PubMed · 7390915
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A L Boyer. 1980. A linear accelerator beam profile scanner.. https://doi.org/10.1016/0360-3016(80)90154-6
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PURPOSE: A calculation formalism is proposed to predict variation of head scatter as a function of field size and treatment distance. METHODS AND MATERIALS: Assuming that the head scatter for the linear accelerator studied was contributed predominantly by the flattening filter, a formalism was devised to predict beam intensity as a function of distance from the target position. The method used the concept of an equivalent collimator field in which a given field at any distance can be equated to a field at the isocenter such that the extent of the flattening filter seen at the two positions is the same. RESULTS: The equation derived from the concept of equivalent collimator field size predicated change in head scatter with distance to within 0.5% for collimator field sizes ranging from 8 x 8 to 40 x 40 cm and distances up to 300 cm from the target. CONCLUSIONS: Considering flattening filter to be the main source of head scatter, the observed deviation from inverse square law for extended treatment distances can be accounted for by an equivalent collimator field size, which sees the same extent of the flattening filter at the isocenter as the field at the given distance.
The Moyer model, based on a semi-empirical method validated in the 7.4 to 350 GeV energy range, is generally used to calculate lateral shielding for high energy proton accelerators. Measurements made for the Saclay Synchrocyclotron, Saturne, have enabled the parameters corresponding to a 2.7 GeV model to be studied for different target thicknesses and angles of observation. These studies show how new data have been used to modify the equations of the model.
The evolution in particle physics requires new detectors at the emergence of new accelerators, requiring higher rates and better position accuracy. The wire chambers have found applications in the imaging of beta rays and low dose radiography. The new detectors foreseen for the end of this century will have position accuracy of the order of 10 microns and high rate capabilities passing by one or two orders of magnitude the wire chambers. They are promised to wide applications in all fields of radiation imaging.