Early experience with linear accelerator in carcinoma oesophagus middle third.
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Adult↗
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Results for “Particle Accelerators”
Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.
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Impaired repair capacity of DNA breaks induced in mammalian cellular DNA by accelerated heavy ions.
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Argon↗
Dynamic collimator and dose rate control: enabling technology for enhanced dynamic wedge.
The key features that make dynamic dose delivery possible in the Enhanced Dynamic Wedge application are computerized position and control of the independent collimating jaws and computerized dynamic control of the linear accelerator dose rate. These features will be described and related to the current implementation of Enhanced Dynamic Wedge.
Particle Accelerators↗
On isocentre adjustment and quality control in linear accelerator based radiosurgery with circular collimators and room lasers.
We have developed a densitometric method for measuring the isocentric accuracy and the accuracy of marking the isocentre position for linear accelerator based radiosurgery with circular collimators and room lasers. Isocentric shots are used to determine the accuracy of marking the isocentre position with room lasers and star shots are used to determine the wobble of the gantry and table rotation movement, the effect of gantry sag, the stereotactic collimator alignment, and the minimal distance between gantry and table rotation axes. Since the method is based on densitometric measurements, beam spot stability is implicitly tested. The method developed is also suitable for quality assurance and has proved to be useful in optimizing isocentric accuracy. The method is simple to perform and only requires a film box and film scanner for instrumentation. Thus, the method has the potential to become widely available and may therefore be useful in standardizing the description of linear accelerator based radiosurgical systems.
Algorithms↗
Neutron source strength measurements for Varian, Siemens, Elekta, and General Electric linear accelerators.
The shielding calculations for high energy (>10 MV) linear accelerators must include the photoneutron production within the head of the accelerator. Procedures have been described to calculate the treatment room door shielding based on the neutron source strength (Q value) for a specific accelerator and energy combination. Unfortunately, there is currently little data in the literature stating the neutron source strengths for the most widely used linear accelerators. In this study, the neutron fluence for 36 linear accelerators, including models from Varian, Siemens, Elekta/Philips, and General Electric, was measured using gold-foil activation. Several of the models and energy combinations had multiple measurements. The neutron fluence measured in the patient plane was independent of the surface area of the room, suggesting that neutron fluence is more dependent on the direct neutron fluence from the head of the accelerator than from room scatter. Neutron source strength, Q, was determined from the measured neutron fluences. As expected, Q increased with increasing photon energy. The Q values ranged from 0.02 for a 10 MV beam to 1.44(x10(12)) neutrons per photon Gy for a 25 MV beam. The most comprehensive set of neutron source strength values, Q, for the current accelerators in clinical use are presented for use in calculating room shielding.
Elementary Particles↗
[An installation control and documentation system for teletherapy equipment. Preliminary information].
The record and verify system (EPS) answers the control and recording of carrying out irradiation. Connection between accelerator and personal computer is done by a process calculator. The EPS-programme runs at a personal computer and is written in TURBO-Pascal. A first realization will be done at linear accelerator NEPTUN 10p.
Computer Systems↗
A simple magnetic spectrometer for radiotherapy electron beams.
A small, lightweight, single-focusing magnetic spectrometer was designed, assembled, and tested for analysis of electron beams from radiotherapy electron linacs. The objective was to develop a low cost, simple device that could be easily replicated in other medical centers, and to demonstrate the practicality of individual electron counting for precise analysis of electron spectra. Two methods of spectroscopy have been developed. One method consists of counting electrons individually as a function of magnetic field setting. Electrons are deflected through 90 degrees in the magnetic spectrometer, through an exit slit, and into a scintillation detector. A second method consists of recording the complete spectrum of electron energies from the accelerator on a strip of film at a single magnetic field setting. A critical design element is the 10-cm long collimator for electrons entering the magnet gap, with defining apertures and scraper slits. The spectrometer's cleanliness of transmission, energy calibration, and resolution were all tested at 10 and 16 MeV using the nearly monoenergetic electron beam of the accelerator at the National Research Council of Canada (NRCC). These accelerator tests, and also Monte Carlo trajectory simulations, both show that contamination of the transmitted spectrum due to scattered or knock-on electrons is negligible. Low-energy characteristics were tested using a 90Sr + 90Y beta-particle source. The energy calibration of the 90 degree spectrometer mode was based on mapping the magnetic field and also electron trajectory computer simulations. That calibration agrees with the NRCC's own calibrated scale to 0.8% for the single-particle counting method and to 1.3% for the film method. The energy resolution was measured to be 2% at 10 MeV, which is adequate for radiotherapy linac measurements. The acceptance half angle is 0.5 degrees or less, depending on the aperture size, which is adequate for electron angular distribution measurements within the forward cone of the electron beam. Used with film, the spectrometer is a simple, accurate, and highly transportable device for measuring radiotherapy electron energy spectra.
Biophysical Phenomena↗
Mutations induced by heavy charged particles.
The relative biological-effectiveness of radiation is increased when cells or tissue are exposed to densely ionizing (high-LET) radiation. A large number of studies focus on the following aspects of the biological effects of high-LET radiation: (i) basic understanding of radiation damage and repair; (ii) developing radiotherapy protocols for accelerated charged particles; and (iii) estimation of human risks from exposure to high-LET heavy charged particles. The increased lethal effectiveness (cell inactivation) of high-LET radiation contributes to new methods for using radiation therapy, but it is also necessary to study the enhanced mutagenic effect of high LET radiation, because higher frequencies of mutation can be expected to provide higher rates of carcinogenicity with human exposure. It is important to note that both measures of biological effectiveness (lethality and mutagenicity) depend on the quality of radiation, the dose, dose-rate effects, and the biological endpoints studied. This paper is intended to provide a review of current research on the mutagenic effects of high-LET radiation, and is organized into three sections. First, are descriptions of the induced mutations studied with various detection systems (section 1) because the detectable mutations induced by ionizing radiation, including heavy-ions, depend largely on the detection system used. Second is a discussion of the biological significance of the dependence of induced mutations on LET (section 2). This is related to the molecular nature of radiation lesions and to the repair mechanisms used to help cells recover from such damage. Finally, applications of mutation detection systems for studies in space (section 3) are described, in which the carcinogenic effects of space environmental radiation are considered.
Animals↗
Design, construction, and performance of an asymmetrical collimator for a cobalt unit.
PURPOSE: Besides four linear accelerators, our institute has a 100-cm SAD cobalt unit which has some specific and useful features for radiotherapy. The unit is equipped with a electronic portal imaging device (EPID) and an asymmetrical collimator to perform similar treatment techniques as on the linear accelerators, using the same shielding and half-beam techniques. The design, construction, and performance of the asymmetrical collimator are described. METHODS AND MATERIALS: The new design includes the doubling of the drive and read-outs for both X and Y jaws. Spare parts of the standard collimator provided by the manufacturer were used as much as possible. Special trimmers were designed to allow asymmetry to the center of the field. The trimmers are removable, but the design allows the use of trimmers, wedges, and shadow tray simultaneously. RESULTS: Transmission through the trimmers is less than 5% of the dose at d(max). The use of the trimmers extends the source to diaphragm distance to 53 cm, resulting in a smaller penumbra as compared to the standard collimator. Without the trimmers, the maximum field size remains unchanged, i.e., 40 x 40 cm(2); with the trimmers, it is 38 x 36 cm(2). Percentage depth doses and output factors were similar to the standard collimator. CONCLUSION: The modified collimator is compact and allows use of the same shielding blocks as the linear accelerators, providing the same treatment techniques and capabilities. This simplifies an exchange of patients between our treatment machines.
Cobalt Radioisotopes↗
A quality control method for detecting energy changes of medical accelerators.
A description is presented of a simple and sensitive method for detecting a change in the energy of the electrons bombarding the target of medical accelerators. This technique is useful for x-ray beams with end point energy in the range of 15.7 to 25 MeV. The method is based on the photoactivation of 160 and 14N in a small sample of ammonium nitrate. It was found that the ratio of the activity induced in the oxygen divided by that produced in the nitrogen can be used as a quality control technique to detect a change in the energy of the electrons that bombard the target of the accelerator. An electron energy change of the order of 0.2 MeV can be determined using this method.
Electrons↗
Induced activity in accelerator structures, air and water.
A summary is given of several rules of thumb' which can be used to predict the formation and decay of radionuclides in the structure of accelerators together with the dose rates from the induced radioactivity. Models are also given for the activation of gases (air of the accelerator vault) and liquids (in particular cooling water), together with their transport from the activation region to the release point.
Air↗
Effect of particle size on the adsorption of theophylline onto activated charcoal, in vitro study.
The effective use of activated charcoal as oral adsorbent in the primary treatment of acute theophylline poisoning was studied in vitro. Adsorption capacities for theophylline onto activated charcoal of varying particle size were investigated. No difference in the equilibrium amount of theophylline adsorbed onto activated charcoal was recognized. This result could be explained by the physical properties of activated charcoal. The amount of theophylline adsorbed from physiological saline solution was greater than that from water. The smaller the particle size of activated charcoal, the faster theophylline was adsorbed. It was assumed that the increase of contact area by grounding activated charcoal of large particle size accelerated the adsorption of theophylline onto activated charcoal.
Adsorption↗
[The improved determination of the dose rate in irregular photon fields].
A revised formula for calculation of dose per time or monitor unit ("dose rate") of irregular megavoltage photon beams is proposed. The formula considers additionally the shading by secondary shieldings of the plane source describing the scattered radiation in the head. Therefore, in addition to the primary output factor C(ac) as function of the equivalent square ac x ac of the collimator field size a secondary output factor S(as) is introduced denoted as function of the equivalent square as x as of the irregular field. S is determined using a satellite diaphragm formed of shielding blocks in combination with a totally opened collimator. In this definition, S includes both the effects of radiation scattered in tissue (phantom scatter factor PSF) and of missing photons from the plane source by the blocks (satellite diaphragm factor SAT). In the usual formula to calculate the "dose rate" (output) at reference point in depth t, PSF is replaced by S: D = D0 x C(ac) x [PSF(as)/PSF(ac)] x T x R(as,t). There T is representing the block tray factor and R(as,t) the tissue phantom ratio or relative depth dose, depending on the irradiation technique used. Thus the modified formula is given by D = D0 x C(ac) x [S(as)/S(ac)] x T x R(as,t). Measurements show that the revised formula provides an additional precision of up to 2% in the calculation of dose, depending on the type of accelerator respectively on the size of the plane source of scattered radiation.
Humans↗
[A universal verification and protocol system for teletherapy].
To increase the quality of radiotherapy a verify and record system (VPS) was developed for teletherapy equipments, that takes control of manually adjusted irradiation parameters and of recording all relevant data of radiotherapy. The VPS can be adapted to special wishes of the user and it lends itself to application on different irradiation equipments. In the represented paper especially the extent of efficiency of the system is shown which is characterized by high operating comfort, flexible reacting to exceptional cases and by high date and operating security. The testing phase on an accelerator model has been brought to a close, actually the system is installed to an electron linear accelerator "Neptun 10p" and led to clinical trial.
Humans↗
[Problems of multiple field technique in radiation therapy of cancer of the breast (author's transl)].
A method of adjustment frequently used for postoperative telecobalt irradiation of the mammary carcinoma was verified with the help of film-dosimetric measurements at a phantom. Special interest was taken in the regions with possible overlapping of contiguous fields, where serious complications may occur as a consequence of overlapping. Thus, apposition of several fields requires consideration of the divergence of rays and of the mapping precision of 50%-isodoses in the radiation field, as there lie the principal reasons. For realization of a nearly homogeneous dose distribution, on the one hand, there is necessary parallelism of marginal rays of the neighbouring useful ray beams, the radiation head being tilted laterally by half the angle of aperture; on the other hand, the 50% boundary lines at the light beam localizer have to be shifted parallel by a corresponding distance. In spite of this possibility of optimization, it is distinctly more advantageous, with regard to time and technical aspects, to use a linear accelerator, being additionally applicable for electron pendulum irradiation of the thoracic wall.
Breast Neoplasms↗
Accelerated partial breast irradiation: current modalities and investigations.
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Brachytherapy↗
[Effect of accelerated boron, carbon, and neon ions on human lymphocyte chromosomes in vitro].
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Boron↗
Characterization of fragmented heavy-ion beams using a three-stage telescope detector: measurements of 670-MeV/amu 20Ne beams.
Measurements of a 670-MeV/amu 20Ne beam at the Lawrence Berkeley Laboratory Bevalac heavy-ion accelerator with various thicknesses of water absorber were obtained with the BERKLET. The BERKLET, a simple three-stage solid-state telescope detector, has been described previously. This instrument measures the linear energy transfer (LET) and residual energy of particles, allows the identification of the particle's charge, and provides a means of obtaining LET and energy statistics for the beam, separated by particle charge. The track and dose averaged LET dependence on the amount of water absorber was determined for each species of fragment in the beam. Large numbers of low-LET particles in the fragmented beam were detected. The results of the analysis are presented followed by a discussion of the effects of multiple scattering and secondary fragmentation on the measurements. A brief discussion of the implications of the BERKLET measurements for radiobiology is also presented.
Energy Transfer↗