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At least 523 records · Page 29Linked to original sources
PubMed1985

Malignant obstructive jaundice: treatment with external-beam and intracavitary radiotherapy.

Eleven patients with obstructive jaundice from unresectable cholangiocarcinoma, metastatic porta hepatis adenopathy, or direct compression from a pancreatic malignancy were treated at the Stanford University Medical Center from 1978-1983 with an external drainage procedure followed by high-dose external-beam radiotherapy and by an intracavitary boost to the site of obstruction with Iridium192 (Ir192). A median dose of 5000 cGy was delivered with 4-6 Mv photons to the tumor bed and regional lymphatics in 9 patients, 1 patient received 2100 cGy to the liver in accelerated fractions because of extensive intrahepatic disease, and 1 patient received 7000 "equivalent" cGy to his pancreatic tumor bed and regional lymphatics with neon heavy particles. An Ir192 wire source later delivered a 3100-10,647 cGy boost to the site of biliary obstruction in each patient, for a mean combined dose of 10,202 cGy to a point 5 mm from the line source. Few acute complications were noted, but 3/11 patients (27%) subsequently developed upper gastrointestinal bleeding from duodenitis or frank duodenal ulceration 4 weeks, 4 months, and 7.5 months following treatment. Eight patients died--5 with local recurrence +/- distant metastasis, 2 with sepsis, and 1 with widespread systemic metastasis. Autopsies revealed no evidence of biliary tree obstruction in 3/3 patients. Mean survival time from initial laparotomy and bypass was 16.1 months, and from radiotherapy completion was 8.3 months. Evolution of radiation treatment techniques for biliary obstruction in the literature is reviewed. High-dose external-beam therapy followed by high-dose Ir192 intracavitary boost is well tolerated and provides significant palliation. Survival of these aggressively managed patients approaches that of patients with primarily resectable tumors.

Adenoma, Bile Duct↗
PubMed1999

Solar energetic particles: is there time to hide?

In the large solar energetic particle (SEP) events that constitute a serious radiation hazard, particles are accelerated at shock waves driven out from the Sun by coronal mass ejections (CMEs). A self-regulating mechanism of wave formation by the streaming particles limits SEP intensities early in the event. Hazardous intensities do not occur until the arrival of the shock itself. This provides an opportunity to warn astronauts to take shelter after the onset of the event at the Sun and before arrival of the shock, a time of approximately 12 h or more. The actual time history of particle intensities depends strongly on the longitude of the event at the Sun, on the width the CME, and especially on the speed of the shock. Fortunately, hazardous events are relatively rare. Unfortunately, this gives us few events to study, so we are forced to extrapolate knowledge gained at lower energies in the frequent smaller events. It is essential that the spacecraft with our best instrumentation be positioned outside the Earth's magnetosphere where they can observe these rare large events when they do occur.

Forecasting↗
PubMed2005

High Intensity Proton Accelerator Project in Japan (J-PARC).

The High Intensity Proton Accelerator Project, named as J-PARC, was started on 1 April 2001 at Tokai-site of JAERI. The accelerator complex of J-PARC consists of three accelerators: 400 MeV Linac, 3 GeV rapid cycle synchrotron and 50 GeV synchrotron; and four major experimental facilities: Material and Life Science Facility, Nuclear and Particle Physics Facility, Nuclear Transmutation Experiment Facility and Neutrino Facility. The outline of the J-PARC is presented with the current status of construction.

Biological Science Disciplines↗
PubMed1999

Analysis of Gaussian beam and Bessel beam driven laser accelerators.

This paper presents a comparison of Gaussian and Bessel beam driven laser accelerators. The emphasis is on the vacuum beat wave accelerator (VBWA), employing two laser beams of differing wavelengths to impart a net acceleration to particles. Generation of Bessel beams by means of circular slits, holographic optical elements, and axicons is outlined and the image space fields are determined by making use of Huygens' principle. Bessel beams-like Gaussian beams-experience a Guoy phase shift in the vicinity of a focal region, resulting in a phase velocity that exceeds c, the speed of light in vacuo. In the VBWA, by appropriate choice of parameters, the Guoy phases of the laser beams cancel out and the beat wave phase velocity equals c. The particle energy gain and beam quality are determined by making use of an analytical model as well as simulations. The analytical model--including the v x B interaction--predicts that for equal laser powers Gaussian and Bessel beams lead to identical energy gains. However, three-dimensional, finite-emittance simulations, allowing for detuning, transverse displacements, and including all the electromagnetic field components, show that the energy gain of a Gaussian beam driven VBWA exceeds that of a Bessel beam driven VBWA by a factor of 2-3. The particle beam emerging from the interaction is azimuthally symmetric and collimated, with a relatively small angular divergence. A table summarizing the ratios of final energies, acceleration lengths, and gradients for a number of acceleration mechanisms is given.

Journal Article↗
PubMed2002

[Hadron therapy in carcinoma].

According to some statistics, in the developed countries of west Europe, one in three of population will have an encounter with cancer and, only one in eight of this will have treated by use a linear accelerator. Conventional accelerator-based treatments use photon or electron or proton beams collimated to the tumour place. However, some tumors are resistant on this therapy, while others have complex shapes or are located around vital radiosensitive organs. In those cases it is necessary higher radiobiological efficiency and higher precision. New generation of hadron therapy accelerators are arming with light ions. This therapy is characterized with high precision, in millimeter range over complex volumes. That is also good example how particle physics can benefit medical treatments.

Humans↗
PubMed1994

Mutation induction by accelerated heavy ions in bacteria.

Induction of lacI- forward mutations in Escherichia coli Ymcl and his(-)-->his+ reversions in Salmonella typhimurium TA102 was investigated after irradiation with heavy ions in the range of Z = 1-36. Particle specific energies (E) were in the range of 1-600 MeV/u. A strong dependence of the mutation induction cross-section (sigma m) on both particle energy and LETinfinity was observed. The results suggest that two different ranges of LETinfinity can be distinguished. In the range of high LETinfinity (> 100 keV/micron) sigma m increases with increasing specific particle energy if LETinfinity is kept constant (Fe ions as compared with carbon ions or alpha-particles). In the range of low LETinfinity (< 100 keV/micron) sigma m decreases with increasing energy (Ne ions as compared with He ions).

Deuterium↗
PubMed1988

Stable Transformation of Soybean Callus by DNA-Coated Gold Particles.

Immature soybean (Glycine max L.) embryos from commercially important cultivars were the targets of rapidly accelerated, DNA-coated, gold particles. Protoplasts were prepared from these tissues and propagated in culture under selection conditions for the introduced neomycin phosphotransferase II gene. Kanamycin-resistant calli were obtained at a rate of approximately 10(-5). Enzyme assays and Southern blot hybridization confirmed the expression of the foreign gene and its stable integration into the soybean genome. Our results show that particle acceleration can be used for the introduction of foreign DNA into the soybean genome and indicate the technique may be useful in the recovery of engineered plants by transformation of regenerable tissues.

Journal Article↗
PubMed1990

Blood irradiation: rationale and technique.

Upon request by the local American Red Cross, the Savannah Regional Center for Cancer Care irradiates whole blood or blood components to prevent post-transfusion graft-versus-host reaction in patients who have severely depressed immune systems. The rationale for blood irradiation, the total absorbed dose, the type of patients who require irradiated blood, and the regulations that apply to irradiated blood are presented. A method of irradiating blood using a linear accelerator is described.

Blood↗
PubMed1996

Respiration gated radiotherapy treatment: a technical study.

In order to optimize external-beam conformal radiotherapy, patient movement during treatment must be minimized. For treatment on the upper torso, the target organs are known to move substantially due to patient respiration. This paper deals with the technical aspects of gating the radiotherapy beam synchronously with respiration: the optimal respiration monitoring system, measurements of organ displacement and linear accelerator gating. Several respiration sensors including a thermistor, a thermocouple, a strain gauge and a pneumotachograph were examined to find the optimal sensor. The magnitude of breast, chest wall and lung motion were determined using playback of fluoroscopic x-ray images recorded on a VCR during routine radiotherapy simulation. Total dose, beam symmetry and beam uniformity were examined to determine any effects on the Varian 2100C linear accelerator due to gating.

Brachytherapy↗
PubMed2001

Improved delivery efficiency for step and shoot intensity modulated radiotherapy using a fast-tuning magnetron.

The delivery efficiency of step and shoot intensity modulated radiotherapy (IMRT) has been improved by the installation of fast-tuning magnetrons into three travelling wave linear accelerators. The IMRT delivery efficiency and the beam start-up performance have been compared before and after installation. Start-up and inter sub-field times were reduced by an average of 3.0 s. A typical start-up time from depression of the start button to beam on is now around 4 s. Delivery efficiency for a variety of clinical and quality control prescriptions was improved by an average of 30.7% (range 7.4-60.9%), depending on a complex combination of the number of sub-fields, distance moved by leaves and dose rate. For the oldest accelerator (7 years old), dosimetric accuracy was significantly improved for low dose sub-fields. The dose output was within 2% for a 1 monitor unit (MU) sub-field and 1% for a 2 MU sub-field. The two newer accelerators displayed similar or better dose characteristics even before fast-tuning magnetron installation. Beam symmetries and flatnesses were acceptable at all energies and dose rates, and showed no obvious degradation in low dose sub-fields. It is recommended that fast-tuning magnetrons are adopted for accelerators of this design performing step and shoot IMRT.

Magnetics↗