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At least 1,171 records · Page 65Linked to original sources

PubMed2004

Linear accelerator thalamotomy.

BACKGROUND: The capability of performing functional radiosurgery lesions in the brain using a dedicated linear accelerator (LINAC) have not yet been demonstrated. This study evaluates modern LINAC technology for the creation of a sharp, small and functionally eloquent lesion in the thalamus. METHODS: Three patients underwent thalamotomy using a dedicated linear accelerator to radiosurgery, 2 females and 1 male, ages were 52, 53, and 73 years. Two patients presented with unilateral poststroke central pain and 1 with unilateral upper extremity pain secondary to metastatic infiltration of the brachial plexus. Maximal doses varied from 150 to 200 Gy, delivered by a 5-mm diameter collimator and 5 to 8 noncoplanar arcs evenly distributed. RESULTS: All patients gained substantial relief of their pain. They were able to reduce their medications and improve their activity levels. The patient with end-stage metastatic disease died of his malignancy 2 weeks after the treatment. One patient presented with recurrence of the pain 4 months after the treatment. No clinical complications were noticed. CONCLUSIONS: A dedicated linear accelerator is able to perform a precise and circumscribed lesion in the thalamus for pain control. Moreover, it proved to be safe, because no complications were observed. For patients using chronic anticoagulant therapy or with severe disabilities caused by cardiac, pulmonary or malignant diseases, this technique represents an alternative of treatment to radiofrequency thalamotomy.

Aged↗

PubMed2003

Neutron production associated with radiotherapy linear accelerators using intensity modulated radiation therapy mode.

A number of experiments were conducted on a Clinac 21EX radiotherapy accelerator using an IMRT treatment plan to determine neutron dose equivalent as a function of both patient dose delivered and machine workload. It was determined that IMRT mode is more neutron dose intensive as a function of patient dose when compared to a similar standard non-IMRT treatment. It was found that when the neutron production is normalized to workload, the measured neutron dose equivalents are similar. It is therefore recommended that neutron production be reported as a function of workload when considering IMRT treatment modes.

Humans↗

PubMedDate not supplied

Variation of output with atmospheric pressure and ambient temperature for Therac-20 linear accelerator.

The Therac-20 (a linear accelerator manufactured by the Atomic Energy of Canada, Ltd.) employs an unsealed monitor chamber to control the dose output. Daily fluctuations in machine output for both x rays and electron beams were observed to vary with ambient temperature and atmospheric pressure. These variations were not related to any other machine parameters. Variations as large as 3.5% were seen by monitoring 18-MV x-ray output over several months. We recommend that the manufacturers take steps to eliminate the atmospheric dependence of dose rate.

Atmospheric Pressure↗

PubMedDate not supplied

Characteristics of photon beams from Philips SL25 linear accelerators.

The Philips SL25 accelerator is a multimodality machine offering asymmetric collimator jaws and a new type of beam bending and transport system. It produces photon beams, nominally at 6 and 25 MV, and a scattered electron beam with nine selectable energies between 4 and 22 MeV. Dosimetric characteristics for the 6- and 25-MV photon beams are presented with respect to field flatness, surface and depth dose characteristics, isodose distribution, field size factors for both open and wedged fields, and narrow beam transmission data in different materials.

Humans↗

PubMed1996

Use of routine quality assurance procedures to detect the loss of a linear accelerator primary scattering foil.

The effects of the mechanical loss of a stainless steel primary scattering foil on a 12-MeV electron beam from a dedicated intraoperative electron accelerator are discussed. Routine quality assurance tests, including dose output constancy, energy constancy, and beam uniformity (flatness and symmetry), were used to determine the nature of the malfunction when it occurred. It is concluded that these quality assurance checks, if done with the frequencies recommended by the AAPM Task Group 40 Report [Med. Phys. 21, 581-619 (1994)] and repeated at the time of occurrence, are sufficient to detect loss of an electron scattering foil.

Biophysical Phenomena↗

PubMed1981

[Effect of radiations with varying linear energy transfer on the skin of mice].

Experiments were carried out to measure the time and severity of the radiation reaction of the skin of mice exposed to X- and gamma-radiations, protons with energies of 645 and 50 MeV as well as accelerated helium ions at doses of 200 to 4000 rad. It was found that relative biological effectiveness coefficients of 645 and 50 MeV protons were 1.0 and those of helium ions were 1.3 for the skin reaction at early and late stages of observation. No significant difference in the time of manifestation of radiation-induced skin lesions as related to radiations with various LET was detected.

Animals↗

PubMed1984

The influence of the overall treatment time in radiotherapy on the acute reaction: comparison of the effects of daily and twice-a-week fractionation on human skin.

A comparison of the acute skin erythema and pigmentation after daily fractions of 2 Gy and twice-a-week fractions of 4 Gy was performed on post-operatively irradiated parasternal fields in patients with breast cancer. The radiation quality used was electron beams with an energy of about 12 MeV. The overall treatment time varied between 4 and 6 weeks. The two schedules were also compared for an overall treatment time of 10 weeks, with a rest period of 3 weeks after 4 weeks of irradiation, followed by another 3 weeks of treatment. With 5 to 6 weeks irradiation, daily fractions resulted in a significantly more pronounced skin erythema (p less than 0.05) than twice-a-week fractions, corresponding to about 10% in terms of absorbed dose. With 4 weeks irradiation and split-course therapy, the acute reactions were identical with both schedules. We interpret these findings as indicating a radiation-induced accelerated repopulation of the basal cells in the epidermis, with a fairly abrupt onset after 4 weeks. The higher effect after more frequent fractions of smaller size would be expected from a sensitizing effect of redistribution. In conclusion, the overall treatment time is of importance for establishment of iso-effect relationships for acutely responding tissues. The implication is that different fractionation parameters used in models to predict equivalent radiation effects of different fractionation schedules also vary significantly with the overall treatment time.

Breast Neoplasms↗

PubMed1997

[Successful irradiation of ciliary processes with electrons in therapy refractory aphakic glaucoma].

BACKGROUND: Successful radiation was already reported by Genée and Weitzel (1968): Electrons from a Betatron were used for irradiation of the ciliary epithelium to lower aqueous humor secretion. To our knowledge, no other paper on this topic has been published so far. PATIENT: A 26-year-old man had history of concussion trauma and cataract surgery in childhood. In adult age, cataract surgery and retinal operations were followed by numerous surgical procedures and maximal medical treatment because of a secondary glaucoma. The patient refused further surgical and medical treatment with the exception of the administered systemic carbo-anhydrase inhibitor. Because of severe side-effects caused by the acetozolamide, irradiation of the ciliary processes with electrons, emitted from a linear accelerator, was performed. The total amount of 12 Gy both on the nasal and on the temporal side of the ciliary body was fractionated in several sessions. RESULTS: During a follow-up of 22 months without medication, the mean value of i.o. pressure was 22.1 mm Hg. The patient is doing well, corrected VA is 0.8. CONCLUSION: Irradiation of the ciliary processes with electrons for lowering aqueous humor secretion was effective in an otherwise non treatable case of glaucoma.

Adult↗

PubMed1995

Twenty-five years of MTPR--a theoretical and experimental analysis.

The system of modified tissue phantom ratio (called tissue standard factor, or TSF, in this paper) was introduced to facilitate the calculation of monitor units in isocentric configurations. Twenty-five years later, TSFS have been measured at 6 MV on different linear accelerators, and are in agreement with the original values, highlighting the property of machine independence. The utility of TSF is shown by the simplicity of the equation for calculating dose per monitor unit at any depth, field size and distance from source. New equations are given for relating isocentric systems to fixed-SSD systems, and the table of TSFS is extended to include a symbolic zero-area column, which is shown to be the primary-dose component of TSF in electronic equilibrium.

Humans↗

PubMed2005

The TRADE experiment: shielding calculations for the building hosting the subcritical system.

The TRADE project (TRiga Accelerator Driven Experiment), to be performed at the existing TRIGA reactor at ENEA Casaccia, has been proposed as a validation of the accelerator-driven system (ADS) concept. TRADE will be the first experiment in which the three main components of an ADS--the accelerator, spallation target and sub-critical blanket--are coupled at a power level sufficient to encounter reactivity feedback effects. As such, TRADE represents the necessary intermediate step in the development of hybrid transmutation systems, its expected outcomes being considered crucial--in terms of proof of stability of operation, dynamic behaviour and licensing issues--for the subsequent realisation of an ADS Transmutation Demonstrator. An essential role in the feasibility study of the experiment is played by radioprotection calculations. Such a system exhibits new characteristics with respect to a traditional reactor, owing to the presence of the proton accelerator. As beam losses always occur under normal operating conditions of an accelerator, shielding studies need to be performed not only around the reactor but also along the beam line from the accelerator to the spallation target. This paper illustrates a preliminary evaluation, using Monte Carlo methods, of the additional shielding to be located around the reactor structures, the beam transport line and the existing reactor building to allow access into the reactor hall and to restrict the doses outside to their legal limits.

Computer Simulation↗

PubMed1986

[Immunoglobulins for the prevention of radiation pneumonitis following large-volume irradiation in bronchial carcinoma].

In a randomized study 20 patients with non small cell lung cancer were treated for cure at a linear accelerator. Before, during and after treatment levels of immunoglobulins were measured. At the end of radiation therapy levels of IgA, IgG and IgM decreased. After therapy they increased slowly. 3 months after irradiation the average immunoglobulin levels showed a reduction of 16%. After substitution of immunoglobulins no decrease of the levels was seen. After substitution of immunoglobulins the Karnofsky index was significantly higher. Substituted patients showed a lower rate of radiation pneumonitis.

Carcinoma, Bronchogenic↗

PubMed2006

Scatter from radiotherapy beams emerging from primary barriers: an aid to bunker design.

Charts to assist in linear accelerator bunker design have been produced using the Monte Carlo framework, Geant4. These charts assess the amount of forward scatter produced at different angles to the beam axis by concrete and steel barriers irradiated by 6 MV and 10 MV photon beams at normal incidence. These new charts complement existing charts of broad-beam transmission through walls. This is because the existing charts give no indication of the amount of scatter emerging at large angles from the beam axis, for example, towards the maze entrance.

Equipment Design↗

PubMed1986

[Cyclotrons in medicine. A survey of commercial models and their biomedical applications].

At present in Italy there is a great interest in the use of cyclotrons for medical applications: according to a plan of CNR (National Research Council), accelerators of this kind are going to be installed in some hospitals. After the explanation of the cyclotron operation principles, an outline is given of the possible applications with particular care for the clinical ones. An up-to-date review of commercial models so far developed is reported and finally, after a short note concerning installation problems, some suggestions are given about criteria to be followed in the choice of a model, according to the foreseen scientific program.

Equipment and Supplies, Hospital↗

PubMed1986

A beam width improving device for a 25 MV X ray beam.

We have made a device that improves the dose distributions of X ray fields from a 25 MV accelerator by increasing the width of the 95% dose relative to the 50%. This device, called a beam width improving device, is a specially designed "compensator," consisting of two lead sheets taped onto a plastic blocking tray and is tailored for each field so that it can accommodate square fields, rectangular fields and fields with corner cuts. Comparison of profiles with and without this compensator indicates an increase in the width of the 95% dose of approximately 8 mm for small fields to approximately 14 mm for large fields.

Humans↗

PubMed1982

Heavy ion effects on yeast cells: induction of canavanine-resistant mutants.

The induction of forward mutations (resistance to canavanine) by heavy ion bombardment was investigated in wild type haploid yeast Saccharomyces cerevisiae. Accelerated ions of argon, titanium, nickel, krypton, xenon, lead and uranium with specific energies between 1.7 and 9.25 MeV/u were obtained from the UNILAC machine at the Gesellschaft für Schwerionenforschung, Darmstadt/Germany. LET-values ranged from 1200 to about 15 000 keV/microns. There was no unequivocal dependence of mutation induction cross section on either LET or Z*2/beta 2, but also a prominent influence of ion specific energy. This is explained by the action of long-ranging delta-electrons.

Canavanine↗

PubMedDate not supplied

X-ray depth-dose characteristics of the Toshiba LMR-16.

The depth-dose characteristics of the Toshiba LMR-16 linear accelerator for 14-MeV x rays have been measured at an SSD of 100 cm using diodes and ion chambers. The surface dose and build-up depth both exhibit a considerable variation with field size. A new central axis model has been developed which takes account of these variations, and the agreement between the measured and computed data using this model is found to be excellent. Formulas are also presented to estimate the surface dose, buildup depth, and output factor as a function of field size.

Models, Theoretical↗

PubMed2003

An accidental exposure by a medical linear accelerator under construction.

A radiation accident occurred at a medical linear accelerator facility under construction in Japan. The radiation source was a 3- and 6-MV potential drop accelerator designed to produce X-rays for radiation therapy. This accelerator was also capable of producing a 5 to14-MV swept electron beam. During setting up, an operator turned on the accelerator to test the beam not knowing that a man was working on the ceiling above the accelerator. Thus, an X-ray beam was emitted against the ceiling and the man was exposed to 10-MV of X-ray irradiation. However, no obvious physical symptoms were noted. Dose estimation was made from reconstruction of the accident and clinical examinations including chromosome analysis. Mean dose of the whole body ranged from 70 to 180 mSv. Estimated dose from his right foot to hand was between180 to 900 mSv.

Humans↗

PubMed1977

[Breakdown of the energy of a fixed 7 MeV electron bundle in the treatment of mycosis fungoides (author's transl)].

In order to treat patients with mycosis fungoides, the authors were led to breakdown the energy of a 7 MeV electron bundle emitted by a linear accelerator. With this aim, they sought to determine the nature, thickness and position of the decelerating which should be used to obtain adequate flow and energy of the electron bundle. They then explain the technique of total body irradiation of the patients, and in particular the way in which the functions of the bundle are effected. Finally, in order to diminish under-dosage in regions of the human body irradiated tangentially, they suggest the use of a perspex screen of variable thickness.

Electrons↗