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PubMed1991

The dose to lung in TBI.

Many physical problems are associated with TBI prior to BMT. Determination of the dose to lung, the organ at risk in TBI, is the most demanding task the DGMP working group on "Physical Aspects of TBI" has to solve. At an international workshop held at Essen in May 1990 the 50 participants discussed the problems and possibilities to measure, calculate, plan, modify, confirm, verify, and report the dose to lung. Some highlights are discussed here. The review lectures are summarized as abstracts in this issue. Details are published separately in the proceedings.

Algorithms↗
PubMed1991

[Evaluation of the accuracy of the study on diverse techniques of planning radiotherapy of breast tumors].

The authors report the results of the analysis of several factors contributing to the accuracy of treatment planning in the radiation therapy of breast cancer. Different techniques (non-radiological vs CT-based) were used for the acquisition of patients' data; different methods (manual vs computerized) were employed for dose calculation. As for geometric parameters describing the external outline and target volume, mean differences were lower than 4%. Switching from a completely manual method to a CT-based one with computerized calculation, a 3.56% mean decrease in the value of reference isodose (p less than 0.01) was observed, together with a 3.87% mean increase in the estimated inhomogeneity (p less than 0.001). The non-CT-based outline of target volume exhibited geographic missing of inner portions of the target in 8/16 patients. Our results demonstrate that treatment planning procedures can be a significant source of clinically relevant inaccuracy, which may affect treatment outcome and tumor control.

Breast Neoplasms↗
PubMed1991

[Assessment of radiotherapy plans: dose-volume histograms, integral effects and tumor control].

Suitable criteria are necessary for judgement and for comparison of treatment plans. These criteria must take into account radiobiological effects, i.e. tumor control and treatment complications. Quantitative evaluation of dose volume histograms gives helpful criteria for radiation treatment planning and for the choice between different treatment plans. For normal tissue and organs at risk it is shown, how to assign integral dose effect to inhomogeneous dose distribution. The evaluation algorithm is based on the assumption of a power law for volume dependence of dose effect. The algorithm is discussed for arbitrary form of dose effect function. Explicit evaluation is given in terms of the linear quadratic model. Hot spots influence integral dose effect much stronger than low dose level irradiation. For judgement of treatment plans, the significance of mean organ dose is only poor. Higher moments of dose distribution are more suitable. An effective tumor control probability is derived for judgement of tumor dose distribution. It is shown that tumor control is determined by mean dose and dose inhomogeneity in tumor volume. Control probability falls with increasing dose inhomogeneity in tumor region-in first order approximation characterized by variance of dose distribution. Using a clinical example, the evaluation rules for normal and tumor tissue are demonstrated. Two different treatment techniques are analyzed and discussed. Only numerical evaluation of dose volume histograms for lung region shows the better technique.

Algorithms↗
PubMed1991

Integration of multimodality imaging data for radiotherapy treatment planning.

This paper describes computational techniques to permit the quantitative integration of magnetic resonance (MR), positron emission tomography (PET), and x-ray computed tomography (CT) imaging data sets. These methods are used to incorporate unique diagnostic information provided by PET and MR imaging into CT-based treatment planning for radiotherapy of intracranial tumors and vascular malformations. Integration of information from the different imaging modalities is treated as a two-step process. The first step is to determine the set of geometric parameters relating the coordinates of two imaging data sets. No universal method for determining these parameters is appropriate because of the diversity of contemporary imaging methods and data formats. Most situations can be handled by one of the four different techniques described. These four methods make use of specific geometric objects contained in the two data sets to determine the parameters. These objects are: (a) anatomical and/or fiducial points, (b) attached line markers, (c) anatomical surfaces, and (d) outlines of anatomical structures. The second step involves using the derived transformation to transfer outlines of treatment volumes and/or anatomical structures drawn on the images of one imaging study to the images of another study, usually the treatment planning CT. Solid modelling and image processing techniques have been adapted and developed further to accomplish this task. Clinical examples and phantom studies are presented which verify the different aspects of these techniques and demonstrate the accuracy with which they can be applied. Clinical use of these techniques for treatment planning has resulted in improvements in localization of treatment volumes and critical structures in the brain. These improvements have allowed greater sparing of normal tissues and more precise delivery of energy to the desired irradiation volume. It is believed that these improvements will have a positive impact on the outcome of radiation therapy.

Algorithms↗
PubMed1992

A megavoltage CT scanner for radiotherapy verification.

We have further developed a system for generating megavoltage CT images immediately prior to the administration of external beam radiotherapy. The detector is based on the scanner of Simpson (Simpson et al 1982)--the major differences being a significant reduction in dose required for image formation, faster image formation and greater convenience of use in the clinical setting. Attention has been paid to the problem of ring artefacts in the images. Specifically, a Fourier-space filter has been applied to the sinogram data. After suitable detector calibration, it has been shown that the device operates close to its theoretical specification of 3 mm spatial resolution and a few percent contrast resolution. Ring artefacts continue to be a major source of image degradation. A number of clinical images have been presented. The next stage of this work is to use the system to make clinical measurements of patient set-up inaccuracies building on our work making such measurements from digital portal images (Evans et al 1992).

Evaluation Studies as Topic↗
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↗
PubMed1992

Limited-angle 3D reconstruction of PET images for dose localization in light ion tumour therapy.

In vivo dose localization in light ion tumour therapy can be performed by measuring the range distributions of beta+ active ions in tissue employing positron emission tomographic techniques. For this purpose a multiplicative iteration scheme for reconstructing three-dimensional images from shift-variant, limited-angle data is presented. In the iterative correction steps the algorithm uses the geometric means of quotients calculated from the three-dimensional Radon transforms of the backprojected measured and approximated source distributions. When sources measured with poor statistics are reconstructed, an effective noise suppression is achieved.

Algorithms↗
PubMed1991

Dynamic stereotactic radiosurgery using a linear accelerator.

We describe a system for stereotactic radiosurgery with a linear accelerator. This technique allows treatment of small (less than 40 mm diameter) intracranial lesions, including vascular malformations, and primary and metastatic tumors that are deep within the brain or in areas not amenable to open surgery. A beam of ionizing radiation (1800 to 2500 cGy) is focused on the center of the lesion, which is determined by stereotactic localization. "Dynamic rotation" of the linac gantry and table continuously about this predetermined point ensures that only the lesion receives the full radiation dose, while the normal structures in the head receive minimal amounts of radiation. The system combines, for the first time in one place, elements of radiosurgical technique developed at various centers. Testing for accuracy compares favorably with results at other centers using linac-based systems as well as comparing favorably with the gamma knife.

Brain Neoplasms↗
PubMedDate not supplied

Radiotherapy technique integrates MRI into CT.

The 1970s saw the introduction of computed tomography, which enabled soft tissue anatomy to be seen. Today simulation of therapeutic fields by x-ray is augmented by radiotherapy treatment planning using CT data. The 1980s brought magnetic resonance imaging with superior soft tissue contrast. This article describes a technique correlating three-dimensional MRI/CT data sets used routinely in treatment planning of tumors in the head.

Brain Neoplasms↗
PubMed1992

High-performance computing in radiation cancer treatment.

In 1989 a consortium of the Radiation Oncology and Computer Science Departments at the University of North Carolina, BellSouth Corporation, GTE, and the MCNC was formed in response to the high-speed network initiative proposed by the National Science Foundation and the Defense Advanced Research Projects Agency. One of the purposes of this effort has been to demonstrate that applications exist that require gigabit per second networks. Our consortium, known as VISTAnet, proposed to use real-time radiation therapy treatment planning as the application that would require the use of a gigabit network. The plan was to develop a system that could rapidly calculate and display a three-dimensional radiation dose distribution for any configuration of radiation beams. The gigabit network would be used to tie the dose calculations done with the Cray Y-MP at the Research Triangle to the graphics engine at the Department of Computer Science (Pixel-Planes 5) and the medical workstation at Radiation Oncology. The system would then provide the radiation physician with the capability of considering hundreds of potential treatment plans, instead of the usual two or three, with the goal of arriving at a highly optimized plan within a few minutes.

Computer Communication Networks↗
PubMedDate not supplied

Bayesian statistics: a guided tour.

An overview of Bayesian statistical decision theory is presented in the tutorial spirit. A section on fundamental principles is followed by selected applications of the Bayesian approach to parameter estimation, pattern recognition, image processing, computer-aided medical diagnosis, optimal diagnostic test selection, and radiotherapy treatment planning.

Decision Making↗
PubMed1977

Computer-aided medical decision making in radiotherapy.

Radiotherapy departments are becoming sophisticated in working with computers for isodose computations, treatment machine verifications and administrative and medical records. The next step lies in computer-assisted medical decision making. The logic for a patient's diagnostic work-up and treatment protocol can be stored in a computer. It can then be used as an aid in making the diagnosis, in prescribing the treatment and for quality control. For patients who fit established protocols the computer can select and list treatment using the logic of that protocol. Such a system has been implemented for the postoperative radiotherapy of breast cancer on a trial basis. Its potential usefulness is illustrated by results in 25 consecutive patients. Physician acceptance and costs of the program are under investigation.

Breast Neoplasms↗
PubMed1991

A software system for interactive and quantitative visualization of multidimensional biomedical images.

A comprehensive software system called ANALYZE has been developed which permits detailed investigation and evaluation of 3-D biomedical images. The software can be used with any 2-D or 3-D imaging modality, including x-ray computed tomography, radionuclide emission tomography, ultrasound tomography, magnetic resonance imaging and both light and electron microscopy. The package is unique in its synergistic integration of fully interactive modules for direct display, manipulation and measurement of multidimensional image data. Several original algorithms are included which improve image display efficiency and quality. One of the most versatile and powerful algorithms is interactive volume rendering, which is optimized to be fast without compromising image quality. An important advantage of this technique is to display 3-D images directly from the original data and to provide on-the-fly combinations of selected image transformations and/or volume set operations (union, intersection, difference, etc.). The inclusion of a variety of interactive editing and quantitative mensuration tools significantly extends the usefulness of the software. Any curvilinear path or region-of-interest can be manually specified and/or automatically segmented for numerical determination and statistical analyses of distances, areas, volumes, shapes, densities and textures. ANALYZE is written entirely in "C" and runs on several standard UNIX workstations. It is being used in a variety of applications by over 40 institutions around the world, and has been licensed by Mayo to several imaging companies. The software architecture permits systematic enhancements and upgrades which has fostered development of a readily expandable package. ANALYZE comprises a powerful "visualization workshop" for rapid prototyping of specific application packages, including applications to interactive surgery simulation and radiation treatment planning. ANALYZE offers the potential to accurately and reproducibly examine, from images, the structure and function of any cell, tissue, limb, organ or organ system of the body, much like a surgeon or pathologist might do in real life, but entirely non-invasively, without pain or destruction of tissue. These capabilities promise exciting new insights into the basic processes of life, and major advances in health care delivery through improved diagnosis and treatment of disease.

Computer Graphics↗
PubMed1978

[Ultrasound in tumor diagnostics and treatment planning (author's transl)].

The fundamental requirements of irradiation planning are discussed delimitating the minimum and maximum demands of planning. Different possibilities to represent the topographic relations within the irradiation plane of the patient's cross-section are described. The computer-assisted system for irradiation planning, installed at our hospital by means of MAT construction, is discussed. A pathway is shown which leads to individual treatment planning and considers dosimetrically the actual conditions of the patient who will undergo radiation therapy. The possibilities and limits of ultrasonic cross-sectional imaging are demonstrated.

Diagnosis, Computer-Assisted↗
PubMedDate not supplied

A finite-size pencil beam model for photon dose calculations in three dimensions.

A three-dimensional dose computation model employing a finite-size, diverging, pencil beam has been developed and is demonstrated for Cobalt-60 gamma rays. The square cross-section pencil beam is simulated in a semi-infinite water phantom by convolving the pencil beam photon fluence with the Monte Carlo point dose kernel for Cobalt-60. This finite-size pencil beam is calculated one time and becomes a new data base with which to build larger beams by two-dimensional superposition. The pencil beam fluence profile, angle correction for beam divergence, the Mayneord inverse square correction, radial and angular sampling rates, error propagation, and computation time have been investigated and are reported. Radial and angular sampling rates have a great effect on accuracy and their appropriate selection is important. Percent depth doses calculated by finite-size pencil beam superposition are within 1% of values calculated by full convolution and the agreement with values from the literature is within 6%. The latter disagreement is shown to be due to a low-energy photon component which is not modeled in other calculations. Computation time measurements show the pencil beam method to be faster than full convolution and one implementation of the differential-scatter-air-ratio (dSAR) method.

Cobalt Radioisotopes↗
PubMed1991

Code of practice for clinical proton dosimetry.

The objective of this document is to make recommendations for the determination of absorbed dose to tissue for clinical proton beams and to achieve uniformity in proton dosimetry. A Code of Practice has been chosen, providing specific guidelines for the choice of the detector and the method of determination of absorbed dose for proton beams only. This Code of Practice is confined specifically to the determination of absorbed dose and is not concerned with the biological effects of proton beams. It is recommended that dosimeters be calibrated by comparison with a calorimeter. If this is not available, a Faraday cup, or alternatively, an ionization chamber, with a 60Co calibration factor should be used. Physical parameters for determining the dose from tissue-equivalent ionization chamber measurements are given together with a worksheet. It is recommended that calibrations be carried out in water at the centre of the spread-out-Bragg-peak and that dose distributions be measured in a water phantom. It is estimated that the error in the calibrations will be less than +/- 5% (1 S.D.) in all cases. Adoption and implementation of this Code of Practice will facilitate the exchange of clinical information.

Cobalt Radioisotopes↗