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PubMedDate not supplied

An interactive beam-weight optimization tool for three-dimensional radiotherapy treatment planning.

A computer software tool has been developed to aid the treatment planner in selecting beam weights for three-dimensional radiotherapy treatment planning. The program consists of a feasibility search algorithm embedded in an interactive, user-friendly driving program. The feasibility search algorithm is based on the iterative relaxation algorithm of Cimmino [La Ricerca Scientifica, Vol. I, pp. 326-333 (1938)] as applied to the radiotherapy inverse problem by Altschuler et al. [Med. Phys. 13, 590 (1986)]. Relative importances of structures based upon clinical considerations can be incorporated into the algorithm. In order to speed convergence, the relaxation parameter is made to vary, with its value based upon a measure of deviation from feasibility. The interactive driving program is designed so that the treatment planner can make reasonable judgments regarding the acceptability of a plan in the event that the dose constraints yield no feasible solution. An example of the use of this program applied to a problem in three-dimensional radiotherapy treatment planning is illustrated.

Algorithms↗

PubMed1991

[Technical aspects of proton irradiation of intraocular tumors].

The paper is concerned with the description of some technical aspects of irradiation of intraocular melanomas of the preequatorial and retroequatorial localizations with a proton beam on a synchrotron at the Institute of Theoretical and Experimental Physics. Potentialities of a program of design of irradiation of intraocular tumors were considered. The parameters of an optimized plan of irradiation were determined by analysis of computer-simulated dose topographic and anatomic situations at different variants of irradiation. Reproducibility of an optimized plan of irradiation was no worse than 1 mm.

Eye Neoplasms↗

PubMed1992

Computer-assisted 3D-reconstruction and statistics of the limbic system. 1. Computer-assisted 3D-reconstruction of the hippocampal formation, the fornix, and the mamillary bodies.

The hippocampal formation of eight perfusion-fixed human brains was examined using new methods according to stereotactic and morphometric principles (macrovibratome and computer-aided 3D reconstruction). The reconstructions form part of a neuroanatomical reference system (NeuRef). This reference system allows for 3D visualisation of the brain and its components on a computer graphic workstation, as well as for the presentation of the union set based on a neuroanatomical structure taken from this sample of brains. This retrievable knowledge of neurofunctional systems is important for the preoperative planning of neurosurgeons and the adjustment of radiotherapy.

Adult↗

PubMed1991

[Three-dimensional reconstructions in neuroanatomy].

Computer-aided 3D reconstructions of neurofunctional systems and structures are generated as a reference for neuroimaging (CT, MRI, PET). The clinical application of these 3D reconstructions requires a coordinate system and conditions resembling the intravital neuroanatomy as far as possible. In this paper the neuroanatomical Reference System (NeuRef) of the Department of Neuroanatomy of Hannover Medical School is presented. This consists of methods to record brain structures from serial sections with minimal error (less than 1 mm) and to display 3D brain models derived from such a data base. In addition, NeuRef is able to generate sections through, for instance, the visual and pyramidal system and to transfer these data onto a corresponding CT image. Therefore, this method can serve as a diagnostic aid in neuroradiology, in operation planning, and radiotherapy. It can also be used in PACS.

Brain↗

PubMed1976

New methods of imaging in diagnostic radiology Sylvanus Thompson Memorial Lecture.

A brief history of the recent developments in computer-assisted tomography (CAT) is presented. The development of whole-body scanners from the basic brain scanner, the trend towards higher-speed scanners using multiple detectors in a fan-type geometry, and some of the unsolved problems related to CAT scanners are discussed, as well as the potential use of whole-body scanning in radiotherapy treatment planning and in radiobiology. A review of recent developments in electrostatic imaging is presented and a new method of imaging called ionography is described in detail. It is shown how a single exposure can be used to produce a number of copies, each with a different amount of edge contrast, under the control of the radiologist. Further, it is shown how this can be done using a closed system so that the ionography chamber never needs to be opened. Some of the recent commercial developments in this field are described. It is suggested that in the future radiology departments may be replaced by departments of imaging, which will include all ways of obtaining diagnostic information and where such a department would be problem oriented rather than technique oriented. The need for basic scientific support by a medical physics and engineering group in such a department is emphasized.

Electrons↗

PubMed1992

True three-dimensional dose computations for megavoltage x-ray therapy: a role for the superposition principle.

The objective of radiation therapy is to concentrate a prescribed radiation dose accurately within a target volume in the patient. Major advances in imaging technology have greatly improved our ability to plan radiation treatments in three dimensions (3D) and to verify the treatment geometrically, but there is a concomitant need to improve dosimetric accuracy. It has been recommended that radiation doses should be computed with an accuracy of 3% within the target volume and in radiosensitive normal tissues. We review the rationale behind this recommendation, and describe a new generation of 3D dose algorithms which are capable of achieving this goal. A true 3D dose calculation tracks primary and scattered radiations in 3D space while accounting for tissue inhomogeneities. In the past, dose distributions have been computed in a 2D transverse slice with the assumption that the anatomy of the patient dose not change abruptly in nearby slices. We demonstrate the importance of computing 3D scatter contributions to dose from photons and electrons correctly, and show the magnitude of dose errors caused by using traditional 2D methods. The Monte Carlo technique is the most general and rigorous approach since individual primary and secondary particle tracks are simulated. However, this approach is too time-consuming for clinical treatment planning. We review an approach that is based on the superposition principle and achieves a reasonable compromise between the speed of computation and accuracy in dose. In this approach, dose deposition is separated into two steps. Firstly, the attenuation of incident photons interacting in the absorber is computed to determine the total energy released in the material (TERMA). This quantity is treated as an impulse at each irradiated point. Secondly, the transport of energy by scattered photons and electrons is described by a point dose spread kernel. The dose distribution is the superposition of the kernels, weighted by the magnitude of the TERMA impulse for all interaction sites. In this review, we demonstrate the capabilities of the superposition method, particularly for situations of charged particle disequilibrium, and we report on the progress made by several research groups in adapting this method to clinical treatment planning. In the future, the superposition method will have a significant role in dose optimization for conformal irradiation techniques because of its close correspondence to image reconstruction by filtered back-projection.

Image Processing, Computer-Assisted↗

PubMed1992

High dose rate treatment of a maxillary sarcomatoid carcinoma: a case report.

A 37-year old Native American woman presented with a rare sarcomatoid carcinoma of the left maxilla. She underwent extensive resection, but developed an orbital cavity recurrence. This was treated with external beam radiation therapy. The boost posed dosimetric difficulties due to the anatomic peculiarities of the treatment area. Extensive treatment planning for a high dose rate Iridium 192 source helped overcome these problems. Control of the tumor was achieved in the site of recurrence.

Adult↗

PubMed1992

Reduction of the dose to the lens in prophylactic cranial irradiation: a comparison of three different treatment techniques and two different beam qualities.

Three treatment techniques using two beam qualities have been compared on the basis of dose to the lens in prophylactic cranial irradiation. The dose to the lens and the globe was measured with thermoluminescent crystals in an anthropomorphic phantom and calculated by a computer-assisted planning system. A comparison was made of large field and small field techniques using 60Co and 8 MV photons. Modifications to the basic techniques studied included angulation of the gantry, angulation of the couch, and placement of an additional eye block close to the surface. The dose to the lens could be reduced to four percent of the midplane dose by applying the small-field technique combined with the use of 8 MV energy photons, by placing an additional block close to the surface, and by five degree occipitally angling the gantry, as well as rotating the treatment couch to account for the divergence of the beam. The use of 60Co produced an underdosage of the posterior segment of the globe in angled treatment techniques.

Cataract↗

PubMed1992

Various wedge isodose angles for treatment planning.

Various wedge isodose angles or simply wedge angles smaller than the nominal wedge angle were created by combining the isodose distributions generated from a single physical wedge with the isodose distributions of the open field for the 8-MV photon beam. The particular wedge angle generated depends on the weights imposed on these isodose distributions. The relationship between these weights and the wedge angle were examined and found to be nonlinear. The difference between the wedge angles defined at 10 cm depth and those defined using the 50% isodose curve is less 6 degrees. The present data was fitted using two proposed empirical equations.

Humans↗

PubMed1992

Optimization of a cord shielding technique for electrons.

Large anterior electron fields are sometimes used to irradiate the neck when treating head & neck tumors. To offer a degree of spinal cord shielding, wax bolus, approximately the width of the vertebral bodies, is placed on the immobilization shell. The thickness of the bolus is adjusted so that the radiological depth of the anterior edge of the vertebral bodies is equal to the R80 depth for the energy used. This approach ignores electron scattering. Using a CT study of a thyroid cancer patient, neck contours were generated at 0.5 cm intervals and entered into the Alberta Treatment Planning system. Internal contours for the trachea and vertebral bodies were added and CT information was used for treatment planning purposes. The bolus outline was added as described above, and the dose calculated using a 3D implementation of the M.D. Anderson (Hogstrom) algorithm. The calculation shows that the simple bolus technique described above is inappropriate. The spinal cord is adequately shielded, but the target volume is not covered by the 80% isodose line. Qualitatively, the results can be explained by the lateral scatter non-equilibrium introduced by the bolus. By iteratively adjusting the shape and thickness of the wax bolus and recalculating the dose distribution, we were able to better fulfill the dose prescription. Comparison with measured data shows reasonable, but not perfect agreement. In conclusion, electron beam treatments must be examined closely to ensure that the treatment goals are met. In some cases, treatment integrity may be compromised by incorrect assumptions regarding the nature of the electron transport and dose deposition.

Humans↗

PubMed1991

Application of the LQ model to the interpretation of absorbed dose distribution in the daily practice of radiotherapy.

In 1991, the vast majority of radiotherapy centers are implemented with computer treatment planning systems (TPS), and it has become routine practice to compute full absorbed dose distribution (ADD) in almost all treatment situations. Usually the target is covered by the 100% isodose and the surrounding normal tissues receive a lesser dose than the tumor. It implies, that, as the dose per fraction of, say, 2 Gy is prescribed at the 100%, normal tissues receive a daily dose different than 2 Gy. The absorbed doses delivered at different organs have therefore not the same biological effectiveness and must be corrected according to the actual dose per fraction for a proper interpretation of the treatment planning. This is of great importance since most of the "tolerance levels" used in the practice have been determined for doses per fraction around 1.8-2 Gy. The linear-quadratic (LQ) model provides a simple method for establishing biological equivalencies and has been used throughout this article to establish the difference between the absorbed dose computed by the TPS and its biological equivalent. It is shown that normal tissues receiving less than 100% of the daily dose are relatively more protected than suggested by the ADD, and, inversely, that normal structures overdosed and thus receiving more than the 100% daily dose are relatively more at risk for complications than suggested from the ADD.

Bronchial Neoplasms↗

PubMed1992

Radiation oncology residents' computer workstation.

We are investigating the feasibility of using the Macintosh computer as a workstation platform for radiation oncology residents because of its ease of use, graphics capability, and low cost. Hypercard was chosen as the programming environment because it easily mixes graphics, text, and control functions in an integrated screen display. Furthermore, it results in a system that can be relatively easily extended and customized by individual users with varying degrees of computer skills. We have developed several software modules in order to test the ability of this environment to support the demands of such a workstation. Modules created thus far include various clinical physics aids and tutorials, treatment planning guides, oncology databases, and others. The software runs on all Macintosh configurations, but calculation speeds are improved when a 68020 or greater processor is used. In general, we have been pleased with the implementation thus far. Graphics display capability is good, but design and entry of graphics have proved labor-intensive. Searching is fast and text is easily entered and manipulated. Finished modules can be customized with minimal computer training, but implementing complex new functions requires familiarity with Hypercard's programming language. New modules, once developed, are easily integrated into the workstation universe, suggesting that cooperative development of the workstation by multiple contributors is realistically achievable.

Computer Graphics↗

PubMed1991

The use of T2 distribution to study tumor extent and heterogeneity in head and neck cancer.

Demarcation of the extent of malignant tissue is essential for planning a course of radiotherapy. MR images may provide additional information for delineating the target volume because of the large difference in the proton magnetic resonance relaxation times between normal and malignant tissues. In 13 patients with head and neck tumors the distribution of the proton spin-spin relaxation times, T2, at 1.5 Tesla were evaluated throughout the physician designated target volume and normal surrounding tissue. The T2 values within the tumor were always elevated compared with normal tissue, the highest values being in the nominal center of the tumor and decreasing toward the periphery. The regional distribution of T2 values within the tumor is a measure of the tissue heterogeneity within the tumor volume. In addition, the large differences in T2 relaxation times between normal and disease tissues were used in a computer algorithm to automatically demarcate the boundary of abnormal tissue in each axial MRI section. This potentially could significantly expedite the time required to identify the target volume on multiple sections and thus remove one of the major time constraints for 3D treatment planning.

Head and Neck Neoplasms↗

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↗

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↗