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Results for “Particle Accelerators”

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PubMed1991

Biological response in vitro to pulsed high dose rate electrons from a clinical accelerator.

Several studies of biological response to ionizing radiation of high absorbed dose rates have been performed, often with conflicting results. The aim of this study was to establish whether a difference between irradiation at high dose rates and at more conventional dose rates could be verified. Pulsed 50 MeV electrons from a clinical accelerator were used both for the high dose rate experiments (mean dose rate: 3.8 x 10(2) Gy/s) and the reference experiments (mean dose rate: 9.6 x 10(-2) Gy/s). In this study V-79 cells were irradiated in vitro. The experiments were carried out under both oxic and anoxic conditions. No significant difference in relative biological effectiveness (RBE) or oxygen enhancement ratio (OER) was observed at the different dose rates investigated.

Animals↗

PubMed1988

[Preliminary study of the use of a narrow photon beam for radiotherapy of neurosurgical patients].

Acute subarachnoidal hemorrhage or focal epilepsy in 5 patients was shown to be based on inoperable arteriovenous brain malformations (ABM) which was treated with the help of a linear accelerator. In one case 1 year 9 months after irradiation repeated hemorrhage was noted, the malformation was removed by an open surgical method. Clinical convalescence after irradiation was observed in the other 4 patients without side-effects during a follow-up period of 1-3 yrs. Angiography after irradiation was not performed. Teleroentgenotherapy was regarded as a good alternative in the treatment ofinoperable arteriovenous brain malformations.

Adolescent↗

PubMed1991

Modification of a three-dimensional treatment planning system for the use of multi-leaf collimators in conformation radiotherapy.

The multi-leaf collimator of the DKFZ is designed as a low cost add-on device for conventional linear accelerators for radiotherapy. The technical specification of the computer controlled collimator is described briefly. A major limitation in the use of the wide capabilities of multi-leaf collimators in the clinic is still an appropriate treatment planning system. This paper describes treatment planning and dose calculation techniques for multi-leaf collimators and shows examples where the capabilities of the collimator are used extensively.

Dose-Response Relationship, Radiation↗

PubMed1994

A feasibility study of partially accelerated radiotherapy for invasive bladder cancer.

Thirty-nine patients with histologically confirmed invasive bladder carcinoma (T2-3, N0, M0) were treated with a partially accelerated radiotherapy scheme. After 40 Gy/4 weeks of conventional fractionation we have accelerated the treatment in the last week giving two daily fractions of 2 Gy each, 4-6 h apart in the bladder only. Although the follow-up of some of the patients is not very long our results indicate that this relatively short radiotherapeutic scheme is feasible, convenient and probably safe for patients living in remote areas.

Aged↗

PubMed1993

The design of an adjustable half block for nonasymmetric linear accelerators.

Half-block techniques in radiotherapy may be used to junction two abutting radiation fields. Removable half blocks for linear accelerators not equipped with asymmetrical jaws can accomplish this technique providing the block edge is properly secured with respect to the beam central axis to achieve a smooth beam junction. Successive block edge cuts with a milling machine are, however, required to achieve an acceptable junction of the fields. The design of a half-block device that allows secure adjustment of the block edge on the linac thus alleviating the need for successive milling procedures is presented.

Equipment Design↗

PubMed2005

The PDS-XADS reference accelerator and its radioprotection issues.

At the start-up of the FP5 project PDS-XADS, the main initial specifications for the accelerator system (e.g. beam energy, beam intensity, beam profile, their stability and the accelerator availability and reliability) have been defined by Working Package 1 (WP1), 'Global Coherence', in connection with the other WPs of the project. From this, WP3 ('The Accelerator') has assessed the main requirements and the corresponding technical answers. A reference solution, based on a linear superconducting accelerator with its associated doubly achromatic beam line has been worked out to some detail. For high reliability, the proposed design is intrinsically fault tolerant, relying on highly modular 'de-rated' components associated with a fast digital feedback system. The proposed solution also appears to be robust in terms of operational aspects like maintenance and radioprotection. A programme for the remaining R&D required has been elaborated and is proposed within the FP6 project EUROTRANS.

Equipment Design↗

PubMedDate not supplied

Elongation effects on the Therac 6 linear accelerator.

The effects of field elongation on the central-axis output at dmax and on the depth-dose curves for the 6-MV x rays from the Therac 6 linear accelerator are considered. These parameters are independent of the collimator angle for both square and elongated fields. The exchange of collimator pairs results in significant output differences but has a negligible effect on the depth-dose curves. Both the central-axis output at dmax and the depth-dose curves agree satisfactorily with the predictions of the equivalent-square technique. An alternative method of greater accuracy is also indicated for the prediction of central-axis outputs at dmax for elongated fields.

Humans↗

PubMed2000

Breathing-synchronized radiotherapy program at the University of California Davis Cancer Center.

In this paper we present a complete description of the breathing synchronized radiotherapy (BSRT) system, which has been jointly developed between the University of California Davis Cancer Center and Varian Associates. BSRT is a description of an emerging radiation oncology procedure, where simulation, CT scan, treatment planning, and radiation treatment are synchronized with voluntary breath-hold, forced breath-hold, or breathing gating. The BSRT system consists of a breathing monitoring system (BMOS) and a linear accelerator gating hardware and software package. Two methods, a video camera-based method and the use of wraparound inductive plethysmography (RespiTrace), generate the BMOS signals. The BMOS signals and the synchronized fluoroscopic images are simultaneously recorded in the simulation room and are later analyzed to define the ideal treatment point (ITP) where organ motion is stationary. The BMOS signals at ITP can be used to gate a CT scanner or a linear accelerator to maintain the same organ configuration as in the simulation. The BSRT system allows breath-hold or gating. This dual role allows the system to be applicable for a variety of patients, i.e., the breath-hold method for those patients who can maintain and reproduce the ITP, and the forced breath-hold or gating method for those who are not ideal for voluntary breath-hold.

Fluoroscopy↗

PubMed1977

[The value of routine in vivo measurements in radiotherapy (author's transl)].

The authors carried out routine measurements in vivo, and emphasise their value in radiotherapy. After reviewing the objectives of in vivo measurements in general, and showing the problems posed by routine measurements, they describe the technique of measurement using thermoluminescent dosimeters and the problems associated with their use in patients treated with the aid of a 5.5 MV linear accelerator. Results based upon 232 routine measurements made it possible to establish a correlation between the dose delivered and the expected dose. Under optimal functional conditions, almost all the deviations seen were less than 5% whilst higher deviations occurred when the apparatus showed signs of instability. They conclude that routine in vivo measurements are extremely useful in ensuring that planned treatment is carried out in a satisfactory manner and also in the early detection of potential faults in equipment.

Humans↗

PubMed2006

Development and commissioning of a Monte Carlo photon beam model for Varian Clinac 2100EX linear accelerator.

Monte Carlo modeling of a linear accelerator is the first and most important step in Monte Carlo dose calculations in radiotherapy. We developed a photon beam model for Varian 2100EX for dose calculation purposes using MCNP4C Monte Carlo code. Results of our modeling were in close agreement with our measurements. The effect of beam width on percentage depth doses and beam profiles was studied. Our results showed that electron beam width could be tuned using large field beam profile at the depth of maximum dose.

Monte Carlo Method↗

PubMedDate not supplied

X-ray beam characteristics of the Varian Clinac 6-100 linear accelerator.

Beam characteristics and dosimetry measurements of the 6 MV x-ray beam from a Varian Associates Clinac 6-100 linear accelerator are presented. Percentage depth dose tables are given as a function of field size for square fields. Tissue-maximum ratios and scatter-maximum ratios are tabulated as a function of depth and field size. Investigation of surface dose and depth of maximum dose reveal a dependence on field size. Other beam parameters measured are presented include field flatness, symmetry, SSD dependence, and penumbra. Treatment planning parameters including field size output factors and wedge factors are discussed.

Particle Accelerators↗

PubMedDate not supplied

Effect of the accelerator design on the position of the effective electron source.

An analysis of the effective source-surface distance was made taking into account the influence of energy, field size, equivalent square field size, and the accelerator design. Measurements made in three accelerators showed the influence of parameters like beam flattening and collimation systems on the effective source-surface distance. A brief review of the theory is made leading to a mathematical expression for the effective source-surface distance, showing a good agreement with the experimental results. An alternative method for correcting the dose rate, maintaining the nominal source-surface distance, and not using the inverse square law, but a greater power function, is suggested.

Electrons↗

PubMedDate not supplied

Unexpectedly large dose rate dependent output from a linear accelerator.

During our routine calibration of a Varian Clinac-20 linear accelerator, the absorbed dose for a fixed monitor unit (mu) was found to decrease with increasing dose rate. Between dose rates of 100 and 500 mu/min, there was up to 20% difference in absorbed dose for a 20-MeV electron beam. The cause of this problem was a failure in the electronics circuit of an integrating board. This paper presents our analysis of the problem and suggests a possible means of isolating such a failure to warn technologists, physicists, and engineers.

Biophysical Phenomena↗

PubMedDate not supplied

Therapy imaging: source sizes of radiotherapy beams.

We have developed a novel method, which employs large lead collimators and computed tomography reconstruction techniques, to measure the intensity distributions of x-ray sources of radiotherapy devices. Using this method, we have measured the intensity distributions of x-ray sources from 60Co, 6-, 18-, and 25-MV radiotherapy devices. The x-ray sources of the accelerators were all elliptical in shape, but varied in eccentricity, and the sizes of the accelerator sources varied from 0.7 to 3.3 mm full width at half-maximum. The 60Co source was circular in shape and 20 mm in diameter, however, the output from this source was not uniform across its face. The modulation transfer functions (MTF's) (at the image plane) calculated for the accelerator sources, assuming an image magnification of 1.2, had similar magnitudes at low spatial frequencies as the MTF's of the metal plate/film detectors commonly used for therapy imaging. However, the source MTF's declined much more rapidly at high spatial frequencies. Therefore, for geometries commonly found in radiotherapy, the loss in spatial resolution due to the x-ray source was at least equal to that caused by electron and photon scatter within the metal plate/film detectors.

Cobalt Radioisotopes↗

PubMed1988

[Topometric and clinico-dosimetric aspects of the radiotherapy of cancer of the oropharynx].

The use of modern diagnostic facilities led to a study of the physico-dosimetric, topometric and clinical aspects of radiotherapy of oropharyngeal cancer. The most effective approaches to therapy of oropharyngeal tumors with account of their site, spread and degrees of differentiation were developed. The most effective method was shown to be the combination of gamma-beam therapy (50 Gy) with electron-photon radiation (20 Gy) of an accelerator of 18-20 MeV, radiation exposure of normal tissues being lowered by approximately 10-20% as compared to that in gamma-beam therapy used alone. The use of the above method in 45 oropharyngeal cancer patients resulted in an immediate clinical effect (disappearance of a tumor and regional metastases (if any) in 60% of the patients. The 2-year survival rate calculated by actuarial curves, was 62 +/- 10%.

Adult↗

PubMed1983

[Somatic radiation risk in brain irradiation].

The somatic dose index for irradiation of the brain was determined for the 10 MeV bremsstrahlung of a linear electron accelerator. A small volume rotation technique and the irradiation of the total neurocranium were chosen as extreme conditions for the radiation exposure of the skull. On the basis of a target volume dose of 50 Gy for the total irradiation series, the somatic dose index of the small volume technique is within the scope of coronarography. In case of irradiation of the total neurocranium, however, the somatic dose index largely exceeds the maximum values of X-ray diagnosis.

Brain↗

PubMedDate not supplied

Shaped field electron dosimetry for a Philips SL75/10 linear accelerator.

Both small and irregular fields are frequently the treatment of choice in many clinical applications of electron therapy. The fields are often shaped by lead or low melting point alloy placed at the end of the cone or on the patient's surface. The dosimetry for electrons of energies of 4, 6, 8, and 10 MeV is examined with particular emphasis on very small fields for treatment such as the lip, nose, and eye and irregular fields of various area/perimeter ratios. The paper discusses the dosimetry correction due to field shaping as a function of the location of the shield.

Humans↗

PubMed2001

Dosimetry of low-energy protons on the vertical-beam facility at the Munich accelerator.

Various methods of dosimetry for protons with energies up to 25 MeV were compared for radiation fields as might be used in the skin treatment of patients or in biological experiments. The methods used were: Fluence of individually registered protons; Charge deposition in commercially available ionisation chambers; Thermoluminescence detectors, exposed in Munich and evaluated in Krakow; Photometricallly evaluated commercial Fricke dosimeter. An overall agreement within 5% was found between the absolute dose measurements. Depth-dose distributions for Bragg curves measured by a Markus chamber with a depth resolution of 10 micrometers agreed with calculations.

Ferrous Compounds↗