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Biomedical subjects

L E Reinstein

Publications and source records attributed to L E Reinstein.

At least 37 records · Page 2Linked to original sources
PubMed1995

A new isocenter shift method for ideal geometric matching of two adjacent fields.

The most commonly used technique for matching two adjoining parallel opposed fields has been geometric matching with a skin gap calculation. Many modifications have been suggested in order to minimize the shortcomings of this technique. Most of these, however, are more complex and time consuming in clinical practice, with little dosimetric improvement. We propose a simple new method for adjacent field abutment that eliminates hot and cold spots due to different beam divergences. This method is based upon the use of a single match plane for both the cephalad and caudad parallel opposed beams. The divergence angle of these opposed beams is forced to be equal at the junction through the use of the same field length and the same target axis distance (TAD). For the isocentric treatment case, the procedure is summarized as follows. After setting up the cephalad AP/PA fields to midplane in the conventional manner, the patient support couch is shifted longitudinally in the cephalad direction by a precise distance equal to the cephalad field length. The superior collimator of the caudad field is kept the same as for the cephalad field to ensure equal divergence angles. The actual irradiated volume of the caudad field is adjusted as needed by a large block or an asymmetric jaw. An analogous procedure is described for the nonisocentric case. This new isocenter shift method culminates in several distinct advantages over the other geometric methods.(ABSTRACT TRUNCATED AT 250 WORDS)

Film Dosimetry↗
PubMed1995

Monitor unit calculation for large wedged high-energy photon beams.

With the modern high-energy linear accelerators, the following beam characteristics have to be taken into account in the monitor unit (MU) calculation of a wedged treatment: (i) the field size dependence of wedge factors; (ii) the changes in depth dose and maximum build-up depth (dmax) induced by wedges; and (iii) the field size dependence of dmax. The incorporation of a field size specific wedge factor in an MU calculation is straightforward. Effects (ii) and (iii) however, often cause confusion and inconsistency in the choices of the reference depth for wedge factors and the normalization depth for wedged depth dose, and consequently can lead to inconsistent MU calculation formalism with additional efforts of up to 7% in the delivered dose. In this note, we illustrate a derivation of an exact central axis MU calculation for wedged treatments, which correctly accounts for the effects mentioned above.

Biophysical Phenomena↗
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↗
PubMed1983

Quality control of radiotherapy in acute lymphocytic leukemia protocol treatment: experience with 610 cases.

Quality assurance programs are necessary in multi-institutional cooperative group clinical trials to ensure that possible inter-institutional differences in selection, treatment and evaluation of patients will not erode the statistical assessment of these clinical trials. The Radiotherapy Committee of the Cancer and Leukemia Group B examined the evaluability and appropriateness of treatment of patients entered into two protocols for childhood acute lymphocytic leukemia, 7411 prior to and 7611 after the development of a quality assurance review program. Of the 348 patients entered into 7411, 37% were evaluable and 26% were appropriately treated in 1974 when the protocol opened. This rose to 53 and 35% in the last year of the study. On the other hand, in 7611 with an ongoing quality assurance program, the evaluability rate initially was 63% and rose to 73% and the appropriateness rate rose from 37 to 61%. This change in performance which was statistically significant at the P = 0.001 level is attributed to the impact of the Quality Assurance Review Center correspondence. Improvement in performance occurred almost entirely in the principal centers and not in satellite institutions. This difference in performance was statistically significant at the P = 0.05 level, indicating that adherence to protocol requirements increases with increased participation in studies.

Child↗
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↗