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Results for “Particle Accelerators”

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At least 991 records · Page 55Linked to original sources

PubMed1983

[Tumor regression rate and the effectiveness of the radiation therapy of cervical cancer patients].

The paper deals with a correlation between the rate of tumor regression in response to radiation and the results of radiation treatment of cancer of the uterine cervix. The period of 50% decrease in tumor size in response to radiation treatment was established in 116 patients with cervical carcinoma by means of a dynamical cytological examination. Acceleration of tumor regression was followed by an increase in 5-year survival rates. A reverse correlation was established between growth and regression rates of cervical carcinoma. Thanks to the determination of tumor regression rates, various modalities of radiation treatment could be evaluated in the course of therapy and their efficacy predicted.

Brachytherapy↗

PubMed1999

The GSI Cancer Therapy Project.

At the Heavy Ion Research Institute GSI in Darmstadt an experimental cancer treatment program with a five years duration has been developed. A new method for cancer treatment with ions is applied, using rasterscan method in addition to an active pulse to pulse variation of ion beam properties, including the energy, intensity and focusing. An overview of this Cancer Therapy Project is presented, that covers both accelerator aspects to provide the required beam variations within a short time and the installations at the treatment place for rasterscan control. In addition to a description of the technical design (control-hard- and software) experimental results will be shown, containing the achieved beam properties and measurements of rasterscan performance.

Academies and Institutes↗

PubMed1991

Cyclotron production of NCA 99mTc and 99Mo. An alternative non-reactor supply source of instant 99mTc and 99Mo----99mTc generators.

The direct production of no-carrier-added (NCA) 6.02 h 99mTc and of 66 h 99mMo using proton beams of natural Mo targets was investigated. The major objective of this work was to evaluate the potential of utilizing high-intensity proton accelerators as a supply source of 99mTc and 99Mo for use in diagnostic nuclear medicine. The excitation functions for the production of the directly-made 99mTc via the 100Mo(p, 2n)99mTc (Q = -7.85 MeV) reaction, and of its parent 99Mo via the 100Mo(p, pn) 99Mo (Q = -8.30 MeV) and 100Mo(p, 2p)99mNb(15 s)----99Mo (Q = -11.14 MeV) reactions, were measured in the 68-8 MeV energy range. Single and cumulative yields for 99mTc and 99Mo, and for other Tc, Mo, Zr, Nb and Y radiocontaminants were also determined. The prospects of integrating the use of enriched 100Mo targets with high-intensity, dual beam, H- accelerators was analyzed. The potential of this combined method to replace or complement the current reactor-based supply sources of 99Mo----99mTc generators, is also discussed. Finally, a brief analysis is made on the potential use of this combined technology to support the anticipated expansion of nuclear medicine in developing nations.

Molybdenum↗

PubMed2001

Experimental simulation of A-bomb gamma ray spectra for radiobiology studies.

Improved radiation protection of humans requires a better understanding of the mechanisms of radiation action and accurate estimates of radiation risk for both internal and external radiations. The Japanese atomic bomb survivors represent one of the most important sources of human data on the late carcinogenic effects of ionising radiations. The present study was undertaken to investigate whether it would be possible to use hospital radiotherapy/radiobiology equipment to mimic the spectra encountered in Hiroshima and Nagasaki. The estimated total gamma ray fluence spectra (including both prompt and delayed photons) at both Hiroshima and Nagasaki, for distances of 500, 1000, 1500 and 2000 m have been evaluated using DS86 data and previously unpublished information for delayed gamma radiations which constitute the major contribution to survivor doses. Monte Carlo (EGS4) simulations were performed to transport these photons through the body in order to investigate the variation in electron spectra for various body organs. The electron spectra obtained for these fluences at, for example, the colon, have been matched with combinations of electron spectra produced by linear accelerators to within 5% SD. These will, for the first time, enable a direct link to be made between radiobiological studies (for example, on mammography spectra) and the epidemiological data from Japan, which currently underpin radiation risk estimates.

Computer Simulation↗

PubMed2001

Shielding high energy accelerators.

After introducing the subject or shielding high energy accelerators, point source, line-of-sight models, and in particular the Moyer Model, are discussed. Their use in the shielding of proton and electron accelerators is demonstrated and their limitations noted, especially in relation to shielding in the forward direction provided by large, flat walls. The limitations of reducing problems to those using a cylindrical geometry description are stressed. Finally the use of different estimators for predicting dose is discussed. It is suggested that dose calculated from track-length estimators will generally give the most satisfactory estimate.

Electrons↗

PubMed1996

Radiation protection systems for the final focus test beam at SLAC.

The Final Focus Test Beam (FFTB) is a new beam line at the Stanford Linear Accelerator Center designed to test new beam optics concepts, hardware, and techniques necessary to achieve and measure the small spot sizes required for future generations of high-energy e+e- linear colliders. The FFTB takes a 47 GeVc-1, 1 kW electron beam at the end of the Stanford Linear Accelerator Center linear accelerator and transports it to the FFTB beam dump. A radiation protection system was designed and installed for the FFTB with the primary goal that the integrated dose equivalent outside the shielding resulting from beam loss would not exceed 10 mSv y-1. This system is comprised of shielding, a beam containment system and a personnel protection system. This paper presents various aspects of radiation safety at Stanford Linear Accelerator Center that were considered in the design of the FFTB radiation protection system. Beam tests were conducted in which the performance of various beam containment devices and the shielding effectiveness were evaluated. Preliminary results from these tests are presented.

California↗

PubMedDate not supplied

Evaluation of a photon and an electron beam of a 6-MV linear accelerator.

The first Mitsubishi medical linear accelerator in the United States was commissioned in April 1985. This unit EXL-8 (marketed by Mitsubishi International Corporation) produces 8-MeV electron beams in addition to 6-MV x rays. It is a 100-cm source-axis distance isocentric machine. Acceptance testing and performance evaluation of this accelerator were completed. Our measurements included beam characteristics and dosimetry parameters for both modalities. Central axis % depth dose (% DD), tissue-maximum ratio, field size output factors, wedge factors, etc., for this Linac 6-MV beam, are reported. Characteristics of the 8-MeV electron beam, namely % DD data, isodose curves, and cone ratios for various electron applicators are presented.

Electrons↗

PubMedDate not supplied

Long-term use of an isotope check source for verification of ion chamber calibration.

A radioactive check source is recommended for operational and constancy checks of dosimetry systems used for the calibration of therapeutic x-ray generators, including linear accelerators. Eight years of data have been analyzed for two ion chambers (and their associated electrometers) irradiated at fixed geometry in such a device. These dosimetry systems have also been calibrated every 2 years at a single Accredited Dosimetry Calibration Laboratory. Our analysis suggests that when a check source is used, and the results are consistent, the interval between formal calibrations can be lengthened.

Humans↗

PubMed1983

Operating characteristics of the Dynaray 18 linear accelerator.

The operating system of a Dynaray 18 linear accelerator is described. Central axis depth dose data for the 10 MV roentgen ray beam are given and compared with published data. The alignment of the roentgen ray beam and the modifications required to obtain satisfactory uniformity and reliable dosimetry are described. The characteristics of the electron beams are also described, central axis depth dose data are given and the derived estimates of energy are discussed.

Electrons↗

PubMedDate not supplied

The influence of the magnetron frequency, the servo settings and the gantry angle on the flatness and the dose calibration of a linear accelerator.

For the Philips SL75/5, we have noticed that the performance of the beam (e.g. the hump) varies with the settings of the magnetron frequency and the gantry angle. This study investigated these changes and the optimum magnetron frequency setting was determined. The relation between the relative absorbed dose measured by the accelerator and the relative absorbed dose measured for different amounts of the hump in the centre of the beam was found. Results from a model and from measured values were compared. The beam was studied for different gantry angles and for different adjustments of the beam servo systems. The profiles obtained showed some variations, but were reduced when optimal adjustments of the servos were performed.

Particle Accelerators↗

PubMed1978

External small-field irradiation of cervical carcinoma with linear accelerator.

Since 1966, 125 patients with carcinoma of the uterine cervix were treated with a 6 MV roentgen beam from a linear accelatro. The pelvis was irradiated with 60 Gy followed by 30 to 45 Gy to a small volume using a lateral pendulum. The small-field irradiation was performed using a new beam-directing device consisting of a rod with a central pivot. Favourable results were achieved, despite the fact that most of the patients had advanced carcinoma.

Female↗

PubMed2006

Fast, daily linac verification for segmented IMRT using electronic portal imaging.

PURPOSE: Intensity modulated radiotherapy (IMRT) requires dedicated quality assurance (QA). Recently, we have published a method for fast (1-2 min) and accurate linac quality control for dynamic multileaf collimation, using a portal imaging device. This method is in routine use for daily leaf motion verification. The purpose of the present study was to develop an equivalent procedure for QA of IMRT with segmented (static) multileaf collimation (SMLC). MATERIALS AND METHODS: The QA procedure is based on measurements performed during 3- to 8-month periods at Elekta, Siemens and Varian accelerators. On each measurement day, images were acquired for a field consisting of five 3 x 22 cm(2) segments. These 10 monitor unit (MU) segments were delivered in SMLC mode, moving the leaves from left to right. Deviations of realized leaf gap widths from the prescribed width were analysed to study the leaf positioning accuracy. To assess hysteresis in leaf positioning, the sequential delivery of the SMLC segments was also inverted. A static 20 x 20 cm(2) field was delivered with exposures between 1 and 50 MU to study the beam output and beam profile at low exposures. Comparisons with an ionisation chamber were made to verify the EPID dose measurements at low MU. Dedicated software was developed to improve the signal-to-noise ratio and to correct for image distortion. RESULTS AND CONCLUSIONS: The observed long-term leaf gap reproducibility (1 standard deviation) was 0.1 mm for the Varian, and 0.2 mm for the Siemens and the Elekta accelerators. In all cases the hysteresis was negligible. Down to the lowest MU, beam output measurements performed with the EPID agreed within 1+/-1% (1SD) with ionisation chamber measurements. These findings led to a fast (3-4 min) procedure for accurate, daily linac quality control for SMLC.

Calibration↗

PubMed2001

Mobile linear accelerators for intraoperative radiation therapy.

Intraoperative radiation therapy (IORT) is becoming an increasingly common procedure for treating gross tumors or tumor beds after resection. Traditionally, IORT delivery required either heavily shielded ORs or transporting anesthetized patients to the department of radiation oncology. The availability of a self-shielded mobile electron linear accelerator has made this treatment modality accessible to institutions that otherwise would not consider performing IORT. This article describes IORT equipment and supplies and addresses perioperative nursing issues, as well as the roles of other team members involved in the delivery of IORT.

Combined Modality Therapy↗

PubMed2003

[Study of theoretical cases of intensity-modulated beams with step-and-shoot technique].

To initiate Intensity-Modulated Radiation Therapy (IMRT) in our department, theoretical cases were used as a training, to define methods of measurements and to verify the software by comparing results of calculation and measurement on a PMMA phantom. Irradiation was performed with 6 and 25 MV X-rays from a linear accelerator. For measurements, films and ionization chambers have been chosen. The comparison between calculations and measurements shows some discrepancies at the level of junctions and also in areas of low doses especially when many segments were used. These theoretical cases provide a first step on the way towards treatments with intensity modulation.

Bias↗

PubMed2005

Benchmarking of MCNPX with the experimental measurements of high-energy helium ions in HIMAC facility.

The main aim of this study is the qualfication of MCNPX code by using the experimental information obtained at HIMAC facility on the bombardment of different materials with He ions accelerated to 100 and 180 MeV/nucleon. The flux of secondary neutrons at different angles relative to ion direction is calculated and compared with published experimental data. Main findings are the reasonable modelling of the high-energy part of the secondary neutrons at forward angles and the code fail for the low-energy part.

Computer Simulation↗

PubMed1992

Photoneutron fields in medical accelerator rooms with primary barriers constructed of concrete and metals.

This study investigates the photoneutron field found in medical accelerator rooms with primary barriers constructed of metal slabs plus concrete. An increased neutron dose equivalent was observed for barriers containing lead or steel as compared to barriers fabricated entirely of concrete. The effect of the beam's size and distance from the primary barriers on the neutron dose was evaluated and the portion of the neutron dose due to the metal slabs was determined.

Construction Materials↗

PubMedDate not supplied

Algorithm for dosimetry of multiarc linear-accelerator stereotactic radiosurgery.

Treatment planning for multiarc radiosurgery is an inherently complex three-dimensional dosimetry problem. Characteristics of small-field x-ray beams suggest that major simplification of the dose computation algorithm is possible without significant loss of accuracy compared to calculations based on large-field algorithms. The simplification makes it practical to efficiently implement accurate multiplanar dosimetry calculations on a desktop computer. An algorithm is described that is based on data from fixed-beam tissue-maximum-ratio (TMR) and profile measurements at isocenter. The profile for each fixed beam is scaled geometrically according to distance from the x-ray source. Beam broadening due to scatter is taken into account by a simple formula that interpolates the full width at half maximum (FWHM) between profiles at isocenter at different depths in phantom. TMR and profile data for two representative small-field collimators (10- and 25-mm projected diameter) were obtained by TLD and film measurements in a phantom. The accuracy of the calculational method and the associated computer program were verified by TLD and film measurements of noncoplanar multiarc irradiations from these collimators on a 4-MV linear accelerator. Comparison of film measurements in two orthogonal planes showed close agreement with calculations in the shape of the dose distribution. Maximal separation of measured and calculated 90%, 80%, and 50% isodose curves was less than or equal to 0.5 mm for all planes and collimators. All TLD and film measurements of dose to isocenter agreed with calculations to within 2%.

Algorithms↗

PubMed2001

Radiation therapy vault shielding calculational methods when IMRT and TBI procedures contribute.

The additional intensity modulated radiation therapy (IMRT) and total body irradiation (TBI) to conventional treatment clinical treatment procedures can significantly increase the contribution of accelerator head leakage radiation. Previously recommended procedures by the National Council on Radiation Protection and Measurements (NCRP) for vault design, specifically calculations of primary and secondary barrier thicknesses, are not valid when leakage radiation significantly exceeds direct radiation. Use factor distributions are also influenced by IMRT and TBI procedures. Methods are proposed to extend the NCRP barrier design formulas to resolve these problems. The medical accelerator (weekly) workload is separately determined for the direct, leakage, and scatter radiation components. Applications of the formulas to the calculation of primary and secondary barriers are discussed. The addition of IMRT to the shielding design is explored as a function of the fraction patients receiving IMRT and the MU to dose ratio. Secondary barrier thicknesses could be increased by as much as 1 TVL.

Humans↗