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M S Weinhous

Publications and source records attributed to M S Weinhous.

At least 19 recordsLinked to original sources
PubMed2001

Fluoroscopic study of tumor motion due to breathing: facilitating precise radiation therapy for lung cancer patients.

Target motion due to breathing is one of the major obstacles in dose escalation of radiation therapy to some tumors in the thoracoabdominal region. The development of beam gating or target motion tracking techniques provides a possibility to reduce normal tissue volume in a treatment field. Tumor motion monitoring in those techniques plays a crucial role, but has not yet been adequately explored. This paper reports our preliminary investigation on breath introduced tumor motion. Tumor locations and motion properties were determined from digitized fluoroscopic videos acquired during patient simulation. Image distortion due to irregularities in the imaging chain, such as the pincushion distortion, was corrected with a polynomial unwarping method. Temporal Fourier transformation of the fluoroscopic video was introduced to convert the motion information over time to a static view of a motion field, in which regions with different motion ranges can be directly measured. Patient breathing patterns vary from patient to patient and so does the kinematic behavior of individual tumors. In order to evaluate the feasibility for tracking internal target motion with nonionizing-radiation techniques, motion patterns between internal targets and external radio opaque markers placed on patient's chest during fluoroscopic video acquisition were compared. For some patients, significant motion phase discrepancies between an internal target and an external marker have been observed. Quantitative measurements are reported. These results will be useful in the design of a motion tracking or gated radiotherapy system.

Fluoroscopy↗
PubMed2000

GammaPlan-Leksell Gamma Knife radiosurgery treatment planning verification method.

This work provides a method for an independent check of Gamma Knife GammaPlan radiosurgery calculations, named the spherical approximation method or SAM. Based on skull dimension measurements, the treated volume of the head is modeled as a sphere of radius R. With this approximation, an analytical solution for fast ray tracing of the path length, for each of the 201 beamlets, of the Gamma Knife helmet collimator was possible. The dose rate at the focus of a single shot is the sum of the contributions of all active beamlets adjusted for both the collimator factor and attenuation. For an arbitrary point, the dose rate is derived at the beamlet level from the focus values adjusted for the new path length attenuation and the appropriate collimators' off-axis profiles. The sum over all beamlets' contributions gives the dose rate at that particular point. At the single shot level, SAM independent check results agree with the GammaPlan for patient calculations to better than +/-6% and, as expected, in spherical phantoms the agreements improve to better than +/-1.0%. For an arbitrary point, multi-shot procedure, the agreement is better than +/-3% and +/-1.5, respectively.

Humans↗
PubMed2000

Dosimetry of a W-188/Re-188 beta line source for endovascular brachytherapy.

PURPOSE: The objective was to determine the dosimetry of a potential endovascular brachytherapy source consisting of a coiled tungsten wire mounted on the distal end of a drive wire and neutron-activated to contain the parent-daughter nuclides tungsten-188 (188W) and rhenium-188 (188Re). METHODS: A coiled tungsten wire 40 mm in length was neutron-activated by double-neutron capture for 78 hours at 1.9 x 10(15) h/cm2/s to contain 925 MBq (25 mCi) of 188W/188Re in equilibrium. The dose-fall off from this source was determined using three independent methods: (a) Thermoluminescence dosimetry with small LiF-100 rods, (b) Gafchromic film dosimetry, and (c) Bang gel dosimetry. In addition, a Monte Carlo simulation was performed to compute the beta-dose. RESULTS: Each of the three measurement methods recorded similar values for the dose fall-off within the distances useful for endovascular brachytherapy. The Monte Carlo calculations closely approximated the measured results in the treatment range between 1 and 3 mm and may thus be useful for evaluating changing geometries in the development of catheters and source setups. A 2 min restenosis treatment delivering 20 Gy at a radius of 2 mm would require a source of 1384.8 MBq/cm (37.4 mCi/cm). CONCLUSIONS: The dose distribution from a 188W/188Re source is similar to that of a 90Y-source. An added advantage of the 188W/188Re source is that it can be used for at least two months and still provides fast treatment times because of the parent isotope's half-life of 69 days. The additional gamma emission from the source is too small to impose a serious radiological hazard. The high atomic number and density of the source material allows direct fluoroscopic imaging without additional markers.

Beta Particles↗
PubMed1999

The radiobiology and physics of brachytherapy.

The principles of radiobiology are the same for both EBRT and brachytherapy. Strict spatial limitation of the delivered dose, a function of the inverse square law, is one reason that brachytherapy is attractive. The biologic rationale of LDR implants is maximization of normal tissue repair to enhance the therapeutic ratio. Fractionated HDR treatment schedules have been formulated that provide good biologic approximation of the well-established LDR practices. The HDR approach improves both patient comfort and radiation safety; also, the brief treatment times can permit geometric improvements by transiently displacing sensitive structures.

Brachytherapy↗
PubMed1999

Subunity coordinate translation with Fourier transform to achieve efficient and quality three-dimensional medical image interpolation.

A new approach to the interpolation of three-dimensional (3D) medical images is presented. Instead of going through the conventional interpolation scheme where the continuous function is first reconstructed from the discrete data set and then resampled, the interpolation is achieved with a subunity coordinate translation technique. The original image is first transformed into the spatial-frequency domain. The phase of the transform is then modified with n-1 linear phase terms in the axial direction to achieve n-1 subunity coordinate translations with a distance 1/n, where n is an interpolation ratio, following the phase shift theorem of Fourier transformation. All the translated images after inverse Fourier transformation are then interspersed in turn into the original image. Since windowing plays an important role in the process, different window functions have been studied and a proper recommendation is provided. The interpolation quality produced with the present method is as good as that with the sampling (sinc) function, while the efficiency, thanks to the fast Fourier transformation, is very much improved. The approach has been validated with both computed tomography (CT) and magnetic resonance (MR) images. The interpolations of 3D CT and MR images are demonstrated.

Algorithms↗
PubMed1999

An automated iterative algorithm for water and fat decomposition in three-point Dixon magnetic resonance imaging.

An iterative, outlier exclusion, second-order surface fitting algorithm has been developed to solve the well-known phase wraparound problem associated with in vivo applications of the three-point Dixon magnetic resonance imaging method. The technique was optimized for speed by reducing the problem to a pair of planar fits. The spatial misalignment between water and fat components due to the chemical shift was handled on a subpixel level by invoking the shift theorem of Fourier transformation. From the chemical shift corrected water and fat images, high quality recombined MR images were generated. The algorithm was validated in both phantom and patient studies. In vivo breast images and pelvic images are provided as a demonstration of the method.

Adipose Tissue↗
PubMed1999

Successful conversion from a linear accelerator-based program to a Gamma Knife radiosurgery program: the Cleveland Clinic experience.

From August 1989 to January 1997, 307 treatments in 293 patients were performed with a linear accelerator-based (LINAC) stereotactic radiosurgery system. Because of the program s success, the need for a dedicated radiosurgery unit in Ohio and the desire to treat functional disorders, the Cleveland Clinic Health System (CCHS) obtained the first Gamma Knife in the state of Ohio. Based on the previous volume of patients for radiosurgery, it was estimated that 75-100 patients would be treated during the first year of operation. However, during the first calendar year, 214 treatments were performed on 205 patients, which far exceeded expectations. The success of the CCHS Gamma Knife Center can be attributed to an increase in a number of factors. These included marketing efforts, patient awareness, increased use for functional disorders, physician understanding of radiosurgery, use by qualified nonaffiliated radiation oncologists and neurosurgeons, and outpatient delivery (95% with the Gamma Knife vs <5% with the LINAC). With proper planning, education, and awareness, the opening of a Gamma Knife Center can greatly increase the volume of radiosurgery performed when compared with a LINAC-based program.

Brain Neoplasms↗
PubMed1998

Error rates in clinical radiotherapy.

PURPOSE: Error rates in clinical oncology are undergoing increasing scrutiny. The purpose of this study was to understand error frequency, error patterns, underlying causal links, consequences, and possible prevention strategies in clinical radiotherapy. PATIENTS AND METHODS: Treatment information, self-reported error documentation, and retrospective analyses of electronic treatment verification transcripts for 1,925 consecutive patients treated with a total of 93,332 individual radiotherapy fields were reviewed and analyzed. RESULTS: A total of 59 separate errors that affected 168 individual treatment fields were detected, which yielded a crude radiation delivery error rate of 0.18%. All 59 errors were judged to be level I (negligible chance of adverse medical outcome) with the most common error category being a minor treatment field block misplacement. A comprehensive quality assurance program and an electronic record-and-verify linear accelerator interlock system seem to have prevented the occurrence of many additional errors. However, nine of the 59 errors were directly related to the use of this system and generally involved the transposition of similar numbers within series of treatment coordinate data-sets. Overall, radiotherapy error rates favorably compare with reported error rates for pharmaceutical administration in large tertiary care hospitals. CONCLUSION: When modern automated error-minimization methods are used along with nonpunitive error reporting systems, clinical radiotherapy seems to be highly safe. Formal error analysis studies may allow the rational design of prevention strategies that are attuned to the frequency, seriousness, and antecedent causes of many classes of potential radiotherapy errors.

Humans↗
PubMed1997

Physics and basic parameters of brachytherapy.

Brachytherapy (short-distance therapy) is the therapeutic process whereby radioactive sources are placed into very close proximity to target tissue. Radioactive materials were so used beginning shortly after the discovery of radium by Marie and Pierre Curie in 1898. For the purposes of brachytherapy, radioactive materials are those that emit "rays" that can cause ionization (and hence DNA damage and the destruction of target cells). The potentially useful rays include beta, gamma, and other possibilities such as neutrons. Beta rays, properly beta particles, are simply high energy electrons. Gamma rays are high energy photons (part of the electromagnetic spectrum like visible light, but with much higher energy). These particles are produced during the radioactive decay of certain isotopes. The physics of those events and the parameters that apply to the therapeutic use of the isotopes are the primary topics of this report.

Brachytherapy↗
PubMed1992

The selection of portal aperture using interactively displayed Beam's Eye Sections.

Portal apertures are often defined by wax-pencil lines drawn on simulator films. The simulator-film images suffer degradation due to X ray absorption and scatter in tissues proximal to and distal to the intended target volume. We describe a method for avoiding the degradation by using a 3-D dataset to produce high-contrast section images with a user-defined orientation. The calculation of these Beam's Eye Section (BES) images requires a set of medium-to high-resolution transverse section data (the 3-D dataset), as well as a medium- to high-performance computer workstation. These CT-like section images, providing more contrast and detail than a projection (that is, a simulator or Digitally Reconstructed Radiograph [DRR]) image, should allow for more accurate selection of portal apertures. The BES image plane is oriented perpendicular to the central axis of a user-selected beam. Once the user has created a beam, the system allows the user to step along that beam with a new BES image produced at each step. Contours manually drawn on these BES images are ultimately projected onto a DRR image. The outermost segments of these sometimes crisscrossing contours (the union of all projected areas) accurately defines the portal aperture needed to encompass the target at all levels.

Computer Simulation↗
PubMed1991

Study of treatment variation in the radiotherapy of head and neck tumors using a fiber-optic on-line radiotherapy imaging system.

On-line radiotherapy imaging systems allow convenient daily acquisition of portal images for treatment verification. The information can also be used to study treatment variability. Using a prototype fiber-optic imaging system, we have measured the treatment variation of 17 head and neck patients. Daily digital portal images were acquired for the on-cord left and right lateral fields. Treatment variations were quantified using the Cumulative Verification Image Analysis (CVIA) method developed at our institute. In the CVIA method, daily portal images were aligned according to three anatomical points predefined on a digitized simulation, or prescription, image. After each image alignment, the block position was cumulated in a bit-map and superimposed on the prescription image to give a cumulative verification summary image. Iso-frequency distributions, or contours, of the block overlap were calculated and examined with respect to the prescription treatment area. The range of the treatment variation was large for the 17 patients. On average, separation of the 0% to 100% block overlap contours was about 10 mm, and the 20% to 80%, 5 mm. The block overlap contours were also used to calculate the frequency with which the prescription area as defined on the simulation film had been treated. The fraction of the prescription area treated depended on the accuracy of the treatment setup and patient repositioning, as expected. At best, approximately 95% of the prescribed area was irradiated 100% of the time during the entire course of radiotherapy. At worst, approximately 70% of the prescribed area was irradiated 100% of the time. These results demonstrate that despite immobilization, large setup variation can still occur. Presenting treatment variation data as population averages does not reflect on the large variation that may be observed in the individual patient.

Adolescent↗
PubMed1990

Treatment verification using a computer workstation.

The outcome of radiation therapy is clearly dependent upon the accuracy with which dose is delivered to the target volume. With the ever increasing use of oblique and even non-coplaner beams, verification issues have become more significant. Presently, radiation oncologists verify the accuracy with which treatments are delivered by comparing a reference ("prescription," usually simulator) on-film image to a portal on-film image on a lightbox. This process is fraught with difficulties as the images are usually rendered with different magnifications, orientations, and contrast. Using a computer workstation, a system has been created that allows a physician to enhance, register, and transparently overlay the portal image on the prescription image. As the prescription and portal images are rendered in shades-of-yellow and shades-of-gray, respectively, a physician can interactively adjust the images and can easily detect set-up errors and/or beam placement errors. Thus greater treatment accuracy should be achievable, especially for unfamiliar beam orientations.

Humans↗
PubMed1986

Collection efficiency of an ionisation chamber in a pulsed swept beam: chamber size effects.

Boag's theory for the collection efficiency of a small ionisation chamber in a pulsed swept beam is generalised by taking chamber size into account. The collection efficiency is given in terms of the chamber radius, the Gaussian scale constant of the stationary beam, and the maximum distance between beam and chamber centres. It is shown that, for cases of practical interest, collection efficiency is independent of chamber size.

Humans↗
PubMed1986

Collection efficiency of an ionisation chamber in a pulsed swept beam: collimator scatter effects.

The expressions for calculating the collection efficiency of an ionisation chamber in a pulsed swept beam, as derived by Boag, explicitly assume that the stationary beam has a Gaussian radial intensity distribution and implicitly assumes that this distribution, upon being swept, is unperturbed by extra-phantom scatter. Consequently a hyperbolic pulse-size distribution is expected on the central axis. Measurements of pulse-size distributions at the isocentre of a Sagittaire accelerator for small collimator settings yield hyperbolic distributions in accord with this model. However, measurements of large-field pulse-size distributions yield markedly non-hyperbolic distributions for electron energies from 7 to 32 MeV. It is shown that application of the model in such cases might result in significant errors depending on the inherent collection efficiency of the chamber.

Electrons↗
PubMed1985

Convection currents in a water calorimeter.

A flexible, temperature-regulated water calorimeter has been constructed containing two pairs of thermistor sensors at depths of 6.23 and 10.0 cm. It may be irradiated by vertical or horizontal beams, and operated at temperatures in the range from 3 to 40 degrees C. When irradiated at 30 degrees C with a vertically downward 19 MeV electron beam, the responses of the proximal and midline thermistors were in accordance with the depth-dose curve. When irradiated horizontally, the initial patterns of temperature rise were the same, but after about 30 s (4 Gy) the rate of temperature rise decreased at the proximal thermistors and increased at the midline thermistors. Shortly after irradiation, the temperature curve and increased at the midline thermistors. Shortly after irradiation, the temperature curve of the midline thermistors crossed that for the proximal thermistors, a pattern that suggested the presence of convection currents. To test this hypothesis, the calorimeter was operated at 4 degrees C. The temperature patterns for horizontal irradiation became the same as those obtained with vertical beams, thus demonstrating the production of convection currents in water at a temperature of 30 degrees C for temperature gradients as small as 10(-3) degrees C cm-1.

Calorimetry↗
PubMedDate not supplied

An improved electron energy-loss straggling algorithm for Monte Carlo transport codes.

The commonly used Blunck and Leisegang electron energy-loss distribution falls off too rapidly with increasing energy loss. Also, for large thicknesses and/or low-Z media, where their distribution should approach Landau's, it normalizes to 0.92 rather than 1.0, it overestimates the number of very small energy-loss events, and its peak is shifted from lambda = -0.225 to 0.1. Because of these shortcomings, calculations made using this distribution yield a mean straggled energy loss which is lower than the value predicted by the continuous slowing down approximation (CSDA). An improved version of the Blunck-Leisegang distribution, which exhibits better normalization and falloff, has been developed. Further, an algorithm was created which (depending on the CSDA energy loss, Z,A, electron energy, and transport step size) samples the electron's straggled energy loss from the more accurate of the available distribution functions.

Electrons↗
PubMedDate not supplied

Determining Pion, the correction factor for recombination losses in an ionization chamber.

The 1983 AAPM protocol for the determination of absorbed dose from high-energy photon and electron beams recommends using Pion (the reciprocal of collection efficiency), as determined by the two-voltage technique, to correct for recombination losses in ionization chambers. Methods and data for the determination of ionization chamber collection efficiencies are scattered throughout the literature. The present work consolidates the available information, rectifies certain omissions, and provides several convenient and readily implemented methods for determining Pion. Computer programs, quadratic approximations, and data tables are presented to facilitate the determination of Pion for continuous, pulsed, and pulsed-swept beams.

Radiometry↗