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PubMed2005

Adduction of biomacromolecules with acrylamide (AA) in mice at environmental dose levels studied by accelerator mass spectrometry.

Since 2002, WHO has strongly called scientists to investigate intensively the toxicity and potential carcinogenicity of acrylamide (AA), because humans are widely exposed to AA via various foodstuffs. In this study we measured the biomacromolecule adducts of [2,3-(14)C]AA (0, 7.5 x 10(-2), 7.5 x 10(-1), 7.5, 9.3 x 10(1), 2.4 x 10(2) and 1.0 x 10(3)microg/kg b.w.) in adult male mice by ultrasensitive accelerator mass spectrometry (AMS) technique. The aim is to evaluate the potential molecular toxicity of AA at human relevant dose levels, particularly towards the sperm cells. Hemoglobin (Hb), serum albumin (SA), protamine, sperm DNA, tails and heads were isolated 24h post dosing and the adduct levels were measured by AMS, respectively. Good log/log linear dose-response correlations were established. Moreover, the correlation of AA-protamine adducts, AA-sperm DNA adducts, as well as AA-sperm head/tail adducts with AA-Hb or AA-SA adducts presented a linear log/log mode. In sperm, the formation of AA-protamine adducts were predominating to AA-DNA adducts. The adducts on sperm heads/tails might both influence the fertility efficacy.

Acrylamide↗

PubMed1979

Mutation and inactivation of cultured mammalian cells exposed to beams of accelerated heavy ions. II. Chinese hamster V79 cells.

Inactivation and mutation to thioguanine-resistance of V79 hamster cells were studied after irradiation with accelerated helium, boron or nitrogen ions covering a range of linear energy transfer from 28 to 470 keV micrometers-1. For all radiation qualities a dose-dependent increase in mutant frequency was found for doses giving surviving fractions greater than about 0.20. The effectiveness per unit dose for both inactivation and mutation induction increased with the linear energy transfer of the radiation to a maximum in the range 90-200 keV micrometer-1. However, the maximum mutagenic effectiveness relative to gamma-rays was about two or more times that for inactivation. It is suggested that a proportion of the radiation-induced mutants suffer extensive genetic damage, and that some forms of this damage may be induced with high efficiency by radiations of high linear energy transfer.

Animals↗

PubMed2005

Sensitivity of large-field electron beams to variations in a Monte Carlo accelerator model.

Adjustments made to Monte Carlo models during the commissioning of the simulation should be physically realistic and correspond to actual machine characteristics. Large electron fields, with the jaws fully open and the applicator removed, are sensitive to important source and geometry parameters and may provide the most accurate beam models, including those collimated by an applicator. We report on the results of a comprehensive Monte Carlo sensitivity study documenting the response of these large fields to changes in the configuration of a Siemens Primus linear accelerator. The study was performed for 6, 9 12, 15, 18 and 21 MeV configurations, and included variations of thickness, position and lateral alignment of all treatment head components. Variations of electron beam characteristics were also included in the study. Results were classified by their impact on central-axis depth dose distributions, including the bremsstrahlung tail, and on beam profiles near D(max) and in the bremsstrahlung region. Low-energy results show an increased sensitivity to electron beam properties. High-energy bremsstrahlung profiles are shown to be useful in determining misalignments between the beam axis and mechanical isocentre. For all energies, the alignment of the secondary scattering foil and monitor chamber are shown to be critical for correctly modelling beam asymmetries. The results suggest a methodology for commissioning of electron beams using Monte Carlo treatment head simulation.

Electrons↗

PubMed2005

Preliminary shielding assessment for the 100 MeV proton linac (KOMAC).

The Proton Engineering Frontier Project is building the Korea Multipurpose Accelerator Complex facilities from 2002 to 2012, which consists of a high-current 100 MeV proton linear accelerator and various beam-lines. This paper provides a preliminary estimate of the shielding required for the 20 mA proton linac and the beam-dump. For an accurate information on secondary neutron production from the guiding magnet and primary heat sink of the beam dump, proton-induced 63Cu and 65Cu cross section data were evaluated and applied to shielding calculations. The required thickness of the concrete was assessed by a simple line-of-sight model for the lateral shielding of the beam-line and the full shielding of the beam dump. Monte Carlo simulations were also performed using the MCNPX code to obtain the source term and attenuation coefficients for the three-dimensional lateral shielding model of the beam-line.

Computer Simulation↗

PubMed2002

An accelerator based system for in vivo neutron activation analysis measurements of manganese in human hand bones.

Manganese (Mn) is an essential nutrient for growth and development. Unfortunately, overexposure can lead to neurological damage, which is manifested as a movement disorder marked by tremors. Preclinical symptoms have been found in populations occupationally exposed to the element, and it is suggested that in late stages of the disorder, removing the Mn exposure will not prevent symptoms from progressing. Hence, it is desirable to have a means of monitoring Mn body burden. In vivo neutron activation analysis (IVNAA) is a technique which allows the concentration of some elements to be determined within sites of the body without invasive procedures. Data in the literature suggests that the Mn concentration in bone is greater than other tissues, and that it may be a long term storage site following exposure. Therefore, using the McMaster KN-accelerator to produce neutrons through the 7Li(p,n)7Be reaction, the feasibility of IVNAA for measuring Mn levels in the human hand bone was investigated. Mn is activated through the 55Mn(n,gamma)56Mn reaction, and the 847 keV gamma rays emitted when 56Mn decays are measured outside the body using NaI(Tl) detectors. An optimal incident proton energy of 2.00 MeV was determined from indium foil and microdosimetry measurements. Hand phantom data suggest a minimum detectable limit of approximately 1.8 ppm could be achieved with a reasonably low dose of 50 mSv to the hand (normal manganese levels in the human hand are approximately 1 ppm). It is recommended the technique be developed further to make human in vivo measurements.

Bone and Bones↗

PubMedDate not supplied

Fast Fourier transform convolution calculations of x-ray isodose distributions in homogeneous media.

Convolution concepts were implemented using the discrete fast Fourier transform (FFT) to model the three-dimensional dose distribution due to x-rays produced by a medical linear accelerator. Convolution kernels were employed that had been calculated by Mackie using the EGS4 Monte Carlo code. The EGS4 code was also used to estimate initially the spectrum by simulating the production, filtering, and flattening of the beam in the collimator of the linear accelerator. The continuous bremsstrahlung spectrum was modeled using five discrete energies. The more subtle field-size effects of collimator scattering on the spectrum were obtained by calculating corrections to the spectral components using a least-squares search technique. Dose distributions were obtained using FFT convolutions of the kernels for each energy with the spectrally weighted fluence distributions for that energy. The dose distributions were compared with isodose distributions measured in a water phantom. The agreement was generally found to be better than 1% on the central axis. The calculation time for a single three-dimensional beam was approximately 20 min using a VAX/750 without an array processor. Methods were explored to reduce the calculation time using similar hardware, and estimates were made of how to reduce the calculation time using a more sophisticated computer system.

Electrons↗

PubMed1999

Toward a final design for the Birmingham boron neutron capture therapy neutron beam.

This paper is concerned with the proposed Birmingham accelerator-based epithermal neutron beam for boron neutron capture therapy (BNCT). Details of the final moderator design, such as beam delimiter, shield, and beam exit surface shape are considered. Monte Carlo radiation transport simulations with a head and body phantom have shown that a simple flat moderator beam exit surface is preferable to the previously envisioned spherical design. Dose rates to individual body organs during treatment have been calculated using a standard MIRD phantom. We have shown that a simple polyethylene shield, doped with natural lithium, is sufficient to provide adequate protection to the rest of the body during head irradiations. The effect upon the head phantom dose distributions of the use of such a shield to delimit the therapy beam has been evaluated.

Boron Neutron Capture Therapy↗

PubMed1989

[Radiation pneumonitis in the x-ray picture following megavoltage irradiation using the Neptune 10 p. linear accelerator].

For 105 patients with healthy lungs (76 breast carcinomas, 29 testicular tumors) irradiated from 1981 to 1983 with the linear accelerator Neptune 10p. the pulmonary effects of irradiation were monitored over several years. The true dose applied for breast carcinomas was 46 Gy (2 Gy per fraction), for testicular tumors 40 Gy were applied in the mediastinal field. 9% of the patients showed excessive infiltrations, 18% radiation pneumonitis of medium degree. In 35% of the patients slight infiltrations were found. The course of the pneumonitis was, according to its stage, regular. After a latency period 30 days post irradiation the early stadium occurs. Florid pneumonitis develops between the 45th and 90th day after irradiation. Extended radiographic effects occur up to 10 days earlier. Through a period of pneumonitis with pronounced shrinkage fibrosis develops. By CT-based individual radiation planning the pulmonary radiation reaction can be significantly reduced. The differential diagnostics of radiation effects and metastases is discussed.

Aged↗

PubMed1986

Endocrine function after immunosuppression of pancreatic allograft by ionizing irradiation in the primate.

The object of this preliminary study was to evaluate the endocrine function after heterotopic intraperitoneal segmental pancreatic allotransplantation with unligated duct in irradiated, totally pancreatectomized primates. All allograft recipients received, pre- and peroperative donor-specific blood transfusions and peroperative external irradiation from a linear accelerator; 200 rads was administered weekly and increased to a total dose of 1,500 rads. Pancreatic transplantation was performed between 2 and 6 weeks after completion of irradiation and preoperative blood transfusions. As previously reported, only minimal pancreatic allograft survival was achieved following preoperative irradiation. One recipient remained normoglycaemic for greater than 100 days after transplantation, the longest surviving pancreatic allograft recipient reported from this laboratory. Intravenous glucose tolerance test results in this recipient revealed normoglycaemia, reduced K-value, hypoinsulinaemia, normal glucagon response, reduced C-peptide values, and moderate glucose intolerance. Aortography and electron-microscopic examination of allograft biopsy tissue confirmed the presence of a functioning allograft.

Animals↗

PubMed2005

Quantitating isotopic molecular labels with accelerator mass spectrometry.

Accelerator mass spectrometry (AMS) traces isotopically labeled biochemicals and provides significant new directions for understanding molecular kinetics and dynamics in biological systems. AMS traces low-abundance radioisotopes for high specificity but detects them with MS for high sensitivity. AMS reduces radiation exposure doses to levels safe for use in human volunteers of all ages. Total radiation exposures are equivalent to those obtained in very short airplane flights, a commonly accepted radiation risk. Waste products seldom reach the Nuclear Regulatory Commission (NRC) definition of radioactive waste material for (14)C and (3)H. Attomoles of labeled compounds are quantified in milligram-sized samples, such as 20 microl of blood. AMS is available from several facilities that offer services and new spectrometers that are affordable. Detailed examples of designing AMS studies are provided, and the methods of analyzing AMS data are outlined.

Carbon Radioisotopes↗

PubMed2005

[Verification of the VEF photon beam model for dose calculations by the Voxel-Monte-Carlo-Algorithm].

The VEF linac head model (VEF, virtual energy fluence) was developed at the University of Tübingen to determine the primary fluence for calculations of dose distributions in patients by the Voxel-Monte-Carlo-Algorithm (XVMC). This analytical model can be fitted to any therapy accelerator head by measuring only a few basic dose data; therefore, time-consuming Monte-Carlo simulations of the linac head become unnecessary. The aim of the present study was the verification of the VEF model by means of water-phantom measurements, as well as the comparison of this system with a common analytical linac head model of a commercial planning system (TMS, formerly HELAX or MDS Nordion, respectively). The results show that both the VEF and the TMS models can very well simulate the primary fluence. However, the VEF model proved superior in the simulations of scattered radiation and in the calculations of strongly irregular MLC fields. Thus, an accurate and clinically practicable tool for the determination of the primary fluence for Monte-Carlo-Simulations with photons was established, especially for the use in IMRT planning.

Algorithms↗

PubMed1995

Monitor unit calculation for large wedged high-energy photon beams.

With the modern high-energy linear accelerators, the following beam characteristics have to be taken into account in the monitor unit (MU) calculation of a wedged treatment: (i) the field size dependence of wedge factors; (ii) the changes in depth dose and maximum build-up depth (dmax) induced by wedges; and (iii) the field size dependence of dmax. The incorporation of a field size specific wedge factor in an MU calculation is straightforward. Effects (ii) and (iii) however, often cause confusion and inconsistency in the choices of the reference depth for wedge factors and the normalization depth for wedged depth dose, and consequently can lead to inconsistent MU calculation formalism with additional efforts of up to 7% in the delivered dose. In this note, we illustrate a derivation of an exact central axis MU calculation for wedged treatments, which correctly accounts for the effects mentioned above.

Biophysical Phenomena↗

PubMed2006

Back to the future: the history and development of the clinical linear accelerator.

The linear accelerator (linac) is the accepted workhorse in radiotherapy in 2006. The first medical linac treated its first patient, in London, in 1953, so the use of these machines in clinical practice has been almost co-existent with the lifetime of Physics in Medicine and Biology. This review is a personal selection of things the authors feel are interesting in the history, particularly the early history, and development of clinical linacs. A brief look into the future is also given. One significant theme throughout is the continuity of ideas, building on previous experience. We hope the review might re-connect younger radiotherapy physicists in particular with some of the history and emphasize the continual need, in any human activity, to remain aware of the past, in order to make best use of past experience when taking decisions in the present.

Animals↗

PubMed1983

Accelerator room photoneutron and photon background measurements using thermoluminescent dosimeters.

Photoneutron dose equivalents and photon doses in the treatment room of a clinical linear accelerator were measured with sets of isotopically enriched LiF thermoluminescent dosimeters and a moderating sphere. Dosimeter neutron calibrations with 252Cf sources were repeated many times during the extended series of measurements because the 6LiF dosimeter sensitivity increased with successive neutron irradiations. Expressed as a fraction of the primary bremsstrahlung beam dose at maximum, the photoneutron background was 2.04 +/- 0.05 mrem/rad (10(-3) Sv/Gy) at 1 m lateral to beam center in the patient midplane at 25 MV. The fraction of this result due to thermal neutrons was found to be only about 2%. The photon background dose was 2.98 +/- 0.04 mrad/rad (10(-3) Gy/Gy). The photoneutron dose equivalent per unit primary dose was found to be nearly independent of the collimator size used but increased by 40% when the bremsstrahlung endpoint energy was increased from 20 to 35 MeV with no change in flattening filters.

Background Radiation↗

PubMed2006

Evaluation of uncertainty predictions and dose output for model-based dose calculations for megavoltage photon beams.

In many radiotherapy clinics an independent verification of the number of monitor units (MU) used to deliver the prescribed dose to the target volume is performed prior to the treatment start. Traditionally this has been done by using methods mainly based on empirical factors which, at least to some extent, try to separate the influence from input parameters such as field size, depth, distance, etc. The growing complexity of modern treatment techniques does however make this approach increasingly difficult, both in terms of practical application and in terms of the reliability of the results. In the present work the performance of a model-based approach, describing the influence from different input parameters through actual modeling of the physical effects, has been investigated in detail. The investigated model is based on two components related to megavoltage photon beams; one describing the exiting energy fluence per delivered MU, and a second component describing the dose deposition through a pencil kernel algorithm solely based on a measured beam quality index. Together with the output calculations, the basis of a method aiming to predict the inherent calculation uncertainties in individual treatment setups has been developed. This has all emerged from the intention of creating a clinical dose/MU verification tool that requires an absolute minimum of commissioned input data. This evaluation was focused on irregular field shapes and performed through comparison with output factors measured at 5, 10, and 20 cm depth in ten multileaf collimated fields on four different linear accelerators with varying multileaf collimator designs. The measurements were performed both in air and in water and the results of the two components of the model were evaluated separately and combined. When compared with the corresponding measurements the resulting deviations in the calculated output factors were in most cases smaller than 1% and in all cases smaller than 1.7%. The distribution describing the calculation errors in the total dose output has a mean value of -0.04% and a standard deviation of 0.47%. In the dose calculations a previously developed correction of the pencil kernel was applied that managed to contract the error distribution considerably. A detailed analysis of the predicted uncertainties versus the observed deviations suggests that the predictions indeed can be used as a basis for creating action levels and tracking dose calculation errors in homogeneous media.

Air↗

PubMed1965

SUPERVOLTAGE RADIATION THERAPY. USE OF THE LINEAR ACCELERATOR FOR TREATING OVARIAN ADENOCARCINOMA.

In a study of patients treated thus far by supervoltage radiation from the Stanford linear accelerator, the following conclusions were reached:Homogenous radiation in doses of 4,000 rads may be delivered to the upper abdomen and 5,500 rads to the lower abdomen and pelvis for the treatment of ovarian cancer by the proper utilization of modern super-voltage radiation sources. Patients with Stage 2 and Stage 3 lesions are best treated by total hysterectomy and bilateral salpingo-oophorectomy followed by total pelvic irradiation. Stage 4 disease was seldom controlled by high dose radiation therapy to the entire peritoneal cavity. An unusual histologic pattern has been found in the liver of three patients who died three to nine months after 4,000 to 5,000 rads had been given in a period of five or six weeks.

Adenocarcinoma↗

PubMed1998

A comparative study of the work involved in measuring profiles using an ion chamber, a linear diode array and film.

In this work a method of using Kodak X-Omat V film to measure beam profiles for dynamically wedged fields is presented. Also, the profiles determined by film measurement are compared with those measured with an ion chamber (0.12 cm3 Scanditronix RFA 300 RK) and an array of silicon diodes (11 channel Scanditronix linear diode array). The beam investigated is a 6 MV photon beam from a Varian 2100 C linear accelerator. The geometric method of positioning film and determining the central axis (CAX) position of the beam yielded results which agreed to within 1 mm with the software determined position of the CAX. The profiles measured by film agreed well with the ion chamber measured profiles in terms of overall field size, position, penumbral width, height and position of maximum and profile shape between the 20% dose levels. Film profiles deviated most from ion chamber profiles in the post-penumbra regions. Linear diode array (LDA) measured profiles matched ion chamber profiles in the post-penumbra regions, field size and general profile shape. In the region of maximum dose differences in dose of up to 4% were seen along with horizontal shifts of around 2 mm between LDA and ion chamber profiles.

Biophysical Phenomena↗

PubMed1984

Radiation leakage from linac electron applicator assembly.

The electron beam applicator system currently in use on the linear accelerator is constructed of light-weight fiberglass and aluminum. With an applicator in place on the accelerator, the photon collimator jaws are automatically set several centimeters greater than the electron field size projected at the patient's surface. To ensure that no regions of high dose levels exist outside the useful beam, ionization and film measurements were made to quantitate the amount of leakage radiation through the 10 cm X 10 cm and 25 cm X 25 cm applicators. In most regions, the ionization levels at the patient's surface were below 5% of the central axis dose. In one area for the 25 cm applicator, the percentage ionization was 8.5%, which could be reduced by the addition of a small piece of 1/8 inch thick lead. However, ionization levels on the outside surface of the applicator were found to be considerably higher at certain locations for the 25 cm applicator. Results for 6, 9, 12 and 20 MeV electrons are reported here.

Electrons↗