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PubMedDate not supplied

Modification of the fault logic circuit of a high-energy linear accelerator to accommodate selectively coded, large-field wedges.

A modification to the fault logic circuit that controls the collimator (COLL) fault is described. This modification permits the use of large-field wedges by adding an additional input into the reference voltage that determines the fault condition. The resistor controlling the amount of additional voltage is carried on board each wedge, within the wedge plug. This allows each wedge to determine its own, individual field size limit. Additionally, if no coding resistor is provided, the factory-supplied reference voltage is used, which sets the maximum allowable field size to 15 cm. This permits the use of factory-supplied wedges in conjunction with selected, large-field wedges, allowing proper sensing of the field size maximum in all conditions.

Equipment Safety↗

PubMedDate not supplied

Dose distributions in radiosurgery.

A PC-based, three-dimensional treatment planning system, which may be used for planning of radiosurgical treatments with the Gamma unit or with any of the radiosurgical techniques based on isocentric linear accelerators (linacs), is described and used to calculate isodose distributions for various linac-based radiosurgical techniques ranging from the single plane rotation to a 4-pi geometry. The latter gives an isotropic dose falloff outside the target volume but cannot be used for practical radiosurgery, while the single plane rotation is simple to use but gives unacceptably shallow dose falloffs in the transverse plane. Dose falloffs for several other techniques of varying degrees of complexity are shown and discussed. Also discussed is the effect of beam energy and beam profiles on radiosurgical dose distributions.

Humans↗

PubMedDate not supplied

Accelerated helium-ion beams for radiotherapy and stereotactic radiosurgery.

A new beam line for radiotherapy and radiosurgery with accelerated helium-ion beams has been set up at the Bevalac. The new treatment room has been equipped with a very precise patient positioner in order to utilize the superior dose localization properties of light-ion beams. The beam spreading and shaping system is described, the trade-offs involved in positioning the beam modifying devices are discussed, and the physical properties of the generated radiation fields are reported. The Bragg peak modulation by axial beam stacking employing a variable range shifter is explained and the control system including beam monitoring and dosimetry is presented.

Helium↗

PubMed1985

The 8 MeV linear accelerator at the MRC Cyclotron Unit, Hammersmith Hospital, London.

This machine was the first linear accelerator designed for medical use and the first to be installed in a hospital. The first patient was treated in 1953 and the last in 1969. During this period the machine was used for research during the evenings and latterly it was available for research all day long. It was switched off for the last time in February 1984. In addition to the X-ray beam, electrons were used for treatment and for research, where the high dose rate and large field size were particularly useful. An account is given of some of the highlights of the clinical and research programmes.

Animals↗

PubMed2000

Determining clinical photon beam spectra from measured depth dose with the Cimmino algorithm.

A method to determine the spectrum of a clinical photon beam from measured depth-dose data is described. At shallow depths, where the range of Compton-generated electrons increases rapidly with photon energy, the depth dose provides the information to discriminate the spectral contributions. To minimize the influence of contaminating electrons, small (6 x 6 cm2) fields were used. The measured depth dose is represented as a linear combination of basis functions, namely the depth doses of monoenergetic photon beams derived by Monte Carlo simulations. The weights of the basis functions were obtained with the Cimmino feasibility algorithm, which examines in each iteration the discrepancy between predicted and measured depth dose. For 6 and 15 MV photon beams of a clinical accelerator, the depth dose obtained from the derived spectral weights was within about 1% of the measured depth dose at all depths. Because the problem is ill conditioned, solutions for the spectrum can fluctuate with energy. Physically realistic smooth spectra for these photon beams appeared when a small margin (about +/- 1%) was attributed to the measured depth dose. The maximum energy of both derived spectra agreed with the measured energy of the electrons striking the target to within 1 MeV. The use of a feasibility method on minimally relaxed constraints provides realistic spectra quickly and interactively.

Algorithms↗

PubMed2001

The impact of ICRP/ICRU quantities on high energy neutron dosimetry: a review.

Unlike other fields of toxicology, radiation protection has a dual system of quantities, one set for assessment and the derivation of authorised limits and another set for monitoring radiation performance and compliance. Neutrons are an important or dominant constituent of the radiation field around high energy accelerators and the evolution of the radiation protection quantities used to measure neutrons is described. In 1990 ICRP introduced a new quantity, the effective dose. E. with which to express its protection limits. E represented a radical departure from previous advice of the Commission, particularly in the manner by which it weighted the absorbed dose deposited by high LET radiations. This advice had profound consequences for neutron dosimetry. Over the past decade analyses have revealed logical flaws and inconsistencies in the definition of effective dose. These are briefly discussed with most emphasis being placed on inconsistencies in radiation weighting. Suggestions are made with a view to resolving these inconsistencies.

Neutrons↗

PubMedDate not supplied

Evaluation of a beam-spot camera for megavoltage x rays.

A beam-spot camera for measurements of x-ray focal spots of accelerators has been evaluated. The device consists of closely packed 0.25-mm-thick lead and 0.25-mm-thick cardboard strips. It is placed on radiographic film with the lamellae parallel to the beam axis and an exposure made. The images were scanned with a microdensitometer. The results indicate that the broadening of the source intensity profile at half maximum is of the order 1 mm, which permits the use of the beam-spot camera for acceptance testing and quality control. Longer tails in the density profile limit the quantitative information that can be extracted from the images.

Cobalt Radioisotopes↗

PubMed1999

Finding mechanisms responsible for the spectral distribution of electron beams produced by a linear accelerator.

The measured electron spectra of linear accelerators from several manufacturers differ in comparison to the spectral form and width. As part of our investigations of linac performance and stability, we analyzed the electron spectra of our linacs. After building a spectrometer the electron spectra were measured. The measured spectral widths were comparable with the results published in the literature. It appeared that the phase of the recycled radio pulse in combination with the limited bandwidth of the bending magnet are responsible for unusual (multipeak) electron spectra. The scatter filters only have a relatively small widening effect on the spectrum. There was no indication that multipeak or wide spectra are related to linac instabilities.

Electrons↗

PubMed1986

A study of neutron leakage through an Fe shield at an accelerator.

The spectrum of neutrons, produced in the interactions of hadrons with energies up to several hundred GeV, that are emitted through a large Fe electro magnet has been determined by use of a multisphere spectrometer both before and after the shielding was augmented with concrete. The existence of leakage neutrons at energies of approximately 0.005-1.0 MeV was verified in the initial configuration, and found to be completely eliminated in the spectrum obtained after the concrete was added. The quality factor of the radiation field was measured; the values are reduced from about six to three with the extra shielding. Additional fluence measurements in the environs of the magnet can be interpreted in terms of a skyshine mechanism with source and attenuation parameters consistent with the energies and intensity of the leakage neutrons.

Iron↗

PubMed2003

Current calibration, treatment, and treatment planning techniques among institutions participating in the Children's Oncology Group.

PURPOSE: To report current technology implementation, radiation therapy physics and treatment planning practices, and results of treatment planning exercises among 261 institutions belonging to the Children's Oncology Group (COG). METHODS AND MATERIALS: The Radiation Therapy Committee of the newly formed COG mandated that each institution demonstrate basic physics and treatment planning abilities by satisfactorily completing a questionnaire and four treatment planning exercises designed by the Quality Assurance Review Center. The planning cases are (1) a maxillary sinus target volume (for two-dimensional planning), (2) a Hodgkin's disease mantle field (for irregular-field and off-axis dose calculations), (3) a central axis blocked case, and (4) a craniospinal irradiation case. The questionnaire and treatment plans were submitted (as of 1/30/02) by 243 institutions and completed satisfactorily by 233. Data from this questionnaire and analyses of the treatment plans with monitor unit calculations are presented. RESULTS: Of the 243 clinics responding, 54% use multileaf collimators routinely, 94% use asymmetric jaws routinely, and 13% use dynamic wedges. Nearly all institutions calibrate their linear accelerators following American Association of Physicists in Medicine protocols, currently 16% with TG-51 and 81% with TG-21 protocol. Treatment planning systems are relied on very heavily for all calculations, including monitor units. Techniques and results of each of the treatment planning exercises are presented. CONCLUSIONS: Together, these data provide a unique compilation of current (2001) radiation therapy practices in institutions treating pediatric patients. Overall, the COG facilities have the equipment and the personnel to perform high-quality radiation therapy. With ongoing quality assurance review, radiation therapy compliance with COG protocols should be high.

Brain↗

PubMed1984

Differential recovery from potentially lethal damage in normal human lung fibroblasts after irradiation with 60Co gamma-rays and accelerated N-ion beam.

PLD recovery after irradiation with accelerated N-ion was examined and compared with that after irradiation with 60Co gamma-rays in normal human lung fibroblasts (IMR-90). No shoulder region was observed in the survival curve of the cells after N-ion irradiation. Ratios of D0 values before and after a 6-hour incubation in plateau phase were 1.1 and 1.8 for N-ion irradiation and gamma-ray irradiation, respectively. The results show that recovery after irradiation with high-LET radiation is slow and much less than after low-LET irradiation.

Cell Survival↗

PubMed1996

Particle-mediated gene transfer of granulocyte-macrophage colony-stimulating factor cDNA to tumor cells: implications for a clinically relevant tumor vaccine.

The necessity for prolonged tissue culture manipulations limits the clinical application of many form of gene therapy in patients with malignancies. We hypothesized that granulocyte-macrophage colony-stimulating factor (GM-CSF) cDNA in a plasmid expression vector could be effectively introduced into resting tumor cells, without the need for tissue culture propagation prior to or following transfection, and that efficient expression of transgenic GM-CSF by the transfected tumor cells would confer an effective immune response against tumors. GM-CSF cDNA in expression vectors was coated onto gold particles and accelerated with a gene gun device into mouse and human tumor cells. Human tumor tissue transfected within 4 hr of surgery produced significant levels of transgenic human GM-CSF protein in vitro. Human GM-CSF was readily detectable in serum and at the injection site following subcutaneous implantation of these transfected tumor cells into nude mice. Transfected and irradiated murine B16 melanoma cells produced > or = 100 ng/ml murine GM-CSF/10(6) cells per 24 hr in vitro for at least 10 days. The antitumor efficacy of this nonviral approach was tested using irradiated B16 tumor cells that were transfected with mGM-CSF cDNA and injected into mice as tumor "vaccine". Subsequent challenge of these mice with nonirradiated, nontransfected B16 tumor cells showed that 58% of the animals wer protected from the tumor by the prior vaccine treatment. In contrast, only 2% of control animals were protected by prior treatment with irradiated B16 cells transfected with the vector containing the luciferase gene. These results suggest that particle-mediated transfection of fresh tumor explants with cytokine cDNA is an effective and clinically attractive approach for cancer therapy.

Animals↗

PubMed1994

Design criteria for prompt radiation limits on the relativistic heavy ion collider site.

The Relativistic Heavy Ion Collider (RHIC) is a superconducting colliding beam accelerator facility that is currently under construction. Relatively small amounts of energy depositing in the coils of superconducting magnets can result in a "quench," the irreversible transition to the normal resistive state. The quench limit of superconducting magnets, therefore, constrains local beam loss throughout the injection, acceleration, and storage cycles to extremely low levels. From a practical standpoint, it follows that there is essentially no prompt radiation in most regions due to normal operations. The design of shielding is, therefore, principally driven by the consequences of a single pulse fault at full energy in one of the two storage rings. Since there are no regulatory requirements or guidance documents that prescribe radiological performance goals for this situation, the RHIC Project has proposed a scheme to classify the various areas of the RHIC complex based on Design Basis Accident faults. The criteria is then compared to existing regulatory requirements and guidance recommendations.

Equipment Design↗

PubMed1991

Radiosurgery: a nursing perspective.

The term radiosurgery, originally applied to three-dimensional stereotactic irradiation of small intracranial targets with low-energy x-rays, has more recently been applied to widely differing techniques and radiation sources. These include gamma units using cobalt-60; beams of protons, helium ions and neutrons; and modified cobalt-60 or linear accelerator units. These techniques allow delivery of a high dose of radiation in a single fraction to a small and well-defined intracranial volume, without delivering significant radiation to adjacent normal tissue. The most usual targets for radiosurgery are arteriovenous malformations. It is occasionally used for acoustic neuromas and primary or metastatic brain malignancies as well. Although radiosurgery is not a new procedure, its use is becoming more widespread. Nurses, as critical members of radiosurgery teams, must be informed about all aspects of the procedures and associated nursing care skills.

Brain Neoplasms↗

PubMed2000

Analysis of photoneutron spectra produced in medical accelerators.

A complete method is presented for the evaluation of photoneutron spectra produced in linear accelerators for cancer radiotherapy. It consists of a computer simulation code based on the MCNP4B Monte Carlo code, in which the new routine GAMMAN was implemented, allowing the accurate study of photoneutron production in high Z elements. In addition an experimental method based on a passive bubble spectrometer allows direct measurements of the photoneutron spectrum at the patient plane, also under the photon beam. The results are presented both for a 15 MeV linac with a traditional collimator system and for an 18 MeV linac equipped with a multileaf collimator, used in conformational radiotherapy.

Computer Simulation↗

PubMed1994

Moscow hospital-based proton therapy facility design.

An innovative design for a hospital-based proton therapy facility is described here in two versions: a single level (3600 m2) and a three-level plan (700-720 m2). The facility is designed to have 5 to 6 treatment rooms working simultaneously and independently of each other. The accelerator is a 250 MeV H-synchrotron, which produces a small external beam capable of pencil-beam scanning treatments. The small emittance of the beam yields cost savings in the size and weight of the magnets and the amount of concrete shielding. The beam delivery systems, including an isocentric gantry, are designed to use elements that are well known and thoroughly tested. Initial cost of a facility using this new design is estimated to be only 25-30% higher than construction of a facility delivering conventional photon treatments.

Cancer Care Facilities↗

PubMedDate not supplied

Radiation parameters of 6 to 20 MeV scanning electron beams from the Saturne linear accelerator.

Depth doses of the scanning electron beams from the Saturne Therac-20 linear accelerator at nominal energies of 6,9,13,17, and 20 MeV were measured in polystyrene using a thin window parallel plate ionization chamber. Central axis depth dose curves are derived and are analyzed according to the method of Brahme and Svensson. For each of the five electron energies, values are obtained for the most probable energy at the absorber surface Ep,0, the practical range Rp, the 50% range R50, the therapeutic range R85, the electron dose gradients, total collision energy losses, and other radiation parameters, and these are compared to corresponding values for electron beams from a 22 MeV medical microtron and a 20 MeV betatron.

Electrons↗

PubMedDate not supplied

A study of quality of bremsstrahlung spectra reconstructed from transmission measurements.

A numerical method for the reconstruction of bremsstrahlung spectra has been applied to the analysis of simulated data. The method is found to be reliable in reconstructing x-ray spectra of maximum energy up to 10 MeV. Measurements of aluminum transmission data carried out for five linear accelerators have also been analyzed by this method to determine the fractional energy fluence. The values of the Spencer-Attix water/air stopping power ratio, SS.A. w,air, reported as a function of the ratios TPR20 10, are in good agreement with computed results. Quality index values were correlated to mean incident energies of x-ray beams used in radiotherapy. The experimental setup has also provided information regarding the softening effect on the off-axis beam, which can be used in clinical computer dosimetry to correct conventional zero field size tissue maximum ratio.

Image Processing, Computer-Assisted↗