SEARCH · PubMed Health

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,189 records · Page 66Linked to original sources

PubMed1995

A microbiological screening method for the indication of irradiation of frozen poultry meat.

A microbiological screening method for the detection of irradiation of frozen poultry meat was developed on the basis of the combined use of total cell count by the direct epifluorescent filter technique (DEFT) and viable cell count by the aerobic plate count method (APC). Samples of ground, deboned poultry leg were irradiated or not with dose levels of 3, 5 and 7 kGy using an electron beam accelerator. All samples were frozen before the irradiation treatment. The average values of the differences between DEFT and APC counts in control samples and those irradiated with doses of 3, 5 and 7 kGy were 1.14 log units for control samples, and 3.16, 3.68 and 3.79 log units for the irradiated samples. A difference of at least 2 log units can therefore be considered as a limit value indicating probable irradiation treatment necessitating further investigations.

Aerobiosis↗

PubMed1990

Shielding considerations for an operating room based intraoperative electron radiotherapy unit.

The leakage radiation characteristics of a dedicated intraoperative radiotherapy linear accelerator have been measured on a machine designed to minimize the shielding required to allow it to be placed in an operating room suite. The scattering foil design was optimized to produce a flat beam for the field sizes employed while generating minimal bremsstrahlung contamination over the available energy range. More lead shielding was used in the treatment head than is used in conventional accelerators. A small amount of borated polyethylene shielding was also employed since neutron production was present at measurable levels. The room shielding installed in the operating room was demonstrated to be adequate to treat at least 20 patients each month to an average dose of 20 Gy. The worst case exposure was found to be 73% maximum permissible exposure. Administrative control was required for adjoining areas when calibrations and maintenance were performed.

Intraoperative Period↗

PubMed1979

The Clinac-18 linear accelerator. 10 MeV photon beam data.

Measurements were carried out on a Clinac-18 linear accelerator in order to characterize the 10 MeV photon beam. Depth dose data and tissue-maximum-ratios were obtained for field sizes up to 35 x 35 cm2. Using a parabolic expression a least square fit to the tissue-maximum-ratios was performed. The radiation field flatness and the penumbra were found to be in good agreement with the tolerances recommended by the IEC standard (draft). The radiation field and the light field isocentre were determined as suggested by the IEC. The distance between both isocentres was less than 1 mm.

Particle Accelerators↗

PubMed1991

[Pre- and postoperative radiotherapy of operable carcinoma of the rectum].

This was a non-randomized prospective study on the "sandwich" radiosurgical treatment of resectable rectal and rectosigmoid carcinomas. From December 1984 to December 1989, 100 patients were treated 86 of them are now evaluable. Mean follow-up was 38 months (range: 9-69). Surgery was abdomino-perineal resection in 33 cases and anterior resection in 53 cases. Radiotherapy was preoperative pelvic irradiation, with a single 500-Gy fraction, the day before surgery. To stages B2, C1 and C2 patients (Astler and Coller) postoperative radiotherapy was administered for a total dose of 4500 Gy (180 Gy/fraction, 5 fractions/week), with box technique, from a Co 60 unit or Linear Accelerator (photon 18 MV). Preliminary results indicate 8% (7/86) local recurrences and 9.3% (8/86) distant metastases. Five-year actuarial disease-free survival is 63.2% +/- 8 for stage B1, 55.6% +/- 19 for stage B2, and 40.2% +/- 13 for stages C1 + C2. Overall 5-year actuarial disease-free survival is 53% +/- 10. No lethal or severe complications were observed following treatment.

Adult↗

PubMed1982

[Induced radioactivities in treatment head of 10 MV X-ray linear Accelerator (author's transl)].

The concentration of 60Co and stable cobalt in the shellfishes and seaweeds which were collected from the coast around Japan were obtained by low background beta counting for 60Co and spectrometric determination of stable cobalt. The results obtained were as follows: (1) The 60Co was found in the shellfishes which were enriched in the stable cobalt. (2) The correlation between 60Co and stable cobalt was rather good in the shellfishes. (3) The activities of 60Co was found in the seaweeds taken from seashore near the nuclear power plant. (4) There was great differences in the specific activities between samples collected from contaminated and not contaminated area.

Gold Radioisotopes↗

PubMed1990

An experimental study of the moderator assembly for a low-energy proton accelerator neutron irradiation facility for BNCT.

An accelerator-based neutron irradiation facility (ANIF), which has been proposed for BNCT, is based on a 2.5-MeV proton beam bombarding a thick lithium target. Neutrons which are emitted from the lithium target are too energetic for BNCT and must be moderated. A calculational study, which was done previously on the moderator assembly for an ANIF, shows that, with an optimized moderator assembly, an ANIF can produce a neutron flux which has quality and intensity sufficient for BNCT. In order to verify our previous calculational study, a lithium target and a non-optimized moderator assembly (a cylindrical tank of D2O) have been constructed and tested at the Ohio State University Van de Graaff proton accelerator. The neutron spectrum was measured for neutrons emerging from the moderator assembly. The measured neutron spectrum agrees reasonably well with that obtained from Monte Carlo calculations, except for neutrons with energies above 100 keV. For those neutrons, the measured spectrum is lower by a factor of two than the calculated one. In addition to the neutron spectrum measurement, the boron-10 absorbed dose was measured on the axis of the neutron field in a 20 cm x 20 cm x 20 cm water phantom, and the result agrees quite well with that obtained from calculation. This experiment confirms that the calculated optimized moderator assembly, consisting of a 22.5-cm thick, 25-cm diameter cylinder of beryllia (BeO) surrounded by a 30-cm thick jacket of alumina (Al2O3), produces an epithermal neutron flux of 3.12 x 10(7) n/cm2-s per mA of protons. For an accelerator delivering 30 mA of 2.5-MeV protons, the irradiation time for a single-session treatment can be as short as 50 minutes. The calculated ratio of absorbed neutron dose to fluence for the optimized moderator assembly is 4.9 x 10(-11) cGy-cm2/n, which is equal to that of a 5-keV neutron beam. Our experimental measurements indicate that the ratio of absorbed neutron dose to fluence may in fact be lower (better) than calculated.

Boron↗

PubMed1995

Evaluating the dose to the contralateral breast when using a dynamic wedge versus a regular wedge.

The incidence of secondary cancers in the contralateral breast after primary breast irradiation is several times higher than the incidence of first time breast cancer. Studies have shown that the scatter radiation to the contralateral breast may play a large part in the induction of secondary breast cancers. Factors that may contribute to the contralateral breast dose may include the use of blocks, the orientation of the field, and wedges. Reports have shown that the use of regular wedges, particularly for the medial tangential field, gives a significantly higher dose to the contralateral breast compared to an open field. This paper compares the peripheral dose outside the field using a regular wedge, a dynamic wedge, and an open field technique. The data collected consisted of measurements taken with patients, solid water and a Rando phantom using a Varian 2300CD linear accelerator. Ion chambers, thermoluminescent dosimeters (TLD), diodes, and films were the primary means for collecting the data. The measurements show that the peripheral dose outside the field using a dynamic wedge is close to that of open fields, and significantly lower than that of regular wedges. This information indicates that when using a medial wedge, a dynamic wedge should be used.

Breast↗

PubMed2005

Neutron radiation area monitoring system for proton therapy facilities.

A neutron radiation area monitoring system has been developed for proton accelerator facilities dedicated to cancer therapy. The system comprises commercial measurement equipment, computer hardware and a suite of software applications that were developed specifically for use in a medical accelerator environment. The system is designed to record and display the neutron dose-equivalent readings from 16 to 24 locations (depending on the size of the proton therapy centre) throughout the facility. Additional software applications provide for convenient data analysis, plotting, radiation protection reporting, and system maintenance and administration tasks. The system performs with a mean time between failures of >6 months. Required data storage capabilities and application execution times are met with inexpensive off-the-shelf computer hardware.

Equipment Design↗

PubMed2006

Monte Carlo study of photon fields from a flattening filter-free clinical accelerator.

In conventional clinical linear accelerators, the flattening filter scatters and absorbs a large fraction of primary photons. Increasing the beam-on time, which also increases the out-of-field exposure to patients, compensates for the reduction in photon fluence. In recent years, intensity modulated radiation therapy has been introduced, yielding better dose distributions than conventional three-dimensional conformal therapy. The drawback of this method is the further increase in beam-on time. An accelerator with the flattening filter removed, which would increase photon fluence greatly, could deliver considerably higher dose rates. The objective of the present study is to investigate the dosimetric properties of 6 and 18 MV photon beams from an accelerator without a flattening filter. The dosimetric data were generated using the Monte Carlo programs BEAMnrc and DOSXYZnrc. The accelerator model was based on the Varian Clinac 2100 design. We compared depth doses, dose rates, lateral profiles, doses outside collimation, total and collimator scatter factors for an accelerator with and without a flatteneing filter. The study showed that removing the filter increased the dose rate on the central axis by a factor of 2.31 (6 MV) and 5.45 (18 MV) at a given target current. Because the flattening filter is a major source of head scatter photons, its removal from the beam line could reduce the out-of-field dose.

Computer Simulation↗

PubMedDate not supplied

Establishment of a beam line at the Fermi National Accelerator Laboratory for proton radiography.

A proton beam is extracted from the 200-MeV linear accelerator at the Fermi National Accelerator Laboratory to investigate the efficacy of proton radiography in medical diagnosis. Fluence rates from 2 X 10(3) to 2 X 10(5) protons/cm2s over a 28-cm diameter field are obtained with a full width at half-maximum beam-energy spread of less than 3.61 MeV. The system is designed to radiography most parts of the human body, including the head, with high-speed screen-film as the imaging medium. Beam extraction and test results along with the medical implications of the beam quality are reported.

Laboratories↗

PubMed2004

Noninvasive linear accelerator radiosurgery as the primary treatment for trigeminal neuralgia.

The application of a dedicated linear accelerator (DLINAC) as a noninvasive surgical treatment for trigeminal neuralgia has not yet been demonstrated. This work evaluates the outcome and indications of 22 patients submitted to DLINAC radiosurgery as a primary treatment for essential trigeminal neuralgia. At last follow-up evaluation, 21 patients (95.5%) had sustained significant pain relief. DLINAC radiosurgery is safe and effective as a primary noninvasive surgical treatment for selected patients with essential trigeminal neuralgia.

Aged↗

PubMed2006

[Approximation of collimator scatter factor Sc by a saturation model].

To more easily estimate accurate values of collimator scatter facor, S(c), we suggest a two-component saturation model that accounts for scatter from the primary collimator and flattening filter and from the collimator jaws. This model, which assumes an exponential distribution of scatter intensity, was tested by in-air measurements using a mini-phantom for 4 MV and 10 MV X-rays of a Clinac 2100 C/D linear accelerator. The results showed a good fit of this model to our measured data (R(2)>0.9993). When the measured value was divided into the primary collimator/flattening filter component and the collimator jaw component, as expected, the former component showed a rapid and full saturation curve with increased field size, while the latter showed an almost linearly increasing curve. Therefore, we think that this saturation model is useful for the estimation of S(c) and is applicable to monitor unit calculation for an asymmetric field.

Filtration↗

PubMedDate not supplied

Properties of the 18-MV photon beam from a dual energy linear accelerator.

The beam characteristics of the 18-MV photon beam of a Varian Clinac 1800 are presented. The clinically relevant parameters of central axis depth dose, tissue-phantom ratios, peak-scatter factors, and relative output factors are discussed and compared to 18-MV beam data previously reported. The nominal beam energy was found to be 18.3 +/- 0.8 MV on the central axis. The beam symmetry and uniformity meet the manufacturer's specifications. The inverse-square law is applicable within 1.4% over the clinically useful range of distances and field sizes. An empirical fit equation for the central axis depth dose is presented.

Humans↗

PubMed1991

Fractionated radiotherapy of small inoperable lesions of the brain using a non-invasive stereotactic frame.

Arteriovenous malformations (AVMs) and benign or low grade, small malignant tumors can be treated by stereotactic radiotherapy in a single fraction. This report describes a technique for stereotactic treatment of small lesions using conventional, fractionated, photon beam irradiation. The Laitinen's stereoadapter, non-invasive head frame was used. This device was tested for accuracy by serial mountings and found to be accurate within 1 mm. The accuracy of the dose delivered was within 2%. Adaptation of this device to the linear accelerator required the design of secondary circular collimators which decreased the penumbra from 3-4 mm to 2-3 mm. The dose fall off outside the target volume is steep enough when using two non-coplanar arcs (90 to 10% within 1 cm). Thermoluminescent dosimetry (TLD) in a humanoid phantom showed good correlation with the calculated dose. This system permits delivery of fractionated radiation therapy to small volumes, easily and accurately, under stereotactic conditions.

Adolescent↗

PubMed1990

[The recombination factor in an ionizing chamber used for dosimetry of a linear accelerator].

The authors starting from the discussion of Boag address experimentally the ion recombination in an ionizing camera. They outline the fact that several basic dosimetry protocols do not highlight the importance of the used radiation sources, beam width, ionizing camera dimensions, even though they mention to take into account the recombination factor. The authors determine experimentally the recombination factor with two kinds of ionizing camera, one cylindrical and the other flat, on a linac pulsed and scanned radiation beams. As a result it ensued that it is advisable to use a Markus type ionizing camera rather than a cylindrical one, especially when scanning beams are used, to reduce the recombination phenomena.

Models, Theoretical↗

PubMed1994

Application of the Moyer method to transverse shielding of a linear bremsstrahlung source.

The Moyer method is applied to the design of transverse shielding for an electron linear accelerator, assuming uniform beam power loss along the accelerator structure. The limitations of the method with respect to primary beam energy are discussed. Only the component of the radiation field due to bremsstrahlung is considered in this paper. Parameters for this application are given and sample calculations are shown. For a beam power loss uniformly distributed with distance along a straight line of 0.5 W m-1, it is predicted that 1.2 m of concrete are needed to reduce the dose equivalent rate to 50 muSv h-1 (1.39 x 10(-8) Sv s-1), at a transverse distance of 3.5 m from the source.

Particle Accelerators↗

PubMed2001

Dependence of virtual wedge factor on dose calibration and monitor units.

One of the important features of the Siemens Virtual Wedge (VW) is that the VW factor (VWF) is approximately equal to unity for all beams with a total deviation for a given wedge no greater than 0.05, as specified by Siemens. In this note we report the observed dependence of VWF on dose calibration (cGy/MU), monitor units (MU), and beam tuning for a Primus, a linear accelerator with two dose-rate ranges available for VW operation. The VWF is defined as the ratio of doses measured on the beam central axis for the wedge field to the open field; the open field dose is always measured with the nominal high dose-rate beam. When VW operates in the high dose-rate range, the VWF is independent of calibration (cGy/MU). When VW works in the low dose-rate range, the VWF varies linearly with the calibration of the low dose-rate mode. For a linear accelerator that has only one dose-rate range for VW, there is no observable dependence of VWF on the calibration. We also studied the monitor unit dependence of VWF. A discontinuity in VWF was observed at the switching point between the high and low dose-rate ranges. Working with Siemens, we have investigated causes of this discontinuity. As a result of this investigation, the discontinuity in VWF as a function monitor unit is practically removed.

Biophysical Phenomena↗

PubMedDate not supplied

Neutron measurements around medical electron accelerators by active and passive detection techniques.

Passive and active detection techniques have been employed in order to measure neutron fluence rates and corresponding exposure rates around medical electron accelerators operating at energies well above the neutron binding energies of the structural materials. In these conditions from the treatment head, in the direct photon flux and from the shielded region, a fast neutron flux emerges which is partly absorbed and partly scattered by the walls, eventually establishing a nearly uniform thermal and epithermal flux in the room. Both direct and scattered flux contribute to the dose to the patient. A smaller neutron dose rate can also be found outside the treatment room, where the therapy staff works. Passive detectors, of moderation type, have been employed in the treatment room and 3He active detectors in the external zones. For the treatment room the activation data were compared with results of Monte Carlo simulation of the neutron transport in the room. Technical features of the two measures are briefly presented and results obtained around three different types of accelerators are reported. At the higher beam energies, i.e., 25 MV, a neutron dose of 0.36 Sv was estimated in the treatment field in addition to a therapeutic x-ray dose of 50 Gy. At lower energies or out of the treatment field the neutron dose drops significantly. In the external zones the dose rates everywhere are below the recommended limits and normally very low, the highest values being recorded in positions very close to the access door of the treatment room.

Humans↗