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At least 649 records · Page 36Linked to original sources
PubMed2000

Inactivation of aerobic and hypoxic cells from three different cell lines by accelerated (3)He-, (12)C- and (20)Ne-ion beams.

The LET-RBE spectra for cell killing for cultured mammalian cells exposed to accelerated heavy ions were investigated to design a spread-out Bragg peak beam for cancer therapy at HIMAC, National Institute of Radiological Sciences, Chiba, prior to clinical trials. Cells that originated from a human salivary gland tumor (HSG cells) as well as V79 and T1 cells were exposed to (3)He-, (12)C- and (20)Ne-ion beams with an LET ranging from approximately 20-600 keV/micrometer under both aerobic and hypoxic conditions. Cell survival curves were fitted by equations from the linear-quadratic model and the target model to obtain survival parameters. RBE, OER, alpha and D(0) were analyzed as a function of LET. The RBE increased with LET, reaching a maximum at around 200 keV/micrometer, then decreased with a further increase in LET. Clear splits of the LET-RBE or -OER spectra were found among ion species and/or cell lines. At a given LET, the RBE value for (3)He ions was higher than that for the other ions. The position of the maximum RBE shifts to higher LET values for heavier ions. The OER value was 3 for X rays but started to decrease at an LET of around 50 keV/micrometer, passed below 2 at around 100 keV/micrometer, and then reached a minimum above 300 keV/micrometer, but the values remained greater than 1. The OER was significantly lower for (3)He ions than the others.

Acceleration↗
PubMed1997

Modulation transfer function for a large-area amorphous silicon image receptor.

The modulation transfer function (MTF) of an amorphous silicon (aSi) sensor array was measured using proper sampling techniques to determine the edge spread function (ESF). The detector under study was a 10 cm2 area detector (EG&G Heimann, RTM128) consisting of 128 x 128 aSi photodiodes arranged in a square array. Two independent methods for calculating the presampling MTF were implemented, based on finely sampling the ESF measurements produced using 40 kV x-rays from a Faxitron microfocal spot x-ray tube. The two calculations of the detector's presampling MTF are in excellent agreement, and are within 20% at the Nyquist frequency when compared with the ideal MTF based only on the size of the detector elements. ESF measurements were also made at 6 MV on a Siemens MD-2 linear accelerator. A calculation of the system presampling MTF was performed which included effects from the linear accelerator source, the lead block used to create the high contrast edge, and the aSi detector response.

Equipment Design↗
PubMed2001

A method for determining the alignment accuracy of the treatment table axis at an isocentric irradiation facility.

At an isocentric irradiation facility, the rotation axis of the treatment table has to be accurately aligned in vertical orientation to the isocentre, which is usually marked by three perpendicular laser planes. In particular, high precision radiotherapy techniques, such as radiosurgery or intensity modulated radiotherapy, require a higher alignment accuracy of the table axis than routinely specified by the manufacturers. A simple and efficient method is presented to measure the direction and the size of the displacement of the table axis from the isocentre as marked by the lasers. In addition, the inclination of the table axis against the vertical direction can be determined. The measured displacement and inclination provide the required data to correct for possible misalignments of the treatment table axis and to maintain its alignment. Measurements were performed over a period of two years for a treatment table located at the German heavy ion therapy facility. The mean radial distance between the table axis and the isocentre was found to be 0.25 +/- 0.25 mm. The mean inclination of the table axis in the XZ- and YZ-planes was measured to be -0.03 +/- 0.02 degrees and -0.04 +/- 0.01 degrees, respectively. The measurements demonstrate the good alignment of the treatment table over the analysed time period. The described method can be applied to any isocentric irradiation facility, especially including isocentric linear accelerators used for radiosurgery or other high precision irradiation techniques.

Algorithms↗
PubMed2001

Monte Carlo calculation of output factors for circular, rectangular, and square fields of electron accelerators (6-20 MeV).

Monte Carlo (MC) techniques can be used to build a simulation model of an electron accelerator to calculate output factors for electron fields. This can be useful during commissioning of electron beams from a linac and in clinical practice where irregular fields are also encountered. The Monte Carlo code BEAM/EGS4 was used to model electron beams (6-20 MeV) from a Varian 2100C linear accelerator. After optimization of the Monte Carlo simulation model, agreement within 1% to 2% was obtained between calculated and measured (with a Si diode) lateral and depth dose distributions or within 1 mm in the penumbral regions. Output factors for square, rectangular, and circular fields were measured using two different plane-parallel ion chambers (Markus and NACP) and compared to MC simulations. The agreement was usually within 1% to 2%. This study was not primarily concerned with minimizing the simulation time required to obtain output factors but some considerations with respect to this are presented. It would be particularly useful if the MC model could also be used to calculate output factors for other, similar linacs. To see if this was possible, the primary electron energies in the MC model were retuned to model a recently commissioned similar linac. Good agreement between calculated and measured output factors was obtained for most field sizes for this second accelerator.

Biophysical Phenomena↗
PubMed2002

[Experimental study of taxol combining accelerated radiation on laryngeal carcinoma cells].

OBJECTIVE: To investigate the effect of taxol combining accelerated radiation on the human laryngeal squamous cell carcinoma Hep-2 cell lines in vitro, and to provide the experimental basis for the usage of these two combined theraputic methods. METHOD: Using techniques of tumor cells culture in vitro, the suppressive and time-dependency effects of taxol (1 x 10(-8) mol/L) combine 2 Gy X-rays generated by accelerator on the human laryngeal squamous cell carcinoma Hep-2 cell lines were observed. RESULT: Cell growth is obviously suppressed in group taxol combined accelerated radiation and it's livability is 11.11%, much lower than accelerated radiation combined taxol. After adding taxol 12 h or 24 h then combined accelerated radiation, the two groups were no difference statistically. Cell livability of group taxol is lower than group accelerated radiation. CONCLUSION: Cell growth is obviously suppressed in the human laryngeal squamous cell carcinoma Hep-2 cell lines after given 1 x 10(-8) mol/L taxol combined 2 Gy X-rays generated by accelerator. Taxol acts as a radiation sensitizer.

Antineoplastic Agents, Phytogenic↗
PubMed1986

Treatment of advanced head and neck cancer with accelerated fractionation.

Forty-eight patients with locally advanced head and neck cancer have been treated with 1.80 Gy 3 times daily, 4 hours between fractions, 3 days per week (Monday, Wednesday and Friday). At 37.80 Gy, fields were reduced and a final tumor dose of 59.40 Gy in 33 fractions given in three and a half weeks. Fifty-six percent of patients had complete resolution of tumor; the overall local control rate was 52% with an average follow-up of 12.5 months. Actuarial survival was 74% at 12 months and 50% at 24 months. Disease-free survival was 48% at 12 months and 32% at 24 months. Acute complications were common, but late complications were rare, two cases of asymptomatic subcutaneous fibrosis. Radiation therapy with accelerated fractionation shows promise of improving the therapeutic ratio.

Adult↗
PubMed1989

Radiosurgery with high energy photon beams: a comparison among techniques.

The presently known radiosurgical techniques with high energy photon beams are based either on the commercially available Gamma unit utilizing 201 stationary cobalt beams or on isocentric linear accelerators. The techniques using linear accelerators are divided into the single plane rotation, the multiple non-coplanar arcs, and the dynamic rotation. A brief description of these techniques is given, and their physical characteristics, such as precision of dose delivery, dose fall-off outside the target volume, and isodose distributions are discussed. It is shown that the multiple non-coplanar arcs technique and the dynamic rotation give dose distributions similar to those of the Gamma unit, which makes these two linear accelerator based techniques attractive alternatives to radiosurgery with the Gamma unit.

Brain Diseases↗
PubMed1995

Variation of electron beam uniformity with beam angulation and scatterer position for total skin irradiation with the Stanford technique.

PURPOSE: The influence of different scatterer-degraders and beam angulations on beam uniformity for total skin electron irradiation using the six dual beam Stanford technique is investigated. METHODS AND MATERIALS: The 6 MeV high dose rate total skin electron irradiation mode on a linear accelerator was used. Beam profiles and percentage depth doses in the patient plane for single, dual, and six dual beams were measured for different dual beam angulations and acrylic scatterer-degraders of different thicknesses mounted on the treatment head or in front of the patient in the treatment plane. RESULTS: It is demonstrated that, with the same electron nominal energy, total skin irradiation techniques with different beam penetrations can be obtained by inserting various beam scatterer-degraders into the beam, either mounted on the accelerator head or close to the patient. For our patient treatment, a beam penetration was selected so that the 80% dose lay at 8-9 mm and the 50% dose at 15-16 mm depth. This was achieved by mounting a 0.32-cm thick acrylic beam scatterer-degrader on the accelerator head. A uniform vertical profile was obtained for gantry angulations of +/- 21 degrees. CONCLUSIONS: To implement a total skin electron irradiation technique using the Stanford method, the required depth of penetration needs to be selected. Based on this, the appropriate combination of scatterer-degraders and dual beam angulations to produce a uniform beam in the treatment plane needs to be determined. Different techniques with different beam penetrations can be developed using the same high dose rate mode on the linear accelerator by a proper choice of scatterer-degraders and beam angulations.

Humans↗
PubMed1996

Commissioning and periodic quality assurance of a clinical electronic portal imaging device.

PURPOSE: An electronic portal imaging device (EPID) was recently installed on our dual-energy linear accelerator. Commissioning and quality assurance techniques were developed for the EPID. METHODS AND MATERIALS: A commissioning procedure was developed consisting of five parts: (a) physical operation and safety; (b) image acquisition, resolution, and sensitivity calibration; (c) image storage, analysis, and handling; (d) reference image acquisition; and (e) clinical operations. RESULTS: The physical operation and safety tests relate to the motions of the unit, stability of the unit supports, safety interlocks, and interlock overrides. Imager contrast and spatial resolutions are monitored by imaging a contrast-detail phantom. The imager calibration procedure consists of a no-radiation image to compensate for signal offsets, as well as a "flat-field image." The flat-field image is taken with 5.0 cm of homogeneous phantom material placed at isocenter to provide some photon scatter and to approximate the presence of a patient. Daily quality assurance procedures consists of safety tests and the acquisition and inspection of images of the contrast-detail phantom. After 1 year, the frequency of the daily procedure was reduced to weekly. Quarterly QA procedures are conducted by the physicist and consist of the same procedures conducted in the weekly test. The annual QA procedure consists of a duplication of the commissioning procedure. CONCLUSION: The procedures discussed in this article were applied to an ionization-chamber device. They have been useful in identifying difficulties with the EPID operation, including the need for recalibrating and monitoring the accelerator output stability.

Calibration↗
PubMed1993

Incident angle dependence of proton response of CR-39 (TS-16) track detector.

The proton response of the TS-16 type of CR-39 plastic nuclear track detector has been studied with accelerated and fast neutron induced protons in vacuum and in air. The diameters of etched tracks were measured as a function of etching time and the etch rate ratio and the etch induction layer were determined from the growth curve of the diameter using a variable etch rate ratio model. In the case of the accelerated protons in vacuum an anomalous incident angle dependence of the response is observed.

Calibration↗
PubMed2004

Lithium neutron producing target for BINP accelerator-based neutron source.

Pilot innovative accelerator-based neutron source for neutron capture therapy is under construction now at the Budker Institute of Nuclear Physics, Novosibirsk, Russia. One of the main elements of the facility is lithium target, that produces neutrons via threshold (7)Li(p,n)(7)Be reaction at 25 kW proton beam with energies 1.915 or 2.5 MeV. In the present report, the results of experiments on neutron producing target prototype are presented, the results of calculations of hydraulic resistance for heat carrier flow and lithium layer temperature are shown. Calculation showed that the lithium target could run up to 10 mA proton beam before melting. Choice of target variant is substantiated. Program of immediate necessary experiments is described. Target design for neutron source constructed at BINP is presented. Manufacturing the neutron producing target up to the end of 2004 and obtaining a neutron beam on BINP accelerator-based neutron source are planned during 2005.

Boron Neutron Capture Therapy↗
PubMed1999

Calibration of strontium-90 eye applicator using a strontium external beam standard.

Four techniques for measuring the dose rate from Sr-90 concave eye plaques are presented. The techniques involve calibrating a concave eye plaque against a Sr-90 teletherapy unit using X-Omat film, radiochromic film, black LiF TLD discs and LiF chips. The mean dose rate predicted by these dosimeters is 7.5 cGy s(-1). The dose rate quoted by the manufacturer is 33% lower than this value, which is consistent with discrepancies reported by other authors. Calibration against a 6 MV linear accelerator was also carried out using each of the above dosimetric devices, and appropriate sensitivity correction factors have been presented.

Brachytherapy↗
PubMed2006

Generation and modelling of megavoltage photon beams for contrast-enhanced radiation therapy.

Contrast-enhanced radiation therapy (CERT) is a treatment approach involving the irradiation of tumours containing high atomic number (Z) contrast media, using low-quality x-ray beams. This work describes the experimental generation of x-ray beams using a linear accelerator with low-Z target materials (beryllium and aluminium), in order to produce photon energy spectra appropriate for CERT. Measurements were made to compare the experimental beams to conventional linear accelerator photon beams in terms of per cent depth dose. Monte Carlo simulation was used to model the generation of each beam, and models were validated against experimental measurement. Validated models were used to demonstrate changes in photon spectra as well as to quantify the variation of tumour dose enhancement with iodinated contrast medium concentration in a simulated tumour volume. Finally, the ratio of the linear attenuation coefficient for iodinated contrast medium relative to water was determined experimentally as a function of iodine concentration. Beams created with low-Z targets show significant changes in energy spectra compared to conventional beams. For the 4 MeV/Be beam, for example, 33% of photons have energies below 60 keV. Measurements and calculation show that both the linear attenuation coefficient ratio and dose enhancement factor (DEF) increase most rapidly at concentrations below 46 mg I ml(-1). There is a significant dependence of DEF on electron energy and a lesser dependence on target material. The 4 MeV/Be beam is the most promising in terms of magnitude of DEF - for example, DEF values of 1.16 and 1.29 are obtained for concentrations of 20 mg I ml(-1) and 50 mg I ml(-1), respectively. DEF will increase or decrease, respectively, for shallower or deeper tumours at a rate of approximately 1.1% cm(-1). In summary, we show that significant dose enhancement is possible by altering the linear accelerator target and filtration, but the magnitude is highly dependent on contrast medium concentration.

Aluminum↗
PubMed2001

The history and future of accelerator radiological protection.

The development of accelerator radiological protection from the mid-1930s, just after the invention of the cyclotron, to the present day is described. Three major themes--physics, personalities and politics--are developed. In the sections describing physics the development of shielding design though measurement, radiation transport calculations, the impact of accelerators on the environment and dosimetry in accelerator radiation fields are described. The discussion is limited to high-energy, high-intensity electron and proton accelerators. The impact of notable personalities on the development of both the basic science and on the accelerator health physics profession itself is described. The important role played by scholars and teachers is discussed. In the final section. which discusses the future of accelerator radiological protection, some emphasis is given to the social and political aspects that must he faced in the years ahead.

History, 20th Century↗
PubMed2001

Shielding assessment of a mobile electron accelerator for intraoperative radiotherapy.

A new approach to intraoperative radiotherapy makes use of a mobile electron linear accelerator delivering therapeutic radiation doses in an operating room suite. This unconventional technology has raised questions concerning protection for personnel and the necessity of shielding the adjoining areas. In this study, the leakage and scatter radiation from the mobile electron accelerator is measured and characterized in a series of spherical projections. An analysis is performed to determine the need for shielding or, alternatively, patient-based load restrictions in the operating room. This investigation provides a resource to assess shielding and/or patient load restrictions for any facility performing intraoperative radiotherapy with a similar unit. The data presented indicates that the mobile electron accelerator may be operated in an area with little or no shielding under nominal patient load expectations.

Electrons↗
PubMed1983

[Operating characteristics and potential use of the LUEV-15M1 linear electron accelerator].

The manufacture of a series of medical electron accelerators LUEV-15M1 is in line with a tendency to equip radiological units in our country with electron linear accelerators. Clinical and dosimetric characteristics of a linear accelerator of this design that are distinguished by a high penetrating power, a high dose gradient along the beam edge, were studied in the Central Research Roentgeno-Radiological Institute. Its main distinctive feature is an ability to exercise programmed control over a depth dose field in the static and moving irradiation regimens by measuring the dose rate. Computed depth dose fields demonstrated an opportunity to use effectively the accelerator for irradiation of deep foci. Ten patients with head, chest and pelvic tumors were irradiated. Short-term positive results were obtained. Radiation complications hampering radiotherapy, were absent. The shortcomings are as follows: a small rotation angle of the irradiator, small movement rates of the diaphragm blocks and the adjustment of a light field, absence of a functionally fixed shaft. The accelerator has been shown to meet medical and technical requirements.

Adenoma↗