Browsing by Author "Company, FZ"

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    Monte Carlo calculation of microbeam radiation in a tissue/lung/tissue phantom
    (Australian Institute of Nuclear Science and Engineering, 1994-11-16) Company, FZ; Allen, BJ; Miskelly, P
    Recent advances in synchrotron generated X-ray beams with high fluence rate, small divergence and sharply defined microbeam margins permit investigation of the application of an array of closely spaced, parallel or converging microbeams in radiotherapy. The proposed technique takes advantage of the hypothesis repair mechanism of capillary cells between alternate microbeam zones, which regenerates the lethally irradiated capillaries. Unlike a pencil beam, more accurate dose calculation, beam width and spacing are essential to minimise radiation damage to normal tissue cells outside the target. The absorbed dose between microbeam zones should be kept below the threshold for radiation damage. Thus the peak-to-valley ratio for the dose distribution should be optimized. The absorbed dose profile depends on the energy of the incident beam and the composition and density of the medium. In this study, using Monte Carlo computations, the radial absorbed dose of single 24 x 24 μm2 cross-section X-ray beams of 100 and 300 keV in a tissue/lung/tissue phantom are investigated. Two parallel, 100 keV, 24 x 24 μm2 cross-section beams, using 200 μm center-to-center spacing, give similar peak-to-valley ratio in both media at the same depth. These results indicate that at 100 KeV, closely spaced microbeam therapy can be applied to the lung as well as the tissue. It is found that in the 300 keV region the peak-to-valley ratio decreases 200 times compared with 100 KeV. At the center of a bundle of a 1 x 1 cm2 cross-section, 200 μm center-to-center microbeams, the ratio approaches unity, indicating the unsuitability of this energy region when using closely spaced microbeam therapy. In the 33 KeV region the peak-to-valley ratio is similar to the 100 KeV. The relatively high surface absorbed dose of 33 KeV microbeam rules out its possible application in the deep microbeam therapy.