or the NRC proposed Nx. These measurements also confirmed the validity of the double‐voltage technique in the collection efficiency correction, even for swept electron beams. Assuming the correctness of the ionization derived doses, the radiation yield appeared to be 1% higher and to increase with photon energy when irradiation vessels were made of Pyrex but not with polystyrene cells. These glass wall effects could be due to the scattering perturbation of electrons between inhomogeneous materials and, in particular for photon beams, due to the mismatch in mass energy absorption ratios and mass collision stopping power ratios between the Fricke dosimeter and the wall materials.
Surface dose in intracavitary orthovoltage radiotherapy
Authors: Podgorsak Matthew B. , Schreiner L. John , Podgorsak Ervin B.
Published: March 2003

Radiotherapy with orthovoltage techniques is often the prime treatment for localized superficial malignancies. Surface doses and depth doses measured with cylindrical and end‐window Farmer chambers are presented for various orthovoltage x‐ray beams in the range from 80 to 300 kVp, both for open beams and beams collimated with commercial intracavitary leaded‐glass cones. For radiation fields collimated by a diaphragm positioned at a distance from the patient surface (open beams) there is a small skin‐sparing effect. On the other hand, the surface doses with commercial leaded‐glass intracavitary cones can exhibit a fivefold increase compared to the open‐beam dose maxima. Beyond a depth of ∼0.2 mm in a tissue‐equivalent phantom, the doses measured for open beams and beams collimated with intracavitary cones are essentially identical. The increase in the surface dose observed with intracavitary cones is attributed to photoelectrons and recoil electrons produced in the cones. The high surface doses are measured by thin‐wall parallel‐plate ionization chambers but cannot be measured with cylindrical Farmer chambers since these chambers have wall thicknesses too large for the transmission of electrons produced in the cone. Since cylindrical Farmer chambers are typically used for calibration of radiation output, the high surface doses produced by the intracavitary cones may be overlooked; they can, however, be reduced to open‐beam values by simple modifications to the cones.