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Results for “Particle Accelerators”

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At least 865 records · Page 48Linked to original sources

PubMed2005

Effects of internal and external scatter on the build-up characteristics of Monte Carlo calculated absorbed dose for electron irradiation.

The effects of internal and external scatter on surface, build-up and depth dose characteristics simulated by Monte Carlo code EGSnrc for varying field size and SSD for a 10 MeV monoenergetic electron beam with and without an accelerator model are extensively studied in this paper. In particular, sub-millimetre surface PDD was investigated. The percentage depth doses affected significantly by the external scatter show a larger build-up dose. A forward shifted Dmax depth and a sharper fall-off region compared to PDDs with only internal scatter considered. The surface dose with both internal and external scatter shows a marked decrease at 110 cm SSD, and then slight further changes with the increasing SSD since few external scattered particles from accelerator model can reach the phantom for large SSDs. The sharp PDD increase for the 5 cm x 5 cm field compared to other fields seen when only internal scatter is considered is significantly less when external scatter is also present. The effect of external scatter on surface PDD is more pronounced for large fields than small fields (5 cm x 5 cm field).

Algorithms↗

PubMed1983

Dosimetry of the Siemens Mevatron 67 linear accelerator.

Measurements have been made on a Siemens Mevatron 67 linear accelerator. The change of beam quality has been measured as a function of position off-axis and compared to another Siemens 6 MV linear accelerator. Similarly, beam profiles are compared to a Siemens Mevatron VI. Additional measurements include entrance dose, inverse square applicability, central axis percent depth dose, tissue-maximum ratios, output factors, wedge factors and block transmission factors. Comparison is made with an Atomic Energy of Canada Limited Therac 6 and Varian Clinac 6-100.

Particle Accelerators↗

PubMed1988

Medical proton accelerator facility.

This paper presents a specialized medical accelerator facility designed for proton radiation therapy and for production of short-lived nuclide-labelled radiopharmaceuticals. General features of the facility structure, the choice of principles of beam delivery, physical and technical problems connected with clinical work, and biomedical research are discussed.

Facility Design and Construction↗

PubMed2006

The stability of mechanical calibration for a kV cone beam computed tomography system integrated with linear accelerator.

The geometric accuracy and precision of an image-guided treatment system were assessed. Image guidance is performed using an x-ray volume imaging (XVI) system integrated with a linear accelerator and treatment planning system. Using an amorphous silicon detector and x-ray tube, volumetric computed tomography images are reconstructed from kilovoltage radiographs by filtered backprojection. Image fusion and assessment of geometric targeting are supported by the treatment planning system. To assess the limiting accuracy and precision of image-guided treatment delivery, a rigid spherical target embedded in an opaque phantom was subjected to 21 treatment sessions over a three-month period. For each session, a volumetric data set was acquired and loaded directly into an active treatment planning session. Image fusion was used to ascertain the couch correction required to position the target at the prescribed iso-center. Corrections were validated independently using megavoltage electronic portal imaging to record the target position with respect to symmetric treatment beam apertures. An initial calibration cycle followed by repeated image-guidance sessions demonstrated the XVI system could be used to relocate an unambiguous object to within less than 1 mm of the prescribed location. Treatment could then proceed within the mechanical accuracy and precision of the delivery system. The calibration procedure maintained excellent spatial resolution and delivery precision over the duration of this study, while the linear accelerator was in routine clinical use. Based on these results, the mechanical accuracy and precision of the system are ideal for supporting high-precision localization and treatment of soft-tissue targets.

Calibration↗

PubMedDate not supplied

Characteristic parameters of 6-21 MeV electron beams from a 21 MeV linear accelerator.

Dosimetry measurements have been carried out for the electron beams produced by a linear accelerator at energies 6, 8, 10, 14, 18, and 21 MeV. Characteristic parameters of the central axis dose distributions were derived and compared to corresponding values of electron beams from other accelerators in clinical use where such a comparison is appropriate. A comprehensive set of dosimetric parameters is provided for electron beam treatment planning. The data include central axis depth dose, range-energy parameters, beam penumbra and uniformity.

Electrons↗

PubMed2005

Modelling of output factors for conformal megavoltage X-ray beams.

A method is described for calculating the output from conformally shaped megavoltage X-ray beams. The model has been developed for Varian accelerators but is shown to work for accelerators from another manufacturer. The use of dynamic wedging and both static and dynamic multileaf collimated beams are included in the model. For any linear accelerator, the data required are a set of measured output factors for square beams, an in-air profile and a limited number of readily available parameters defining the geometry of the head of the accelerator. The three components of the output, namely primary, head scatter and phantom scatter are modelled and calculated individually for any point in a beam. An optimization procedure is developed that automatically determines the eight parameters required to model an accelerator in order for these calculations to be performed. The performance of the method is demonstrated for shaped beams using asymmetric and multileaf collimation, both with and without wedging, and for a range of beam energies. The model has been incorporated into a computer program that is used clinically.

Algorithms↗

PubMedDate not supplied

[Radiobiological research at the Joint Institute for Nuclear Research (JINR)].

The Joint Institute for Nuclear Research has the unique sources of ionizing radiation. The different radiobiological researches have been carried out at the JINR accelerators for more than forty years. They are connected not only to the solution of fundamental problems of radiation genetics but also with applied tasks of great social importance. These tasks are concerned with the improvement of targeted therapy methods for treatment of cancer diseases.

Academies and Institutes↗

PubMed1994

Routine linear accelerator calibration measurements and reports logged and generated by the treatment recording and verification computer.

A system is described for recording weekly calibration results for both photon and electron beams for two linear accelerators. The system accommodates all possible combinations of electrometers and ion chambers that can be used in the calibration procedures. The calibration data and dosimetric constants for the instrumentation are password protected with privileged access to make changes only available to the physicist manager of the therapy QA program.

Calibration↗

PubMed2003

Obliteration of giant corpus callosum AVM with linac based stereotactic radiosurgery.

Successful management of large AVMs is difficult. Traditionally they are considered less responsive and even unsuitable for radiosurgery. This case report demonstrates total angiographic obliteration in a complex, large corpus callosum AVM (volume 36.52 cc) in a 39-year-old male. Stereotactic radiation was delivered with a Linear Accelerator using ultra conformal treatment planning. Large volume AVMs can be subjected to stereotactic radiosurgery if the shape and location makes it possible to deliver an adequate radiation dose.

Adult↗

PubMed1995

History of medical radionuclide production.

Radionuclide production for medical use originally was incidental to isotope discoveries by physicists and chemists. Once the available radionuclides were identified they were evaluated for potential medical use. Hevesy first used 32P in 1935 to study phosphorous metabolism in rats. Since that time, the development of cyclotrons, linear accelerators, and nuclear reactors have produced hundreds of radionuclides for potential medical use. The history of medical radionuclide production represents an evolutionary, interdisciplinary development of applied nuclear technology. Today the technology is represented by a mature industry and provides medical benefits to millions of patients annually.

Animals↗

PubMedDate not supplied

A dose-per-pulse monitor for a dual-mode medical accelerator.

On a radiotherapy accelerator, the dose monitoring system is the last level of protection between the patient and the extremely high dose rate which all accelerators are capable of producing. The risk of losing this level of protection is substantially reduced if two or more dose monitoring systems are used which are mechanically and electrically independent in design. This paper describes the installation of an independent radiation monitor in a dual-mode, computer-controlled accelerator with a moveable monitor chamber. The added device is fixed in the beam path, is capable of monitoring each beam pulse, and is capable of terminating irradiation within the pulse repetition period if any measured pulse is unacceptably high.

Electrons↗

PubMed1979

[Results of treatment of breast cancer with a betatron (author's transl)].

The authors analyze the results of post-operative therapy with accelerated electrons from a betatron, more especially with pendular bi-energetic electrontherapy, applied to 459 patients with various stages of breast cancer. They stress that as well as the favourable survival rate, sequelae were rare, and there were very few local recurrences.

Adult↗

PubMed1984

[Eye movements induced by the parallel-swing method in rabbits].

Eye movements induced by sinusoidal linear accelerations generated by the parallel-sled, have been recorded by means of monocular electronystagmographic recordings in the horizontal and vertical plane. Qualitatively the recorded eye movements are vertical sinusoidal eye movements. When the sled moves to the right, the right eye moves upward, and the left eye downward. When the sled moves to the left, the inverse takes place. This seems to suggerate that the vestibulo-ocular reflex tested here, tries to compensate an imaginary rotation of the laboratory animal in the direction of the resultant acceleration stimulus. The false difference between the two eyes is 180 degrees, independant of the frequency of the sled. The false-difference between the sled and the eye movements increases with the frequency. The natural frequency is 0,6 Hz. The maximal amplitude is reached at the same frequency of 0,6 Hz (resonance frequency). Artefacts are present from the frequency of 0,8 Hz on. These are caused by movements of the needle electrodes on their own, due to the big accelerations on these frequencies. They are clearly distinguishable from the real eye movements. The gain "G" is incomplete, higher for the lower frequencies (0,5 for 0,3 Hz), and lower for the higher frequencies (0,1 for 0,8 Hz).

Animals↗

PubMed1980

Comparison between experimental measurements and calculated transport simulation for electron dose distributions inside homogeneous phantoms.

Comparison is made between dosimetric results measured on electron beams delivered by the three medical accelerators Sagittaire, Saturne and Neptune built by CGR MeV with the results simulated by a Monte Carlo method. In depth, the differences are small for moderate energies with scanned electron beams. In the penumbra region, the differences are small in all cases.

Electrons↗

PubMed2005

Electron scattering filter design for a single field rotational total skin irradiation.

The aim of radiotherapy treatment of cutaneous T-cell lymphoma is to irradiate the skin with an appropriately homogeneous dose distribution up to a few millimetres in depth. This can be achieved by applying one of the total skin electron irradiation techniques. An aluminium/polystyrene foam electron scattering filter was designed so that the incident beam is broadened and degraded sufficiently to achieve a mean dose uniformity in a rectangular field of 180 cm height and 40 cm width. This paper reports on the development and construction of the electron scattering filter for use with a Varian 2100C accelerator, without MLCs, with a dose uniformity, over a useful field dimension of 180 cm height and 40 cm width, of +/- 7% about the mean, and an x-ray contamination of less than 2.4% beyond a depth of 3 cm.

Electrons↗

PubMed1996

Development of methods for dynamic radiation therapy with specified dose distributions.

Several methods for dose deposition of a given isodose distribution were developed by implementation of different techniques of accelerator use. Common to all of these methods is the time-dependent change of certain accelerator parameters during radiation treatment. The accelerators for which these methods can be used are equipped with independent collimator jaws, however, not with any kind of multileaf collimation. This method was designed to deposit a certain group of dose distributions that are restricted by a small number of constraints. The developed methods were implemented into a digitally controlled medical linear accelerator and the dosimetric results of such treatments were evaluated. Dose distributions with spatial dependencies in one and in two dimensions were deposited by movement of one X-ray jaw pair. Furthermore, a method for generation of a two-dimensional rotationally symmetric dose distribution was developed.

Algorithms↗

PubMed1997

Basic Treatment Equivalent (BTE): a new measure of linear accelerator workload.

The measurement of linear accelerator workload in radiation oncology departments is usually based on the number of fields treated per unit time. However, this approach ignores variations in treatment complexity. This prospective study, was designed to measure treatment workload directly, taking into account the variations in complexity of different treatment techniques. From this, a model was to be developed, which would be simple to apply and reproducible, both within and between radiation oncology departments in Australasia. It would provide a realistic basis for assessing treatment costs and enable the comparison of patient throughput between departments. This paper describes the derivation of the model. Over a 4-week period in the Radiation Oncology Department of Westmead Hospital, all fractions of radiotherapy were timed. The data collected included: tumour site; treatment intent; number of fields; number of wedges, compensators and shielding blocks; fraction number; patient age; performance status; and need for general anaesthesia. Multivariate modelling was performed to identify factors that significantly affected fraction duration, so that these could be used to develop a model of resource utilization. The durations of 2371 fractions were measured in 219 patients. Seventy-five per cent of fractions were given with radical intent. The factors found to influence fraction duration on multivariate modelling were: number of fields; number of shielding blocks; first treatment fraction; need for anaesthesia; and performance status. The number of wedges and compensators were also found to be significant but were not included in the model in order to maintain simplicity. This was felt to be necessary if the model is to be applied to the widest possible variety of machines. A model of resources utilization called 'Basic Treatment Equivalent' (BTE) was derived, which incorporated these factors. When tested at Westmead Hospital, this model accurately reflected the predicted BTE value over a further 1-week study period. This model of linear accelerator use, which incorporates complexity has been derived and evaluated in one radiation oncology department. This requires further prospective testing before its widespread use. The model appears to reflect linear accelerator workload better than previous measures. An Australasian study to validate the model further will be undertaken. If adopted, this model has implications for comparative workload reports, diagnostic-related groups, waiting list calculations, and patient scheduling.

Efficiency↗

PubMed2001

Special radiation protection aspects of medical accelerators.

Radiation protection aspects relevant to medical accelerators are discussed. An overview is first given of general safety requirements. Next, shielding and labyrinth design are discussed in some detail for the various types of accelerators, devoting more attention to hadron machines as they are far less conventional than electron linear accelerators. Some specific aspects related to patient protection are also addressed. Finally, induced radioactivity in accelerator components and shielding walls is briefly discussed. Three classes of machines are considered: (1) medical electron linacs for 'conventional' radiation therapy, (2) low energy cyclotrons for production of radionuclides mainly for medical diagnostics and (3) medium energy cyclotrons and synchrotrons for advanced radiation therapy with protons or light ion beams (hadron therapy).

Electrons↗