Measurements of some radiobiological and physical properties of neutrons produced by a 4-MV Van de Graaff accelerator.
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Animals↗
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Results for “Particle Accelerators”
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A preliminary evaluation of accelerator mass spectrometry in the biomedical field.
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Animals↗
[Effect of nonlethal irradiation with accelerated high-energy helium ions on the retention of conditioned and formation of new behavioral habits in rats in early and late time periods].
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Animals↗
Cerebral radiation surgery using moving field irradiation at a linear accelerator facility.
A modified irradiation technique at a linear accelerator facility for radiation surgery within the brain is described consisting of several moving field irradiations in non-coplanar planes. Using collimated narrow beams, a localization system and special computer programs for precise patient positioning, a high concentration of dose within small, well circumscribed volumes is obtained. Resulting dose distributions were studied experimentally and by calculations. A simple algorithm for treatment planning was developed and based on CT images. Radiation surgery within the brain is now technically feasible at our linear accelerator. Seventeen patients have now been treated.
Brain↗
Optimized MLC-beam arrangements for tangential breast irradiation.
BACKGROUND AND PURPOSE: Very large numbers of women are treated with tangential breast irradiation after breast-conserving surgery due to mammary carcinoma. The aim of this study was to improve a conventional treatment plan by modifying the dose intensity in the beams to reduce the absorbed dose outside the planning target volume (PTV) and to reduce the absorbed dose variation inside the PTV diotherapy of mammary carcinoma. MATERIALS AND METHODS: Treatment planning was performed both with conventional technique and with a simple intensity modulation technique for 12 consecutive patients. RESULTS: In all cases a higher degree of dose conformity was obtained with the dose intensity modulation technique. The relative gain was found to be similar for all patients irrespective of the size of the target volume or the irradiated lung volume. CONCLUSION: Simple manual intensity modulation can be used to improve the dose distribution in tangential breast irradiation. With modern accelerators the increased time for this technique is less than 2 min per fraction.
Breast Neoplasms↗
Theoretical and experimental determination of phantom scatter factors for photon fields with different radial energy variation.
The output factor used for monitor unit determination in radiotherapy can be divided into two factors: the head scatter factor and the phantom scatter factor. Theoretical and experimental phantom scatter factors have been compared for different beam qualities between 4 MV and 50 MV and field sizes from 5 cm x 5 cm to 30 cm x 30 cm. The theoretical data were obtained through a convolution method based on Monte Carlo calculated energy spectra and dose kernels. The calculations have been performed both for accelerators with a rather large energy variation within the field and for accelerators with a constant energy distribution in the field. Deviations between theoretical and experimental data were found to be less than 1%.
Humans↗
Monitor chamber backscatter for intensity modulated radiation therapy using multileaf collimators.
Backscattered radiation into the machine monitor chamber can affect the machine output variation, with changes in field size and shape. For intensity modulated radiation therapy (IMRT) where many field, which may have small dimensions, are summed to give an intensity modulated field, the magnitude of backscatter will be different due to both the backscattering surface area changing, and the delivered monitor units being larger than for the equivalent static field. The effect of backscatter variation with field size for a Philips SL15 accelerator has been investigated at 8 MV for static and IMRT fields both in the standard clinical operating condition where an anti-backscatter plate is fitted, and also for a case where the anti-backscatter plate has been removed. The results show that in the absence of the anti-backscatter plate the variation in output between a 4 cm by 4 cm field and a 40 cm by 40 cm field size due to backscattered radiation was 5% for static fields. The anti-backscatter plate reduced this variation to less than 1%. When the accelerator operated in IMRT mode, with the backscatter plate in place, changes in the output due to additional backscattered radiation were less than 0.3%. With the backscatter plate removed, the outputs were lower, indicating the presence of additional backscattered radiation. It can be concluded that for the Philips MLC and SL accelerator with its anti-backscatter plate, the effects of backscattered radiation can be ignored for both static and IMRT fields.
Alloys↗
A virtual-accelerator-based verification of a Monte Carlo dose calculation algorithm for electron beam treatment planning in homogeneous phantoms.
By introducing Monte Carlo (MC) techniques to the verification procedure of dose calculation algorithms in treatment planning systems (TPSs), problems associated with conventional measurements can be avoided and properties that are considered unmeasurable can be studied. The aim of the study is to implement a virtual accelerator, based on MC simulations, to evaluate the performance of a dose calculation algorithm for electron beams in a commercial TPS. The TPS algorithm is MC based and the virtual accelerator is used to study the accuracy of the algorithm in water phantoms. The basic test of the implementation of the virtual accelerator is successful for 6 and 12 MeV (gamma < 1.0, 0.02 Gy/2 mm). For 18 MeV, there are problems in the profile data for some of the applicators, where the TPS underestimates the dose. For fields equipped with patient-specific inserts, the agreement is generally good. The exception is 6 MeV where there are slightly larger deviations. The concept of the virtual accelerator is shown to be feasible and has the potential to be a powerful tool for vendors and users.
Algorithms↗
Measurement of radiation leaked from a 45-MeV linear accelerator facility by gated counting.
By the gated counting method that had been developed by the authors the spatial dose distributions at the boundary and inside of a 45-MeV electron linear accelerator (linac) facility were obtained using a NaI(Tl) scintillation probe and a counting system. Both distributions of pulse height and radiation propagation time were also measured. At the facility boundary, dose rates measured ranged from 0.16 microR hr-1 to 0.86 microR hr-1, which were less than one-tenth the natural background. At measurement in the linac control room, two different leakage sources, one originating at and around the accelerator and the other at a microwave power system, were discriminated by measuring pulse height and time distributions simultaneously.
Environmental Exposure↗
Air activation produced by high-energy medical accelerators.
The activity of 15O and 13N per unit volume of air produced by a 25 and a 45-MeV medical accelerator was determined by direct measurement. The accelerators were operated in such a fashion as to produce maximum activation of the treatment room air. Levels of the order of 1% or less of the maximum permissible concentration in air for 15O and 13N were found immediately after accelerator shutdown. Three different techniques for calibrations of the air detector were investigated.
Air Pollution, Radioactive↗
Induction and repair of DNA strand breaks in bovine lens epithelial cells after high LET irradiation.
The lens epithelium is the initiation site for the development of radiation induced cataracts. Radiation in the cortex and nucleus interacts with proteins, while in the epithelium, experimental results reveal mutagenic and cytotoxic effects. It is suggested that incorrectly repaired DNA damage may be lethal in terms of cellular reproduction and also may initiate the development of mutations or transformations in surviving cells. The occurrence of such genetically modified cells may lead to lens opacification. For a quantitative risk estimation for astronauts and space travelers it is necessary to know the relative biological effectiveness (RBE), because the spacial and temporal distribution of initial physical damage induced by cosmic radiation differ significantly from that of X-rays. RBEs for the induction of DNA strand breaks and the efficiency of repair of these breaks were measured in cultured diploid bovine lens epithelial cells exposed to different LET irradiation to either 300 kV X-rays or to heavy ions at the UNILAC accelerator at GSI. Accelerated ions from Z=8 (O) to Z=92 (U) were used. Strand breaks were measured by hydroxyapatite chromatography of alkaline unwound DNA (overall strand breaks). Results showed that DNA damage occurs as a function of dose, of kinetic energy and of LET. For particles having the same LET the severity of the DNA damage increases with dose. For a given particle dose, as the LET rises, the numbers of DNA strand breaks increase to a maximum and then reach a plateau or decrease. Repair kinetics depend on the fluence (irradiation dose). At any LET value, repair is much slower after heavy ion exposure than after X-irradiation. For ions with an LET of less than 10,000 keV micrometers-1 more than 90 percent of the strand breaks induced are repaired within 24 hours. At higher particle fluences, especially for low energetic particles with a very high local density of energy deposition within the particle track, a higher proportion of non-rejoined breaks is found, even after prolonged periods of incubation. At the highest LET value (16,300 keV micrometers-1) no significant repair is observed. These LET-dependencies are consistent with the current mechanistic model for radiation induced cataractogenesis which postulates that genomic damage to the surviving fraction of epithelial cells is responsible for lens opacification.
Animals↗
[New diagnostic tools using proton beams obtained from accelerators in KEK (National Laboratory for High Energy Physics), Tsukuba].
The opportunity exists at present for the application of accelerator beam to clinical diagnosis in the Academic City of Tsukuba wherein the National Laboratory for High Energy Physics (KEK) and Tsukuba University Hospital are located. 250 MeV Proton beams have been available both for clinical proton therapy and experimental proton radiography at the Particle Radiation Medical Center (PARMS) (Tsukuba University). Monoenergetic protons are highly sensitive to density variations and are capable of giving radiographs of very high contrast. As an initial step in exploring their diagnostic potential, protons with energies of 250 MeV were used in the projection radiography of animals. Prior to the above experiments, some characteristics of the proton beam were examined. The detector system in this experiment was films with or without intensifying screens. The problem hampering diagnostic potential of proton radiography was multiple scattering.
Angiography↗
AAPM code of practice for radiotherapy accelerators: report of AAPM Radiation Therapy Task Group No. 45.
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Biophysical Phenomena↗
Proposed definitions for isodose flatness and symmetry in clinical radiotherapy beams.
In clinical radiotherapy it is important that beam intensity be as homogeneous as possible to reduce the probability of treatment failure. As an extension of the well established concepts of beam flatness and symmetry for characterizing radiotherapy beams, the concepts of isodose flatness and symmetry are introduced. The definitions are tested with actual data obtained from a Co-60 unit and a linear accelerator and results are presented. The concepts as defined appear to provide a useful quantitative indication of beam homogeneity.
Cobalt Radioisotopes↗
Total skin high-dose-rate electron therapy dosimetry using TG-51.
An approach to dosimetry for total skin electron therapy (TSET) is discussed using the currently accepted TG-51 high-energy calibration protocol. The methodology incorporates water phantom data for absolute calibration and plastic phantom data for efficient reference dosimetry. The scheme is simplified to include the high-dose-rate mode conversion and provides support for its use, as it becomes more available on newer linear accelerators. Using a 6-field, modified Stanford technique, one may follow the process for accurate determination of absorbed dose.
Algorithms↗
A history of radiation shielding of x-ray therapy rooms.
In this report the history of shielding for radiation treatment rooms is traced from the time of the discovery of x-rays to the present. During the early part of the twentieth century the hazards from ionizing radiation were recognized and the use of lead and other materials became commonplace for shielding against x-rays. Techniques for the calculation of the shield thickness needed for x-ray protection were developed in the 1920's and shielding materials were characterized in terms of the half value layer or simple exponential factors. At the same time, better knowledge of the interaction between radiation and matter was acquired. With the development of high energy medical accelerators after 1940, new and more complex shielding problems had to be addressed. Recently, shielding requirements have become more stringent as standards for exposure of personnel and the general public have been reduced. The art of shielding of radiation treatment facilities is still being developed and the need for a revision of the reports on shielding of medical accelerators from the National Council on Radiation Protection and Measurements is emphasized in this article.
History, 19th Century↗
Induced radioactive potential for a medical accelerator.
Medical accelerators operating over 10 MV can induce short-lived radionuclides in components near the beam and in the air (McGinley 1992). We evaluated a Clinac 2100 C/D at 18 MV photon mode for radionuclidic exposure, contamination, and airborne potential to the accelerator staff entering the room after patient radiation treatment. The gantry, patient couch, wedges, floor, and air were activated. Most activated components appear to decay with a half-life of 2.5 min, except the gantry and port with half-lives approaching 10 min. The highest exposure was from the port at <2 mR h(-1). No removable contamination on any activated component was detected including coolant water in the machine. Airborne radionuclides were measured in the room and at the roof exhaust. The airborne potential is short lived because of ventilation and decay with the highest exposure of 0.3 mR h(-1) lasting for 1 s. Our measurements support the insignificant exposures received by accelerator staff wearing whole body personnel monitors. Accelerator roof effluents to unrestricted areas during patient treatments indicate that regulatory limits are not exceeded.
Environmental Exposure↗
Surface dose perturbation due to air gap between patient and bolus for electron beams.
The effect of air gaps under bolus material on the surface dose for electron beams is investigated. Dose measurements were performed for air gaps from 0.0 to 3.0 cm and bolus thicknesses of 0.5 and 1.0 cm using the various electron energies and cone sizes available on an electron linear accelerator. Our results show that the surface dose decreases for lower electron energies, smaller field sizes, thicker boluses, and larger air gaps.
Electrons↗