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Biomedical subjects

C A Pelizzari

Publications and source records attributed to C A Pelizzari.

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

Evaluation of changes in the size and location of the prostate, seminal vesicles, bladder, and rectum during a course of external beam radiation therapy.

PURPOSE: To document the size and location of the prostate, seminal vesicles, bladder, and rectum throughout the course of external beam radiotherapy. The frequency and range of motion of these organs are quantified. METHODS AND MATERIALS: Ten patients with localized carcinoma of the prostate had conventional simulation followed immediately by a treatment planning computed tomography scan (TPCT0). Once treatment was initiated, each patient had a weekly CT (TPCT1-N) before or after his daily treatment. Anatomical structures from CT were delineated on a computer workstation for analysis. The serial CT sets were spatially registered to the initial scan using image correlation software that brings into congruence the bony pelvis of the different scans. The location of the prostate, seminal vesicles, bladder, and rectum on subsequent scans were compared to TPCT0, as well as to each other. RESULTS: Prostate volumes were observed to vary by an average of +/- 10% during the course of radiation therapy, while the seminal vesicle volumes varied by as much as 100%. Bladder and rectal volumes varied by +/- 30%. Compared to TPCT0, movement of the prostate was demonstrated in all patients. Quantitation of the center-of-mass (CM) showed motion of less than 1 mm in the left-right direction, while motion ranging from 0 to +/- 1 cm was observed in the anterior-posterior and superior-inferior directions. The individual standard deviations of these motions varied from approximately 1-5 mm. These variations were correlated to changes in the dimensions of the bladder and rectum. CONCLUSIONS: Changes in the location of the prostate, seminal vesicles, and normal tissue volumes during the course of radiation therapy occur and have dosimetric consequences that may impact tumor control and normal tissue complication probabilities. Conformal therapy for prostate cancer will require the incorporation of knowledge of the anatomic relationships of these structures as a function of time. Therefore, these uncertainties must be taken into account when designing treatment plans and in considering dose escalation trials.

Humans↗
PubMed1995

Comparison of static conformal field with multiple noncoplanar arc techniques for stereotactic radiosurgery or stereotactic radiotherapy.

PURPOSE: Compare the use of static conformal fields with the use of multiple noncoplanar arcs for stereotactic radiosurgery or stereotactic radiotherapy treatment of intracranial lesions. Evaluate the efficacy of these treatment techniques to deliver dose distributions comparable to those considered acceptable in current radiotherapy practice. METHODS AND MATERIALS: A previously treated radiosurgery case of a patient presenting with an irregularly shaped intracranial lesion was selected. Using a three-dimensional (3D) treatment-planning system, treatment plans using a single isocenter multiple noncoplanar arc technique and multiple noncoplanar conformal static fields were generated. Isodose distributions and dose volume histograms (DVHs) were computed for each treatment plan. We required that the 80% (of maximum dose) isodose surface enclose the target volume for all treatment plans. The prescription isodose was set equal to the minimum target isodose. The DVHs were analyzed to evaluate and compare the different treatment plans. RESULTS: The dose distribution in the target volume becomes more uniform as the number of conformal fields increases. The volume of normal tissue receiving low doses (> 10% of prescription isodose) increases as the number of static fields increases. The single isocenter multiple arc plan treats the greatest volume of normal tissue to low doses, approximately 1.6 times more volume than that treated by four static fields. The volume of normal tissue receiving high (> 90% of prescription isodose) and intermediate (> 50% of prescription isodose) doses decreases by 29 and 22%, respectively, as the number of static fields is increased from four to eight. Increasing the number of static fields to 12 only further reduces the high and intermediate dose volumes by 10 and 6%, respectively. The volume receiving the prescription dose is more than 3.5 times larger than the target volume for all treatment plans. CONCLUSIONS: Use of a multiple noncoplanar conformal static field treatment technique can significantly reduce the volume of normal tissue receiving high and intermediate doses compared with a single isocenter multiple arc treatment technique, while providing a more uniform dose in the target volume. Close conformation of the prescription isodose to the target volume is not possible using static uniform conformal fields for target shapes lacking an axis of rotational symmetry or plane of mirror symmetry.

Brain Neoplasms↗
PubMed1995

Intermodality, retrospective image registration in the thorax.

UNLABELLED: The purpose of this study was to develop an accurate, retrospectively applicable procedure for registering thoracic studies from different modalities in a short amount of time and with minimal operator intervention. METHODS: CT and PET studies were acquired from six patients. The pleural surfaces in both image sets were determined by segmenting based on 50% of the maximum soft-tissue value in the study. These surfaces were converted into three-dimensional volumes and used to register the CT and PET studies in three dimensions using a sum of least squares fitting approach. The registered PET study was then displayed in a hot metal scale overlayed on top of the gray scale CT study. The accuracy of the fit was evaluated through a phantom study and preliminary clinical evaluation. RESULTS: A phantom study was performed to determine the limits of this technique. The accuracy was determined to be less than 2.3 mm in the x and y direction and 3 mm in the z direction. Preliminary clinical evaluation was also performed with encouraging results. CONCLUSION: This technique accurately registers PET and CT images of the thorax, retrospectively, without the need for external fiducial markers or other a priori action.

Aged↗
PubMed1994

Unfolding patient motion with biplane radiographs.

A method of unfolding patient movement between biplane radiographs is presented. This method requires biplane projections of two points with a known separation to determine a translation motion or biplane projections of two or three point pairs to determine a general patient motion. Such a point pair can be provided by two ends of a line source or two radiopaque marks, with a fixed distance between them. The point pairs can be taped on skin, implanted in the target volume, or embedded in the bony structures. After obtaining the point locations on each film, the three-dimensional coordinates of points of interest at the instant of each view can be reconstructed, with an error of less than 0.5 mm. The motion parameters, characterized by a pseudotranslation vector and three axial rotational angles for the region of interest relative to the machine coordinate system, are also provided. In comparing with some other reconstruction algorithms, the point pair method can significantly improve source localization or point reconstruction in the presence of patient motion. Computer simulations and phantom experiments demonstrates the feasibility and accuracy of the method.

Brachytherapy↗
PubMed1994

Computer-aided geometric reconstruction of Fletcher-Suit source positions.

A computer-aided method for reconstruction of the source positions of a Fletcher-Suit applicator has been developed. The tandem source positions are determined by digitizing of the tip and two arbitrary points on the shaft from each of two orthogonal simulator films. A colpostat source position is reconstructed by digitizing of a single point on the endcap and three arbitrary points on the cylindrical sidewalls of the colpostat on the films. This computer-aided method considers the true projection geometry and applicator shape and permits localization of the source positions to within a mean error of less than 1 mm. Compared with the conventional method, the new approach (1) is more time efficient because only a few easily identified points are digitized, (2) allows localization when the tandem sources are shifted by a spacer or when colpostat sources are difficult to visualize on the lateral film, and (3) is more accurate than the conventional technique because no manual drawing of source positions on films is involved.

Algorithms↗
PubMed1993

Online repositioning during treatment of the prostate: a study of potential limits and gains.

PURPOSE: With on-line portal imaging devices and image registration tools, the verification of radiation field position prior to each treatment becomes technically feasible. In this paper, we analyze the impact of pre-treatment verification and field position adjustment on target coverage and normal tissue sparing. METHODS AND MATERIALS: Port films were compared with corresponding simulation films to determine the magnitude of setup variations in patients treated for prostate cancer. From these data, an analytic function was determined between geometric coverage of the target and field margin size. A paradigm for on-line patient repositioning was employed to generate a new relationship between margin and target coverage. Margins were selected for the situations of normal treatment and on-line repositioning to ensure target coverage. Dose-volume histograms were generated for a typical prostate treatment using these margins. RESULTS: On-line repositioning, when setup errors exceed 1 cm, results in a 6 mm reduction in margin, suggesting that 10% of the volume of bladder and rectum may be spared of high dose. CONCLUSION: The use of on-line imaging and image registration to guide adjustment of patient setup may lead to a reduction in the volume of normal tissues irradiated, and possibly improve the probability of complication-free survival in future treatments.

Computer Simulation↗
PubMed1993

Integrated 3D display of brain surface anatomy and MR spectral data.

We describe a method of displaying the relationship between MR spectral data and an MRI-derived three-dimensional (3D) model of the same subject's brain surface. In this way, biochemical abnormalities in the MR spectra can be localized with respect to specific gyral convolutions (e.g., those associated with movement and sensation), which are best identified on 3D brain models. This was accomplished by retrospectively registering spectral data and MR images, acquired with different head coils. The highly resolved MR images were used to identify the brain surface in the poorly resolved spectral data and to produce a 3D rendition of brain surface metabolite distributions. This was then integrated with an MRI-derived 3D model of brain gyral anatomy. The method was tested on P31 spectral data from a phantom and from a human volunteer.

Adult↗
PubMed1993

Normal brain F-18 FDG-PET and MRI anatomy.

Image registration techniques will become increasingly important in correlative multimodality imaging. In the case of PET, a structural imaging study can be invaluable in correlating structure metabolism relationships. A registered brain atlas of PET and MRI has been developed by the authors that allows clinicians, residents, fellows, and others to refer to a structural abnormality on MRI or metabolic abnormality on PET and correlate it neuro-anatomically.

Brain↗
PubMed1993

A frameless stereotactic approach to neurosurgical planning based on retrospective patient-image registration. Technical note.

A frameless stereotactic device interfacing an electromagnetic three-dimensional (3-D) digitizer to a computer workstation is described. The patient-image coordinate transformation was found by retrospectively registering a digitizer-derived model of the patient's scalp with a magnetic resonance (MR) imaging-derived model of the same surface. This procedure was performed with routine imaging data, eliminating the need to obtain special-purpose MR images with fiducial markers in place. After patient-image fusion was achieved, a hand-held digitizing stylus was moved over the scalp and tracked in real time on cross-sectional and 3-D brain images on the computer screen. This device was used for presurgical localization of lesions in 10 patients with meningeal and superficial brain tumors. The results suggest that the system is accurate enough (typical error range 3 to 8 mm) to enable the surgeon to reduce the craniotomy to one-half the size advisable with conventional qualitative presurgical planning.

Adult↗
PubMed1993

Accuracy of registration of PET, SPECT and MR images of a brain phantom.

Accuracy of a surface-fitting algorithm for three-dimensional image registration of single photon emission computed tomography (SPECT), positron emission tomography (PET), and magnetic resonance (MR) images was tested using a three-dimensional, water-fillable brain phantom. Multislice or volume image sets were acquired for each modality. Small fiducial markers were attached to assess accuracy of surface fitting and provide an alternate fitting technique. A maximum gradient technique was found to work well for SPECT and PET edge detection. Transformation parameters for translation, rotation and scaling were determined by surface fit to match each SPECT and PET scan with MR images. Using the markers, overall translation errors were found to be < 2 mm in each direction and rotational errors < 2 degrees in every case. Errors for specific internal regions were also determined to be < 2 mm for most regions, with only a few fits resulting in errors > 3 mm for some cortical regions. Results indicate surface fitting to be sufficiently accurate for visual comparison of registered images and for enhanced SPECT and PET region of interest (ROI) determination and image reconstruction.

Algorithms↗
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↗