PubMed · 715014
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D C Rust, C J Karzmark. 1978. Modernising an accelerator dosemeter system.. https://doi.org/10.1088/0031-9155%2F23%2F5%2F018
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Basic dosimetric properties of 6 MV and 18 MV photon beams from a Varian Clinac 21EX accelerator operating without the flattening filter have been measured. These include dose rate data, depth dose dependencies and lateral profiles in a water phantom, total scatter factors and transmission factors of a multileaf collimator. The data are reviewed and compared with measurements for the flattened beams. The unflattened beams have the following: a higher dose rate by factors of 2.3 (6 MV) and 5.5 (18 MV) on the central axis; lower out-of-field dose due to reduced head scatter and softer spectra; less variation of the total scatter factor with field size; and less variation of the shape of lateral dose profiles with depth. The findings suggest that with a flattening filter free accelerator better radiation treatments can be developed, with shorter delivery times and lower doses to normal tissues and organs.
We investigated the applicability of single-use MOSFET detectors as quality-assurance devices. Using ten accelerators available at our institution, we performed output measurements in both water and solid phantoms under photon irradiation. The MOSFET detectors performed well within the manufacturer's specifications, with average deviations of 2.1% and 0.7% for the 6 and 18 MV beams, respectively. The strength of the detector's design, including its wireless set-up, factory calibration and direct read-out, makes the system an acceptable independent quality-assurance device for use in verifying machine output within an accuracy of +/-5%. The MOSFET detectors provide a quick check of machine output, which can be efficacious in detecting gross errors in machine calibrations.
Charged-particle microbeams are unique tools to mimic low-dose exposure in vitro by delivering a defined number of particles to single mammalian cells down to only one particle per cell or group of cells. A horizontal single-ion microbeam facility has been built at the INFN-Laboratori Nazionali di Legnaro 7 MV Van de Graaff accelerator. Different light ions (1H+, 2H+, 3He2+, 4He2+) are available covering a wide range of LET from 7 to 150 keV/microm. Collimators of different geometries and materials have been tested, and beam spots 2-3 microm in diameter have been obtained using a tantalum disc. Cell visualization and recognition are performed with a phase-contrast optical microscope coupled with dedicated software. One unique characteristic of such a system is that neither cell staining nor UV light is used. Cells are automatically positioned on the beam spot through remotely controlled precision XY translation stages. A particle detector is positioned downstream of a specially designed petri dish to perform energy measurements and count particles crossing the cell. A particle counting rate of less than 1 ion/s can be reached. This feature, combined with a fast beam deflection system, ensures high reproducibility in administering a preset number of particles per cell.