Treatment planning for heavy ion radiotherapy.
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Computers↗
Biomedical subjects
G T Chen
Publications and source records attributed to G T Chen.
Initiation of human parturition. IX. Progesterone metabolism by placentas of early and late human gestation.
In in vitro studies it was found that, in the presence of added NADPH, the human placenta metabolizes progesterone to 20alpha-hydroxy-4-pregnen-3-one at increasing rates as pregnancy advances. A fivefold increase in 20alpha-hydroxysteroid oxidoreductase activity is observed in term placentas compared with the enzymic activity of placentas of 12 to 20 weeks' gestation (368 +/- 53 pmoles/mg protein/hr vs 71 +/- 8 pmoles/mg protein/hr). The 5alpha-reductase and 3beta-hydroxysteroid oxidoreductase activities were similar in placentas obtained from early and late human pregnancies.
20-Hydroxysteroid Dehydrogenases↗
Initiation of human parturition. VI. Identification and quantification of progesterone metabolites produced by the components of human fetal membranes.
The fetal membranes play a central role in the initiation of human parturition, a role that may be subserved in part by quantitative changes in progesterone metabolism. In order to identify and to quantify the metabolites of progesterone produced by the components of the human fetal membranes, amnion and chorion laeve tissues and homogenates were incubated with [3H]progesterone in the presence of added NADPH. The radioactive metabolites, 20alpha-hydroxy-4-pregnen-3-one, 5alpha-pregnane-3,20-dione and 3beta-hydroxy-5alpha-pregnan-20-one, were isolated and identified by derivative formation, a combination of chromatographic techniques, and by crystallization to constant specific activity after addition of authentic standards. A simplified technique of metabolite quantification was developed that involves one thin layer chromatographic procedure and liquid scintillation assay of radioactivity. The accuracy of this method was established by comparison with data obtained using classical techniques. This study demonstrates the presence of human fetal membranes 5alpha-reductase, 20alpha-hydroxysteroid oxidoreductase, and 3beta-hydroxy-steroid oxidoreductase, and a qualitative difference between amnion and chorion laeve.
20-alpha-Dihydroprogesterone↗
Initiation of human parturition. VIII. Metabolism of progesterone by fetal membranes of early and late human gestation.
A decreased rate of progesterone metabolism is detected in human fetal membranes several weeks preceding normal parturition at term. A 10- to 20-fold decrease in 20alpha-hydroxysteroid oxidoreductase activity and a 2- to 6-fold decrease in 5alpha-reductase activity are observed in human amnion and chorion laeve after 33 weeks' gestation.
Extraembryonic Membranes↗
Initiation of human parturition--VII Partial characterization of progesterone metabolizing enzymes of human amnion and chorion laeve.
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20-Hydroxysteroid Dehydrogenases↗
Superficial doses in treatment of breast with tangential fields using 4MV x-rays.
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Breast Neoplasms↗
Aanlysis of dose distributions in whole body superficial electron therapy.
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Electrons↗
Image correlation techniques in radiation therapy treatment planning.
A technique to spatially correlate multi-modality or serial imaging studies of the head is described. Surface fitting of a well defined structure in different imaging studies is used to determine the optimal three dimensional transformation between the coordinate systems. The transformation is then used to map volumes of interest between studies or to reslice the studies along comparable planes. The approach is feasible in the presence of variations in slice thickness, pixel size, imaging plane, or head position, and for correlations between different modalities. Correlations have been performed between serial CT, CT/MRI, and PET/CT/MRI studies. Phantom studies and clinical cases are presented. Accuracy is typically on the order of the sum of the pixel sizes between studies. Applications in radiation therapy treatment planning are described.
Brain Neoplasms↗
Accurate three-dimensional registration of CT, PET, and/or MR images of the brain.
A surface matching technique has been developed to register multiple imaging scans of the brain in three dimensions, with accuracy on the order of the image pixel sizes. Anatomic information visualized in X-ray CT and magnetic resonance images may be integrated with each other and with functional information from positron emission tomography. Anatomical structures and other volumes of interest may be mapped from one scan to another, and corresponding sections through multiple scans may be directly compared. This capability provides a novel quantitative method to address the fundamental problem of relating structure to function in the brain. Applications include basic and clinical problems in the neurosciences and delivery and assessment of brain tumor therapy.
Brain↗
Retrospective fusion of radiographic and MR data for localization of subdural electrodes.
Prior to epilepsy surgery, subdural electrodes are often implanted and monitored for a few days to identify the focus of abnormal electrical activity. During the implantation and subsequent brain resection, there may be uncertainty about the exact location of the electrodes with respect to features of brain anatomy such as specific gyral convolutions or lesions. In experiments with a phantom and patients, implanted electrodes were imaged with multiplanar skull radiographs (or CT scans). After retrospective registration with preimplantation MR data, the electrodes were mapped from these studies onto an MR-derived three-dimensional brain model. The resulting multimodality displays showed the relationship of the electrodes to brain anatomy. In one patient the position of each electrode with respect to a metabolic lesion was also displayed by mapping preimplantation PET data onto the same brain model. This new display of electrode positions may strengthen the interpretation of subdural electrical recordings and thereby reduce uncertainty in planning the resection of epileptic tissue.
Adult↗
Accuracy of object depiction and opacity transfer function optimization in CT volume-rendered images.
Volume rendering is a visualization technique that has important applications in diagnostic radiology and radiotherapy. A methodology is presented for (a) evaluation of the quantitative accuracy of representation of known objects in volume-rendered scenes and for (b) optimization of the opacity transfer function to achieve the most accurate representation of a particular structure. Results using this methodology are shown for structures representing each of the major tissue interfaces and are discussed.
Algorithms↗
High-resolution dosimetry with stimulated phosphorescence.
Thermally stimulated radiophosphorescence has been studied as a means of high-resolution dosimetry. Small grains of CaSO4:Mn phosphor, embedded in a thin Teflon tape, constitute the dosimeter. The light emitted after irradiation is measured with a photomultiplier coupled to the eyepiece of a scanning microscope. With CaSO4:Mn, the phosphorescence at room temperature is sufficient for measurement after doses in excess of 3000 rads. The spatial resolution of the technique is about 0.2 mm. The method has been tested by measuring the dose distributions from a radium needle and a beta-emitting eye applicator.
Calcium↗
Measurements and calculations of the influence of thin inhomogeneities on charged particle beams.
The predictions of an analytic technique for calculating fluence and dose distributions beneath thin inhomogeneities are presented for a number of structures, including a rectangular cavity or bar, a cylinder, a disk, and an angled or diffuse edge. Experiments with both electrons and protons for several geometries are presented and compared with predictions based on this technique. We offer some clinical guidelines for avoiding large perturbations due to scattering effects.
Elementary Particles↗
Beam scanning for heavy charged particle radiotherapy.
An important aspect of heavy charged particle radiotherapy is its ability to localize dose to the target volume. Current techniques generally employ beam delivery schemes which use range modulated beams in which the Bragg peak is spread out over a range of depths. The range modulation is constant over the entire beam cross section. This paper examines the potential gain from the use of variable range modulation over the beam cross section which can be achieved through beam scanning. An analytic technique has been developed to calculate a gain factor, related to integral dose, for a number of different charged particle beams. The dependence of the gain factor on tumor depth, diameter, and size has been examined. These analytic results have been compared with computer calculations of treatment plans simulating beam scanning and fixed modulation delivery techniques for actual clinical cases. The rationale for beam scanning, and its potential impact on tumor control is discussed.
Carbon↗
Correlation of projection radiographs in radiation therapy using open curve segments and points.
A method for determining differences in patient position between projection radiographs such as those routinely used in radiation therapy has been developed. Determination of a transformation relating two radiographs permits registration of simulation and portal images and the transfer of information between them. The algorithm is based on spatially registering segments of open curves or points seen on both images, and does not require identification of corresponding curve endpoints. The method as implemented is both fast and accurate. After user definition of the curves or points to be registered, the optimal transformation is calculated in approximately 1 s. Calculational experiments indicate that corresponding points on open curves are registered to better than 2 mm, even when random errors (FWHM 1 mm) in digitization are included. Experiments on the registration of clinical portal and simulation images (pixel size = 0.5 by 0.5 mm) indicate an accuracy on the order of 2 mm or less in translation and 2 deg or less in rotation. Analysis of portal and simulation radiographs of the brain, thorax, and pelvis indicates this algorithm to be robust and clinically applicable. The rapid and accurate registration of portal and simulation images is potentially important in the application of real time portal imaging devices in radiation therapy.
Algorithms↗
Microdosimetric concepts in radioimmunotherapy.
In microdosimetry particular emphasis is placed on the stochastic fluctuation of dose in small target volumes such as individual cell nuclei or chromatin fiber, and their relevance to radiobiologic toxicity. Thus microdosimetry is intimately associated with models of radiation action. There are three principal areas where microdosimetry has been applied: (1) radiation protection, (2) high LET radiotherapy, e.g., neutron therapy, and (3) incorporated radionuclides, and in this latter category the importance of microdosimetry to the radiobiology of radiolabeled antibodies is becoming increasingly recognized. The objective of microdosimetry is the complete characterization of energy deposition within all target volumes throughout the tissue of interest. The importance and relevance of this pursuit will depend upon the properties of the radionuclide emissions and the spatial distribution of the radionuclide relative to the target volumes. If the distribution of internal emitters within both malignant and normal tissue is uniform, the application of microdosimetry to radioimmunotherapy (RIT) is limited to alpha-emitters and Auger emitters. Under such circumstances the traditional MIRD formalism for the evaluation of tumor and tissue doses from the commonly used beta-emitters is entirely adequate. This, however, is rarely the case. When the distribution of radiolabeled antibody is nonuniform, techniques of dose averaging over volumes greater in size than the individual target volumes can become inadequate predictors of the biological effect. The concepts, methods, and realm of applicability of microdosimetry within the field of radioimmunotherapy are emphasized in this paper.
Humans↗
An overview of imaging techniques and physical aspects of treatment planning in radioimmunotherapy.
Planar and tomographic imaging techniques and methods of treatment planning in clinical radioimmunotherapy are reviewed. In clinical trials, the data needed for dosimetry and treatment planning are, in most cases, obtained from noninvasive imaging procedures. The required data include tumor and normal organ volumes, the activity of radiolabeled antibodies taken up in these volumes, and the pharmacokinetics of the administered activity of radiolabeled antibodies. Therefore, the topics addressed in this review include: (1) Volume determination of tumors and normal organs from x-ray-computed tomography and magnetic resonance imaging, (2) quantitation of the activity of radiolabeled antibodies in tumors and normal organs from planar gamma camera views, (3) quantitative single-photon emission computed tomography and positron emission tomography, (4) correlative image analysis, and (5) treatment planning in clinical radioimmunotherapy.
Humans↗
Dosimetry of intraperitoneally administered radiolabeled antibodies.
Intraperitoneal and intracavitary radioimmunotherapy differ from other approaches of radioimmunotherapy in that high activity and dose gradients exist near the solution/tumor interface. Dose to tumor and normal tissue at the interface is a function of depth and is due to three major components: (1) the activity concentration of the administered radiolabeled antibody solution as a function of time within the compartment; (2) the spatial distribution of antibody/radionuclide complex as a function of depth and time as the biomolecules bind to and permeate tumor/normal tissues; and (3) the physical characteristics of the radionuclide in relation to depth of antibody penetration. In this review, the biological and physical aspects of intraperitoneally administered radiolabeled antibodies are discussed, and the state of experimental and calculational studies for this site is described. Areas requiring future investigation are examined, and recommendations are made regarding the type of measurements and calculations which are required for accurate dosimetry.
Antibodies, Monoclonal↗