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Results for “Particle Accelerators”

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PubMed2005

Neutron cross section measurements at ORELA for improved nuclear data and their application.

To support the Nuclear Criticality Safety Program, the Oak Ridge Electron Linear Accelerator (ORELA) has been used to measure the total and capture neutron cross sections of several nuclides in the energy range from 100 eV to -600 keV. Concerns about the use of existing cross section data in nuclear criticality calculations have been a prime motivator for the new cross-section measurements. Our new capture cross sections of aluminium, silicon, chlorine, fluorine and potassium in the energy range from 100 eV to 600 keV are substantially different from the cross sections in evaluated nuclear data files of ENDF/B-VI and JENDL-3.2.

Databases, Factual↗

PubMedDate not supplied

The neutron dose and energy spectrum outside a 20-MV accelerator treatment room.

A maze design is discussed for a Therac 20 linear accelerator (manufactured by Atomic Energy of Canada, Ltd.) which reduces the flux of neutrons at the door to permissible levels in controlled areas. The L-shaped design allows for a relatively light door at the end of the maze, consisting of 5.08-cm (2-in.) borated polyethylene and 2-mm lead. A comparison is made between the neutron dose equivalent (DE) calculated by various methods and the DE measured with a variety of portable neutron survey meters. In addition, the neutron energy spectrum outside the maze at 1 m from the door, measured with a polyethylene multisphere LiI system, is reported.

Humans↗

PubMedDate not supplied

Output factor constituents of a high-energy photon beam.

Measurements designed to separate primary and various scatter components of central axis dose of the highest energy photon beam of the CGR Saturne 25 linear accelerator are described. This beam has an unusually large output variation with field size. The measurements are performed both in air and in a water phantom, with and without an aperture external to the collimator system. Results are presented in the form of relative output factors for different field sizes due to (i) flattening filter scatter, (ii) water phantom scatter, (iii) collimator backscatter into the monitor chamber, and (iv) collimator forward scatter onto the central axis. It is found that the flattening filter is the single largest scatter component, but that each of the other factors is significant in determining the output dose per monitor unit as a function of field size.

Humans↗

PubMed1979

Mutation and inactivation of cultured mammalian cells exposed to beams of accelerated heavy ions. I. Irradiation facilities and methods.

This paper, which is the first of four covering the inactivation of clonogenic capacity and induction of mutation in cultured mammalian cells, deals briefly with the general aims of the work and describes the irradiation techniques used. Human diploid fibroblasts and V79 Chinese hamster cells were irradiated as monolayers with ions of helium, boron or nitrogen at LET's in the range 20 to 479 keV micrometer-1 in H2O. The physical aspects of the irradiation including measurement of ion energies, dosimetry and uniformity of dose and also the methods of handling large numbers of samples are described in detail. Subsequent papers will present the biological methods and results and a biophysical analysis of the data.

Animals↗

PubMed2005

A simple technique for craniospinal radiotherapy in the supine position.

PURPOSE: Craniospinal irradiation poses technical difficulties that may be addressed with the use of the newer technologies that have become available over the past decade. The use of CT simulation allows improved target localisation and beam geometry definition while significantly reducing the treatment simulation time. We have developed a CT-based technique for whole CNS irradiation in the supine position that uses fixed field parameters, asymmetric jaws for field matching and drastically reduces simulation and treatment times. METHODS: The patient is CT scanned and treated in the supine position. The clinical target volume and relevant critical structures are outlined on a planning CT scan. Half beam blocked lateral fields with a collimator rotation are used to match the beam divergence from the superior border of the spinal field at the C2 vertebral body. The shielding for the cranial fields is generated automatically, and the dose distribution is calculated using a 3D treatment planning system. Fixed field parameters are used for the planning and treatment. The position of the isocenter of the spine field is always a fixed longitudinal distance from the isocenter of the brain fields. If multiple posterior fields are required, the isocenter of the second spine field is always a fixed longitudinal distance from that of the first and the gap between the fields is determined using virtual simulation and feathered during treatment using the asymmetric jaws of the linear accelerator. All treatment portals are filmed daily during the first week of treatment, and after each junction change thereafter. RESULTS AND CONCLUSION: The supine position provides numerous advantages. Patients are more comfortable, the treatment position is more reproducible, and access to the airway is possible, if necessary, for patient sedation. The use of CT simulation decreases the simulation time, allows for increased planning accuracy, and enables the use of multimodality image registration, and 3D treatment planning. The use of asymmetric jaws allows for junction feathering without changing the patient setup or using a couch angle.

Axis, Cervical Vertebra↗

PubMed2003

Development of a low-energy monoenergetic neutron source for applications in low-dose radiobiological and radiochemical research.

The McMaster University 3 MV KN Van de Graff accelerator facility primarily dedicated to in vivo neutron activation measurements has been used to produce moderate dose rates of monoenergetic fast neutrons of energy ranging from 150 to 600 keV with a small energy spread of about 25 keV (1sigma width of Gaussian) by bombarding thin lithium targets with 2.00-2.40 MeV protons. The calculated dose rate of the monoenergetic neutrons produced using thin lithium targets as functions of beam energy, target thickness, lab angle relative to beam direction, and the solid angle subtended by the sample with the target has also been reported.

Equipment Design↗

PubMed2002

[Quality control of intensity modulated treatments in radiotherapy].

Since January 2001, radiotherapy treatments with modulated intensity beams (IMRT) have started at the Centre Oscar-Lambret. This paper presents the tests and measurements made before the clinical implementation as well the quality control performed before each routine treatment. We use the treatment planning system Helax-TMS (MDS-Nordion) and the Primus accelerator (Siemens) linked to the Lantis network with Primeview and Simtec modules (Siemens) allowing to deliver intensity modulated beams with Step-and-Shoot technique. A prostate case and a head and neck case have been studied and have permitted to evaluate the benefit of IMRT compared to a "classical" conformal radiotherapy. In a second time, we have tested the accelerator's capabilities to deliver these intensity modulated beams, id-est, the accuracy of the leaf positions and the linearity of the monitor chamber. The third step has been the verification of the dose distributions calculated by Helax-TMS, id-est, the dose for different segment sizes, the dose profiles for an intensity modulated beam and the dose distribution for all the traitment beams. The used phantom has been especially developed at the Centre Oscar-Lambret for IMRT. The results have allowed to start clinical treatments and to establish a quality control set for this technique. The next step is the real time dosimetry with a portal imager.

Humans↗

PubMedDate not supplied

Dose delivery error detection by a computer-controlled linear accelerator.

A commercial dual photon energy, computer-controlled linear accelerator has a complex collimation and beam delivery system. For accurate dose delivery, six separate motorized elements must be properly positioned for a given beam selection. Experimentally instituted misalignments of the primary electron scattering foils, the primary collimator, the flattening filter, the scattering foil carousel, and the backscatter shield or shutter produced significant dose delivery errors. The ability of the Mylar window monitor chamber to detect these errors was examined for x-ray beams. The fault detection system failed to interrupt dose delivery in a number of situations where the error in dose per monitor unit delivered ranged from -6% to +270% of the calibrated value.

Computers↗

PubMed1983

Geometric parameters of clinical electron beams.

The influence of different components in the treatment head of a therapy accelerator on the geometric properties of the delivered electron beams have been analysed based on the theory of small angle multiple scattering. The analyses show that it is possible to define and compute the properties of an effective electron source which, when placed in vacuum at some distance from the patient, produces exactly the same electron fluence at the patient as the real beam. The effective source is fully described by three parameters: its angular spread, its radial width and the distance from the patient. A numerical example indicates that the half width of the effective source could be considerable, often as large as 10 cm or more at low energies.

Computers↗

PubMed2006

On measuring the output of an IORT mobile dedicated accelerator.

In the present work, dose-to-water values derived from Fricke (operated by the Italian Primary Standard Dosimetry Laboratory) and alanine (operated by the Istituto Superiore di Sanità, Italy) measurements in IORT electron beams characterised by a high dose per pulse were compared to show the extent of equivalence of the two dosimetry systems. This study demonstrates agreement (within 2%) of the two dosimetry systems for plane-base IORT applicators, but in the case of small diameter (40 mm) and bevelled (22.5 degrees ) applicators, Fricke dosemeters underestimated doses by 2.4%. For base bevelled IORT applicators (22.5 degrees or more) with small diameter ( approximately 40 mm or less) reduced dimensions of the dosemeter are needed. Under these measurement conditions, the alanine dosemeter gives better accuracy in beam output determination compared with the Fricke dosemeter used.

Equipment Failure Analysis↗

PubMed1999

[The establishment of prescription dose system for radiotherapy on accelerator's X-ray].

This study aimed at how to calculate the prescription dose quickly and accurately. According to the conditions of radiotherapy and the dose of target point. RT-100 Radiotherapy Dosemetre, which was calibrated at the Industrial Health Institute of National Ministry of Health, was used to detect the dose distribution of special points in the phantom. Functions of dose distribution were fitted on the basis of the detected points. The dose ratio was introduced, and the calculation protocol indexed with Chinese for prescription dose was programmed. The doses of assumed points at the phantom which imitated various conditions of radiotherapy were detected. The detected doses were very close to the calculated doses, with the relative error less than 1.2%. It is concluded that dose of target point can be transformed to the prescription dose quickly and accurately with the method of dose ratio.

Particle Accelerators↗

PubMedDate not supplied

Leakage radiation from electron applicators on a medical accelerator.

The leakage characteristics of electron applicators on our Clinac 2500 linear accelerator have been measured. The leakage radiation in the patient plane and at the surface of the electron applicators has been measured for applicator sizes from 6 cm X 6 cm to 25 cm X 25 cm and beam energies from 6 to 22 MeV. For certain applicator/energy combinations the leakage radiation was significant. The leakage radiation, relative to the central axis dose, was found to be up to 7% in the patient plane and up to 39% at the applicator surface. Reducing the collimator setting or adding lead at select locations on the applicator surface was effective in reducing the magnitude of the radiation leakage.

Biophysical Phenomena↗

PubMedDate not supplied

Mechanical and radiation isocenter coincidence: an experience in linear accelerator alignment.

As part of the commissioning procedure of a linear accelerator at our cancer center, the defining laser lines were aligned with the optical and radiation isocenter of the linac. When a mechanical checkout jig was set up at the same point, a discrepancy of 4 mm resulted when the gantry was moved from 0 degrees to 180 degrees. Extensive measurements, some with custom-designed devices, confirmed the observations and provided an explanation. Even though the mechanical isocenter is within the specified tolerance of 1-mm radius, the clinically observable discrepancy of 4-mm results from the noncoincidence of the mechanical and radiation isocenters. The clinical significance of the final setup is discussed and future commissioning procedures are recommended.

Particle Accelerators↗

PubMed1999

Analytical considerations of beam hardening in medical accelerator photon spectra.

Beam hardening is a well-known phenomenon for therapeutic accelerator beams passing through matter in narrow beam geometry. This study assesses quantitatively the magnitude of beam hardening of therapeutic beams in water. A formal concept of beam hardening is proposed which is based on the decrease of the mean attenuation coefficient with depth. On the basis of this concept calculations of beam hardening effects are easily performed by means of a commercial spreadsheet program. Published accelerator spectra and the tabulated values of attenuation coefficients serve as input for these calculations. It is shown that the mean attenuation coefficient starts at depth zero with an almost linear decrease and then slowly levels off to a limit value. A similar behavior is found for the beam hardening coefficient. A physically reasonable, semianalytical model is given which fits the data better than previously published functions. The energy dependence of the initial attenuation coefficient is evaluated and shown. It fits well to published experimental data. The initial beam hardening coefficient, however, shows no energy dependence. Its mean value (eta0) approximately 0.006 cm(-1)) is also in close agreement to the measured data.

Algorithms↗

PubMed1978

[Advantages and disadvantages of a 5.7 MeV linear accelerator compared to a 60Co-unit (author's transl)].

A comparison between a 60Co therapy unit and a 5.7 MeV linac shows the following advantages of the accelerator: 1. More favourable depth dose distribution with an improvement of the field homogeneity in the midplane for mantle techniques by a factor of 3 without the use of compensating filters. 2. Change of the maximum from 4 to 12 mm depth and thereby better skin sparing and greater dose tolerance of the skin and subcutaneous tissue. 3. Up to 10 times less penumbra. 4. Increased and stable dose rate of approximately 250 rd/min. At the moment the main disadvantages are the 20 to 30% higher purchase and running costs, and furthermore a downtime of at least 1 week per year for servicing and repair.

Adipose Tissue↗

PubMed1977

[Dosimetry using the linear accelerator (author's transl)].

On the basis of data employed in radiation therapy with megavoltage X-radiation from the linear accelerator Philips SL 75/10 have been developed clearly arranged and practicable treatment schedules for the use of the radiotherapist. Application of a fixed focal dose, for instance 250 R per session, makes the number of days needed for irradiation easy to calculate. The possible field sizes are classified with regard to equivalent relative deviations at the class limits, and represented by a pattern of diaphragms. Thus, and by the use of constant focus-skin distance of 90 cm, well-arranged tables are obtained. Two-year experiences with the utilization of these schedules as well as the check-up by daily measurements and the necessary controls of operating conditions are summarized in diagrams.

Humans↗

PubMed1996

Forty years' experience with a special, non-tumorous application of radiotherapy for the eye.

This paper recapitulates experience made over 40 years with a special nontumorous radiotherapy for the eye. Following a review of the development of therapy, which began with the pendular convergence x-ray machine and later changed to the linear accelerator, an overview is presented of the most important indications for the safe use of x-rays in exudative inflammatory processes in the posterior segment of the eye. We show that in many cases radiotherapy can achieve a permanent improvement for years or at least the preservation of the status quo, while also protecting the important visual cells, especially if it is administered at the earliest possible stage alone. However, it is even more effective in combination with retrobulbar injection therapy that is adjusted individually. Statistics on the results in cases of disciform macular degeneration, doubtlessly the most frequent indication for non-tumorous radiotherapy in the eye, exemplify its efficacy.

Eye Diseases↗

PubMedDate not supplied

Temperature-pressure compensation for a linear accelerator electron beam dosimeter.

Routine weekly calibration of a Siemens Mevatron 20 linear accelerator with 3-, 5-, 7-, 10-, 12-, 15-, and 18-MeV electron energies demonstrated fluctuations in dose/monitor unit for the electron beam on the order of 3%-6%. Evaluations and study of the problem demonstrated that the electron chamber, which is open to atmosphere, was undergoing significant temperature changes during the course of a treatment day. The inability of the chamber to compensate for these changes in temperature and pressure led to the addition of a compensating circuit by the manufacturer. The results of the addition of this circuit were evaluated for several extended periods throughout the year, and it was found that the changes in dose/monitor were reduced to approximately +/- 0.5%.

Calibration↗