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Biomedical subjects

L E Reinstein

Publications and source records attributed to L E Reinstein.

At least 19 recordsLinked to original sources
PubMed1992

Assessment of geometric treatment accuracy using time-lapse display of electronic portal images.

During the past two years, several electronic portal imaging systems have been introduced to the market by therapy accelerator manufacturers and other vendors. While these systems differ substantially in their detection technology, they are all capable of displaying portal images on a video screen in near real-time, and of creating multiple static (or "movie") images during each treatment. Major questions confront the users of such systems as to the best utilization of this wealth of information, and to its value in comparison to traditional weekly portal film methods. Using an "in-house" video based system, a new technique was established to aid in the assessment of on-line images so that immediate "go/no-go" decisions can be made by the therapy technologist. A video "movie-loop" is displayed which consists of the static image of the initial (approved) set-up, and the current treatment image. Multiple images of successive treatments can also be viewed in this "time-lapse" display mode to provide a quick visual means for review of an entire course of therapy. The on-line imaging system hardware is composed of a combination copper-plate/fluorescent-screen detector, a front surface mirror angled at 45 degrees to remove the camera from the direct radiation beam, and a high sensitivity SIT video camera. This assembly is attached to a rigid base and mounted directly to the isocentric gantry. The geometry is fixed to within +/- 1 mm and assures the precise day-to-day reproducibility which is necessary for the success of the time-lapse display technique. Experience with this technique shows it to enhance the user's ability to notice small changes in patient's position with respect to the radiation field. Radiation treatment sites reviewed using this procedure were Hodgkin's (mantle), Lung, Brain and extremities. Shifts in patient position on the order of several millimeters were readily detectable, as will be demonstrated in this paper. Somewhat surprisingly, grosser movements (greater than 1 cm) were also noted despite overall technical excellence as assessed by weekly portal filming. The eye senses day-to-day movement with greater ease when the fields are seen in time-lapse display than when compared as discrete portal images. Ultimately, persistent movement appreciated on the time-lapse display can suggest the need for a change in patient set-up or immobilization technique.

Humans↗
PubMed1992

Microdosimetry for boron neutron capture therapy.

Preclinical studies for boron neutron capture therapy (BNCT) using epithermal neutrons are ongoing at several laboratories. The absorbed dose in tumor cells is a function of the thermal neutron flux at depth, the microscopic boron concentration, and the size of the cell. Dosimetry is therefore complicated by the admixture of thermal, epithermal, and fast neutrons, plus gamma rays, and the array of secondary high-linear-energy-transfer particles produced within the patient from neutron interactions. Microdosimetry can be a viable technique for determining absorbed dose and radiation quality. A 2.5-cm-diameter tissue-equivalent gas proportional counter has been built with 50 parts per million (ppm) 10B incorporated into the walls and counting gas to simulate the boron uptake anticipated in tumors. Measurements of lineal energy (y) spectra for BNCT in simulated volumes of 1-10 microns diameter show a dose enhancement factor of 4.3 for 30 ppm boron, and a "y" of 250 keV/microns for the boron capture process. Chamber design plus details of experimental and calculated linear energy spectra will be presented.

Boron↗
PubMed1990

An assessment of a film enhancement system for use in a radiation therapy department.

The clinical uses of a radiotherapy film enhancement system are explored. The primary functions of the system are to improve the quality of poorly exposed simulator and portal films, and to perform comparisons between the two films to determine whether patient or block positioning errors are present. Other features include: the production of inexpensive, high quality hardcopy images of simulation films and initial portal films for chart documentation, the capacity to overlay lateral simulation films with sagittal MRI films to aid in field design, and a mode to zoom in on individual CT or MRI images and enlarge them for video display during chart rounds or instructional sessions. This commercially available system is comprised of a microcomputer, frame grabber, CCD camera with zoom lens, and a high-resolution thermal printer. The user-friendly software is menu driven and utilizes both keyboard and track ball to perform its functions. At the heart of the software is a very fast Adaptive Histogram Equalization (AHE) routine, which enhances and improves the readability of most portal films. The system has been evaluated for several disease sites, and its advantages and limitations will be presented.

Humans↗
PubMed1988

Boron neutron capture therapy of a murine melanoma.

Boron neutron capture therapy has been carried out on BALB/c mice carrying the Harding-Passey melanoma s.c. on the thigh. p-Boronophenylalanine (BPA), a boronated analogue of natural melanin precursors, was used to target boron selectively to melanoma. BPA was administered to the mice either via i.p. injection or p.o. by intubation. 10B concentrations in tumor ranged from 15 to 40 ppm depending on the route and timing of administration. Irradiations with a predominantly thermal neutron beam were performed at the Brookhaven Medical Research Reactor. In the absence of BPA, only transient tumor growth delays were observed at low neutron fluences. At 5 x 10(16) n/m2, 4 of 22 tumors irradiated in the absence of BPA underwent long-term tumor growth control; after p.o. administration of BPA (40 ppm 10B in the tumor), the fraction of tumors controlled increased to 11 of 19. The average dose to the tumor in the latter group was 17.8 Gy, of which 14.8 Gy were due to the 10B neutron capture reaction. The biological effectiveness of the absorbed dose from the neutron capture reaction, at the 50% tumor control level, was found to be twice that of 100 kVp X-rays.

Animals↗
PubMed1987

Technical structure of a radiotherapy protocol.

Multi-institutional cooperative group trials require conformity to a uniform set of therapeutic guidelines so that all patients entered on the study are treated the same regardless of which participating center enters the case. This can come about only if an unambiguous, clearly defined treatment program is included in the protocol. Examples of confusing protocol guidelines from recent Group studies demonstrate how well-meaning participants can inadvertently deviate from study requirements. The Quality Assurance Review Center has developed an outline for the radiotherapy component of a study which has alleviated this problem considerably.

Clinical Trials as Topic↗
PubMed1985

Impact of a dosimetry review program on radiotherapy in group trials.

The impact of a quality assurance program on protocol compliance has been explored. A sample of 2258 patients, who received radiation therapy on 18 different NCI funded protocols, was selected for this study from the more than 6200 cases reviewed by the Quality Assurance Review Center (QARC) from 1974 to 1983. Analysis of this sample reveals a significant decrease in the protocol non-compliance rate as a function of QA participation time (35% down to 5%). The educational impact of the QA program is demonstrated by the drop in the protocol dose deviation rate from 11.4% (before QARC feedback) to 3.6% (after feedback, p less than .001). The corresponding drop in protocol deviations in treatment volume is from 21.5% to 10.5% (p less than .001). The effect of the "on-treatment" review process is studied; it is demonstrated that this process cuts the rate of major deviations in half. The technical discrepancies in dose are also analyzed and discussed.

Clinical Trials as Topic↗
PubMed1979

A computerized three-dimensional treatment planning system utilizing interactive colour graphics.

A new computerized radiation treatment planning system has been developed to aid in three-dimensional treatment planning. Using interactive colour graphics in conjunction with a DPD 11/45 computer, the system can take multiple transverse contours and construct a perspective display of the treatment region showing organ surfaces as well as cross-sectional contours. With interactively selected orientations, the display allows easy perception of the relative positioning of the treatment volume and neighbouring anatomy. For external beam treatment planning, interactive computer simulation is used to select diaphragm sizes which best conform to the target area while avoiding sensitive structures. Dose calculations for the selected beams are carried out on multiple transverse planes. The calculational planes and surfaces are displayed in perspective with radiation dosage displayed in an interactively manipulated colour display. Altogether the system provides an easy assessment of the volume to be irradiated, interactive selection of optimal arrangements of treatment fields and a means for visualizing and evaluating the resulting dose distributions.

Color↗
PubMed1979

Contrast enhancement of high-energy radiotherapy films.

An order-of-magnitude improvment in the contrast of high-energy localization and verification films has been achieved through the application of a simple, inexpensive, contrast enhancement technique. The method involves making reversal contact "prints" of the original film onto ordinary X-ray fi-m with equipment commonly available in any radiotherapy department. This results in "gamma multiplication". The theory as well as several applications of this effect are presented.

Humans↗
PubMed1978

A computer-assisted three-dimensional treatment planning system.

The three-dimensional treatment planning system developed at the Rhode Island Hospital visualizes the spatial interrelationships of the radiation beam, the tumor, and the adjacent organs within the patient. It is possible to rotate and vary the scale of the display to better comprehend the extent of these structures. By viewing the display as if from along the radiation beam, one can design shaped treatment fields which best suit the three-dimensional nature of the disease. With this system, it is possible to reduce the volume of normal tissue which would typically be irradiated if two-dimensional treatment planning techniques and assumptions were employed.

Computers↗
PubMedDate not supplied

Polyacrylamide-based phantoms as tissue substitute in experimental radiation physics.

Polyacrylamide-based tissue-equivalent phantoms simulating cortical bone and muscle are described. The equivalency is based upon similar elemental composition and density, and partial similarity in the morphology of bone. Satisfactory results were obtained when the phantoms were tested at low (20 keV) and high (15 MeV) gamma radiation. Applicability of this phantom material to neutron transport is discussed. The material can be molded and shaped and its composition is easily modified by altering the proportions of the constituents. Trace elements or radionuclides are easily added. Details of the physical and radiation characteristics of the formulated systems are given together with the manufacturing procedures.

Acrylic Resins↗
PubMedDate not supplied

A quantitative assessment of portal film contrast as a function of beam energy.

Portal film contrast on a specially designed test phantom has been studied as a function of photon beam energy and object-to-film distance. The results provide important insights into the physical processes responsible for image contrast. In particular, theoretical calculations of Compton scatter reactions in the phantom can be used to predict visual film contrast. Good agreement between theory and experiment can be achieved by evaluating the double differential Compton cross sections [d sigma (E,theta)/dE d theta] in the test object without resorting to variable parameters or artificial normalization. These calculations demonstrate the importance of low-energy photons, object-to-film distance, and object size on portal film contrast.

Biophysical Phenomena↗
PubMedDate not supplied

Continuous three-dimensional radiation dosimetry in tissue-equivalent phantoms using electron paramagnetic resonance in L-alpha-alanine.

A new tissue-equivalent phantom material has been developed which also acts as a dosimeter. The new phantom material has a similar elemental composition to that of soft tissue and has a density 1.1 g/cm3. The phantom has an agar-gel base, and contains crystallized L-alpha-alanine which traps radiation-induced free radicals. Samples from the phantom were analyzed by an electron paramagnetic resonance (EPR) spectrometer and the intensity of the EPR signal was related to the absorbed dose. When calibrated, the phantom material acts as a dosimeter, with applications in radiation therapy.

Alanine↗
PubMedDate not supplied

Quantitative evaluation of a portal film contrast enhancement technique.

A study was conducted to evaluate the subjective improvement in portal film image quality resulting from the contact copy contrast enhancement technique which was introduced six years ago. Five observers were asked to identify and orient polyvinyl chloride cylinder images on both original and contrast-enhanced portal films taken with a 10-MeV linear accelerator. Fixed reviewing periods (T) were alloted of 20, 40, and 60 s as well as unlimited viewing time in order to increase the clinical relevance of this comparison. A scoring system and a probability representation were used to compare the original and enhanced films as a function of T. The results show a substantial increase in object detectability for the enhanced films at the short viewing times (T = 20, 40, and 60 s). For longer times (T greater than or equal to 80 s) the object detectability for enhanced and original films is not statistically different.

Humans↗
PubMedDate not supplied

The variability of clinical thermoluminescent dosimetry systems: a multi-institutional study.

Thirty-two radiotherapy centers in the USA and Canada cooperated in a study of the variability of clinical thermoluminescent dosimetry (TLD) systems. The primary purpose of the survey was to ascertain the accuracy of TLD for the determination of in vivo dose measurements. Each participating institution provided two TLD packets for irradiation on a Clinac 4, at a prearranged time. Two batch irradiations were made. Thirty-two TLD packets, one from each institution, were uniformly irradiated to a dose of 22.35 cGy (known by us, but not by the participants). A second group of 32 packets were likewise irradiated to a dose of 179.0 cGy. Participants were told only that their TLD's would be irradiated to doses between 10 and 50 cGy, and 100 to 200 cGy. TLD's were then returned to the institutions of origin for readout, and the doses reported to us for analysis. Calibration factors, readout and annealing procedures, etc., were all established independently by each participant. Although these procedures varied widely between institutions, the mean values of the reported doses were within 5% and 3% of the expected values for the low and high doses, respectively. Standard deviations in the reported doses were 10% and 5%. Also of interest, however, is the finding that 22% (i.e., 14 out of 64) of the dose reportings were in error by more than 10%. The implications of these findings vis à vis radiotherapy are discussed.

Evaluation Studies as Topic↗
PubMedDate not supplied

The energy response of agar-alanine phantom dosimeter to gamma radiation.

Calculations of the energy response of an electron paramagnetic resonance (EPR) signal induced by gamma radiation in an agar-alanine phantom dosimeter are presented. Theoretically calculated slopes of the EPR signal calibration lines are comparable with those obtained experimentally for low-(50 kVp), medium-(662 keV), and high-(15 MVp) energy photons. The sensitivity of the phantom dosimeter (EPR signal amplitude/Gray) varies less than 2% within the 150- to 20-MeV energy range. For energies above 150 keV, the influence of variations in the size of alanine crystals is negligible.

Agar↗