Portal film duplication using instant photography.
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Humans↗
Biomedical subjects
L E Reinstein
Publications and source records attributed to L E Reinstein.
Computer-controlled direct TMR measurement.
It is common practice to derive tissue maximum ratios (TMRs) indirectly by calculation from percent depth dose (PDD) data which are more convenient to measure using currently available automated scanners. A system has been developed, however, for the completely automatic direct measurement of TMR, using an ionization chamber which is rigidly supported at the isocenter of a teletherapy machine. The chamber is immersed in a water phantom which is moved up and down by computer control of the motorized treatment couch. Ionization current is sampled by the computer which simultaneously regulates both the radiation field size and chamber depth. This system provides a means of rapidly measuring and processing complete sets of TMR and output factor values for both square and elongated field shapes. The results of such measurements performed on the Clinac 18 accelerator are described in this paper.
Computers↗
A dosimetry review system for cooperative group research.
The validity of conclusions drawn from multi-institutional radiotherapy studies is dependent upon the degree to which participating hospitals adhere to study requirements. A major effort undertaken by the Quality Assurance Review Center (QARC) assesses whether or not patient data which are deemed evaluable actually conform to the radiotherapy requirements of the research protocol. This paper presents the methods and results of this effort which has been ongoing for the past five years. The Dosimetry Review System (DRS) is a set of computer programs which make use of verified radiation beam data to evaluate the daily dose, total dose, dose uniformity, and TDF for protocol treatment. These programs can be adapted to facilitate and document the routine chart-checking procedures at any large radiotherapy department. The DRS data base includes radiotherapy parameters of 600 teletherapy units at more than 250 institutions in the United States and abroad. The design of the data base, the computerized review process, and the calculational algorithms are discussed.
Computers↗
Portal film quality: a multiple institutional study.
The variation in quality of the several thousand portal films submitted to the Quality Assurance Review Center (QARC) has been substantial. To ascertain the nature and severity of this problem, a detailed study of "whole brain" portal films which were taken at 23 different radiotherapy departments for patients entered on three national leukemia studies was performed. Each film was analyzed in two ways: (a) independent subjective evaluation by four experienced radiotherapists and (b) measurement of objective parameters. Scores from 416 evaluations together with measured parameters were stored in a data base system for easy statistical manipulation. The dependence of perceived film quality on these objective parameters has been correlated and is the subject of this report.
Humans↗
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↗
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↗
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↗
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↗
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↗
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↗
Dose enhancement in buildup region by lead, aluminum, and lucite absorbers for 15 MVp photon beam.
Changes in dose distributions in buildup region resulting from the presence of lead, aluminum, and lucite absorbers above the surface of a polystyrene phantom were evaluated. The surface dose, as a function of the absorber thickness, is presented as well as the influence of the air gap between the lead absorber and the phantom surface. It has been found that the surface dose does not depend on absorber thickness for absorbers thicker than the range of secondary electrons in the absorber material (after corrections for the attenuation of the primary beam in the absorber). Similarly, the depth dose curves in the phantom were elevated only at depths lower than the range of secondary electrons in the phantom. The applicability of the presented data in clinical radiotherapy is discussed.
Absorption↗
Tests of an electron monitor for routine quality control measurements of electron energies.
The depth dose for electrons is sensitive to energy and the AAPM Task Group 24 has recommended that tests be performed at monthly intervals to assure electron beam energy constancy by verifying the depth for the 80% dose to within +/- 3 mm. Typically, this is accomplished by using a two-depth dose ratio technique. Recently, a new device, the Geske monitor, has been introduced that is designed for verifying energy constancy in a single reading. The monitor consists of nine parallel plate detectors that alternate with 5-mm-thick absorbers made of an aluminum alloy. An evaluation of the clinical usefulness of this monitor for the electron beams available on a Varian Clinac 20 has been undertaken with respect to energy discrimination. Beam energy changes of 3 mm of the 80% dose give rise to measurable output changes ranging from 1.7% for 20-MeV electron beams to 15% for 6-MeV electron beams.
Electrons↗
A review of electronic portal imaging devices (EPIDs).
On-line electronic portal imaging devices are beginning to come into clinical service in support of radiotherapy. A variety of technologies are being explored to provide real-time or near real-time images of patient anatomy within x-ray fields during treatment on linear accelerators. The availability of these devices makes it feasible to verify treatment portals with much greater frequency and clarity than with film. This article reviews the physics of high-energy imaging and describes the operation principles of the electronic portal imaging devices that are under development or are beginning to be used clinically.
Humans↗
Energy response of agar-alanine free radical dosimetry to therapeutic electron beams.
Calculations of the energy response of an agar-alanine phantom dosimeter (AAPD) to electrons in the energy range of 0.15-20 MeV together with experimental results at 16 MeV are presented. It is shown that the sensitivity of the EPR dosimeter (EPR signal/Gray) is independent of alanine crystal size and varies less than 2%, in the electron energy range indicated. Thus, the measured free radical density distribution may be used directly as an indication of the absorbed dose distribution in an irradiated phantom.
Agar↗
Calculation of dose distribution near an innovative concentric balloon catheter for endovascular brachytherapy.
PURPOSE: Using a radioactive solution-filled catheter for intravascular irradiation has the potential problem of chemical and radiological toxicity in the case of a balloon rupture. In order to reduce this risk, an innovative concentric balloon catheter was developed. METHODS AND MATERIALS: The concentric balloon was made by inner and outer balloons filled with saline and radioactive solution, respectively. The optimal inner radius was determined by comparing the dose rate reduction vs. the volume reduction for various inner and outer radii for 188Re, 32P, and 90Y solutions. RESULTS: For a balloon with an outer radius of 1.5 mm, there was no advantage of a concentric balloon. For balloons with outer radii of 3.0 and 5 mm, the optimal inner radius was 1.5 and 3 mm, respectively. CONCLUSIONS: With the newly designed concentric balloon, the risk of toxicity can be reduced while keeping the dose rate high enough so that the treatment times within tolerable limits are still maintained.
Brachytherapy↗
Quality assurance programs in clinical trials.
Quality assurance programs attempt to assess the uniformity of compliance with a stated study program so that the results from one institution will indeed be comparable to those of all of the other institutions in the group. In the best situation, it should be easy to compare results from one group to those of any other group and any other studies of the same disease, because the basis of selection of the patient population, the treatment of patients, and the endpoints have been uniformly defined throughout. The evaluation of the end results includes a quantitative assessment of the appropriateness of these parameters. Quality assurance programs document the validity of interinstitutional, intergroup, and international studies. They are time-consuming and costly. They can be ulcerogenic. But, in the end, they are the firm basis upon which the statistical analysis can proceed.
Clinical Trials as Topic↗