bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of filters and wedges on skin sparing and gamma/neutron dose ratios in neutron teletherapy
Authors: Smathers J. , Graves R. , Almond P. , Otte V. , Grant W.
Published: August 2003

The effects of skin sparing and the gamma/neutron dose ratios in the clinical situations presently in use at the TAMVEC neutron teletherapy facility are not appreciably affected by the presence of filters and/or wedges. It is also shown that if skin sparing is lost due to close proximity of a hydrogenous scattering source, it can be restored by the use of thin lead filters.
Software balancing of multiple detectors during CT scanning
Authors: Erdos John , Abele Manlio
Published: August 2003

The general requirements for balancing of detectors in a multiple detector CT scanner are discussed, and the specific requirements for software balancing using data acquired within the body section during the scan are outlned. A particular technique which can be implemented in a scanner employing a simultaneous translation and rotation of the source/detector package is presented. The technique produces an exact balancing of offset and gain factors, to within accuracy limits imposed by the statistical uncertainty due to noise in the measurements. However, the technique admits a redundancy of solutions with allows the statistical sample to be expanded to include virtually all data acquired during the scan, thereby suppressing detector imbalance artifacts to the same level as overall quantum noise in the image.
Pion in vivo dosimetry using aluminum activation
Authors: Hogstrom Kenneth R. , Amols Howard I.
Published: August 2003

The method of aluminum activation to 24Na has been shown feasible as a high‐LET, in vivo dosimeter for clinical pion beams at the Clinton P. Anderson Meson Physics Facility in Los Alamos. A 3×3 in. φ NaI (Tl) well detector measures the 24Na activity following exposure by windowing the 2.75 MeV photopeak. Calculations of the 24Na activity agree well with experiment if one assumes a production ratio of 0.075 24Na/stopped π− in aluminum, and an in‐flight cross section of 26 mb. The activity is produced primarily by stopping pions although 15–25% of the activity is the result of neutrons. Thus, the induced activation is a good measure of high‐LET dose. By comparison with high‐LET dose measured by a 7.6 μ silicon detector and a Rossi chamber, the amount of high‐LET dose per activation is found to be 1.35×10−6 rad/(24Na/gm Al). A clinical setup has been installed and a sample patient measurement is compared with high‐LET dose calculated by treatment planning programs.
Thermal interactions between normal and neoplastic tissues in the rat, rabbit, swine, and dog during hyperthermia
Authors: Chryanthopoulos George S. , Jain Rakesh K.
Published: August 2003

Thermal interactions between normal and neoplastic tissues in mammalian species are modeled by a set of simultaneous first order nonlinear differential equations. Thermal regulation is introduced in the model, accounting for increases in the rates of metabolism, blood flow, and respiration of the normal tissues, taking under consideration the modes of reaction of the specific animals to thermal stress. The model adequately simulated the available temperature distributions data for localized hyperthermia in the rat and is also used for predictions of temperature distributions during localized and whole body hyperthermia in the rat, rabbit, swine, and dog.
Evaluation of edge‐induced streaking artifacts in CT scanners
Authors: Sheridan William T. , Keller Mark R. , O'Connor Christopher M. , Brooks Rodney A. , Hanson Kenneth M.
Published: August 2003

A phantom is presented which permits the evaluation of streaking artifacts produced in CT reconstructions by abrupt edges. Its application is demonstrated by results obtained from nine CT scanners. It is observed that even in regions where streaking is not readily apparent, edge‐induced artifacts can significantly increase the variance in the reconstruction.
Simulation of mammographic x‐ray spectra
Authors: Johnson G. Allan , O'Foghludha F.
Published: August 2003

Attempts to simulate Mo‐anode spectra for film mammography by using Mo filters with W‐anode tubes have been reported by several workers, and others have generated W‐like continua for xeromammographic purposes by heavy Al filtration of Mo‐anode tubes. In the present work the success of these simulations was tested by Si(Li) spectrometric methods that measured the spectral shapes and the exposure levels. Comparisons of Mo‐anode/Al‐filter with W‐anode/Al‐filter combinations were made, and also of W‐anode/Mo‐filter with Mo‐anode/Mo‐filter combinations. In certain circumstances the spectral shape is moderately well simulated but in all cases the useful output is less in the simulations than in the original spectra. The general conclusion is that simulation is always less attractive than direct use of the desired anode.
Build‐up curves of scanned high energy electron beams from the Sagittaire linear accelerator
Authors: Sibata Claudio H. , de Almeida Carlos E.
Published: August 2003

A study of the build‐up curves using an extrapolation chamber for 7, 10, 13, 16, and 19 MeV electron beams, from a Sagittaire linear accelerator, is presented. The effect of the ionization chamber bias polarity, field size, collimation and surface obliquity on the shape of the relative ionization curve was investigated. No clinically significant change is observed except the displacement of the maximum ionization point was observed for the oblique incidence of the beam.
A new method of calculating absolute thyroid activity in intravenous I‐123 uptake tests
Authors: Harpen Michael D. , Siegel Jeffry A. , Lee Wai‐Nang P. , Greenfield Moses A.
Published: August 2003

A technique for determining the absolute activity of I‐123 in early thyroidal uptake tests is presented. The method is independent of geometry, tissue attenuation, and extrathyroidal neck activity (ENA). It utilizes the efficiency factors and εγT) derivable for the thyroid gland using coincidence counting techniques, and a quantity, α, characteristic of the vascularity of the individual patient. Although ENA is not determined in absolute terms (e.g., percent of injected dose), count rates due to ENA are determined. After subtracting the ENA from the total count rates thyroidal uptake can be determined as absolute activity by means of the efficiency factors. The validity and usefulness of the technique have been demonstrated in phantom and patient studies. Thyroid uptakes of less than 0.1% of injected dose can be measured accurately in our patient studies.
Multivariate analysis of TLD orientation effects
Authors: Archer Benjamin R. , Bushong Stewart C. , Thornby J. I.
Published: August 2003

The effect of orientation on extruded thermoluminescent dosimeters has been investigated. TLD's placed on the surface and within a phantom were exposed separately to five diagnostic beam qualities and to 60Co γ rays. The resulting data were subjected to analysis of variance and examined for significant correlations. The response of dosimeters on the phantom surface varied with orientation and was energy dependent. In the phantom and with 60Co, no orientation effects were observed.
Noninvasive magnetic detection of cardiac mechanical activity: Experiments
Authors: Wikswo John P. , Opfer James E. , Fairbank William M.
Published: August 2003

The magnetic susceptibility of the heart and the intracardiac blood is substantially greater than that of the surrounding lung tissue. The periodic redistribution of blood and tissue during the cardiac cycle will thus alter an externally applied magnetic field. These magnetic field changes can be detected by a magnetometer outside the body, and have been termed magnetic susceptibility plethysmography (MSPG) signals. A differential magnetometer, a liquid helium dewar, and a superconducting persistent‐current magnet have been developed to detect the x component of the MSPG signal. The theoretical analysis of this instrument is presented to understand the spatial sensitivity of an MSPG susceptometer with a nonuniform magnetizing field. Preliminary measurements are shown to be in fair agreement with the model calculations. Several possible improvements of the technique are discussed.
Theoretical and experimental determination of sensitivity and edge enhancement in xeroradiography and ionography
Authors: Plewes D. , Johns H. E.
Published: August 2003

A study of the factors affecting image quality and x‐ray sensitivity of ionography and xeroradiography is presented. First, the relative charge sensitivities (nC/cm2 mR) are compared. It is shown that high pressure xenon (10 atm cm) as used in ionography produces more than 2.5–3.5 times more charge than the selenium layers used in xeroradiography for the same x‐ray exposure. The influence of development time and toner deposition on the appearance of images is investigated theoretically and experimentally. A parameter describing development sensitivity is proposed. It is shown that an increase in development sensitivity (OD cm2/nC) with increasing development time is accompanied by a loss in edge enhancement. The development sensitivity of ionography is about twice that typical of xeroradiography. This makes the total sensitivity (OD/mR) of the ionography process more than 4.5–6.5 times that of xeroradiography. The total sensitivity of ionography is about 1/2 that of par speed film screen combinations.
A precise CT phantom alignment procedure
Authors: Schneiders Nicholas J. , Bushong Stewart C.
Published: August 2003

Two of the AAPM CT performance phantom inserts require precise alignment. We present a method for aligning an insert which makes use of the partial volume effect. We demonstrate that the procedure is sensitive to tilts of less than one degree and, using the slice thickness insert, allows reproducible positioning.
CT scanner selection and specification for radiation therapy
Authors: Kelsey C. A. , Berardo P. A. , Smith A. R. , Kligerman M. M.
Published: August 2003

The underlying considerations necessary for selecting a CT scanner for radiation therapy treatment planning are analyzed and discussed. To obtain best value for funds expended it is desirable to compare CT scanner mechanical characteristics, data quality, and data handling capabilities. Specifications can be written to ensure prompt delivery of a unit containing all essential features without adding to the cost or complexity of the unit.
A low‐cost gate for ultrasound pulse‐echo studies
Authors: Langrill Lawrence N. , Goldstein Albert
Published: August 2003

Selective gating of ultrasound echoes usually requires an expensive piece of electronics, a stepless gate. This note presents a simple circuit utilizing low‐cost components which is easily built, and gives satisfactory performance as a gate for the study of individual ultrasound echoes. The gate has been measured to have a transmission loss of −2 dB and an isolation of −50 dB.
A simple device for testing the equilibrium of ion chambers in ambient conditions
Authors: de Almeida Carlos E. , Cecatti Eugenio R.
Published: August 2003

A simple device for testing the response of ion chambers when ambient pressure is varied was built from an inexpensive device normally used to maintain tennis balls under pressure. The results show that one may use this system in routine as well as for teaching purposes.
A review of time–dose effects in radiation therapy
Authors: Peschel Richard E. , Fischer James J.
Published: August 2003

A historical review of conventional fractionation offers little confidence that such treatment is optimal for all tumors. Thus manipulation of time–dose schedules may provide a relatively inexpensive yet potentially useful technique for improving therapeutic results in radiation therapy. Consideration of basic radiobiological principles and animal model data illustrates the complex and heterogeneous nature of normal tissue and tumor response to time–dose effects and supports the hypothesis that better time–dose prescriptions can be found in clinical practice. The number of possible time–dose prescriptions is very large, and a review of the clinical trials using nonconventional fractionation demonstrates that the sampled portion of the total three‐dimensional space of time, fraction number, and dose has been very small. Only carefully designed clinical trials can establish the therapeutic advantage of a new treatment schedule, and methods for selecting the most promising schedules are discussed. The use of simple data reduction formulas for time–dose effects should be discarded since they ignore the very complexity and heterogeneity of tissues and tumors which may form the basis of improved clinical results.
Flow cytometry
Authors: Norman Amos
Published: August 2003

A brief review of flow cytometry is presented. Emphasis is on the construction of relatively simple instruments and on their application to problems in medical physics. Among these are the problems of measuring the biological parameters that determine the response of tumors to therapy and of measuring the biological damage in people exposed to ionizing radiations.
Preclinical studies of dynamic treatment modes in pion therapy
Authors: Amols Howard I. , Kittell Richard , Paciotti Michael A. , Helland Jerome A. , Hogstrom Kenneth R. , Collier Michael , Heller Peter
Published: August 2003

Preliminary results on a system for delivering dynamic pion radiotherapy treatments are reported. The desired treatment volume is scanned across a small, focused pion beam using a computer‐controlled treatment couch. A computer‐controlled rangeshifting device modulates the stopping pion depth distribution in coordination with the couch motion to conform the dose to the shape of the treatment volume. For certain shaped tumors, the system can result in substantial normal tissue dose sparing and better field flatness as compared to irradiation by static treatments with broad beams. The characteristics of this new system, plus preliminary results for typical dose distributions as measured with thermoluminescent dosimeters (TLDs), are presented.
Noise analysis in isolation of iodine using three energies
Authors: Yeh P.‐S. , Macovski A. , Brody W.
Published: August 2003

The Poisson noise inherent in multispectral x‐ray imaging systems is formulated to give the SNR under a limited exposure constraint. The SNR value is maximized with respect to the exposure partition among different x‐ray energies. The study shows how to choose suitable spectra and the dose weights. The robustness of these dose weights is also demonstrated for systems of varying bone and tissue contents.
B‐mode registration: A new procedure for analyzing errors
Authors: Insana Michael F. , Goldstein Albert
Published: August 2003

The theory of a new B‐mode registration test procedure is presented along with experimental verification of the detailed theoretical predictions. The new procedure separately tests the B‐scan articulated arm calibration and the equipment acoustic velocity calibration. Readily verifiable secondary standards are incorporated into the procedure for self‐calibration purposes. The procedure provides a specific and reproducible analysis of angular misregistration errors while maintaining an acceptable level of sensitivity. No coupling gels or oils or operator skill is required. A special test has been found which permits the service person to verify that the equipment is capable of attaining proper B‐mode registration before beginning the recalibration procedure.
Neutron and gamma spectroscopy for clinical dosimetry
Authors: Schmidt Rainer , Magiera Eberhard , Scobel Wolfgang
Published: August 2003

Neutron and photon energy spectra were measured in different depths and lateral positions in tissue‐equivalent phantoms exposed to a therapeutical 14.1 MeV neutron beam. Intensity weighted mass energy absorption coefficients were derived for application in ionization chamber dosimetry in mixed neutron‐gamma fields. The resulting relative depth doses show that on the beam axis for depths in excess of 20 cm, gamma radiation contributes with more than 10% to the total dose; off the axis outside the direct beam neutron and gamma doses are comparable. The differences between these doses and those neglecting the spectra distribution increase with depth and with the distance from the beam axis.
Conceptual design of beryllium targets for the generation of neutron beams for radiation therapy by the (p,n) reaction
Authors: Awschalom Miguel , Rosenberg Ivan
Published: August 2003

A conceptual design is presented showing that, by judiciously choosing the beryllium target thickness and the backstop material, improvements can be achieved in dose–rate, skin sparing, and penetration of neutron beams generated by the same proton accelerator.
Electron backscattering
Authors: Baily Norman A.
Published: August 2003

Although electron backscatter has been a subject of investigation for many years, both theory and experimental data are sparse. This article examines the available data and shows that a large percentage of both the theoretical and experimental values fit an empirical relationship for a large range of electron energies. This relationship appears to be valid both for β‐ray spectra and monoenergetic electrons. The empirical relation describing the intensity of electron backscatter is also valid over the entire range of atomic elements. The relationship proposed is that the backscatter of electrons is proportional to the log (Z+1). Effective atomic numbers of compound and mixtures arrived at using this relationship can be used to predict backscatter coefficients for these.
A review of the discrepancy between the in‐air and in‐water calibration of cobalt‐60 machines
Authors: Berkley L. W. , Gagnon W. F. , Hanson W. F. , Weaver K. A. , Shalek R. J.
Published: August 2003

Causes for the discrepancy noted by Grant et al. between the in‐water and in‐air calibration of 60Co are discussed. Data are presented from measurements with a set of ionization chambers with thimbles of 0.5, 1.0, and 1.5 cm outside radii. These data include measurements of percentage depth dose, backscatter factors, and displacement factors. The results show that the discrepancy noted by Grant et al. is caused by a combination of small errors both in depth dose data and in the displacement factor incorporated into Cλ.
Microwave time delay spectroscopic imagery of isolated canine kidney
Authors: Jacobi John H. , Larsen Lawrence E.
Published: August 2003

A method for producing microwave images that are improved through the reduction of multipath propagation effects is described. This method employs water immersed antennas and microwave time delay spectroscopy (TDS) at S‐band. It is shown that objects as small as 6 mm in diameter can be detected. Objects 10 mm apart appear as separate responses on the image. It is also shown that is possible to generate a physiologically and anatomically relevant image of an isolated canine renal specimen.
CT quality assurance: Computer assisted slice thickness determination
Authors: Schneiders Nicholas J. , Bushong Stewart C.
Published: August 2003

The precise slice geometry of a CT scanner is an important, albeit tedious to determine, characteristic. A series of computer programs have been developed to analyze the slice thickness insert of the AAPM phantom. Without operator assistance they generate the beam profiles and slice thicknesses at three points in the scan field. A representative analysis is done on an AS&E scanner with slice thickness settings of 2 to 10 mm. The resulting discrepent measured thicknesses, ranging from 3 to 8 mm, indicate the need to perform such slice thickness measurements as part of a regular quality assurance program.
Information and artifact in computed tomography image statistics
Authors: Duerinckx Andre J. , Macovski Albert
Published: August 2003

In conventional computed tomography images only the average CT number, which is a first‐order statistical parameter, is used to characterize the tisues by giving an estimate of tissue density. Second order statistical parameters such as the signal variance and cross‐correlation function have also been used to obtain additional information to discriminate between certain tissues and lesions. However, the contribution of quantum noise to the signal variance and cross‐correlation function creates, for the conventional CT patient dose, a background signal often larger than the signal containing the information about tissue structure. The misleading information, called “artifacts”, in second‐order image statistics caused by quantum noise, is studied.
Model to analyze radiographic factors in mammography
Authors: Shrivastava Prakash N.
Published: August 2003

A regression model and analysis is presented to determine the effect of various radiographic factors on mammographic breast exposures. The analysis is based on data collected jointly by the six Regional Centers for Radiological Physics (CRPs) at some sixty installations throughout the United States. A “stepwise regression analysis” of this data projects that the choice between xerox and screen‐film receptors is the most critical factor affecting breast exposure followed by choice of HVL and target material. The analysis also shows that, although, for a given receptor category, the breast surface exposure varied over a wide range for the diverse techniques acceptable to radiologists, the receptor exposures varied over a rather narrow range of ±12%.
Effect of reduced scatter on radiographic information content and patient exposure: A quantitative demonstration
Authors: Wagner Robert F. , Barnes Gary T. , Askins Barbara S.
Published: August 2003

If a normal screen‐film exposure is made using a conventional grid, a reduced exposure may be used with a superior scatter removal device to record the same image information. This theoretical conclusion is not readily demonstrated because of the limited visibility on the underexposed film. In this study radiographs underexposed by a factor of three with a scanning multiple slit assembly (SMSA) were enhanced autoradiographically and found visually to contain more information than properly exposed radiographs obtained under similar conditions using a conventional Bucky grid. This observation was confirmed by contrast scale and noise measurements. Futhermore, the entrance skin exposure of the radiograph using the SMSA was 45% of that required with the grid technique at the same beam quality.
Dosimetric properties of p(90)+(Be+Ta) and p(101)+(Be+Al) neutrons
Authors: Harrison George H. , Balcer‐Kubiczek Elizabeth K. , Cox Colin R.
Published: August 2003

Dosimetric data were obtained for p(90)+(Be+Ta) and p(101)+(Be+Al) radiation with field size 9×11 cm at a 125‐cm SSD impinging on a tissue‐equivalent liquid phantom with density 1.10. The radiation was unfiltered or filtered by 10 cm of polyethylene. Dose rates measured with a 0.5‐cm3 ion chamber at a depth of 5 cm ranged from 0.046 Gy min−1 μA−1 for filtered p(90)+(Be+Ta) to 0.11 Gy min−1 μA−1 for unfiltered p(101)+(Be+Al). Neutron time of flight energy spectra in air averaged above 10 MeV indicate mean neutron energies ranging from 42.0–51.4 MeV for the four beams under study. The central axis depths at which 50% dose attentuation occurred ranged from 15 to 20 cm for these beams. At 3 cm depth the gamma dose component of the total p(101)+(Be+Al) dose was 14.5%, or 17% with filtration.
Image information transfer properties of x‐ray fluorescent screens
Authors: Dick C. E. , Motz J. W.
Published: August 2003

The image information transfer efficiency for five x‐ray fluorescent screens (calcium tungstate, barium halide, and three rare earth screens) has been experimentally determined with monoenergetic x‐ray beams at energies of 18, 22, 32, 49, 51, 58, and 69 keV. The transfer efficiency, which is defined by the ratio of the output to input signal‐to‐noise ratios, was determined from measurements of (a) the fraction of incident x rays absorbed in the screen and (b) the statistical distribution of the number of light photons emitted from the screen per absorbed x ray which was determined by light photon counting techniques. Comparisons of the information transfer efficiency, the average number of light photons emitted per absorbed x ray, and the light output energy per Roentgen are given for the above screens and x‐ray energies.
Design for a multiple target system for a medical cyclotron
Authors: Lee Richard , Dahl J. Robert , Bigler Rodney E. , Laughlin John S.
Published: August 2003

A novel target system has been designed for a compact cyclotron. The system permits one of three or more targets to be selected remotely for bombardment, permits all target and chemical operations to be controlled remotely, causes no change in beam energy or beam current, occupies a limited space, and is simple to construct and maintain. The targets are mounted to a flexible bellows‐multiple port manifold assembly, supported on a fan‐shaped turntable. A motor moves the system to align the target to be bombarded with the main beam axis. Designs for two subassemblies are also presented. These are a retractable target chamber for water and a remotely controlled variable collimator.
Dose minimization in computed tomography overscanning
Authors: Parker Dennis L. , Smith Vernon , Stanley James H.
Published: August 2003

The relationship of noise and dose in overscanning in computed tomography is reviewed to show that maximal variance reduction is obtained when the overscanning weights are proportional to the x‐ray flux. It is also shown that maximal motion artifact suppression requires that the weights vary smoothly from zero at the beginning and ending of the scan to one in the central portion of the scan. Optimal noise and dose considerations suggest that the x‐ray flux should be varied during the course of a scan in order to be proportional to the desired weighting. Computer simulations of a head phantom with a moving pin are used to show that such x‐ray flux variations do achieve maximal artifact suppression with no additional dose to the patient over a standard (non‐overscanned) scan.
Fast neutron radiotherapy: For equal or for better?
Authors: Broerse Johan J. , Battermann Jan J.
Published: August 2003

The renewed application of fast neutrons in clinical radiotherapy has been stimulated by fundamental radiobiological findings. The biological effects of high LET radiation, including fast neutrons, are different from those obtained with x rays in at least three respects: the oxygen enhancement ratio, the sensitivity of cells at different phases of the cell cycle, and the contribution of sublethal damage to cell reproductive death. Furthermore, wide variations in relative biological effectiveness (RBE) have been observed for different tumors and normal tissues. Measurements of volume changes in human pulmonary metastases indicate that the RBE for slowly growing tumors which are generally well‐differentiated is higher than that for poorly differentiated lesions. Six thousand patients have now been treated with fast neutron beams. The results of the clinical applications vary according to the method of application and to the type of cancer involved: treatment of inoperable malignancies of the salivary gland is very encouraging; the therapeutic gain is rather small for bladder and rectal cancers, soft tissue sarcomas and advanced carcinomas of the cervix; the responses of brain tumors are very disappointing. Most neutron radiotherapy applications have been less than optimal because of inadequate physical and technical conditions. Despite these difficulties, some interesting clinical data have become available. Due to the technical shortcomings, the possible advantages of fast neutrons are probably underestimated for many tumor sites. Well‐designed clinical trials, preferably performed with high energy cyclotrons in clinical environments, will provide a decisive answer to the question of the usefulness of the new radiation modality. Key words: fast neutrons, radiotherapy, radiobiology
Solution to treatment planning problems using coordinate transformations
Authors: Siddon Robert L.
Published: August 2003

The majority of radiation treatment planning problems are relatively straightforward, involving only specified gantry angles in a treatment plane which is perpendicular to the patient longitudinal axis. In addition, there are a number of more complex three‐dimensional problems which require combined rotation of the gantry, collimator, and turntable for their solutions. These include, for example, the use of non‐coplanar fields and oblique treatment planes, the matching of field edges in three dimensions, the treatment of the breast with opposing tangential fields, and the treatment of inclined elongated lesions. Unfortunately, there is no general systematic approach to the solution of these more complex problems. One may attempt an analytic solution, but this approach is often too cumbersome and tedious. On the other hand, one may resort to a “trial and error” session with the simulator. This paper, therefore, presents a mathematical method which is easily applied and applicable to a wide variety of complex three‐dimensional treatment planning problems. The method considers the gantry, collimator, and turntable as coordinate systems. These coordinate systems are derivable from each other by specified coordinate transformations, which contain the rotation angles of the gantry, collimator, and turntable. Within this mathematical framework, the treatment planning problems are found to reduce to two general types, of which various clinical examples are then given. Key words: treatment planning, coordinate systems, coordinate transformations, three‐dimensional treatment planning, rotation operators
The physics of cancer therapy with negative pions
Authors: Richman Chaim
Published: August 2003

The introduction of negative pions into cancer therapy has required the construction of large new proton accelerators together with special magnetic systems to form and direct the pion beam to a patient. A summary is presented of the fundamental properties of pions and of the methods used to study the therapeutic beams. The dosimetry of these beams requires the use of the older techniques as well as new methods for determining the different LET components. The data for a number of beams is given and the utilization of this data in treatment planning is reviewed. An important problem for therapy is the behavior of inhomogeneities in the pion beam, and experimental methods are described which illuminate this problem. The studies of the effects of inhomogeneities in a beam point the way toward fruitful comparisons with the computerized treatment planning codes known as PION‐1 and PIPLAN. A useful step in treatment is the verification of doses in patients during therapy. For this purpose the new methods for measuring the high LET doses in patients are described as well as a timing measurement for checking the stopping effect of the tissues as obtained from the CT scans.
In vivo neutron activation analysis: State of the art and future prospects
Authors: Cohn Stanton H.
Published: August 2003

From the inauspicious beginning arising in the aftermath of a reactor accident in 1957, in vivo analysis of body elements by neutron activation has become an important tool in medical research. In particular, it provides a much needed means to make quantitative assessments of body composition of human beings in vivo. The data are useful both for basic physiological understanding and for diagnosis and management of a variety of diseases and disorders. The paper traces the development of the in vivo neutron activation technique in the past quarter of a century from basic systems to the present state of the art facilities, and discusses the advantages and disadvantages of the various systems. A scan of some of the numerous clinical applications that have been made of this technique reveals the broad potentialities of in vivo neutron activation. The paper also considers alternative routes of future development and raises some of the questions now faced in making the techniques more widely available to both medical practitioners and medical investigators.
Lesion detection and signal–to–noise ratio in CT images
Authors: Judy Philip F. , Swensson Richard G. , Szulc Massimiliano
Published: August 2003

This study measured observers’ ability to detect and locate focal lesions on simulated CT images. The difficulty of the detection task was manipulated by changing the difference in attenuation between the lesion and its background (contrast), the random variation in the CT values (noise) or the lesion's size. The human observers’ performance was compared to that of matched filter detector, modified to include the effects introduced by the display window and the uncertainty about the lesion's location on the image. Changes in lesion contrast, lesion size and noise produced large variations in both the lesion signal–to–noise ratio (a measure of the matched filter detector's performance) and estimated measures of the observer's detection and localization ability. Changes in observers’ performance were closely related to changes in lesion signal–to–noise ratio. Generally, changes in lesion contrast, lesion size or noise that produced similar values of lesion signal–to–noise ratios had equivalent effects upon the observers’ performance.
Calorimetric and ionimetric dosimetry intercomparisons II: d+T neutron source at the Antoni Van Leeuwenhoek hospital
Authors: McDonald Joseph C. , Ma I‐Chang , Mijhnheer Ben J. , Zoetelief Hans
Published: August 2003

A series of dosimetric measurements was carried out at the Antoni van Leeuwenhoek Hospital, Amsterdam, using a Philips d+T generator, which produces neutrons with energies of approximately 14 MeV. A‐150 plastic ionization chambers, an A‐150 plastic calorimeter, and a GM dosimeter were used to determine total absorbed dose and the photon absorbed dose fraction. The ion chambers were calibrated in a 60Co gamma‐ray field in air and compared in a phantom placed in the 60Co gamma‐ray beam. Comparison of the total absorbed dose derived from the ionization chamber measurements to that determined using the calorimeter indicated agreement for the neutron measurements between the techniques to within ±2%.
Experimental study of the relationship between the base impedance and its time derivative in impedance plethysmography
Authors: Djordjevich L. , Sadove M. S.
Published: August 2003

Transthoracic electrical impedance Z consists of a constant baseline component Z0 and the time variable component ΔZ such that Z=Z0+ΔZ. The first time derivative of Z has a negative peak, the magnitude of which is (dZ/dt)min. Measurements of 170 volunteers show that (dZ/dt)min is a function of the constant baseline component Z0. This implies that at least a part of the difference of the magnitudes of (dZ/dt)min on Z0 must be taken into account in order to avoid erroneous conclusions or inaccurate calculations.
Hyperthermia with implanted electrodes
Authors: Brezovich Ivan A. , Young John H.
Published: August 2003

A general solution is given for the steady state form of the heat conduction equation applied to a simple tumor model which is imagined as being heated by means of electrical currents flowing between metallic electrodes. The model assumes a homogeneous tumor with no bloodflow. The solution for the special case of constant temperature and potential at the surface of the heated volume is examined in detail. The solution shows that there exists, independent of the particular tumor and electrode geometry, a close relationship between the steady state temperature distribution and the electrical potential. Among the more important implications of this relationship are that equipotential surfaces within the heated volume are also isothermal surfaces and that no areas of excessive heat at or near any sharp edges or corners of the electrodes should develop, despite the high electric field intensity. Based on the theory, a procedure is outlined which might greatly facilitate the determination of temperature distributions in phantoms. Finally, the usefulness and the limitations of the theoretical models in clinical hyperthermia are discussed.
Characterization of a p(66)Be(49) neutron therapy beam II: Skin‐sparing and dose transition effects
Authors: Awschalom M. , Rosenberg I.
Published: August 2003

Results of buildup measurements in A‐150 tissue equivalent plastic are presented for a p(66) Be(49) neutron beam. These measurements were taken in air and behind various materials to answer questions about skin‐sparing, bolussing materials, recovery of skin‐sparing, and dosimetry in small radiobiological samples. The depth for Dmax for this beam is 1.6 g cm−2. An algorithm is also presented that reproduces the measured dose buildup curves.
Concerning fat in NMR imaging
Authors: Kaufman L. , Crooks L. , Margulis Al. R.
Published: August 2003

Variables affecting the nuclear magnetic resonance image are examined. (AIP)
An analysis of dose efficiency in image intensified fluoroscopic examinations
Authors: Bernstein H. , Muntz E. P.
Published: August 2003

In this paper we have developed expressions for assessing radiographic systems where grids, air gaps, or both are used. The application of these expressions to film‐screen detectors gives predictions in good agreement with data that are found in the literature. Using this analytical tool, image intensified fluoroscopy has been studied. We have shown that under certain circumstances with air gaps there are potential gains in the efficient use of dose in fluoroscopy. The air gaps are of particular value where relatively thin body parts or small lesions are being examined using small focal spot generators. An independent gain control on the image intensifier would be useful for achieving the greatest flexibility when using magnification in fluoroscopy.
Day's integration of scatter dose with an analytical expression
Authors: Brown Lisa Hartnagel , Svensson Göran K. , Bjärngard Bengt E.
Published: August 2003

Analytical formulae have been developed to describe the scatter dose on the central axis of rectangular fields as a function of depth and field size for 60Co γ radiation and 4 and 8 MV x rays. The basic relationship expresses the scatter–to–primary dose ratio as a function of the area–to–perimeter ratio A/P, with depth and energy dependent parameters for which analytical expressions are given. The accuracy of the total dose on and off the central axis, calculated with these formulae, is compared to that resulting from the use of Day's method with tabulated values. The differences are generally less than 1% of the total dose on the central axis.
Dosimetry considerations in phototherapy
Authors: Profio A. Edward , Doiron Daniel R.
Published: August 2003

Dosimetry in phototherapy involves a determination of the energy absorbed per unit mass of tissue, corrected for the quantum yield in a photochemical reaction. The dose rate in photochemotherapy of cancer with hematoporphyrin derivative and visible light is related to the extinction coefficient, quantum yield for singlet oxygen production, concentration of sensitizer and energy flux density at depth. Data or methods of determining these quantities are presented. Calculations have been performed for the energy flux density at depth, as a function of the total attenuation coefficient and ratio of scattering coefficient to total attenuation coefficient, for isotropic scattering in slab geometry. For small absorption, these depth dose curves exhibit a maximum within the tissue followed by an exponential decrease.
Contrast effects of a gadolinium filter
Authors: Burgess A. E.
Published: August 2003

Several authors have suggested using heavy metal filters with K edges in the diagnostic energy range to reduce the width of the x‐ray spectrum and hence reduce patient radiation exposure. This spectral narrowing also increases subject contrast and permits an increase in tube potential. Results of contrast measurements are presented for a 250 μ gadolinium filter. It was found that aluminum filter contrast could be matched by using 8 to 10 kVp higher potential with the gadolinium filter. Similar results were found for calcium tungstate and rare‐earth screens. Measurements were also done to determine skin exposure and mAs ratios for both constant contrast and constant kVp technique conversion methods. A simple theory with one adjustable parameter gives a reasonable fit to the experimental results.
A three‐film technique for reconstruction of radioactive seed implants
Authors: Amols Howard I. , Rosen Isaac I.
Published: August 2003

Computer dose calculations for interstitial implants of radioactive seeds require a knowledge of the spatial coordinates of each seed in the implant. These coordinates are usually constructed from the seed images on either an orthogonal or a stereo pair of radiographs. Such a procedure, however, requires that each seed can be identified on each film. We have developed a computer algorithm which computes the locations of the seeds from a set of two stereo and one AP radiographs, even when seed identities on all films are indeterminable. This is done by means of a ray tracing technique. Under ideal conditions the projections from the three films uniquely define all seed locations. Under clinical conditions, however, where digitizing uncertainties and patient movement are inevitable, the algorithm must determine the most likely set of seed locations from the larger set of all possible seed locations. The criteria for making this selection, as well as clinical examples, are presented.
A new technique for the calculation of scattered radiation for 10 MV photon beams
Authors: Edwards Fred H. , Coffey Charles W.
Published: August 2003

An alternative to the Clarkson technique for calculating total scattered radiation is presented for use with 10 MV photon beams. When compared to the same field size and depth parameters, the resultant TMR values are in good agreement with results utilizing the Clarkson technique. Lengthy iterative procedures are avoided in this new scatter technique in favor of a more efficient SMR algorithm, thereby reducing the amount of required computation time. The speed and simplicity of this method make it especially amenable to use with small desk top computers and even programmable pocket calculators.
Importance of magnification in star test pattern use
Authors: Van Swearingen Frederick L. , Watts Finley C.
Published: August 2003

The influence of magnification on focal spot size determinations using the star pattern has been re‐examined with interesting results. Two methods of obtaining the magnification have been compared. The resultant information on the consequences of utilizing various magnifications for focal spot size measurement are discussed. Data indicate definitive guidelines for magnification selected.
A computed tomography–radiation therapy treatment planning system utilizing a whole body CT scanner
Authors: Edwards M. , Keller J. , Larsen G. , Rowberg A. , Sandler B. , Whitaker F.
Published: August 2003

An external beam radiation therapy treatment planning system has been developed to run on the GE CT/T whole body scanner. The system interactively obtains treatment planning information directly from CT scans, including relative density conversion of user input inhomogeneity regions. The program generates beam isodose tables from input TAR–SAR data using the Cunningham model. Inhomogeneity corrections are applied using the power law TAR method at low energies and the TAR ratio method at high energies. Beam data are generated on the central axis and at off‐axis locations coplanar with each CT scan, and isodose distributions are displayed on any transverse, coronal or sagittal plane. Examples of plans and initial verification results are discussed.
Contrast‐detail‐Dose and dose efficiency analysis of a scanning digital and a screen‐film‐grid radiographic system
Authors: Cohen Gerald , Wagner Louis K. , Amtey Sharad R. , Di Bianca Frank A.
Published: August 2003

The purpose of this study is to examine the diagnostic potential of a scanning digital radiography (SDR) system currently used clinically as a CT localization device. The technique of contrast‐detail‐dose analysis is used to compare the low‐contrast sensitivity and dose efficiency of an SDR unit with standard radiography (SR). The theory of threshold perceptibility in both digital radiography and SR is described, including the effects of scattered radiation and antiscatter devices, object attenuation, geometry, system image processing, and recorder quantum efficiency. The concept of dose efficiency is defined and derived from the contrast‐detail‐dose data. The SDR system is shown to operate with a threshold signal‐to‐noise ratio of 7.3±1.2 for large area detection (d≳2 mm); to be relatively scatter‐free; and to be as much as 100× more dose efficient than SR for visualization of large low contrast objects (C≲0.04, d≳2 mm).
Spectral characterization of 4 MV Bremsstrahlung by attenuation analysis
Authors: Huang Pin‐Hua , Kase Kenneth R. , Bjärngard Bengt E.
Published: August 2003

The “quality of radiation” for a high energy x‐ray beam can be specified by its attenuation curve in a selected material. The inverse Laplace transform of the attenuation curve can be used as an approximate indication of the energy spectrum of the beam. Existing mathematical procedures for this purpose have been evaluated and were found to poorly represent measured transmission data for 4 MV x‐rays from a linear accelerator. The transmission data between 1 and 0.002 could be fitted within the experimental uncertainty by expressing the logarithmic transmission as a second order polynomial of attenuator thickness. The inverse Laplace transform then becomes a Gaussian function of the attenuation coefficient. This new version of “attenuation analysis” provides a practical method for specification of the quality of the radiation in this energy range.
Improved measurement of neutron spectrum from 35 MeV protons on thick beryllium
Authors: Ullmann J. L. , Peek Neal , Johnsen S. W. , Raventos A. , Heintz P.
Published: August 2003

The energy spectrum of neutrons produced by 35 MeV protons on 1.6 cm thick beryllium has been measured at 0 ° by means of proton recoil spectroscopy. We find substantial agreement with other measurements.
Optimal x‐ray spectra for screen‐film mammography
Authors: Jennings R. J. , Eastgate R. J. , Siedband M. P. , Ergun D. L.
Published: August 2003

Theoretical and experimental techniques have been used to study optimal x‐ray spectra for screen‐film mammography. A simple model of mammographic imaging predicts optimum x‐ray energies which are significantly higher than the K‐characteristic energies of Mo. A subjective comparison of x‐ray spectra from Mo‐anode and W‐anode tubes indicates that spectra produced by a W‐anode tube filtered with materials of atomic number just above that of Mo are more suitable for screen‐film mammography than spectra produced by the Mo‐anode/Mo‐filter system. The imaging performance of K‐edge filtered, W‐anode tube spectra was compared to the performance of Mo‐anode spectra using phantom measurements and mastectomy specimen radiography. It was shown that optimal W‐anode spectra can produce equal contrast with an exposure reduction of a factor of two to three, a dose reduction of a factor of two, and equal or reduced tube loading, compared to Mo‐anode spectra. A computer simulation was carried out to extend the initial, monoenergetic theory to the case of real, polychromatic sources. The effects of varying filter material and thickness, tube operating potential, and breast thickness were all studied. Since W‐anode x‐ray tubes are considered to be better for Xerox mammography than Mo‐anode tubes, this study has shown that both Xerox and screen‐film techniques can be performed optimally with a single, properly designed, W‐anode x‐ray tube.
Density dependence of signal detection in radiographs
Authors: Burgess A. E. , Humphrey K.
Published: August 2003

We report results of the variation of signal detectability with radiographic film density for Lanex screens and four different x‐ray films. We found that maximum signal detectability occurs near (but not precisely at) the maximum slope of the characteristic curve. We interpret our results using a model that includes film gamma quantum noise, film granularity, and an intrinsic observer contrast threshold.