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Biomedical subjects

C A Pelizzari

Publications and source records attributed to C A Pelizzari.

15 recordsLinked to original sources
PubMed1992

The use of beam's eye view volumetrics in the selection of non-coplanar radiation portals.

In 3-dimensional treatment planning, beam's eye view (BEV) is used as an interactive tool to define portal entry angles that exclude critical structures while fully encompassing the target volume. With beam's eye view volumetrics (BEV volumetrics), the volume of intersected normal tissues is also calculated and is used as a quantitative tool to choose portal orientations that minimize normal tissue volumes irradiated. The axial beam entry angle and a polar angle (relative to the patient longitudinal axis) are specified to define the central axis orientation. Using BEV volumetrics, we have studied the quantities of normal tissues irradiated when treating tumors in the abdomen, thorax, and pelvis. The reduction of normal tissue irradiated is a strong function of site and patient-specific tumor size and location. Volumetrics combined with BEV is found to be useful in treatment planning because it (a) provides quantitative information needed in rationally choosing portal entry angles, (b) provides a near interactive speed approach to understanding the relative merits of different multiple field plans, and (c) compliments the information provided by the more time-consuming generation of dose volume histograms.

Humans↗
PubMed1992

Beam's eye view volumetrics: an aid in rapid treatment plan development and evaluation.

A well-designed treatment plan fully irradiates the target to the prescribed dose while minimizing radiation to adjacent critical structures. Beam's eye view is an important component of treatment planning systems because it provides the operator with tools needed to achieve this goal. Through interactive manipulation of displays, the planner uses beam's eye view to adequately cover the target volume while geometrically avoiding certain critical, normal structures. A factor not considered in current beam's eye view programs is the fractional volume of each structure irradiated given a specified beam direction. We have incorporated a rapid volume calculation capability in our beam's eye view program, and have applied it to provide a quantitative aid to treatment planning development and evaluation. Treatment planning of lung tumors has been studied using this tool. Volumes of lung and spinal cord treated as a function of portal angle may be calculated much more rapidly than dose volume histograms and yet provide quantitative indices which follow the trends of dose volume histograms as a function of field angle. Plots of normal tissue volume irradiated as a function of field angle identify the optimal angle to minimize irradiated volume of a structure at a glance. For multiple field plans, a bitmap approach identifies areas treated by various combinations of beams. Volumetrics combined with beam's eye view are useful in treatment planning because they (a) provide quantitative information needed in choosing and optimizing portal entry angle (b) provide an interactive approach to understanding the relative merits of different multiple field plans and (c) complement the information provided by the more time consuming generation of dose volume histograms. The clinical application of this tool in treatment planning is presented.

Computer Graphics↗
PubMed1991

Computer-assisted superimposition of magnetic resonance and high-resolution technetium-99m-HMPAO and thallium-201 SPECT images of the brain.

A method for registering three-dimensional CT, MR, and PET data sets that require no special patient immobilization or other precise positioning measures was adapted to high-resolution SPECT and MRI and was applied in 14 subjects (five normal volunteers, four patients with dementia (Alzheimer's disease), two patients with recurrent glioblastoma, and three patients with focal lesions (stroke, arachnoid cyst and head trauma]. T2-weighted axial magnetic resonance images and transaxial 99mTc-HMPAO and 201Tl images acquired with an annular gamma camera were merged using an objective registration (translation, rotation and rescaling) program. In the normal subjects and patients with dementia and focal lesions, focal areas of high uptake corresponded to gray matter structures. Focal lesions observed on MRI corresponded to perfusion defects on SPECT. In the patients who had undergone surgical resection of glioblastoma followed by interstitial brachytherapy, increased 201Tl corresponding to recurrent tumor could be localized from the superimposed images. The method was evaluated by measuring the residuals in all subjects and translational errors due to superimposition of deep structures in the 12 subjects with normal thalamic anatomy and 99mTc-HMPAO uptake. This method for superimposing magnetic resonance and high-resolution SPECT images of the brain is a useful technique for correlating regional function with brain anatomy.

Alzheimer Disease↗
PubMed1990

Modeling of dose to tumor and normal tissue from intraperitoneal radioimmunotherapy with alpha and beta emitters.

Dose distributions for normal and tumor tissues from intraperitoneally administered radiolabeled antibodies have been calculated for 90-Yttrium (90Y), 131-Iodine (131I), and 211-Astatine (211At). The dose calculations use data on the activity of intraperitoneal fluid administered, the percent injected dose/gm uptake by tumor, biological half life, and a model for diffusion of antibody/radionuclide complex into peritoneal tissues. Calculations are performed for planar and hemispherical tumor shapes, ranging in size to establish the influence of geometry on dose distribution. Calculations for tumor geometry obtained from biopsies are also performed. When the activity is concentrated on or near the tumor surface, the maximum dose to a planar tumor for a 20 mci administration of 90Y is approximately 60 Gy, and falls rapidly to 50% of this value within 1 mm. However, for a hemispherical tumor, the dose is a maximum of 26 Gy, with an average of approximately 20 Gy. The surface dose from 131I (130 mci) is 240 Gy, and diminishes to 20 Gy in .05 cm in the planar case, whereas a hemispherical tumor receives a dose of 90 Gy over a large fraction of the volume, with the distal portions receiving 40 Gy. The surface dose for an administration of 70 mci of 211 At is 450 Gy and decreases to 50% of this value in 30 microns. Both surface geometry and tumor size are important determinants in the heterogeneity of tumor dose, as are the dose administered, antibody uptake, biodistribution, and residence time factors. These initial studies suggest that the size of disease which may be effectively treated is much less than the range of the particle emitted by radiolabeled antibodies. Furthermore, therapy is ultimately limited by the degree to which the antibody/radionuclide complex can diffuse and permeate the tumor.

Antibodies, Monoclonal↗
PubMed1990

Image correlation in oncology.

Image correlation techniques can provide objective spatial registration between multimodality data sets acquired during the planning and follow-up phases of radiation therapy. Correlation of pre-CT/MRI with follow-up CT/MRI and 3D dose matrices may provide insights into normal tissue tolerance. Correlation of SPECT and planar scintigraphs with anatomical maps derived from CT/MRI may be useful in the precise localization of disease and in the evaluation of new modalities, such as radiolabeled monoclonal antibodies, in the diagnosis and treatment of cancer. Correlation of PET and MRI may lead to a more precise understanding of structure-function relationships of the brain. The development and refinement of multimodality image-correlation techniques is a logical step in the evolving role of imaging in radiation therapy.

Brain Neoplasms↗
PubMed1989

Effect of lung-density correction in treatment planning for tangential-fields breast irradiation: a case report.

We report on the effect of lung-density correction on dose distribution in a transverse slice containing the isocenter for tangential-fields breast irradiation. In this case study we analyzed the target coverage as well as hot spots for four types of treatment plans: Plan 1 assumes uniform unit density throughout, Plan 2 utilizes all the treatment parameters of Plan 1, but takes into account the lower lung density. Plan 3 is generated by optimizing the dose distribution in the presence of the lower lung density, and Plan 4 is an improvement on Plan 3 by using custom instead of standard wedges. Our analysis shows that consideration of the lower lung density is important for optimal treatment planning for the breast and that specially designed wedges can improve the dose distribution.

Breast Neoplasms↗
PubMed1989

The brain: integrated three-dimensional display of MR and PET images.

Three patients with intractable epilepsy, two with brain tumors, and one with encephalitis were imaged with magnetic resonance (MR) and positron emission tomography (PET). MR data were used to construct a three-dimensional (3D) computer model of the brain surface depicting the precentral (movement), postcentral (sensation), left inferior frontal (speech), and left superior temporal (hearing) gyri. PET-derived measurements of average surface metabolism were encoded as colors and mapped onto the 3D model by means of a retrospective technique for registering the two scans. The integrated 3D model depicted the location of PET-detected metabolic abnormalities with respect to the gyral anatomy visualized with MR. In each case, the predicted relationships were confirmed intraoperatively by means of inspection of the brain and electroencephalography. Multimodality 3D displays are likely to be particularly valuable for interpreting PET studies of epileptic patients and others with normal MR anatomy.

Brain↗
PubMed1988

Retrospective geometric correlation of MR, CT, and PET images.

Magnetic resonance imaging, computed tomographic, and positron emission tomographic studies of the brain provide complementary information, and many patients undergo more than one of these studies during the course of their diagnostic workup and treatment. A new technique for quantitative geometric correlation of such studies makes it possible to create integrated multimodality images by mapping features from one image onto an image obtained with another modality. The coordinate transformation between any pair of images is found by a semiautomatic algorithm for matching models of the patient's external surface as depicted in the two data sets. The resultant hybrid images, which combine complementary features of different studies, are often more useful for diagnosis and treatment planning than are the original single-modality images. The algorithm can also be used for spatial registration of baseline studies with follow-up images created with the same modality, which allows tracking of a lesion to detect subtle interval changes in size and shape. This technique can be applied to images acquired in routine clinical practice, since it is completely retrospective and does not necessitate special positioning or landmarking of the patient.

Adolescent↗
PubMedDate not supplied

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↗
PubMedDate not supplied

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↗
PubMedDate not supplied

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↗
PubMedDate not supplied

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↗