bluuebunny/crossref_metadata_2025 huggingface dataset:
Dose calculation in static or dynamic off‐axis fields
Authors: Loshek David D. , Parker Timothy T.
Published: March 2003

X‐ray fields that are shifted away from the conventional central axis exhibit alterations in output, beam profile, and beam energy. An extension of a conventional dose calculation algorithm to correct for these perturbations is presented. This algorithm employs the product of three functions describing the dose at the center of the field at dmax, the relative off‐center dose at dmax, and the relative dose at depth along a fanline passing through the point of interest. The nature of the problem is characterized, a basic data set necessary to support the algorithm is described and an abridged set of data that may assist in the development of an independent collimator dose calculation capability is presented. The appropriateness of this technique for both conventional and dynamically collimated fields is illustrated.
Resolution properties of a 2048×2048 matrix image intensifier‐TV based digital radiography system
Authors: Ogura Toshihiro , Fujita Hiroshi
Published: March 2003

Spatial resolution properties of a 2048×2048 matrix image intensifier (II) TV based real‐time digital radiography (DR) system were investigated. The presampling modulation transfer function (MTF), which includes the unsharpness of the detector and the blurring effect of the sampling aperture, was measured by a slit method. Also determined was the limiting resolution using a bar pattern. It was found that, the spatial resolution in this system is substantially improved relative to previous II‐TV based DR systems, and is comparable or even superior to that in a computed radiography system depending on the imaging plate employed. However, the presampling MTF for 2048×2048 matrix is comparable to that for 1024×1024 matrix in this DR system, because the same sampling aperture is assumed to be used for both matrices. Even under these conditions obtained the improved clinical image since the Nyquist frequency is doubled for 2048×2048 matrix. It should be noted that the resolution property in the II‐TV based DR system depends on the signal current from the TV image pickup tube (level of image pixel value) and also on the size of the iris in the TV lens. We must pay attention to these parameters when acquiring clinical images and evaluating the resolution properties. Finally, it was demonstrated that smaller focus than that used in a screen–film system can be employed in the DR system due to its high sensitivity, so the geometric unsharpness can be reduced. Therefore, the image resolution of our system was found to be superior to a screen–film system at some geometric magnification factors.
Multifractal radiographic analysis of osteoporosis
Authors: Caligiuri Philip , Giger Maryellen L. , Favus Murray
Published: March 2003

An important complication of osteoporosis is fracture. Alteration in bone structure, as well as decreased bone mass, contribute to the tendency to fracture in osteoporosis. Current methods that measure bone mass alone show substantial overlap of the measurements of osteoporotic patients who fracture with those that do not. Our aim is to develop noninvasive methods of evaluating bone structure on plain film radiographs to better predict fracture risk in osteoporosis. Regions of interest (ROIs) were selected from digitized lateral lumbar spine radiographs of 43 patients being seen in an osteoporosis clinic. The fractal dimension of these ROIs was estimated using a surface area method. The ability of fractal dimension to distinguish between cases that had fracture elsewhere in the spine from those that did not, was evaluated using receiver operating characteristic (ROC) analysis. These results were compared with ROC analysis for these same patients using bone mineral density (BMD) measurements (bone mass). Significantly larger Az (area under ROC curve) values were obtained using fractal dimension (0.87) than from using BMD (0.58), indicating a better test performance using fractal dimension. Therefore, computerized radiographic methods to evaluate bone structure, such as fractal analysis, may be helpful in better determining fracture risk in osteoporosis.
A semiautomatic method for registration of portal images
Authors: Moseley J. , Munro P.
Published: March 2003

A method to register pairs of portal images quickly and accurately has been developed. The approach uses a cross‐correlation operator to find the optimal match between corresponding anatomic regions that have been selected by a user on pairs of portal images. The cross‐correlation operator determines the translation that best registers each pair of anatomic features independently, and then the images are translated, rotated, and scaled so that the least squares difference between the coordinates of all of the paired regions is minimized. Tests using simulated images have shown that the accuracy of the algorithm is dependent on (i) the size and shape of the structures within the paired regions; (ii) the subject contrast of the anatomic features being matched; (iii) the rotational difference between the anatomic features; and, (iv) the noise in the image. Tests using contrast‐detail phantom images have shown that the semiautomated registration algorithm is only slightly less accurate than human observers, but is considerably faster. The semiautomated algorithm shows great promise as a method of quickly and accurately estimating discrepancies in patient positioning when used in conjunction with an on‐line portal imaging system.
Photoacoustic ultrasound: Pulse production and detection in 0.5% Liposyn
Authors: Kruger Robert A. , Liu Pingyu
Published: March 2003

Theoretical predictions and experimental measurements of photoacoustic pulse production within a 0.5% solution of Liposyn, a highly scattering, optical propagation medium, are reported. A simple model for photoacoustic energetics is developed that predicts photoacoustic signal pressure as a function of depth within a turbid medium following surface irradiation from an infrared source. The model is valid for very short irradiation duration. The model predicts that the acoustic pressure produced at a distance r from the center of a small, highly absorbing sphere of radius R consists of two, opposite polarity pulses, one originating from the near and one from the far side of the sphere. The magnitude of these biphasic pulses is expected to be proportional to the energy fluence (E) incident on the surface of the sphere and to the ratio, R/r. Furthermore, the energy fluence (E) that reaches the sphere is roughly proportional to , where μeff is the effective attenuation coefficient of the turbid medium and Z is the depth of the embedded sphere below the irradiated surface. The variation of E with depth within the absorber and biphasic acoustic pulse production have been verified experimentally. Further experiments demonstrate that a small (3‐mm diameter), highly absorbing sphere can be detected and localized at a depth of 37.5 mm within a 0.5% solution of Liposyn with a spatial resolution of 1×6 mm2, using a biologically safe level of infrared irradiation (λ=1064 nm) and a conventional ultrasound transducer (frequency=2.25 MHz). These results suggest that photoacoustic ultrasound imaging may have application to biologic systems such as the human breast.
A Bayesian network model for radiological diagnosis and procedure selection: Work‐up of suspected gallbladder disease
Authors: Haddawy Peter , Kahn Charles E. , Butarbutar Manonton
Published: March 2003

Bayesian networks, a technique for reasoning under uncertainty, currently are being developed for application to medical decision making. To explore their usefulness for radiologic decision support, a Bayesian belief network was constructed in the domain of hepatobiliary disease. The network model's nodes represent diagnoses, physical findings, laboratory test results, and imaging study findings. The connections between nodes incorporate conditional probabilities, such as sensitivity and specificity, to represent probabilistic influences. Statistical data were abstracted from peer‐reviewed journal articles on hepatobiliary disease, and a network was created to reflect the data. The network successfully determined the a priori probabilities of various diseases, and incorporated laboratory and imaging results to calculate the a posteriori probabilities. The most informative examination was identified, that is, the laboratory study or imaging procedure that led to the greatest diagnostic certainty. Bayesian networks represent a very promising technique for decision support in radiology: they can assist physicians in formulating diagnoses and in selecting imaging procedures.
A model for optimization of spectral shape in digital mammography
Authors: Fahrig Rebecca , Yaffe Martin J.
Published: March 2003

X‐ray mammography is the most sensitive imaging modality available for the detection of breast cancer. The highest performance can only be achieved, however, if the complete imaging system is optimized. The development of digital mammography offers an opportunity to obtain improved sensitivity in mammography. In such systems, the decoupling of the recording and display processes allows each component of the imaging system to be optimized separately. In this paper we describe a method for optimizing the recording process for digital mammographic techniques. Our method uses an energy transport model of the propagation of signal and noise through the imaging system. The computations make use of experimentally determined data wherever possible so that the number of assumptions in the model can be minimized. The model predicts the signal‐to‐noise ratio for a constant dose to the breast, and therefore allows comparison and optimization both for different x‐ray spectra and for different imaging tasks. The major energy‐dependent components of the model have been verified, and good agreement is demonstrated between predictions by the model of both contrast and SNR and experimentally measured values. Calculations for a particular imaging task, detection of a 200‐μm cubic calcification in a 6‐cm, 50% adipose–50% glandular breast, illustrate application of the model for optimization of spectral shape.
Attenuation properties of diagnostic x‐ray shielding materials
Authors: Archer Benjamin R. , Fewell Thomas R. , Conway Burton J. , Quinn Philip W.
Published: March 2003

Single‐ and three‐phase broad‐beam x‐ray attenuation data have been obtained using lead, steel, plate glass, gypsum wallboard, lead acrylic, and wood. Tube voltages of 50, 70, 100, 125, and 150 kVp were employed and the resulting curves were compared to transmission data found in the literature. To simplify computation of barrier requirements, all data sets were parametrized by nonlinear least‐squares fit to a previously described mathematical model. High attenuation half value layers and the lead equivalence of the alternate materials were also determined.
Flattening of the contrast‐detail curve for large lesions on liver CT images
Authors: Seltzer Steven E. , Judy Philip F. , Swensson Richard G. , Chan Karen H. , Nawfel Richard D.
Published: March 2003

This study evaluated the relative roles of physical and perceptual factors in flattening the contrast‐detail (CD) curve on liver CT scans. To estimate the role of physical factors, the theoretical CD curve for a calculated theoretical observer (i.e., a nonprewhitening matched filter) was predicted using the measured noise power spectrum and measured modulation transfer function of the CT system. Another theoretical CD curve was also produced from the output of the same calculated observer after taking the human visual response function (VRF) into account. Perceptual factors were evaluated by analyzing human observers' replicated ratings of the visibility of details superimposed on liver CT scans. The CD curve for the calculated theoretical observer was below the CD curve actually measured for nine human observers and showed no flattening. With the VRF included, flattening of the theoretical CD curves was only produced by fixed image viewing distances of less than 30 cm, a reading style not employed by the human observers. Correlated ROC analysis of observers' replicated ratings indicated that while random, intraobserver variation was present, the magnitude of this so‐called observer noise was insufficient to explain the flattening of CD curves. Use of narrow display windows did not eliminate this flattening effect. The main reason for human observers' inefficient detection of large, low contrast liver lesions appears to be a consistent misuse of the image information.
A Monte Carlo investigation of electron‐beam applicator scatter
Authors: Ebert M. A. , Hoban P. W.
Published: March 2003

An EGS4 Monte Carlo investigation into applicator scatter in clinical electron beams has been undertaken in order to establish the characteristics of electrons incident on the patient surface which have interacted with collimation systems. The applicator scattered component of an electron beam (including that from irregularly shaped cutouts) should be considered when modeling the electron phase space since it represents a component of the beam incident on the patient with widely varying characteristics to those of the primary beam. Scattering off an edge of applicator material is considered in terms of the types and characteristics of incident primary beam, the resulting interactions in the edge, and the fluence and energy characteristics of the emerging particles. Results indicate that the principal component to consider is scattered electrons due to the electron component of the primary beam, and that the fluence and energy characteristics of this component are dependent upon primary beam energy and the configuration of the applicator apertures.
A model for electron‐beam applicator scatter
Authors: Ebert M. A. , Hoban P. W.
Published: March 2003

Applicators (or cones), used in conjunction with patient specific cutouts in electron‐beam radiotherapy, may interact with the primary electron beam to produce a secondary beam component (applicator scatter). This component affects machine output as well as the shape of resulting dose distributions. A model has been developed to simulate this scatter component for applicators consisting of trimming plates of arbitrary shape. This model involves sampling established kernels of scatter from edge elements of appropriate materials, obtained through Monte Carlo simulations. The result of the model is a phase space (position, direction, energy, charge, weighting) of applicator scattered particles which can be incorporated into a further Monte Carlo simulation, or as input into another advanced treatment planning algorithm. This model is evaluated by comparison of measured profiles and applicator scatter component depth dose curves with Monte Carlo simulations using simulated phase‐space data as input. Results are very consistent and reveal information on the angular and spatial variation characteristics of this beam component. The results obtained verify the developed model as an accurate predictor of the characteristics of applicator scattered particles.
Classification of mass and normal breast tissue on digital mammograms: Multiresolution texture analysis
Authors: Wei Datong , Chan Heang‐Ping , Helvie Mark A. , Sahiner Berkman , Petrick Nicholas , Adler Dorit D. , Goodsitt Mitchell M.
Published: March 2003

We investigated the feasibility of using multiresolution texture analysis for differentiation of masses from normal breast tissue on mammograms. The wavelet transform was used to decompose regions of interest (ROIs) on digitized mammograms into several scales. Multiresolution texture features were calculated from the spatial gray level dependence matrices of (1) the original images at variable distances between the pixel pairs, (2) the wavelet coefficients at different scales, and (3) the wavelet coefficients up to certain scale and then at variable distances between the pixel pairs. In this study, 168 ROIs containing biopsy‐proven masses and 504 ROIs containing normal parenchyma were used as the data set. The mass ROIs were randomly and equally divided into training and test groups along with corresponding normal ROIs from the same film. Stepwise linear discriminant analysis was used to select optimal features from the multiresolution texture feature space to maximize the separation of mass and normal tissue for all ROIs. We found that texture features at large pixel distances are important for the classification task. The wavelet transform can effectively condense the image information into its coefficients. With texture features based on the wavelet coefficients and variable distances, the area Az under the receiver operating characteristic curve reached 0.89 and 0.86 for the training and test groups, respectively. The results demonstrate that a linear discriminant classifier using the multiresolution texture features can effectively classify masses from normal tissue on mammograms.
Computer‐aided diagnosis for interstitial infiltrates in chest radiographs: Optical‐density dependence of texture measures
Authors: Morishita Junji , Doi Kunio , Katsuragawa Shigehiko , Monnier‐Cholley Laurence , MacMahon Heber
Published: March 2003

We have been developing a computerized scheme for automated detection and characterization of interstitial infiltrates based on the Fourier transform of lung texture. To improve the performance of the scheme, which was developed using digitized screen‐film radiographs, optical‐density dependence of both the gradient of the film used and the system noise associated with the laser scanner were investigated. Two hundred chest radiographs, including 100 abnormal cases with interstitial infiltrates, were digitized using a laser scanner. The root‐mean‐square (RMS) variations and the first moments of the power spectra, which correspond to the magnitude and coarseness of lung texture, were determined by Fourier transform of lung textures in numerous regions of interest (ROIs). The RMS variation was dependent upon the average optical density in the ROI, though no obvious trend existed for the first moment of the power spectrum. Dependence of the RMS variations on optical density was corrected for using the gradient curve of the film. Also, system noise associated with the laser scanner was corrected. Results indicated that the specificity was improved from 81% (without correction) to 89% (with corrections), without any loss of sensitivity (90%). Thus, the correspondence between the computer output and consensus interpretation of radiologists was improved with the new scheme compared to the previous one. This improved computerized scheme may be useful to radiologists in detecting interstitial infiltrates in chest radiographs.
The relaxation of supercoiled DNA molecules as a biophysical dosimeter for ionizing radiations: A feasibility study
Authors: Chen Weimin , Blazek Ed Robert , Rosenberg Ivan
Published: March 2003

In this paper we explore the feasibility of using DNA molecules as a biophysical radiation dosimeter. Supercoiled φX174 bacteriophage DNA molecules were irradiated with different gamma radiation doses. The strand breakage produced by ionizing radiation within supercoiled double‐stranded DNA molecules (RFI) yields relaxed circular DNA molecules (RFII) and linear DNA molecules (RFIII) as a result of single‐strand breaks and double‐strand breaks, respectively. The irradiated samples were subjected to electrophoresis on agarose gels to separate the three forms. A proprietary fluorescent dye was used to detect DNA bands within the gel, which was photographed under UV transillumination. The negative was scanned with a computerized imaging densitometric system for DNA band quantitation. The relative fractions of the three molecular forms are dose dependent, and can be modeled mathematically with five parameters. The values of the parameters were determined by optimizing the fit of the model to the data, using a nonlinear regression procedure of a commercial statistical analysis package. Once the parameters of DNA breakage have been determined, absorbed dose can be measured by this technique, which we have termed supercoil relaxation dosimetry. The average accuracy of dose determination for our system over the range of 1–40 Gy was about 5%. Supercoil relaxation dosimetry may be well suited to certain difficult dosimetric problems.
On the correction for radioactive decay in pharmacokinetic modeling
Authors: Williams Lawrence E. , Odom‐Maryon Tamara L. , Liu An , Chai Akiko , Raubitschek Andrew A. , Wong Jeffrey Y. C. , D'Argenio David Z.
Published: March 2003

The question of how to include radioactive decay during biological modeling with first‐order differential equations was considered. Modeling may involve either experimental data y(t) or decay‐corrected data z(t) [≡exp(λt)y(t) where λ is the decay constant] for each compartment. It is sometimes assumed that the latter are solutions to corresponding purely pharmacokinetic models (no decay). We primarily compared the two analyses in the case where the model did not require simultaneous consideration of both labeled and unlabeled material. A general theorem was found which limits the use of decay‐corrected data to pharmacokinetic models containing linear, homogeneous differential equations. By way of verification, an example of this model type was analyzed for a chimeric monoclonal antibody biodistribution in man. Even in this case, statistically significant differences between the two solutions showed that one may find different model parameters depending upon which data set (y or z) was analyzed. For other mathematical forms, the analyst must include the physical decay in all relevant compartments. By analyzing an open, quadratic model, effects of not including decay were seen to be maximized if the biological rate constant was ≥λ, the physical decay constant. Finally, using monoclonal antibody–antigen reactions, similar discrepancies between the z functions and the pharmacokinetic variables were demonstrated. This result was found to persist even if competitive molecules were included. We conclude that decay‐corrected data may be shown, but should not be entered into the modeling equations unless the latter are of the linear, homogeneous form.
Improved conjugate view quantitation of I‐131 by subtraction of scatter and septal penetration events with a triple energy window method
Authors: Macey D. J. , Grant E. J. , Bayouth J. E. , Giap H. B. , Danna S. J. , Sirisriro R. , Podoloff D. A.
Published: March 2003

The majority of radiation absorbed dose estimates for radioimmunotherapy (RIT) with I‐131 labeled antibodies have been calculated based on in vivo quantitation of activity using the conjugate view approach with planar Anger camera images. Scatter and septal penetration events contributed by a small fraction of high‐energy photons emitted by I‐131 with an energy exceeding 600 keV lead to a significant degradation of I‐131 images acquired with an Anger camera, which blurs the images of uptake sites and complicates the definition of background regions. The objective of this study was to evaluate a triple energy window (TEW) subtraction method that has been used to remove these interfering events from I‐131 images. In the method, a primary photopeak image for I‐131 is obtained after sequential subtraction of septal penetration and scatter events by using scatter multipliers derived from a photopeak window and two adjacent scatter window images. Qualitative improvement in image contrast was demonstrated with this technique, together with more accurate and reproducible quantitation for I‐131 in the organs of an abdominal phantom. This TEW scatter subtraction method can be used to provide more precise dosimetry estimates for radionuclide therapy and RIT with I‐131.
Optimization of MR pulse sequences for Bayesian image segmentation
Authors: Prince Jerry L. , Pham Dzung , Tan Qing
Published: March 2003

A method for optimizing MR imaging pulse sequence parameters in a statistical framework is presented. Parameters are defined to be optimal when the resulting scalar images yield optimal image segmentations using Bayesian pixel classification. Thus, Bayes risk is used as the objective function to minimize. Approximations are made to give a tractable solution in a four‐step procedure. A sample calculation is carried out to determine the optimal TR and flip angle for scalar SPGR imaging of the brain. Overall, this paper gives a new approach to optimize MRI pulse sequences for the specific objective of improved image segmentation.
Deconvolution of detector size effect for small field measurement
Authors: Higgins Patrick D. , Sibata Claudio H. , Siskind Lisa , Sohn Jason W.
Published: March 2003

Parametrization of the small fields employed in stereotactic applications is a painstaking process involving extensive film dosimetry to achieve acceptable beam edge definition. Use of cylindrical or spherical detectors for profile measurements would simplify data acquisition but add a volume averaging artifact to beam edge definition. We demonstrate a simple approach to unfolding the chamber size artifact from measured small beam profiles using typical cylindrical chambers. In comparison with film measurements we have found good agreement when the detector response function is deconvoluted from the measured profiles, although the amount of correction needed is fairly minimal for the detectors studied.
Computer‐aided detection of mammographic microcalcifications: Pattern recognition with an artificial neural network
Authors: Chan Heang‐Ping , Lo Shih‐Chung B. , Sahiner Berkman , Lam Kwok Leung , Helvie Mark A.
Published: March 2003

We are developing a computer program for automated detection of clustered microcalcifications on mammograms. In this study, we investigated the effectiveness of a signal classifier based on a convolution neural network (CNN) approach for improvement of the accuracy of the detection program. Fifty‐two mammograms with clustered microcalcifications were selected from patient files. The clusters on the mammograms were ranked by experienced mammographers and divided into an obvious group, an average group, and a subtle group. The average and subtle groups were combined and randomly divided into two sets, each of which was used as training or test set alternately. The obvious group served as an additional independent test set. Regions of interest (ROIs) containing potential individual microcalcifications were first located on each mammogram by the automated detection program. The ROIs from one set of the mammograms were used to train CNNs of different configurations with a back‐propagation method. The generalization capability of the trained CNNs was then examined by their accuracy of classifying the ROIs from the other set and from the obvious group. The classification accuracy of the CNNs for the ROIs was evaluated by receiver operating characteristic (ROC) analysis. It was found that CNNs of many different configurations can reach approximately the same performance level, with the area under the ROC curve (Az) of 0.9. We incorporated a trained CNN into the detection program and evaluated the improvement of the detection accuracy by the CNN using free response ROC analysis. Our results indicated that, over a wide range of true‐positive (TP) cluster detection rate, the CNN classifier could reduce the number of false‐positive (FP) clusters per image by more than 70%. For the obvious cases, at a TP rate of 100%, the FP rate reduced from 0.35 cluster per image to 0.1 cluster per image. For the average and subtle cases, the detection accuracy improved from a TP rate of 87% at an FP rate of four clusters per image to a TP rate of 90% at an FP rate of 1.5 clusters per image.
Quantitation of organ symmetry by diagnostic ultrasonic imaging: A group theoretical approach
Authors: Wang Shu‐Li , Sutton Martin St. John , Sehgal Chandra M.
Published: March 2003

A method based on group theory is proposed to quantify the shape of an organ. It is proposed that a complex shape is characterized by a basic set of symmetry operations involving rotation about the center axis. Based on this concept, partial symmetry elements (PSE) were determined by stepwise rotation of the images and measurement of overlap area between the original and rotated images. These measurements were used to define a symmetry index (SI) and to “decompose” the complex shape into simpler shapes with regular geometry such as a circle, an ellipse, an equilateral triangle, a square, etc. Computer simulations and two‐dimensional (2‐D) ultrasonic images of the prostate were used to demonstrate the feasibility of the method. The method was also applied to a series of clinical ultrasonic cardiac images to determine the dynamic shape changes in left ventricle (LV) of a normal heart and an heart with infarction. The results of this study show that SI increased with an increase in the symmetry of the simulation models and the prostate. Cross‐sectional images of prostate with triangular and ellipsoidal shapes exhibited larger proportion of three‐fold and two‐fold symmetries, respectively. Symmetry index of the LV changed during the cardiac cycle and exhibited a loop‐like structure when plotted as a function of size. Quantitative measurements of SI indicated that the left ventricular chamber is rounder during the diastolic phase of the cardiac cycle. The loop‐like structure was considerably reduced in the heart with infarction. Also, larger distortions in cardiac shape were observed over cardiac cycle in the heart with infarction, as compared to the normal heart. In conclusion, it is feasible to quantitatively characterize 2‐D shapes of the organs by symmetry operations based on group theoretical analysis.
Electron‐beam characteristics at extended treatment distances
Authors: Das Indra J. , McGee Kiaran P. , Cheng Chee‐Wai
Published: March 2003

A uniform dose to the target site is required with a knowledge of delivered dose, central axis depth dose, and beam flatness for successful electron treatment at an extended source to surface distance (SSD). The central axis depth dose is shown to be nearly independent of moderate changes in the treatment distance. The delivered dose at a point could be calculated with the concept of virtual source position and an inverse square correction. In an extended SSD treatment, underdosage of the lateral tissue may occur due to reduced beam flatness. To study the changes in beam characteristics, the depth dose and beam flatness were measured at different SSDs for clinically used field sizes [(3×3)–(15×15) cm2] and beam energies ranging from 6 to 20 MeV. Our results indicate that the changes in depth dose are minimal except in the buildup region for most energies. In general, the surface dose is decreased (≤10%) as the SSD is increased moderately. Beam flatness was measured in terms of target coverage factor (TCF) defined as the ratio of the width of a specified isodose line to the geometrical field width. It was observed that the loss in beam flatness is significant for smaller fields, higher isodose lines, and lower energies. Variations in SSD have a minimal effect on the relative changes in beam flatness for field sizes greater than 8×8 cm2. The lateral loss of beam uniformity could be estimated by various parameters, such as the full width at half maximum, the homogeneity index, the uniformity index, and the TCF; however, TCF is a simpler parameter to use clinically. The beam characteristics (depth dose and TCF) at extended treatment distances are presented for electron beams.
Pierre and Marie Curie‐Sklodowska
Authors: Chavaudra Jean
Published: March 2003

April 20, 1995. Pierre and Marie Curie's mortal remains leave their modest grave in the Sceaux Churchyard near Paris to be admitted to the Pantheon, devoted to a few of the nation's greatest figures. This ceremony took place in the presence of Mr. François Mitterrand, President of the French Republic, and Mr. Lech Walesa, President of the Polish Republic, Eve Curie, their daughter, Hélène Langevin and Pierre Joliot, their grand‐children, and a considerable audience. This recognition of their merit is of a great symbolic value, not only because they were prominent scientists, but also because Marie Curie is the first woman to be received into the Pantheon for her personal fame. The worldwide celebrity of Pierre and Marie Curie can be justified by both their remarkable scientific contribution and the legend built on their personal lives, which were out of the ordinary. Although their main joint contribution is linked to the discovery of polonium and radium, it is also important to acknowledge some of their other contributions to science and medicine. This review of Pierre and Marie Curie's lives and main accomplishments considers three periods of time: their individual lives before their encounter in 1894, their life together and collaboration between 1894 and 1906, and Marie Curie's life after Pierre Curie's death.
Radiology, physical science, and the emergence of medical physics
Authors: Cohen Montague , Trott Nigel G.
Published: March 2003

The early development of medical physics as a separate discipline and profession is briefly reviewed. Although both x rays and radioactivity were discovered by physicists, at first the physical investigations of these phenomena, and their medical applications, proceeded along parallel but independent lines. Radiological journals were founded in Britain, Germany, and the U.S. as early as 1896–1897 but it was not until ten years later that papers on radiation physics began to appear regularly. In 1913 the first full‐time physicists were appointed to posts in medical schools and hospitals: William Duane in the U.S. and Sydney Russ in Britain. Thereafter the number of physicists engaged in medical applications increased slowly but steadily, and in the 1920s they began to apply the new science of radiation dosimetry to both x ray and radium therapy. The “Hospital Physicists' Association” was founded in Britain in 1943 with 53 members and the “American Association of Physicists in Medicine” followed in 1958 with 127 charter members.
Determination of dose components in phantoms irradiated with an epithermal neutron beam for boron neutron capture therapy
Authors: Raaijmakers C. P. J. , Konijnenberg M. W. , Verhagen H. W. , Mijnheer B. J.
Published: March 2003

The application of activation foils, thermoluminescent detectors, and ionization chambers has been investigated for the determination of the different dose components in phantoms irradiated with a mixed gamma‐ray and epithermal neutron beam for boron neutron capture therapy. The thermal neutron fluence has been determined using a set of AuAl and MnNi activation foils. TLD‐700 and a Mg(Ar) ionization chamber have been used for the determination of the gamma‐ray dose. The dose from epithermal neutrons has been determined using a TE(TE) ionization chamber. The detector characteristics and the relative sensitivities of the various detectors to the different dose components in the phantom have been determined. The following accuracies (1 standard deviation) in the determination of the different components have been obtained: thermal neutron fluence rate: 5%; gamma‐ray dose rate: 7%; epithermal neutron dose rate: 15%. These values make these detectors suitable for obtaining the complete set of clinical dosimetry data required for patient dose assessment.
Specific absorbed fractions of energy from internal photon sources in brain tumor and cerebrospinal fluid
Authors: Evans Jeff F. , Stabin Michael G. , Stubbs James B.
Published: March 2003

Transferrin, when injected intracranially into glioblastoma multiforme lesions, acts as a cytotoxic substance. Transferrin, radiolabeled with In‐111, can be coinjected and subsequent scintigraphic imaging can demonstrate the biokinetics of the cytotoxic transferrin. The administration of 111In transferrin into a brain tumor results in distribution of radioactivity in the brain, brain tumor, and the cerebrospinal fluid (CSF). Information about absorbed radiation doses to these regions, as well as other nearby tissues and organs, is important for evaluating radiation‐related risks from this procedure. The radiation dose is usually estimated for a mathematical representation of the human body. We have included source/target regions for the eye, lens of the eye, spinal column, spinal CSF, cranial CSF, and a 100‐g tumor within the brain of an adult male phantom developed by Cristy and Eckerman. The mathematical models of the spinal column, spinal CSF, and the eyes were developed previously, however, these source/targets have not been routinely included in photon transport simulations. Specific absorbed fractions (SAFs) as a function of photon energy were calculated using the ALGAMP computer code, which utilizes Monte Carlo techniques for simulating photon transport. The ALGAMP code was run three times, with the source activity distributed uniformly within the tumor, cranial CSF, and the spinal CSF volumes. These SAFs, which were generated for 12 discrete photon energies ranging from 0.01 to 4.0 MeV, were used with decay scheme data to calculate S‐values needed for estimating absorbed doses. S‐values for 111In are given for three source regions (brain tumor, cranial CSF, and spinal CSF) and all standard target regions/organs, the eye and lens, as well as to tissues within these source regions. S‐values for the skeletal regions containing active marrow are estimated. These results are useful in evaluating the radiation doses from intracranial administration of 111In transferrin. The SAFs are also generally useful for calculation of absorbed dose from any radionuclide in these source regions.
Dose‐surface histograms as treatment planning tool for prostate conformal therapy
Authors: Lu Y. , Li S. , Spelbring D. , Song P. , Vijayakumar S. , Pelizzari C. , Chen G. T. Y.
Published: March 2003

Dose‐surface histograms are studied and compared with dose‐volume histograms, as an evaluation tool for prostate treatment planning. For thin walled hollow organs, such as the rectum and bladder, the surface area irradiated is a more appropriate measure of the biological effect than the full volume. It is also more accurate and efficient to define the surface for a hollow structure and compute the surface area histograms. Application of the dose‐surface histograms provide new insights into prostate treatment planning. A simple idealized geometry model demonstrates that the percentage surface area intersected by the geometric beam edge differs from the percentage volume intersected. For a group of prostate patients, it is shown that the dose‐surface histograms yield substantially different results from the dose‐volume histograms in ranking four‐, six‐, and, eight‐field treatment plans and in calculating the fraction of the rectum irradiated to high dose. The difference in terms of surface area between these plans in the high‐dose region is usually less than that in terms of the volume, and a reverse of plan ranking order can consequently occur. The percentage of organ surface irradiated to high dose is typically greater than the percentage volume by 5% to 10%. The use of the dose‐surface histograms in analysis of organ motion and/or patient setup uncertainty, and analysis of rectal complications, is also discussed.
Quality assurance tool for high dose rate brachytherapy
Authors: DeWerd Larry A. , Jursinic Paul , Kitchen Rebecca , Thomadsen Bruce R.
Published: March 2003

An insert for a well ionization chamber is described for quality assurance tests for high dose rate remote afterloaders. The use of this insert over time has shown its applicability for efficient QA tests for the high dose rate afterloader. The measurement results are six times greater than the uncertainties involved for the measurements. Checks on position can be made better than 1 mm and dwell times better than 1 s. The overall measurements can be done to better than 1.5%. QA checks can be accomplished in a shorter time period with as great or better accuracy than prior film techniques.
X‐ray imaging using amorphous selenium: Inherent spatial resolution
Authors: Que W. , Rowlands J. A.
Published: March 2003

This is a theoretical study of the inherent spatial resolution of the latent image on the surface of an amorphous selenium (a‐Se) plate used for diagnostic x‐ray imaging. The following effects are considered: (A) ranges of primary photoelectrons; (B) reabsorption of K fluorescence; (C) reabsorption of Compton scattered photons; (D) diffusion; (E) the geometric effect due to oblique incidence of x rays; (F) electrostatic effect; and (G) the space charge effect. The modulation transfer function of a‐Se in the diagnostic x‐ray energy range has been estimated. In conclusion, (A) and (E) are the main factors limiting the resolution, and for diagnostic x rays, the inherent spatial resolution of a‐Se plates is much better than that of CsI layers used in x‐ray image intensifiers.
Phase‐contrast radiographs of nonstained rat cerebellar specimen
Authors: Momose Atsushi , Fukuda Jun
Published: March 2003

Phase‐contrast radiography using an x‐ray interferometer is presented for observing organic matter. High sensitivity of phase‐contrast radiography is demonstrated with a rat cerebellar specimen without staining it with a contrast medium. The layer structure of the cerebellum can be observed in the obtained image while there is no clear structure in the corresponding absorption‐contrast image. Quantitative image analysis is made possible by converting an x‐ray interference pattern to an x‐ray phase shift distribution. The lipid distribution in the cerebellum is discussed by evaluating x‐ray phase shifts before and after lipid removal.
A dosimetric investigation of scatter conditions for dual asymmetric collimators in open fields
Authors: Cadman Patrick
Published: March 2003

An investigation of the scattering effects of dual asymmetric collimators on open fields is presented. It has been determined that the output measured in air and in a phantom is radially symmetric and that the scatter as a function of field size is independent of field center offset, for a wide variety of square and rectangular field shapes. The analysis has led to a new and simplified method to represent primary off‐center ratios (POCRs), which requires a minimum set of symmetric field data, including beam profiles, collimator and phantom scatter factors, and tissue maximum ratios. The field edge correction (FEC) method proposed has been shown to accurately model the POCRs to a distance of 17.5 cm from the collimator rotation axis in a plane perpendicular to the isocenter and at depths up to 30 cm without the need for extrapolation of the POCRs or special measurements setups, which may be required for POCR modeling techniques that measure narrow beam attenuation coefficients.
Doses near the surface in high‐energy x‐ray beams
Authors: Bjärngard Bengt E. , Vadash Paul , Zhu Timothy
Published: March 2003

In an irradiation with a high‐energy x‐ray beam, the absorbed dose near the surface is the combined result of incident contaminating electrons and phantom‐generated electrons. We describe an experimental method to characterize these processes under conditions of longitudinal electron disequilibrium but lateral equilibrium. The equilibrium dose at large depths is extrapolated back towards the surface and compared with measured doses. The extrapolation uses an expression that is based on Monte Carlo‐calculated kerma values. The technique was applied to a 6‐MV and a 25‐MV x‐ray beam. The dose from phantom‐generated electrons increased exponentially with depth from zero at the surface. The dose from contaminating electrons decreased rapidly with depth with an attenuation coefficient that was approximately equal to the corresponding coefficient for the increase of dose from phantom‐generated electrons. The surface dose from contaminating electrons increased linearly with the side of the square field at 6 MV but an error‐function agreed better with the data at 25 MV.
Monte Carlo aided dosimetry of the microselectron pulsed and high dose‐rate 192Ir sources
Authors: Williamson Jeffrey F. , Li Zuofeng
Published: March 2003

Despite the large number of single‐stepping source pulsed and high dose‐rate (HDR) remote afterloading devices in clinical use, the published literature contain little data characterizing dose‐rate distributions around the high‐intensity (4×103–4×104 μGy m2 h−1) 192Ir sources currently used in these devices. We have used the Monte Carlo method to calculate complete two‐dimensional dose‐rate distributions about the most widely used high dose‐rate source design, as well as the Nucletron pulsed dose‐rate (PDR) 192Ir source. A Monte Carlo photon transport code, incorporating the detailed internal geometry of the source, was used to calculate the dose rate per unit air‐kerma strength in water medium on the transverse bisecting axis over the 0.15–12 cm distance range. In addition, polar dose profiles were calculated at distances ranging from 0.25 to 5 cm. The PDR and HDR dose‐rate distributions are tabulated using the formalism endorsed by the Interstitial Collaborative Working Group and the AAPM Task Group 43, and includes dose‐rate constant, radial dose function, anisotropy function, geometry function, and anisotropy factors. The dose‐rate constants, Λ, of the MicroSelectron/HDR and PDR sources were found to be 1.115 and 1.128 cGy h−1 per unit air‐kerma strength, respectively, in good agreement with previously published data for low dose‐rate interstitial 192Ir sources. Oblique filtration by the high‐density iridium metal core resulted in deviations from anisotropy as large as 35%–55% near the longitudinal axis of the source. Dose‐rate distributions are also presented in Cartesian (“away” and “along”) coordinates.
p‐type silicon detector for brachytherapy dosimetry
Authors: Piermattei A. , Azario L. , Monaco G. , Soriani A. , Arcovito G.
Published: March 2003

The sensitivity of a cylindrical p‐type silicon detector was studied by means of air and water measurements using different photon beams. A lead filter cap around the diode was used to minimize the dependence of the detector response as a function of the brachytherapy photon energy. The radial dose distribution of a high‐activity 192Ir source in a brachytherapy phantom was measured by means of the shielded diode and the agreement of these data with theoretical evaluations confirms the method used to compensate diode response in the intermediate energy range. The diode sensitivity was constant over a wide range of dose rates of clinical interest; this allowed one to have a small detector calibrated in terms of absorbed dose in a medium. Theoretical evaluations showed that a single shielding filter around the p‐type diode is sufficient to obtain accurate dosimetry for 192Ir, 137Cs, and 60Co brachytherapy sources.
Spatially varying optical property reconstruction using a finite element diffusion equation approximation
Authors: Paulsen Keith D. , Jiang Huabei
Published: March 2003

A finite element reconstruction algorithm for optical data based on a diffusion equation approximation is presented. A frequency domain approach is adopted and a unified formulation for three combinations of boundary observables and conditions is described. A multidetector, multisource measurement and excitation strategy is simulated, which includes a distributed model of the light source that illustrates the flexibility of the methodology to modeling adaptations. Simultaneous reconstruction of both absorption and scattering coefficients for a tissue‐like medium is achieved for all three boundary data types. The algorithm is found to be computationally practical, and can be implemented without major difficulties in a workstation computing environment. Results using simulated data suggest that qualitative images can be produced that readily highlight the location of absorption and scattering heterogeneities within a circular background region of close to 4 cm in diameter over a range of contrast levels. Absorption images appear to more closely identify the true size of the heterogeneity; however, both the absorption and scattering reconstructions have difficulty with sharp transitions at increasing depth. Quantitatively, the reconstructions are not accurate, suggesting that absolute optical imaging involving simultaneous recovery of both absorption and scattering profiles in multicentimeter tissues geometries may prove to be extremely difficult.