Biomedical subjects

B A Fraass

Publications and source records attributed to B A Fraass.

At least 37 records · Page 2Linked to original sources

PubMed1995

A computer-controlled conformal radiotherapy system. II: Sequence processor.

PURPOSE: A sequence processor (SP) is described as part of a larger computer-controlled conformal radiotherapy system (CCRS). The SP provides the means to accept and then translate highly sophisticated radiation therapy treatment plans into vendor specific instructions to control treatment delivery on a computer-controlled treatment machine. METHODS AND MATERIALS: The sequence processor (SP) is a small workstation computer that interfaces to the control computer of computer-controlled treatment machines, and to other parts of the larger CCRS system. The system reported here has been interfaced to a computer-controlled racetrack microtron with two treatment gantries, and also to other linear accelerator treatment machines equipped with multileaf collimators. An extensive design process has been used in defining the role of the SP within the context of the larger CCRS project. Flexibility and integration with various components of the project, including databases, treatment planning system, graphical simulator, were key factors in the development. In conjunction with the planned set of treatment fields, a procedural scripting language is used to define the sequence of treatment events that are performed, including operator interactions, communications to other systems such as dosimetry and portal imaging devices, and database management. RESULTS: A flexible system has been developed to allow investigation into procedural steps required for simulating and delivering complex radiation treatments. The system has been used to automate portions of the acceptance testing for the control system of the microtron, and is used for routine daily quality assurance testing. The sequence processor system described here has been used to deliver all clinical treatments performed on the microtron system in 2 years of clinical treatment (more than 200 patients treated to a variety of treatment sites). CONCLUSIONS: The sequence processor system has enabled the delivery of complex treatment using computer-controlled treatment machines. The flexibility of the system allows integration with secondary devices and modification of procedural steps, making it possible to develop effective techniques for insuring safe and efficient computer-controlled conformal radiation therapy treatments.

Computer Simulation↗

PubMed1995

A computer-controlled conformal radiotherapy system. III: Graphical simulation and monitoring of treatment delivery.

PURPOSE: Safe and efficient delivery of radiotherapy using computer-controlled machines requires new procedures to design and verify the actual delivery of these treatments. Graphical simulation and monitoring techniques for treatment delivery have been developed for this purpose. METHODS AND MATERIALS: A graphics-based simulator of the treatment machine and a set of procedures for creating and manipulating treatment delivery scripts are used to simulate machine motions, detect collisions, and monitor machine positions during treatment. The treatment delivery simulator is composed of four components: a three-dimensional dynamic model of the treatment machine; a motion simulation and collision detection algorithm, user-interface widgets that mimic the treatment machine's control and readout devices; and an icon-based interface for creating and manipulating treatment delivery scripts. These components are used in a stand-alone fashion for interactive treatment delivery planning and integrated with a machine control system for treatment implementation and monitoring. RESULTS: A graphics-based treatment delivery simulator and a set of procedures for planning and monitoring computer-controlled treatment delivery have been developed and implemented as part of a comprehensive computer-controlled conformal radiotherapy system. To date, these techniques have been used to design and help monitor computer-controlled treatments on a radiotherapy machine for more than 200 patients. Examples using these techniques for treatment delivery planning and on-line monitoring of machine motions during therapy are described. CONCLUSION: A system that provides interactive graphics-based tools for defining the sequence of machine motions, simulating treatment delivery including collision detection, and presenting the therapists with continual visual feedback from the treatment machine has been successfully implemented for routine clinical use as part of an overall system for computer-controlled conformal radiotherapy treatment, and is considered a necessary part of the routine treatment methodology.

Computer Graphics↗

PubMed1995

A computer-controlled conformal radiotherapy system. I: Overview.

PURPOSE: Equipment developed for use with computer-controlled conformal radiotherapy (CCRT) treatment techniques, including multileaf collimators and/or computer-control systems for treatment machines, are now available. The purpose of this work is to develop a system that will allow the safe, efficient, and accurate delivery of CCRT treatments as routine clinical treatments, and permit modifications of the system so that the delivery process can be optimized. METHODS AND MATERIALS: The needs and requirements for a system that can fully support modern computer-controlled treatment machines equipped with multileaf collimators and segmental or dynamic conformal therapy capabilities have been analyzed and evaluated. This analysis has been used to design and then implement a complete approach to the delivery of CCRT treatments. RESULTS: The computer-controlled conformal radiotherapy system (CCRS) described here consists of a process for the delivery of CCRT treatments, and a complex software system that implements the treatment process. The CCRS system described here includes systems for plan transfer, treatment delivery planning, sequencing of the actual treatment delivery process, graphical simulation and verification tools, as well as an electronic chart that is an integral part of the system. The CCRS system has been implemented for use with a number of different treatment machines. The system has been used clinically for more than 2 years to perform CCRT treatments for more than 200 patients. CONCLUSIONS: A comprehensive system for the implementation and delivery of computer-controlled conformal radiation therapy (CCRT) plans has been designed and implemented for routine clinical use with multisegment, computer-controlled, multileaf-collimated conformal therapy. The CCRS system has been successfully implemented to perform these complex treatments, and is considered quite important to the clinical use of modern computer-controlled treatment techniques.

Equipment Design↗

PubMed1995

Advanced interactive planning techniques for conformal therapy: high level beam descriptions and volumetric mapping techniques.

PURPOSE: To aid in design of conformal radiation therapy treatment plans involving many conformally shaped fields, this work investigates the use of two methodologies to enhance the ease of interactive treatment planning: high-level beam constructs and beam's-eye view volumetric mapping. METHODS AND MATERIALS: High-performance computer graphics running on various workstations using a graphical visualization system (AVS) have been used in this work. Software specific to this application has been written in standard FORTRAN and C languages. A new methodology is introduced by defining radiation therapy "fields" to be composed of multiple beam "segments." Fields can then be defined as higher-level entities such as arcs, cones, and other shapes. A "segmental cone" field, for example, is defined by a symmetry axis and a cone angle, and can be used to rapidly place a series of beam segments that converge at the target volume, while reducing the degree of overlap elsewhere. A new beam's-eye view (BEV) volumetric mapping technique is presented to aid in selecting the placement of conformal radiation fields. With this technique, the relative average dose within an organ of interest is calculated for a sampling of isocentric, conformally shaped beams and displayed either as a "globe," which can be combined with the display of anatomical surfaces, or as a two-dimensionally mapped projection. The dose maps from multiple organs can be generated, stacked, or composited with relative weightings to aid in the placement of fields that minimize overlap with critical structures. RESULTS: The use of these new methodologies is demonstrated for prostate and lung treatment sites and compared to conventional planning techniques. DISCUSSION: The use of many beams for conformal treatment delivery is difficult with current interactive planning. The use of high-level beam constructs provides a means to quickly specify, place, and configure multiple beam arrangements. The BEV volumetrics aids in the placing of fields, which minimize involvement with critical normal tissues. CONCLUSIONS: Early experience with the new methodologies suggest that the new methods help to enhance (or at least speed up) the ability of a treatment planner to create optimal radiation treatment field arrangements.

Evaluation Studies as Topic↗

PubMed1995

A computer-controlled conformal radiotherapy system. IV: Electronic chart.

PURPOSE: The design and implementation of a system for electronically tracking relevant plan, prescription, and treatment data for computer-controlled conformal radiation therapy is described. METHODS AND MATERIALS: The electronic charting system is implemented on a computer cluster coupled by high-speed networks to computer-controlled therapy machines. A methodical approach to the specification and design of an integrated solution has been used in developing the system. The electronic chart system is designed to allow identification and access of patient-specific data including treatment-planning data, treatment prescription information, and charting of doses. An in-house developed database system is used to provide an integrated approach to the database requirements of the design. A hierarchy of databases is used for both centralization and distribution of the treatment data for specific treatment machines. RESULTS: The basic electronic database system has been implemented and has been in use since July 1993. The system has been used to download and manage treatment data on all patients treated on our first fully computer-controlled treatment machine. To date, electronic dose charting functions have not been fully implemented clinically, requiring the continued use of paper charting for dose tracking. CONCLUSIONS: The routine clinical application of complex computer-controlled conformal treatment procedures requires the management of large quantities of information for describing and tracking treatments. An integrated and comprehensive approach to this problem has led to a full electronic chart for conformal radiation therapy treatments.

Data Display↗

PubMed1995

The development of conformal radiation therapy.

The development and clinical use of conformal radiation therapy, and the application of modern computer-controlled radiation therapy treatment techniques to the delivery of conformal therapy, has been a major research area in the field of radiation oncology in recent years. The introduction of three-dimensional (3-D) patient imaging, 3-D treatment planning systems, computer-controlled treatment machines equipped with multileaf collimators, and the continuing increase in computer power and software sophistication has finally allowed the clinical implementation of the kinds of conformal treatment planning and delivery that were envisioned decades ago. The use of 3-D treatment planning in conjunction with conformal treatments and the analysis of clinical normal tissue complications has also begun to give the field the clinical complication (and eventually tumor control) probability data which can be used to truly optimize radiation treatments. At this centennial anniversary of the discovery of the x ray, it is appropriate to look back at the contributions which have led to the current developments in conformal therapy. Few if any of the "new developments" associated with modern computer-controlled conformal therapy (CCRT) are actually new. However, modern technology has finally progressed to the point that we can integrate all of the features that are necessary to really make the concepts work in the clinic. This paper traces some of the developments which have led to the current interest and progress in CCRT treatments. A brief summary of the current status of conformal therapy and the work still to be done is also included.

History, 19th Century↗

PubMed1995

Mechanical and dosimetric quality control for computer controlled radiotherapy treatment equipment.

Modern computer controlled radiotherapy treatment equipment offers the possibility of delivering complex, multiple field treatments with minimal operator intervention, thus making multiple field conformal therapy practical. Conventional quality control programs are inadequate for this new technology, so new quality control procedures are needed. A reasonably fast, sensitive, and complete daily quality control program has been developed in our clinic that includes nearly automated mechanical as well as dosimetric tests. Automated delivery of these quality control fields is performed by the control system of the MM50 racetrack microtron, directed by the CCRS sequence processor [D. L. McShan and B. A. Fraass, Proceedings of the XIth International Conference on the use of computers in Radiation Therapy, 20-24 March 1994, Manchester, U.K. (North Western Medical Physics Department, Manchester, U.K., 1994), pp. 210-211], which controls the treatment process. The mechanical tests involve multiple irradiations of a single film to check the accuracy and reproducibility of the computer controlled setup of gantry and collimator angles, table orientation, collimator jaws, and multileaf collimator shape. The dosimetric tests, which involve multiple irradiations of an array of ionization chambers in a commercial dose detector (Keithly model 90100 Tracker System) rigidly attached to the head of the treatment gantry, check the output and symmetry of the treatment unit as a function of gantry and collimator angle and other parameters. For each of the dosimetric tests, readings from the five ionization chambers are automatically read out, stored, and analyzed by the computer, along with the geometric parameters of the treatment unit for that beam.(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗

PubMed1995

Aspects of enhanced three-dimensional radiotherapy treatment planning.

Advances in computer technology have led to the availability of sophisticated three-dimensional treatment planning systems for use in many radiotherapy centers. However, additional complexity in both the planning and delivery of treatments has accompanied their use. Thus, even more computer-aided tools are beginning to appear to address these needs. Aspects of recent enhancements to 3-D treatment planning at the University of Michigan are presented.

Dose-Response Relationship, Radiation↗

PubMed1994

Expanding the use and effectiveness of dose-volume histograms for 3-D treatment planning. I: Integration of 3-D dose-display.

PURPOSE: A technique is presented for overcoming a major deficiency of histogram analysis in three-dimensional (3-D) radiotherapy treatment planning; the lack of spatial information. METHODS AND MATERIALS: In this technique, histogram data and anatomic images are displayed in a side-by-side fashion. The histogram curve is used as a guide to interactively probe the nature of the corresponding 3-D dose distribution. Regions of dose that contribute to a specific dose bin or range of bins are interactively highlighted on the anatomic display as a window-style cursor is positioned along the dose-axis of the histogram display. This dose range highlighting can be applied to two-dimensional (2-D) images and to 3-D views which contain anatomic surfaces, multimodality image data, and representations of radiation beams and beam modifiers. Additionally, as a range of histogram bins is specified, dose and volume statistics for the range are continually updated and displayed. RESULTS: The implementation of these techniques is presented and their use illustrated for a nonaxial three field treatment of a hepatic tumor. CONCLUSION: By integrating displays of 3-D doses and the corresponding histogram data, it is possible to recover the positional information inherently lost in the calculation of a histogram. Important questions such as the size and location of hot spots in normal tissues and cold spots within target volumes can be more easily uncovered, making the iterative improvement of treatment plans more efficient.

Humans↗

PubMed1994

Dose-volume histogram and 3-D treatment planning evaluation of patients with pneumonitis.

PURPOSE: Tolerance of normal lung to inhomogeneous irradiation of partial volumes is not well understood. This retrospective study analyzes three-dimensional (3-D) dose distributions and dose-volume histograms for 63 patients who have had normal lung irradiated in two types of treatment situations. METHODS AND MATERIALS: 3-D treatment plans were examined for 21 patients with Hodgkin's disease and 42 patients with nonsmall-cell lung cancer. All patients were treated with conventional fractionation, with a dose of 67 Gy (corrected) or higher for the lung cancer patients. A normal tissue complication probability description and a dose-volume histogram reduction scheme were used to assess the data. Mean dose to lung was also calculated. RESULTS: Five Hodgkin's disease patients and nine lung cancer patients developed pneumonitis. Data were analyzed for each individual independent lung and for the total lung tissue (lung as a paired organ). Comparisons of averages of mean lung dose and normal tissue complication probabilities show a difference between patients with and without complications. Averages of calculated normal tissue complication probabilities for groups of patients show that empirical model parameters correlate with actual complication rates for the Hodgkin's patients, but not as well for the individual lungs of the lung cancer patients treated to larger volumes of normal lung and high doses. CONCLUSION: This retrospective study of the 3-D dose distributions for normal lung for two types of treatment situations for patients with irradiated normal lung gives useful data for the characterization of the dose-volume relationship and the development of pneumonitis. These data can be used to help set up a dose escalation protocol for the treatment of nonsmall-cell lung cancer.

Carcinoma, Non-Small-Cell Lung↗

PubMed1994

Three-dimensional treatment planning of intracavitary gynecologic implants: analysis of ten cases and implications for dose specification.

PURPOSE: Results of 3-dimensional treatment planning for ten intracavitary gynecologic implants and implications for dose specification are presented. METHODS AND MATERIALS: Using a computed tomographic (CT) compatible intracavitary applicator we have performed CT scans during gynecologic brachytherapy in 10 cases. A CT-based treatment planning system with 3-dimensional capabilities was used to calculate and display dose in three dimensions. Conventional point doses including the estimated bladder and rectal maximum doses and dose to Point A were acquired from orthogonal simulation films. CT maximum bladder and rectal doses and minimum cervix doses were ascertained from isodose lines displayed on individual CT images. Dose volume histograms for the bladder, rectum and cervix were generated and used to obtain volume of the cervix target volume receiving less than the prescribed dose and the volume of bladder and rectum receiving more than the orthogonal maximum doses. The 5 cc volume of bladder and rectum receiving the highest dose were also calculated. RESULTS: Average values of CT point doses and volumes are compared with the traditionally obtained doses. As demonstrated by others, much higher bladder and rectal doses are found using the CT information. The minimum dose to the cervix target volume is lower than the dose to Point A in each case. CT maximum bladder and rectum and minimum cervix target doses may not be the best index doses to correlate with outcome because of the small volumes receiving the dose. CONCLUSION: We hypothesize that clinically useful bladder, rectal and cervix target volume doses will include volume information which is obtainable with dose volume histogram analysis.

Brachytherapy↗

PubMed1994

Dosimetric verification of a 3-D electron pencil beam dose calculation algorithm.

A three-dimensional electron beam dose calculational algorithm implemented for use in a three-dimensional treatment planning system is described. The 3-D electron beam calculations have been in use clinically for more than seven years. The algorithm uses a pencil beam model based on small angle multiple Coulomb scattering theory. Our implementation allows volumetric CT-based inhomogeneity corrections and provides for irregular field shapes (fields shaped with cerrobend cutouts) and the use of bolus. As part of NCI-funded work evaluating the state of the art in electron beam treatment planning, extensive algorithm verification was undertaken and results of these tests for our implementation are presented.

Algorithms↗

PubMed1993

A large screen digitizer system for radiation therapy treatment planning.

PURPOSE: This paper describes a new technique for manually drawing contours of anatomy over image data for the purposes of radiation therapy treatment planning. METHODS AND MATERIALS: A large area rear-projectible digitizer tablet is used together with a projection TV system to display computer graphics and image data. Large images of computed tomography or magnetic resonance cross-sections are displayed and the digitizer is used to directly trace outlines of important organs. Digitizer menus allow multiple functions for selecting images and structures, for changing the grayscale level and window, and for zooming and roaming the image. RESULTS: This device has been in clinical operation for many years and has proven to greatly increase the speed of entering cross-sectional outlines defined for serial computed tomography images sets. A small timing study of clinical usage demonstrates up to a factor of ten improvement in the speed of contour entry. CONCLUSION: For 3-dimensional radiation therapy, tumor, and target volumes, as well as important critical organs, must be delineated from serial sets of computed tomography or magnetic resonance images. Often 30 or more slices must be considered and the process of outlining structures on this number of slices can represent a significant fraction of the total treatment planning time. The device described in this paper greatly improve the ease and speed of manual contour entry for 3-dimensional radiation therapy planning.

Humans↗

PubMed1992

A quantitative assessment of the addition of MRI to CT-based, 3-D treatment planning of brain tumors.

Quantitative 3-D volumetric comparisons were made of composite CT-MRI macroscopic and microscopic tumor and target volumes to their independently defined constituents. Volumetric comparisons were also made between volumes derived from coronal and axial MRI data sets, and between CT and MRI volumes redefined at a repeat session in comparison to their original definitions. The degree of 3-D dose coverage obtained from use of CT data only or MRI data only in terms of coverage of composite CT-MRI volumes was also analyzed. On average, MRI defined larger volumes as well as a greater share of composite CT-MRI volumes. On average, increases in block margin on the order of 0.5 cm would have ensured coverage of volumes derived from use of both imaging modalities had only MRI data been used. However, the degree of inter-observer variation in volume definition is on the order of the magnitude of differences in volume definition seen between the modalities, and the question of which imaging modality best describes tumor volumes remains unanswered until detailed histologic studies are performed. Given that tumor volumes independently apparent on CT and MRI have equal validity, composite CT-MRI input should be considered for planning to ensure precise dose coverage for conformal treatments.

Astrocytoma↗

PubMed1992

The clinical utility of magnetic resonance imaging in 3-dimensional treatment planning of brain neoplasms.

Results of the clinical experience gained since 1986 in the treatment planning of patients with brain neoplasms through integration of magnetic resonance imaging (MRI) into computerized tomography (CT)-based, three-dimensional treatment planning are presented. Data from MRI can now be fully registered with CT data using appropriate three-dimensional coordinate transformations allowing: (a) display of MRI defined structures on CT images; (b) treatment planning of composite CT-MRI volumes; (c) dose display on either CT or MRI images. Treatment planning with non-coplanar beam arrangements is also facilitated by MRI because of direct acquisition of information in multiple, orthogonal planes. The advantages of this integration of information are especially evident in certain situations, for example, low grade astrocytomas with indistinct CT margins, tumors with margins obscured by bone artifact on CT scan. Target definitions have repeatedly been altered based on MRI detected abnormalities not visualized on CT scans. Regions of gadolinium enhancement on MRI T1-weighted scans can be compared to the contrast-enhancing CT tumor volumes, while abnormalities detected on MRI T2-weighted scans are the counterpart of CT-defined edema. Generally, MRI markedly increased the apparent macroscopic tumor volume from that seen on contrast-CT alone. However, CT tumor information was also necessary as it defined abnormalities not always perceptible with MRI (on average, 19% of composite CT-MRI volume seen on CT only). In all, the integration of MRI data with CT information has been found to be practical, and often necessary, for the three-dimensional treatment of brain neoplasms.

Astrocytoma↗

PubMed1991

Technical considerations in the use of 3-D beam arrangements in the abdomen.

The practical utilization of 3-D treatment planning to reduce doses to normal tissues in the abdomen is illustrated for irradiation of hepatic masses using fields with central axes rotated out of the transverse plane. The beams were arranged to go through the minimum amount of normal liver tissue, while exiting above or below a kidney. Although these beam arrangements were not coplanar with standard transverse body sections, they were designed for dose delivery through use of standard Megavoltage equipment. The planning process for these techniques illustrates the need for and use of several tools usually associated with 3-D treatment planning systems. Beam's eye-view planning with perspective display of the relevant anatomy in the projective beam geometry is required for designing the placement of focused blocks for these oblique fields. Three-dimensional volumetric dose calculations are required to evaluate dose distributions. Additionally, port-film-type radiographs, digitally reconstructed from the CT dataset, are found to be useful in understanding the correctness of simulation and verification films. The reduction in dose to normal tissues over that achievable using standard plans with beams entering the patient at right angles to the central axis of the body is illustrated using dose-volume histograms. These techniques have allowed the initiation of a radiation dose escalation protocol for tumors involving the liver and porta hepatis.

Abdomen↗

PubMed1991

Three-dimensional treatment planning of astrocytomas: a dosimetric study of cerebral irradiation.

To demonstrate that 3-dimensional planning is both practical and applicable to the treatment of high-grade astrocytomas, 50 patients over a 2-year period have received cerebral irradiation delivered in focussed, non-axial techniques employing from 2 to 5 beams. Astrocytomas have been planned using rapid, practical incorporation of CT data to define appropriate tumor volumes. Tumor + 3.0 cm and tumor + 1.5 cm volumes have been treated to conventional doses of 4500 cGy and 5940 cGy, respectively, using beam orientations that maximally spared normal remaining parenchyma. Analyses of 3-dimensionally calculated plans have been performed using integral dose-volume histograms (DVH) to help select treatment techniques. Using identical CT-based volumetric data as input for generation of Beam's Eye View (BEV) designed blocks, DVH curves demonstrate dosimetric advantages of non-axial techniques over conventional parallel-opposed orientations. Assessment of the non-axial techniques in selected cases indicates that uniform target volume coverage could be maintained with a typical reduction of 30% in the total amount of brain tissue treated to high dose (95% isodose line).

Astrocytoma↗

PubMed1991

Design of MRI scan protocols for use in 3-D, CT-based treatment planning.

MRI has the potential of providing the radiation therapy treatment planner with new insights into the definition of target and normal tissue volumes to augment CT in 3-D treatment planning. The current speed of MR scan sequences is not sufficient to enable the acquisition of both T1 and T2 weighted images in all three orthogonal planes in a reasonable period of time. Therefore, compromises must be made in the design of protocols specifically for use in radiotherapy planning which: (1) provide enough information to readily enable image registration; (2) preserve the three-dimensionality provided by image acquisition directly in coronal and sagittal planes; (3) yield tissue contrast as well as tumor specificity (where available); but (4) can be completed in a short enough span of time (or with enough checks) that the patient position is not compromised. Protocols designed for use in planning treatment of the brain, head and neck, lung, prostate, cervix, and sarcomas are presented.

Humans↗