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Results for “Radiotherapy, Computer-Assisted”

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PubMedDate not supplied

Missing tissue compensators: evaluation and optimization of a commercial system.

A commercial system for producing retracted compensators has been adapted to suit local needs, and is evaluated here. It comprises a magnetic field surface digitizer and computer-driven milling machine. Improvements in dose distributions, resulting in standard deviations of the mean dose between 2% and 3%, have been achieved for treatment fields in wax phantoms simulating the head and neck regions. Optimization of compensator shape to allow for changes in the amount of scattered radiation has resulted in a further improvement in dose uniformity, particularly near the field borders; for these compensators the standard deviation was as low as 1.6%. The system using the basic algorithm has been in clinical use since July.

Humans↗

PubMedDate not supplied

Treatment planning for asymmetric jaws on a commercial TP system.

In this work, the accuracy of the asymmetric jaws planning feature in a commercial treatment planning (TP) system is assessed. In the latest version of this software, the off-axis beam quality variation is handled by a function g(d,r), which is derived from measured horizontal beam profiles at four different depths. The calculated and measured isodoses for a 6-MV linear accelerator with asymmetric jaws agree to +/- 0.5% along the central axis and to within 2 mm at the beam edge. Formulas for treatment time calculations using the output data reported by the computer program are described, as well as formulas for manual calculations based on pregenerated data tables. Doses calculated based on these formulas are compared to measurement and the accuracy is +/- 1% and +/- 2% for the computer and manual calculations, respectively. It is concluded that this version of the treatment planning system as well as the treatment time calculation formulas can be used adequately for asymmetric jaw computerized and manual treatment planning.

Humans↗

PubMedDate not supplied

Gadolinium neutron capture therapy for brain tumors: a computer study.

A Monte Carlo computer study of the total dose distribution from neutrons and prompt gamma emissions (but excluding the contribution from conversion and Auger electrons) for gadolinium neutron capture therapy of brain tumors has been carried out in order to test the theoretic feasibility of this modality using commercially available magnetic resonance contrast media. The three-dimensional dose distribution calculations were performed in a spherical head phantom with a spherical tumor at the center. Potentially achievable gadolinium concentrations of 150 micrograms/g of tissue in tumor and 3 micrograms/g in normal tissue were assumed with enrichment to 79.9% gadolinium-157, as supplied by Oak Ridge National Laboratory. Irradiation was assumed to be with a 2-keV monoenergetic cylindrical epithermal neutron beam having a radius of 4 cm. The three-dimensional thermal neutron fluence resulting from the 2-keV beam propagation through the tissue was modeled. For a single neutron beam, the maximum dose is delivered within the tumor but the dose is very inhomogeneous across the tumor volume due to rapid decrease of thermal neutron fluence with depth. Two parallel opposed neutron beams deliver to the interface of normal and malignant tissue 70%-80% of the maximum dose received at the center of the tumor. To deliver an average tumor dose of 500 cGy in 10 min would require a 2-keV source neutrons number of 8.0 x 10(11) per s within the geometry of the beam.

Brain Neoplasms↗

PubMed1992

Three-dimensional imaging for brachytherapy planning.

A computerized 3-D brachytherapy treatment planning program has been developed which simulates catheter trajectories, radioisotope seed positioning and percentage dosimetry zones about a catheter/seed array in relationship to CT or MRI images. The high activity 125I seed is used in this program. A visual and a non-linear mathematical optimization program will also be described.

Brachytherapy↗

PubMed1992

Template-guided stereotactic implantation of malignant brain tumors for interstitial thermoradiotherapy.

A phase I trial of 25 patients with anaplastic astrocytoma or glioblastoma multiforme is described. Hyperthermia and radiation were delivered stereotactically by means of template-guided interstitial catheters loaded with ferromagnetic wires and then 192Ir seeds. Implant volumes ranged from 15 to 113 ml (mean 54 ml) involving 9-38 catheters (mean 18); parallel catheters used hexagonal spacing of 1.0-1.5 cm. Patient tolerance of these procedures was excellent. Postoperative morbidity due to additional mass effect or edema was low, but there has been one death and one complication of hydrocephalus, bleeding and symptomatic pneumocephalus, each.

Adult↗

PubMed1992

[Development of a moving target aiming system using an ultrasound imaging unit].

We developed an ultrasound imaging unit for gating the irradiation of proton beams or acquiring CT scan data for treatment planning according to the motion of tumors in the abdomen. In proton therapy, it is essential that the maximum region of dose rate distribution in a body always coincide with the volume of the tumor in motion during irradiation. Gated proton bean irradiation based on tumor motion could solve this problem and minimize undesirable dose distribution to normal tissues in the vicinity of the tumor. This device can generate the TTL level signal of time width corresponding to the period that the tumor would be sited in a region determined in advance, to control the various kinds of machines. Results of our preliminary experiment using X-ray irradiation showed that this aiming device was able to make the width of the gated irradiation area coincide with that of the planned area within a difference of about 0.5 mm.

Humans↗

PubMedDate not supplied

[The CT-stereotaxic neutron brachytherapy of brain tumors with californium sources on the ANET-B apparatus].

A method for stereotaxic intratissue radiotherapy of brain tumors based on the findings of computed tomography is described. Radiosurgical implantation of sources with increased 252Cf content emitting mixed neutron + gamma-radiation was accomplished by means of an ANET-B apparatus by the afterloading method. Neutron irradiation is particularly effective in patients with malignant tumors possessing a large fraction of cells in a state of deep anoxia. Dosimetric planning was conducted by means of an original computer system. Devices and radiation-technical equipment for adaptation of the ANET-B apparatus for irradiation of neurosurgical patients are described. The indications for the use of this method and its place among the complex of measures for the treatment of patients with new growths of the brain are discussed. The first experience in using CT-stereotaxic neutron brachytherapy with californium sources on the ANET-B apparatus for the treatment of 6 patients with malignant glial tumors of the brain is dwelt on.

Adult↗

PubMed1992

[Conformal technics by the movement of bars in pendular fields. 1. Prototype realization and the possible applications].

The growing interest for conformal radiotherapy originates from the need of giving the prescribed dose to the target volume, by sparing, at the same time, surrounding healthy tissues and organs. More dose to the target volume with respect to the healthy tissues always increases the curative possibilities of the treatment. However, the development of conformal techniques implies an increased complexity of the treatment and the solution of many technical and dosimetric problems. In our Institute we are developing new conformal techniques, based on the use of moving bars driven by a computer-controlled system in arc therapy. This paper refers to the conclusion of the preliminary part of our work: a movement (translating or rotating) of bars in arc therapy seems to have good chances to tailor dose distribution in a relatively simple way. We realized two mechanical systems driven by computer for translating and rotating movements of a bar. The two techniques have been tested by TLD and film dosimetry on acrylic phantoms. We present the results of these tests, and describe technical problems and the clinical possibilities of this method.

Equipment Design↗

PubMed1992

[Conformal technics by the movement of bars in pendular fields. 2. The dosimetric aspects].

The development of conformal techniques by movement of bars in pendular fields requires a careful examination of many physical and dosimetric problems: bar-critical organ synchronization problems, dose calculation problems, and problems relative to the "shadow effect". The use of a bar in an arc field, causes to a slow gradient of dose between shielded zone and target volume with a loss of homogeneity in dose distribution. This effect is well known ("shadow effect") and depends on the fact that different points spend different times beyond the bar's shadow. In this work the problem is investigated in the case of moving bar technique, mainly for dose calculation possibilities; then the possibility is analyzed of optimizing dose distribution by means of filters whose profile can be calculated for simple geometric conditions (fixed bar on the isocenter without considering the profile of the patient). These filters will be made in our Institute and they will be tested in various conditions, for both fixed bars and moving bars in arc fields.

Equipment Design↗

PubMedDate not supplied

Assessment of exposure to radon decay products in realistic living conditions.

The development of an automated system for activity-weighted size distribution measurements now permits more complete exposure and dose assessment for indoor radon decay products. Exposures characterized by the semi-continuous measurement of activity-weighted size distributions of radon decay products were obtained over four test periods in three normally occupied houses, two of which were occupied by cigarette smokers. These measured activity size distributions were used to calculate exposure-dose conversion coefficients and the annual effective doses. These doses were found to be approximately two-fold higher than the values derived conventionally from the measured radon concentration, on the assumption that indoor exposure to 20 Bq m-3 radon gas concentration corresponds to an annual effective dose 1 mSv y-1. The degree to which aerosol-measurement-based dose estimates were higher than radon-gas-based estimates was found to be influenced if the study house occupant was a cigarette smoker. Reassessment of the measured PAEC-weighted radon progeny particle size distribution in terms of the classical "unattached" and "attached" modes yielded lower estimates of the exposure-effective dose conversion coefficient that were similar to the reference values derived from a recent study by the National Research Council. Thus, by not resolving the measured radon progeny PAEC that is associated with particles intermediate in size between the two classical radon progeny modes, the estimated annual effective doses were also found to be similar to the values derived conventionally from the measured radon gas concentration. It is concluded that the observed presence of 4 to 13% of the radon progeny PAEC in the size-range 1.5 to 15 nm diameter is a dosimetrically significant factor that appears to be commonplace in various home environments.

Air Pollution, Indoor↗

PubMed1992

[Practical use of the TDF factor in radiotherapy of basalioma and squamous cell carcinoma].

For X-ray therapy, the relation between single doses, number of fractions and duration of therapy have been combined in the TDF (time, dose, fraction) factor by Orton and Ellis. This factor seems to be well suited to evaluation of the X-ray therapy of basal cell carcinomas and squamous cell carcinomas of the skin. A simplified TDF formula is presented, together with some methods of calculation. Furthermore, tables are presented containing TDF values for frequently applied single doses and for two to five fractions per week. In addition, some hints are given on the use of the decay factor of Orton and Ellis to compensate for the loss of X-ray effectiveness if therapy has been interrupted.

Basal Cell Carcinoma↗

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↗

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↗

PubMed1992

Our experience in the diagnosis of intraocular tumours by a B-scan computerized system and angiodynography (Doppler). Preliminary results.

The authors compare the ultrasound diagnostic results of intraocular tumours by A/B-scans (Sonomed B 3000, Sonocare, Sonovision STT-100) with images obtained using computerized B-scan (Sonocare, Sonovision STT-100, Acoustic Tissue Typing ATT) and angiodynopgraphy systems (Quantum Philips). The Sonovision uses a computerized ultrasound spectrum analysis to assess the probability that a given lesion is a certain tumour, rather than another. The ATT system provides diagnostic probability for type B and type E melanoma, for haemangioma and metastatic carcinoma. The Quantum ultrasound equipment was developed for studying the heart and the major blood vessels. It is a colour Doppler that simplifies the Doppler technique, allowing it to study small anatomical parts such as tumour-like lesions of the eye. The Doppler technique ascertains the presence and the velocity of blood flow in the tumours. In presenting the preliminary results with the new techniques the authors are aware that the ATT system is not designed for some of the lesions under study (melanomas after conservative radiotherapy).

Blood Flow Velocity↗

PubMed1976

A preloaded radium needle implant device for maintenance of needle spacing.

A small stainless steel bar was machined to accept radium needles. The stainless steel bar will hold a rack of two, three, four, or five radium needles in a single plane. The crossing needle may be affixed to the bar so that textbook-like geometry is possible. The stainless steel bar remains in place during the entire implant. Spacing between needles is close to perfect. The time required to insers the implant is reduced compared to free-hand insertions, and less variation in dose is seen on computer-assisted calculations. Two years' experience in the use and development of the radium needle holder will be reviewed.

Head and Neck Neoplasms↗

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↗

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↗