bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of proton and x‐ray conformal dose distributions for radiosurgery applications
Authors: Serago Christopher F. , Thornton Allan F. , Urie Marcia M. , Chapman Paul , Verhey Lynn , Rosenthal Stanley J. , Gall Kenneth P. , Niemierko Andrzej
Published: March 2003

Highly focused dose distributions for radiosurgery applications are successfully achieved using either multiple static high‐energy particle beams or multiple‐arc circular x‐ray beams from a linac. It has been suggested that conformal x‐ray techniques using dynamically shaped beams with a moving radiation source would offer advantages compared to the use of only circular beams. It is also thought that, generally, charged particle beams such as protons offer dose deposition advantages compared to x‐ray beams. A comparison of dose distributions was made between a small number of discrete proton beams, multiple‐arc circular x‐ray beams, and conformal x‐ray techniques. Treatment planning of a selection of radiosurgery cases was done for these three techniques. Target volumes ranged from 1.0–25.0 cm3. Dose distributions and dose volume histograms of the target and surrounding normal brain were calculated. The advantages and limitations of each technique were primarily dependent upon the shape and size of the target volume. In general, proton dose distributions were superior to x‐ray distributions; both shaped proton and shaped x‐ray beams delivered dose distributions which were more conformal than x‐ray techniques using circular beams; and the differences between all proton and x‐ray distributions were negligible for the smallest target volumes, and greatest for the larger target volumes.
Dosimetric properties of a scanned beam microtron at low monitor unit settings: Importance for conformal therapy
Authors: Humm John L. , Larsson Anders , Lief Eugene P.
Published: March 2003

The dosimetric stability, linearity, dose rate dependence, and flatness of both photon and electron beams have been evaluated for a racetrack microtron at low monitor unit settings. For photons, the variation in dosimetric output about the mean is <0.4% at 100 monitor units (MU), <1% at 10 MU, and <4% at 2 MU. The output dependence on the dose rate varied by <0.6% between 85–300 MU/min. Flatness and symmetry for the 25‐ and 50‐MV beams showed deviations of <3% at both dmax and 10‐cm depths, and only slightly ≳3% at 20 cm, even at only 3 MU, in contrast with other scanned beam accelerators. Broad electron beams on the microtron are created by the superposition of the elementary beam pulses either directly from the scan magnets, or after their broadening through a scattering foil. The dosimetric instability both with and without the foil was less than 0.6% for both the 25‐ and 50‐MeV electrons. Dose nonlinearity was <1% above 10 MU. Field flatness was determined for scan matrices designed to produce a flat field both with and without a scattering foil. Symmetry and flatness deviations were <3% for both electron energies when a scattering foil was used, even for a single scan. The variation of the electron dose per monitor unit between dose rates of 85–300 MU/min was <1% (25 MeV) and <4% (50 MeV) when a scattering foil was used, but as high as 22% (25 MeV) and 36% (50 MeV) for broad beams generated by elementary beam pulses directly from the scanning magnets. The microtron exhibits dosimetric properties which fulfill the recommendations of Task Groups 21 and 25. Based on the stability of the scanned beam at low monitor unit settings, the microtron can be used for 3‐D conformal therapy with both photons and electrons.
The omni wedge: A method to produce wedged fields at arbitrary orientations
Authors: Milliken Barrett D. , Hamilton Russell J. , Rubin Steven J.
Published: March 2003

A method to produce wedged fields at any orientation relative to the collimator is described. The wedged field is generated by combining two appropriately weighted orthogonal wedged field segments at fixed collimator and gantry positions. The method requires only that wedged fields can be produced in orthogonal directions without rotating the collimator, such as is commonly provided on most radiation therapy accelerators by sets of standard and rotated wedges. Expressions are derived relating the effective wedge angle and orientation to the weighting and wedge angles of the orthogonal wedged field segments. This technique will be important when using multileaf collimator field shaping for which collimator rotation is dictated by target or critical structure shape and orientation. The term omni wedge is introduced to describe this technique.
Energy imparted and effective doses in computed tomography
Authors: Atherton James V. , Huda Walter
Published: March 2003

The radiation risk to patients undergoing computed tomography (CT) examinations may be characterized by using the dose descriptors of effective dose equivalent (HE) and effective dose (E). Values of HE and E, however, are much more difficult to obtain than the total energy imparted (ε) to the patient. In this study, representative values of the ratios HE/ε and E/ε were obtained using published Monte Carlo organ dose computations for typical CT x‐ray spectra. Values of patient dose per unit energy imparted can be combined with independent estimates of energy imparted to quantify the dose to a patient undergoing any type of CT examination.
3D electron dose calculation using a Voxel based Monte Carlo algorithm (VMC)
Authors: Kawrakow Iwan , Fippel Matthias , Friedrich Klaus
Published: March 2003

A new model for calculating electron beam dose has been developed. The algorithm is based on a two‐ or three‐dimensional geometry defined by computerized tomography (CT) images. The Monte Carlo technique was used to solve the electron transport equation. However, in contrast to conventional Monte Carlo models (EGS4) several approximations and simplifications in the description of elementary electron processes were introduced reducing in this manner the computational time by a factor of about 35 without significant loss in accuracy. The Monte Carlo computer program does not need any precalculated data. The random access memory required is about 16 Mbytes for a 1282×50 matrix, depending on the resolution of the CT cube. The Voxel Monte Carlo model (VMC) was tested in comparison to calculations by EGS4 and the “Hogstrom algorithm” (MDAH) using several fictive phantoms. In all cases a good coincidence has been found between EGS4 and VMC, especially near tissue inhomogeneities, whereas the MDAH algorithm has produced dose underestimations of up to 40%.
Superposition dose calculation incorporating Monte Carlo generated electron track kernels
Authors: Keall Paul J. , Hoban Peter W.
Published: March 2003

The superposition/convolution method and the transport of pregenerated Monte Carlo electron track data have been combined into the Super‐Monte Carlo (SMC) method, an accurate 3‐D x‐ray dose calculation algorithm. The primary dose (dose due to electrons ejected by primary photons) is calculated by transporting pregenerated (in water) Monte Carlo electron tracks from each primary photon interaction site, weighted by the terma for that site. The length of each electron step is scaled by the inverse of the density of the medium at the beginning of the step. Because the density scaling of the electron tracks is performed for each individual transport step, the limitations of the macroscopic scaling of kernels (in the superposition algorithm) are overcome. This time‐consuming step‐by‐step transport is only performed for the primary dose calculation, where current superposition methods are most lacking. The scattered dose (dose due to electrons set in motion by scattered photons) is calculated by superposition. In both a water–lung–water phantom and a two lung‐block phantom, SMC dose distributions are more consistent with Monte Carlo generated dose distributions than are superposition dose distributions, especially for small fields and high energies—for an 18‐MV, 5×5‐cm2 beam, the central axis dose discrepancy from Monte Carlo is reduced from 4.5% using superposition to 1.5% using SMC. The computation time for this technique is approximately 2 h (depending on the simulation history), 20 times slower than superposition, but 15 times faster than a full Monte Carlo simulation (on our platform).
Capillary optics for neutron capture therapy
Authors: Peurrung A. J.
Published: March 2003

The development of capillary neutron optics permits a new technology for neutron capture therapy involving the application of a focused thermal neutron beam at the medically optimal location within the patient. A subthermal neutron beam begins to converge as it travels through a neutron “lens,” reaching a narrow focus within a tube that allows it to pass directly to the treatment region. This technique results in a substantially lower dose to untreated parts of the patient and a substantially weaker radiation field in the treatment room generally. Additional advantages include the relative ease of thermal neutron generation and the ability to shield the patient completely and effectively from fast neutrons or gamma rays originating at the neutron source. This work describes the application of capillary optics to neutron capture therapy, along with Monte Carlo calculations of the neutron flux profiles within a patient for an optimized system design. Specific dose profiles for the case of boron neutron capture therapy within the brain are also provided.
Use of a micro‐ionization chamber and an anthropomorphic head phantom in a quality assurance program for stereotactic radiosurgery
Authors: Duggan D. M. , Coffey C. W.
Published: March 2003

Quality assurance methods used in association with radiosurgery must include all aspects of the radiosurgery process: visualization and localization of the target, treatment and dose planning and dose delivery. Presented here is a quality assurance method that utilizes an anthromorphic head phantom and a micro‐ionization chamber to demonstrate precise target localization and accurate dose delivery. This micro‐ionization chamber method offers an immediate readout which is both accurate and reproducible. Additionally, this method allows unlimited repetition of the dose measurement process without repeated radiographic localization studies as is necessary with the conventional methods of TLD, film, and Fricke gels. The method and techniques presented can be used in the acceptance testing and routine quality assurance of both linac‐based and Gamma Knife radiosurgery units.
The variability of manual and computer assisted quantification of multiple sclerosis lesion volumes
Authors: Mitchell J. Ross , Karlik Stephen J. , Lee Donald H. , Eliasziw Michael , Rice George P. , Fenster Aaron
Published: March 2003

The high resolution and excellent soft tissue contrast of Magnetic Resonance Imaging (MRI) have enabled direct, noninvasive visualization of Multiple Sclerosis (MS) lesions in vivo. This has allowed the quantification of changes in the appearance of lesions in MR exams to be used as a measure of disease state. Nevertheless, accurate quantification techniques are subject to inter‐ and intra‐operator variability, which may hinder monitoring of disease progression. We have developed a computer program to assist an experienced operator in the quantification of MS lesions in standard spin‐echo MR exams. The accuracy of assisted and manual quantification under known conditions was studied using exams of a test phantom, while inter‐ and intra‐operator reliability and variability were studied using exams of a MS patient. Results from the phantom study show that accuracy is improved by assisted quantification. The patient exam results indicate that assisted quantification reduced inter‐operator variability from 0.34 to 0.17 cm3, and reduced intra‐operator variability from 0.23 to 0.15 cm3. In addition, the minimum significant change between two successive measurements of lesion volume by the same operator was 0.64 cm3 for manual quantification and 0.42 cm3 for assisted quantification. For two different operators making successive measurements, the minimum significant change was 0.94 cm3 for manual quantification, but only 0.47 cm3 for assisted quantification. Finally, the number of lesions to be monitored for an average change in volume at a given power and significance level was reduced by a factor of 2–4 by assisted quantification. These results suggest that assisted quantification may have practical applications in clinical trials, especially those that are large, multicenter, or extended over time, and therefore require lesion measurements by one or more operators.
The effects of lossy compression on the detection of subtle pulmonary nodules
Authors: Cox Glendon G. , Cook Larry T. , Insana Michael F. , McFadden Michael A. , Hall Timothy J. , Harrison Linda A. , Eckard Donald A. , Martin Norman L.
Published: March 2003

We examined the ability of radiologists to detect pulmonary nodules in computed radiographic (CR) chest images subjected to lossy image compression. Low‐contrast 1‐cm diameter targets simulating noncalcified pulmonary nodules were introduced into clinical images and presented to ten radiologists in a series of two‐alternative forced‐choice (2AFC) observer experiments. The percentages of correct observer responses obtained while viewing noncompressed images (1:1) were compared with those obtained for the same images compressed 7:1, 16:1, 44:1, and 127:1. The images were compressed using a standard full‐frame discrete cosine transform (DCT) technique. The degree of compression was determined by quantizing Fourier components in various frequency channels and then Huffman encoding the result. The data show a measurable decline in performance for each compression ratio. Through signal‐to‐noise ratio (SNR) analysis, we found that the reduction in performance was due primarily to the compression algorithm that increased image noise in the frequency channels of the signals to be detected.
Mammography fixed grid versus reciprocating grid: Evaluation using cadaveric breasts as test objects
Authors: Kimme‐Smith C. , Sayre J. , McCombs M. , Gold R. H. , Bassett L. W.
Published: March 2003

In this study we use unfixed cadaveric breasts to obtain mammography images with fixed and reciprocating grids. Sheets of acrylic, containing one or more clusters of simulated calcifications and masses, were superimposed on two fresh cadaveric breasts (3.4 and 6.5 cm thick), and were imaged with a fixed grid and a reciprocating grid. Six radiologists, working independently, attempted to identify the number of clusters and/or masses in 114 images containing 139 clusters of simulated calcifications and 42 simulated masses. Thirty‐four of these images were normal, containing no lesions. For the thinner breast, no statistically significant difference was found in the detection of clusters of calcifications in the images produced with the fixed grid compared to those produced with the reciprocating grid. However, for the detection of calcifications in images of the thicker breast, sensitivity of 74% for detection of calcifications when a fixed grid was used was significantly less than sensitivity of 86% when a reciprocating grid was used (P=0.006). The mass detection sensitivity was 91% for images made with a fixed grid compared to 96% for images made with a reciprocating grid, but the difference was not statistically significant (P=0.346). The use of cadaveric breasts as test objects was well accepted by radiologists. Only for the thick cadaveric breast were differences between the two grids significant, and these differences were restricted to the task of finding calcifications.
Frequency‐domain optical mammography: Edge effect corrections
Authors: Fantini Sergio , Franceschini Maria Angela , Gaida Gerhard , Gratton Enrico , Jess Helge , Mantulin William W. , Moesta K. Thomas , Schlag Peter M. , Kaschke Michael
Published: March 2003

We have investigated the problem of edge effects in laser‐beam transillumination scanning of the human breast. Edge effects arise from tissue thickness variability along the scanned area, and from lateral photon losses through the sides of the breast. Edge effects can be effectively corrected in frequency‐domain measurements by employing a two‐step procedure: (1) use of the phase information to calculate an effective tissue thickness for each pixel location; (2) application of the knowledge of tissue thickness to calculate an edge‐corrected optical image from the ac signal image. The measurements were conducted with a light mammography apparatus (LIMA) designed for feasibility tests in the clinical environment. Operating in the frequency‐domain (110 MHz), this instrument performs a transillumination optical scan at two wavelengths (685 and 825 nm). We applied the proposed two‐step procedure to data from breast phantoms and from human breasts. The processed images provide higher contrast and detectability in optical mammography with respect to raw data breast images.
Water calorimetry and ionization chamber dosimetry in an 85‐MeV clinical proton beam
Authors: Palmans Hugo , Seuntjens Jan , Verhaegen Frank , Denis Jean‐Marc , Vynckier Stefaan , Thierens Hubert
Published: March 2003

In recent years, the increased use of proton beams for clinical purposes has enhanced the demand for accurate absolute dosimetry for protons. As calorimetry is the most direct way to establish the absorbed dose and because water has recently been accepted as standard material for this type of beam, the importance of water calorimetry is obvious. In this work we report water calorimeter operation in an 85‐MeV proton beam and a comparison of the absorbed dose to water measured by ionometry with the dose resulting from water calorimetric measurements. To ensure a proper understanding of the heat defect for defined impurities in water for this type of radiation, a relative response study was first done in comparison with theoretical calculations of the heat defect. The results showed that pure hypoxic water and hydrogen‐saturated water yielded the same response with practically zero heat defect, in agreement with the model calculations. The absorbed dose inferred from these measurements was then compared with the dose derived from ionometry by applying the European Charged Heavy Particle Dosimetry (ECHED) protocol. Restricting the comparison to chambers recommended in the protocol, the calorimeter dose was found to be 2.6%±0.9% lower than the average ionometry dose. In order to estimate the significance of chamber‐dependent effects in this deviation, measurements were performed using a set of ten ionization chambers of five different types. The maximum internal deviation in the ionometry results amounted to 1.1%. We detected no systematic chamber volume dependence, but observed a small but systematic effect of the chamber wall thickness. The observed deviation between calorimetry and ionometry can be attributed to a combination of the value of (Wair/e)p for protons, adopted in the ECHED protocol, the mass stopping power ratios of water to air for protons, and possibly small ionization chamber wall effects.
Evaluation of bremsstrahlung spectra generated by a 4‐MeV linear accelerator
Authors: Krmar M. , Slivka J. , Bikit I. , Vesković M. , Čonkić Lj.
Published: March 2003

A modified method for the evaluation of bremsstrahlung spectra on the basis of transmission measurements is presented. The method is tested for two 4 MeV therapy accelerators. The calculated spectra are compared with other experimental results and Monte Carlo simulation.
Imaging characteristics of x‐ray capillary optics in digital mammography
Authors: Kruger David G. , Abreu Carmen C. , Hendee Eric G. , Kocharian Armen , Peppler Walter W. , Mistretta Charles A. , MacDonald Carolyn A.
Published: March 2003

Computed radiography (CR) has shown promise in digital mammographic screening due to its good low spatial frequency MTF and its relatively wide exposure latitude. The CR image format has not gained acceptance clinically because of reduced high spatial frequency resolution as compared to film‐screen images. X‐ray capillary optics, aligned between the breast and CR phosphor imaging plate, will capture primary x‐ray photons almost exclusively. Due to the very small angle of acceptance, scattered photons angled more than about 1.6×10−3 radians from primary trajectory will not be accepted at the capillary optic entrance. The virtual elimination of detected scatter means almost 100% of the possible primary contrast should be visible in the image. In addition, the image can be magnified without focal spot blurring. Effective resolution of CR images can be increased by a factor equal to that magnification. Clinical implementation of future capillary optics are expected to be either in the form of a large, stationary, post‐patient optic that accepts primary from the entire breast or a fan‐shaped optic that is scanned across the breast. Measurements of a test capillary optic showed a reduction of scatter fraction to 0.018. Images of a lucite contrast detail phantom revealed a corresponding increase in image contrast when compared to anti‐scatter grid and no grid methods. Spectral transmission measurements using a high‐purity germanium detector showed good primary transmission (45%–50%) in the mammographic energy range. The MTF measurements of both stationary and scanned capillary optics showed improvement at the 5% MTF level to 8.4 mm−1 for scanned optics and 9.2 mm−1 for stationary optics representing a 68% and 84% respective increase over the CR MTF without magnification or capillary optics.
A general approach to the reconstruction of x‐ray helical computed tomography
Authors: Hsieh Jiang
Published: March 2003

Helical Computed Tomography (HCT) has become the method of choice for many routine clinical studies. The advantages of HCT include the capability of scanning a complete anatomical volume in a single breath hold, the capability of generating images at any desired location, and the improved patient throughput. However, these advantages come at the expense of some image quality compromises. This is mainly caused by the fact that the projection set is inherently incomplete and inconsistent, due to the constant patient translation during the data acquisition process. In this paper, we will briefly review the research work performed in this area and present a more general approach to the problem. We give two specific examples of the general approach and compare the performance of one of the examples with one of the best methods available today.
Quantitative classification of breast tumors in digitized mammograms
Authors: Pohlman Scott , Powell Kimerly A. , Obuchowski Nancy A. , Chilcote William A. , Grundfest‐Broniatowski Sharon
Published: March 2003

The goal of this study was to develop a technique to distinguish benign and malignant breast lesions in secondarily digitized mammograms. A set of 51 mammograms (two views/patient) containing lesions of known pathology were evaluated using six different morphological descriptors: circularity, μR/σR (where μR=mean radial distance of tumor boundary, σR=standard deviation); compactness, P2/A (where P=perimeter length of tumor boundary and A=area of the tumor); normalized moment classifier; fractal dimension; and a tumor boundary roughness (TBR) measurement (the number of angles in the tumor boundary with more than one boundary point divided by the total number of angles in the boundary). The lesion was segmented from the surrounding background using an adaptive region growing technique. Ninety‐seven percent of the lesions were segmented using this approach. An ROC analysis was performed for each parameter and the results of this analysis were compared to each other and to those obtained from a subjective review by two board‐certified radiologists who specialize in mammography. The results of the analysis indicate that all six parameters are diagnostic for malignancy with areas under their ROC curves ranging from 0.759 to 0.928. We observed a trend towards increased specificity at low false‐negative rates (0.01 and 0.001) with the TBR measurement. Additionally, the diagnostic accuracy of a classification model based on this parameter was similar to that of the subjective reviewers.
Optimization of conformal electron beam therapy using energy‐ and fluence‐modulated beams
Authors: Hyödynmaa Simo , Gustafsson Anders , Brahme Anders
Published: March 2003

Fluence modulation of multiple electron beams of various energies has been used to optimize the delivered dose distribution during electron beam radiation therapy. By maximizing the probability of achieving tumor control without causing severe complications electron beam fluence profiles have been optimized for superficial target volumes. It is possible to use several equiportal fluence‐modulated electron beams to modify the energy deposition with depth in a controlled manner making it possible to use the technique as an alternative to bolus. The technique was tested in two representative phantom geometries and in three clinical patient geometries using a set of five and two different energies. The local maxima in dose for the plans with five energies were typically lower than with the conventional or advanced bolus techniques. The principles for how the technique could be carried out in the future with a fourth generation radiotherapy accelerator are also indicated.
Thermoluminescent dosimetry in electron beams: Energy dependence
Authors: Robar Vlado , Zankowski Corey , Olivares Pla Marina , Podgorsak Ervin B.
Published: March 2003

The response of thermoluminescent dosimeters to electron irradiations depends on the radiation dose, mean electron energy at the position of the dosimeter in phantom, and the size of the dosimeter. In this paper the semi‐empirical expression proposed by Holt et al. [Phys. Med. Biol. 20, 559–570 (1975)] is combined with the calculated electron dose fraction to determine the thermoluminescent dosimetry (TLD) response as a function of the mean electron energy and the dosimeter size. The electron and photon dose fractions, defined as the relative contributions of electrons and bremsstrahlung photons to the total dose for a clinical electron beam, are calculated with Monte Carlo techniques using EGS4. Agreement between the calculated and measured TLD response is very good. We show that the considerable reduction in TLD response per unit dose at low electron energies, i.e., at large depths in phantom, is offset by an ever‐increasing relative contribution of bremsstrahlung photons to the total dose of clinical electron beams. This renders the TLD sufficiently reliable for dose measurements over the entire electron depth dose distribution despite the dependence of the TLD response on electron beam energy.
Systematic verification of a three‐dimensional electron beam dose calculation algorithm
Authors: Cheng Abel , Harms William B. , Gerber Russell L. , Wong John W. , Purdy James A.
Published: March 2003

A three‐dimensional electron beam dose calculation algorithm implemented on a commercial radiotherapy treatment planning system is described. The calculation is based on the M. D. Anderson Hospital (M.D.A.H.) pencil beam model, which uses the Fermi–Eyges theory of thick‐target multiple Coulomb scattering. To establish the calculation algorithm's accuracy as well as its limitations, it was systematically and extensively tested and evaluated against a set of benchmark measurements. Various levels of dose and spatial tolerances were used to validate the calculation quantitatively. Results are presented in terms of the percentage of data points meeting a specific tolerance level. The algorithm's ability to accurately simulate commonly used clinical setup geometries, including standard or extended SSDs, blocked fields, irregular surfaces, and heterogeneities, is demonstrated. Regions of disagreement between calculations and measurements are also shown. The clinical implication of such disagreements is addressed, and the algorithmic assumptions involved are discussed.
Effects of irradiation geometry on treatment plan optimization with linac‐based radiosurgery
Authors: Phillips Mark H. , Stelzer Keith J. , Mayberg Marc R. , Winn H. Richard
Published: March 2003

A comparison was made of different treatment plans to determine the effect on the three‐dimensional dose distributions of varying the allowed parameters in linac‐based stereotactic radiosurgery with circular collimators; these parameters are arc position, length, and weighting, and collimator diameter. For the class of eccentrically shaped target volumes that are not so irregular as to require several separate isocenters, it was found that superior dose distributions could be achieved by varying arc length, arc position, arc weighting, and collimator diameter. An analysis of the results achieved with an automated planning program indicates that, in general, the variables of arc position and arc length are of greater importance than collimator size or beam weighting. However, there are cases where varying these latter two parameters does result in markedly better dose distributions. A deeper investigation into the effects of multiple collimators on the dose distribution in the area of steepest gradient demonstrated that multiple collimator sizes do not significantly degrade the dose falloff, which is in fact mostly determined by the effects of intersecting arcs.
Laser heating of thermoluminescent plates: Application to intraoperative radiotherapy
Authors: Beteille D. , Setzkorn R. , Prévost H. , Dusseau L. , Fesquet J. , Gasiot J. , Muraro S. , Delard R. , Dubois J. B. , Ailleres N. , Missous O.
Published: March 2003

A new system of radiation dose mapping based on laser heating of thermoluminescent dosimetric plates (TLDP) has been developed. Application of this technique to intraoperative radiotherapy (IORT) has been investigated. Preliminary results show that TLDP are a possible alternative to radiological films and ionization chambers since they provide some advantages such as 2D dose measurements with digital storage, large dynamic dose range, and easy processing.
Photon absorbed fractions for cylindrical geometry: Homogeneous nonradioactive cylinder containing a homogeneous cylindrical distribution of activity
Authors: Dreesen James A. , Dumitru Daniela I. , Fearon Thomas C. , Kushner David C.
Published: March 2003

The purpose of this study was to calculate photon absorbed fractions in tissue surrounding a radioactive source where both the source and the surrounding tissue are assumed to have cylindrical geometry. Specifically, we treated two cases: the case of a cylindrical source of homogeneous activity placed in air, and second, the case of a cylindrical source of homogeneous activity placed in a cylindrical nonradioactive absorbing material. In this study we offer an analytical solution to these problems followed by numerical integration. The computer program allowed for very general calculations, e.g., different tissues, different geometrical setups. Tables of absorbed fractions have been developed for commonly used radionuclide energies and tissue‐equivalent material. A comparison between our results and the results of other related studies showed the advantages and limitations of this approach.
EGS4 dosimetry calculations for cylindrically symmetric brachytherapy sources
Authors: Wang Ruqing , Sloboda Ron S.
Published: March 2003

Computer algorithms for electron binding correction to Compton scattering and for detailed simulation of K‐edge characteristic x‐ray production were incorporated into EGS4 unix version 2.0. Based on detailed modelling of the internal structures of sources, the modified version was used to calculate dose rate constants, radial dose functions, and anisotropy functions on the long axis for an 125I model 6711 source, 169Yb Type 5 and Type 8 sources, and a stainless steel clad (SS) 192Ir source. The geometry of these sources is cylindrically symmetric. Calculated results are generally in good agreement with corresponding values recommended by TG‐43 and Monte Carlo results published by other authors. The influence of electron binding in Compton scattering on the calculated dose distribution for an 125I model 6711 source in water, and of different characteristic x‐ray production models for 125I model 6711 and 192Ir SS sources, were also studied.
Analytical description of the high and low contrast behavior of a scan‐rotate geometry for equalization mammography
Authors: Sabol John M. , Plewes D. B.
Published: March 2003

Many solutions have been proposed to overcome the problem of imaging the radiographically dense breast with high contrast mammographic film of limited dynamic range. In previous works, we have proposed utilizing a modulated fan‐beam in a scan‐rotate geometry RSER (Rotary Scanning Equalization Radiography), as an efficient method for producing exposure equalized mammograms. The image quality of RSER is similar to that attained with the inefficient single beam, raster scanning SER (Scanning Equalization Radiography) geometry. RSER has the potential to be a practical, efficient method for improving the detection of cancer in the dense breast. In this work, we present a theoretical analysis of the imaging properties of the RSER geometry in two regimes defined by the variation of x‐ray transmission within the object. For low contrast objects, the imaging geometry was analyzed as a linear system, whereas the high contrast regime was studied by determining the contrast limit at which RSER requires nonphysical (negative) exposure modulation for a breast‐like object. The low contrast transfer function of the RSER system is shown to be very similar to that of the SER geometry. We show that RSER enables the use of wide scanning beam of approximately 4 cm and thereby significantly reduces x‐ray tube heat loading. Analysis of the high contrast behavior shows that a wide range of object contrasts and sizes can be equalized. For example, RSER can equalize a region of 100% glandular tissue within a 4.0 cm thick compressed breast composed of 100% adipose tissue. Thus, the RSER geometry produces images very similar to the more inefficient SER geometry, and is able to produce entrance exposure distributions appropriate for equalization of the range of contrast typically encountered in mammography.
Physical specifications of clinical proton beams from a synchrotron
Authors: Arduini G. , Cambria R. , Canzi C. , Gerardi F. , Gottschalk B. , Leone R. , Sangaletti L. , Silari M.
Published: March 2003

Tumor treatment with charged particle beams is a quickly developing field aimed to translate the potential advantages offered by the superior physical dose distribution and relative biological effectiveness of heavy charged particles into a real improvement of tumor therapy. To this purpose the new proton and light‐ion radiation therapy facilities must be designed according to strict clinical specifications to provide a reliable and effective tool against cancer. This paper provides the performance specifications of the accelerator and of the beam transport and delivery systems of the Italian Hadrontherapy Centre, which should be satisfied to meet the clinical specifications. A discussion is given on the requirements on energy range, energy variability, beam intensity, lateral penumbra, distal dose falloff, source‐to‐surface distance, time structure of the extracted beam, raster scanning system specifications, and beam abort time. Though the physical specifications are given for a particular accelerator, they can be used as a general guideline for the design of future biomedical particle accelerator facilities.
Design and optimization of an aperiodic ultrasound phased array for intracavitary prostate thermal therapies
Authors: Hutchinson E. B. , Buchanan M. T. , Hynynen K.
Published: March 2003

A 57 element aperiodic linear phased array was designed and constructed to investigate the feasibility of using transrectal ultrasound for the thermal therapeutic treatment of prostate cancer and benign prostatic hyperplasia. A method of reducing grating lobe levels by using optimized random distributions of unequally sized elements is introduced. Using this technique, array periodicity is avoided, making it feasible to use larger elements and hence fewer elements and amplifier channels, while still achieving acceptable power field patterns. Acoustic power field simulations determined that the grating lobe levels associated with selected aperiodic element distributions were approximately 30%–45% less than those associated with periodic element spacing and the same average element width. Or by using aperiodic rather than periodic element distributions, the average element width could be increased by approximately 20%–35% (∼λ/4.4), while maintaining a constant grating lobe level. Prior to construction of the 57 element array, the power capabilities of this type of array were demonstrated with a 16 element aperiodic phased array, which delivered over 28 W of acoustical power per cm of array length while focused. The power field patterns produced by the 57 element array closely matched the field patterns predicted by the theoretical model used in the simulations. The array produced acceptable power field patterns for foci at depths up to 5 cm and up to 2 cm off the center axis, in addition to producing multiple foci simultaneously. Based on the power capabilities and field patterns, this aperiodic array design has the potential to be incorporated into a clinical heating device as a means of delivering thermal therapies to the prostate and other target volumes close to body cavities.
Automated detection of breast masses on mammograms using adaptive contrast enhancement and texture classification
Authors: Petrick Nicholas , Chan Heang‐Ping , Wei Datong , Sahiner Berkman , Helvie Mark A. , Adler Dorit D.
Published: March 2003

This paper presents segmentation and classification results of an automated algorithm for the detection of breast masses on digitized mammograms. Potential mass regions were first identified using density‐weighted contrast enhancement (DWCE) segmentation applied to single‐view mammograms. Once the potential mass regions had been identified, multiresolution texture features extracted from wavelet coefficients were calculated, and linear discriminant analysis (LDA) was used to classify the regions as breast masses or normal tissue. In this article the overall detection results for two independent sets of 84 mammograms used alternately for training and test were evaluated by free‐response receiver operating characteristics (FROC) analysis. The test results indicate that this new algorithm produced approximately 4.4 false positive per image at a true positive detection rate of 90% and 2.3 false positives per image at a true positive rate of 80%.
Dosimetry of a radioactive coronary balloon dilitation catheter for treatment of neointimal hyperplasia
Authors: Amols H. I. , Reinstein L. E. , Weinberger J.
Published: March 2003

Recent reports suggest that intraluminal irradiation of coronary arteries in conjunction with balloon angioplasty reduces proliferation of smooth muscle cells and neointima formation, thereby inhibiting restenosis. One possible irradiation technique is to inflate the balloon dilitation catheter with a radioactive solution. This has advantages over other proposed irradiation procedures, in that accurate source positioning and uniform dose to the vessel wall are assured. Several high‐energy beta‐minus emitters may be suitable for this application. We present experimental measurements and analytical calculations of the dose distribution around a 3‐mm‐diam by 20‐mm‐long balloon filled with 90Y‐chloride solution. The dose rate at the surface of the balloon is approximately 0.14 cGy/s per mCi/ml (3.78×10−11 Gy/s per Bq/ml), with the dose decreasing to 53% at 0.5 mm, and <5% at 3.5‐mm radial distance. 90Y and other possible isotopes are currently available at specific concentrations ≥50 mCi/ml (1.85×109 Bq/ml), which enables the delivery of 20 Gy in less than 5 min. The dosimetric and radiation safety advantages of this system warrant further feasibility studies. Issues of concern include incorporating the beta‐emitter into a suitable chemical form, and assessing organ and whole body doses in the (<1 in 103) event of balloon failure.
A consistency monitor for radiation therapy treatments
Authors: Paliwal Bhudatt R. , Zaini Mehran , McNutt Todd , Fairbanks E. Jeffrey , Kitchen Rebecca
Published: March 2003

A thin, large area transparent transmission chamber mounted below the accessory tray is described and its suitability for daily treatment delivery consistency is investigated. The sensitivity of the detector to changes in monitor unit setting, field size, wedge size, missing blocks, and wedges is presented. Some of the other potential applications are also discussed.
The accuracy of dose localization for an image‐guided frameless radiosurgery system
Authors: Murphy Martin J. , Cox Richard S.
Published: March 2003

A compact X‐band accelerator mounted on a robotic arm is under development for frameless stereotaxic radiosurgery. The therapy beam is aimed at the lesion by an imaging system comprised of two diagnostic x‐ray cameras that view the patient during treatment. Patient position and motion are measured by the cameras and communicated in real time to the robotic arm for beam targeting and patient motion tracking. The tests reported here measured the pointing accuracy of the therapy beam and the present targeting and tracking capability of the imaging system. The results show that the system achieves the same level of targeting precision as conventional frame‐based radiosurgery.
An improved neutron collimator for brain tumor irradiations in clinical boron neutron capture therapy
Authors: Liu Hungyuan B. , Greenberg Dennis D. , Capala Jacek , Wheeler Floyd J.
Published: March 2003

To improve beam penetration into a head allowing the treatment of deeper seated tumors, two neutron collimators were built sequentially and tested for use in the clinical boron neutron capture therapy (BNCT) program at the epithermal neutron irradiation facility of the Brookhaven Medical Research Reactor. The collimators were constructed from lithium‐impregnated polyethylene, which comprises Li2CO3 powder (≊93% enriched isotopic 6Li) uniformly dispersed in polyethylene to a total 6Li content of 7.0 wt. %. The first collimator is 7.6 cm thick with a conical cavity 16 cm in diameter on the reactor core side tapering to 8 cm facing the patient's head. The second collimator is 15.2 cm thick with a conical cavity 20 cm in diameter tapering to 12 cm. A clinical trial of BNCT for patients with malignant brain tumors is underway using the first collimator. Results of phantom dosimetry and Monte Carlo computations indicate that the new 15.2 cm thick collimator will improve the neutron beam penetration. Thus, the second collimator was made and will be used in an upcoming clinical trial. In‐air and in‐phantom mixed‐field dosimetric measurements were compared to Monte Carlo computations for both collimators. The deeper penetration is achieved but at a sacrifice in beam intensity. In this report, a performance comparison of both collimators regarding various fluence rate and absorbed dose distributions in a head model is presented and discussed.
A genetic algorithm for the optimization of prostate implants
Authors: Yu Yan , Schell M. C.
Published: March 2003

A genetic algorithm (GA) is presented for the optimization of template‐ and ultrasound‐guided prostate implants. The end points for optimization are incorporated in an objective function of separable cardinal utility terms. As an application of the GA, the minimum 103Pd total source strength required to deliver a given dose was correlated with the average dimension for prostate implants carried out under the current template and seed spacing protocols. Significant improvements in quality were observed, in terms of both the minimum peripheral dose and tumor cell surviving fractions, when GA‐optimized implants were compared to the corresponding unoptimized implants for given target volumes. In addition, numerical simulation of source displacements indicates that the dosimetric and radiobiologic advantages of GA optimization can tolerate a reasonable level of seed placement uncertainties observed clinically. In summary, the GA application provides an automated design strategy for prostate implant planning, and at the same time affords the potential for systematic optimization of a set of end points that can sustain practical variations.
The effect of helical pitch and beam collimation on the lesion contrast and slice profile in helical CT imaging
Authors: Hu Hui , Fox Stanley H.
Published: March 2003

A model is presented in this paper to describe how the contrast of a reconstructed object and slice sensitivity profile are affected by (1) the table speed or helical pitch, (2) the x‐ray collimation, (3) the size of the object, (4) the alignment between the reconstructed slice and the object, (5) the distance of the object from the axis of rotation, and (6) the helical CT reconstruction algorithm employed. This contrast model is validated by both computer simulations and experiments. With this model, the contrast of a reconstructed object, slice sensitivity profile, and the longitudinal MTF can be accurately predicted. The optimal scan strategy and the point of diminishing returns can be determined prior to scanning. Several conclusions can be drawn from this model. First, overlapping reconstruction significantly improves overall scan contrast sensitivity of helical CT. Second, with a given x‐ray collimation, low pitch helical scans provide better longitudinal resolutions. Third, with a given volume coverage rate (i.e., a given table speed), narrow collimation high pitch helical scans provide better longitudinal resolutions than wide collimation low pitch ones and therefore are recommended for high‐contrast thin‐slice applications. A lesion conspicuity model is also established.
On the reporting of mass contrast in CAD research
Authors: Zheng Bin , Chang Yuan‐Hsiang , Gur David
Published: March 2003

As research efforts for developing computer‐aided diagnosis (CAD) schemes of digitized mammograms increase and interscheme results are compared, the desire to establish an acceptable consistent reporting protocol of the distribution of abnormal characteristics is becoming an issue. “Mass contrast” is very important and frequently reported in current CAD studies. In this report, 100 verified mass regions were analyzed systematically using 6 different definitions of “mass contrast.” Measured variability in mass contrast was demonstrated by the distribution shift in this group of masses. The need for universally accepted and largely standardized descriptors of objects of interest is clearly demonstrated.
Measurement of absorbed dose to water for medium energy x rays
Authors: Rosser Karen Elizabeth
Published: March 2003

The aim of this thesis is to determine the factors required to convert the air kerma measured using an ionization chamber to absorbed dose to water when irradiated with medium energy x rays. This involved determining the ratio of the mass energy absorption coefficients of water to air and the chamber correction factor (kch) for an NE2561 ionization chamber. The latter can be expressed as the product of the stem correction, the correction for the angular and energy dependence of the chamber, the replacement correction and a correction for the effect of the waterproof sleeve. The chamber correction factor for a NE2561 chamber was determined using two independent methods. First, the absorbed dose to water was compared using an NE2561 chamber with that using an NE2571 chamber. Second, the air kerma in water was measured using the NE2561 chamber and compared with the absorbed dose to water determined using an ice calorimeter. The validity of the absorbed dose to water measured using the ice calorimeter was then checked by comparison with the primary standard graphite calorimeter irradiated with 60Co gamma rays.