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PubMedDate not supplied

Encoding patient contours using Fourier descriptors for computer treatment planning.

Frequently it is desirable to digitize patient's external and internal contours from computer-assisted tomography (CAT) scan images and to use them for computer treatment planning. After the contours are digitized, each contour could contain over 1000 points. It is a common practice to reduce the number of contour points by interpolation methods in order to use them in a treatment planning program, and in order to save storage space. This paper describes an alternative method for encoding contours. The x-y coordinates of each contour point are represented as a complex number, x + jy. The discrete Fourier transform (DFT) of the array of complex numbers is then computed. Only the 50 lowest frequency components of the DFT are retained. Each contour is then represented by these 50 complex numbers, known as Fourier descriptors. The original contour is restored by performing the inverse Fourier transform. All the frequency components higher than 50 are assumed to be zero during the inverse Fourier transform. The algorithm is described in detail.

Computers↗
PubMedDate not supplied

Acquisition and display of radiation dose distributions using microcomputer technology.

In the commissioning or quality assurance of a medical linear accelerator or a computerized radiotherapy planning system, the traditional approach usually consists of acquiring and comparing one-dimensional dose profiles. This methodology is tedious and incomplete since only a portion of the radiation field can realistically be sampled. We have developed an automated measurement system which allows efficient measurement and display of complete two-dimensional dose distributions. The general purpose microcomputer used (IBM PC/XT compatible) can be interfaced economically to any water phantom dosimetry system equipped with a three axis scan controller, and can also communicate data to the treatment planning system. This allows for direct comparison of measured with computed dose distributions, thus revealing discrepancies in the dose computation algorithms used. In this paper, we describe the interface between the microcomputer, a conventional water dosimetry system (Therados RFA-3), and a treatment planning computer. We report our early experience with acquiring dose distributions and show sample comparisons with computed results for megavoltage electron beams incident on homogeneous and heterogeneous systems.

Humans↗
PubMed1978

A computer-assisted three-dimensional treatment planning system.

The three-dimensional treatment planning system developed at the Rhode Island Hospital visualizes the spatial interrelationships of the radiation beam, the tumor, and the adjacent organs within the patient. It is possible to rotate and vary the scale of the display to better comprehend the extent of these structures. By viewing the display as if from along the radiation beam, one can design shaped treatment fields which best suit the three-dimensional nature of the disease. With this system, it is possible to reduce the volume of normal tissue which would typically be irradiated if two-dimensional treatment planning techniques and assumptions were employed.

Computers↗
PubMed1987

Interstitial brachytherapy of malignant brain tumors using computed tomography-guided stereotaxis and available imaging software: technical report.

The implantation of radioactive sources into malignant intraaxial brain tumors, interstitial brachytherapy, is a theoretically attractive treatment for these nearly uniformly fatal lesions. Optimal application of this treatment modality requires careful preoperative planning, computer-assisted dosimetry, and computed tomography-guided stereotactic implantation of the isotope-bearing catheters. A method is presented by which available computed tomographic imaging software can be used with a standard radiotherapy treatment planning computer and the Brown-Roberts-Wells stereotactic system for preoperative imaging, dosimetry planning, and brachytherapy catheter insertion. Dedicated computer facilities are not required, making this method available to any neurosurgeon with access to a current generation computed tomographic scanner.

Brachytherapy↗
PubMed1992

Quality assurance of computer controlled radiotherapy treatments.

There is a need in conformal therapy, as in any radiation therapy, for adequate quality assurance of the treatment plan and the delivery of the treatment. This paper examines quality assurance of two methods of conformal treatment, on a cobalt treatment unit using computer control. Each of the two methods demonstrates a different aspect of computer controlled treatments. Following completion of each treatment plan, an additional "quality assurance plan" is prepared. This is used to assess the integrity of the treatment plan, and the precision with which the computer controls the treatment unit. A simple method, using solid state detectors in a Perspex phantom, is used to validate the dosimetry of the "quality assurance plan". Quality assurance of the computer control is performed daily prior to treatments. At each treatment, parameters identifying the start position and final position of the computer controlled couch movements and the exposure time are noted by the radiographers. Comparison of the recorded movement of the treatment couch and the exposure time with that intended during each course of treatment has demonstrated, inter alia, limitations on couch speed control at speeds of less than 10 mm per min.

Beds↗
PubMed1975

Backgrounds of computer-assisted treatment planning in radiation therapy.

Interaction of ionising radiation and living materials causes biological damage of tempory or permanent nature. In radiation therapy this phenomenon is used in a controlled fashion in order to stop the proliferation of malignant cells, while at the same time limiting the permanent damage to healthy tissues and organs to at least tolerable levels. Because of the often relatively small differences in response of malignant growths and normal tissues, the margins between tolerable and intolerable are so small that the greatest precision in treatment planning and execution is required. The nature of this treatment agent implies that the radiation therapist has to rely very much on instrumentally obtained and processed information, in all phases of this medical activities around the patient. In this paper a description is given of the backgrounds of computer-assisted methods which have enabled modern individualised and optimised planning for therapy with high enery X - and gamma beams.

Cobalt Radioisotopes↗
PubMedDate not supplied

[Computerized planning of radiotherapy].

The hypophysis was studied by MR tomography in 148 patients with the most prevalent diseases of the hypothalamohypophyseal system and in 13 ones with primary hypothyrosis. The findings evidence a great variety of changes in the MRT picture in the examinees. The method permits a reliable diagnosis of hypophyseal macroadenoma and of an 'empty' sella turcica. Qualitative and quantitative criteria for MRT diagnosis of these conditions are suggested. The diagnostic value of MRT for the detection of macroadenomas is still to be researched. The method was effectively used for a dynamic follow-up of the hypophyseal status in the course of pathogenetic therapy; the formation of an 'empty' sella turcica is possible against the background of dopamine agonist therapy and substitution therapy of primary hypothyrosis.

Adolescent↗
PubMed1992

[High-dose-rate brachytherapy of prostatic carcinoma with iridium 192].

In the therapy of localized prostatic cancer the radical prostatectomy shows good results within a five-year interval with no evidence of disease in nearly 90%. An important alternative is the radiotherapy by external beam or interstitial technique with iodine, gold or iridium. We use the high dose rate technique with Ir-192. In this technique five to seven hollow needles are placed in the prostate from perineal punctures under transrectal sonographic control. The three-dimensional brachytherapy planning is done according the actual needle position. A computer program calculates the radiation dose and distribution for each needle by adjustment of time and stops of the Ir-implants. The Ir-192 is temporary loaded twice with 9 Gy supplemented with external beam radiation (18 x 2 Gy). Since 1985 29 patients with localized tumor (T1-T3, N0, M0) have been irradiated. 21/29 had a pelvic lymphadenectomy before. In 85% of the patients were seen no side effects. Only one patient had a serious complication through a recto-vesical fistula. Out of the 21 followed-up patients 16 were in full remission, three had an androgen deprivation because of progression. A local tumor control could be demonstrated by cytology in 70% of the patients. This rational technique seems to be an alternative for patients not eligible for a radical prostatectomy.

Aged↗
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↗
PubMed1989

Modelling polychromatic high energy photon beams by superposition.

A unified three dimensional superposition approach to dose calculations used in treatment planning of polychromatic high energy photon beams in radiotherapy is developed. The approach we have used involves computing the dose at all points in a medium by superposing the dose spread array (DSA) from the interaction of a photon at a point in the medium with an array of data representing the TERMA (photon fluence times the photon energy) at points in the beam. The polychromatic nature of the beam is accounted for by modelling the beam as having ten spectral components. A "polychromatic dose spread array" (PDSA) for an interaction from a beam with this spectrum was derived. The TERMA array is calculated from a weighted average of the TERMA arrays for the ten photon energies to give a "polychromatic TERMA array". Thus the method accounts for the effect of beam hardening of the TERMA. But it does not account for the effect of beam hardening on the PDSA since a single PDSA (usually for the spectrum at the surface of the medium) is used at all depths. However, by considering measured and calculated beam central axis data, this model is shown to be adequate for computing depth doses for beams in a homogeneous medium penetrating to extreme radiological depths. A computation time advantage is gained because only one superposition per beam is required.

Humans↗
PubMed1977

[Optimization in planning and application of 60 Co gamma irradiations - analysis of the problem (author's transl)].

As an aspect of the complex problem of optimization in therapeutical transmission of radiation energy to Man, the dose distribution within a cross-sectional area of the body is considered. For the judgement on optimal dose distributions, involving judgement on irradiation technique, boundary conditions are needed which encompass important parameters of a dose distribution (= criterion for optima). For computer-assisted optimization the boundary conditions are to be scheduled by an appropriate algorithm. The parameters describing a dose distribution are indicated. Practical utilization of computer-assisted optimization of dose is represented by means of two optimization schedules.

Cobalt Radioisotopes↗
PubMed1978

[Possibilities, limitations and errors with ultrasound tomography in computer-assisted treatment planning (author's transl)].

Ultrasound tomography provides two-dimensional images, true in scale, of sonographic interfaces within nearly every sectional plane desired; it has become especially important, therefore, in irradiation planning. Complementary to results from a therapy simulator, an improvement in localization of tumor and target volume or of critical organs and of tissue inhomogeneities is possible. The hard-copy of gray-scale sonotomograms furnishes all essential geometric and anatomical input data needed for electronic systems used in irradiation planning. Technical, physical and diagnostic limitations of the method are stated. The possible systematic or technical-instrumental errors in sonographic treatment planning are discussed and the necessary calibration controls specified.

Abdomen↗
PubMed1980

[First report of experiences with interstitial radiation therapy of the prostatic carcinoma using 125-I-seeds: indication, practical performance and radioprotection (author's transl)].

The practical and organizing performance of interstitial radiation therapy with 125-I-seeds in prostatic carcinoma is reported. Precautions and measurements for radioprotection are emphasized. First evaluations of these measurements show that this therapeutical technique can be performed in complete accordance with the directive for radioprotection. The computer-assisted isodose-planning and the in-vivo-measurements in the rectum, urethra and bladder confirm the steep decrease of the dose outside the irradiated focal volume. Hence, inflammatory symptoms accompanying the therapy are markedly allayed in comparison with percutaneous radiation therapy, in spite of a higher tumor dose. Because of the extensive operation, attention must be paid to the strict observation of indication criteria.

Brachytherapy↗