Biomedical subjects

F Z Company

Publications and source records attributed to F Z Company.

5 recordsLinked to original sources

PubMed2002

Stereotactic synchrotron microbeam radiotherapy.

Highly collimated synchrotron x-ray beams with high fluence rate may be used in stereotactic radiotherapy of brain tumours. Several monochromatic x-ray beams having uniform microscopic thickness ie (microplanar beams) are directed to the center of the tumour from varying directions, delivering lethal dose to the target volume while sparing normal cells. This proposed technique takes advantage of the hypothesised repair mechanism of capillaries between closely spaced microplanar beam zones. The sharply dropping lateral dose profile of a microplanar beam provides low scattered dose to the off-target interbeam volume. In close proximity to the target volume, relatively high secondary electron doses close to the edge of the beams overlap and produce a high dose region between angled beams. This allows precise targeting and prevents gradual blurring of the higher and lower dose margins in the target volume. The advantages of stereotactic microplanar beam radiotherapy will be lost as the dose between microplanar beams exceeds the tolerance dose of the dose limiting tissues. Therefore to minimize the risks of delayed radiation damage it is essential to optimize the interbeam doses inside a human head phantom. The EGS4 Monte Carlo code is used to calculate the lateral dose profiles and depth dose of a 100 keV single microplanar beam in the phantom. A general equation for absorbed dose as a function of depth and lateral distances is derived for the single beam. Several microplanar beams are directed into the target volume at the center of the phantom. Using the equation, maximum dose on the beam axis (primary + total scattered dose) and the minimum interbeam dose (total scattered dose) are calculated at different depths and an isodose map of the phantom is obtained. A stereotactic microplanar beam radiotherapy model is proposed for a 10 mm diameter (approximately spherical) tumour at the center of the phantom.

Brain Neoplasms↗

PubMed2000

Monte Carlo calculation for microplanar beam radiography.

In radiography the scattered radiation from the off-target region decreases the contrast of the target image. We propose that a bundle of collimated, closely spaced, microplanar beams can reduce the scattered radiation and eliminate the effect of secondary electron dose, thus increasing the image dose contrast in the detector. The lateral and depth dose distributions of 20-200 keV microplanar beams are investigated using the EGS4 Monte Carlo code to calculate the depth doses and dose profiles in a 6 cm x 6 cm x 6 cm tissue phantom. The maximum dose on the primary beam axis (peak) and the minimum inter-beam scattered dose (valley) are compared at different photon energies and the optimum energy range for microbeam radiography is found. Results show that a bundle of closely spaced microplanar beams can give superior contrast imaging to a single macrobeam of the same overall area.

Humans↗

PubMed1999

Contrast enhancement in microplanar beam radiography.

In x-ray radiography, the target produces a useful shadow from absorption of the primary beam, while the scattered radiation into the off-target region decreases the contrast of the target image. A bundle of closely spaced microplanar beams can reduce the scattered radiation and give superior image contrast compared with a single macrobeam of the same dimensions. To further reduce the scattered radiation and increase the image contrast, we place an air gap between the tissue phantom and the detector. The primary and scattered photon flux of a single microplanar beam is measured as a function of thickness inside the phantom and in the air gap. Results show that a bundle of closely spaced, microplanar beams increase the image contrast by 22% and a 2 cm air gap decreases the scattered photon flux by about half, improving the contrast by an additional 16%. Thus an overall improvement of 41% in contrast can be achieved with microplanar beam radiography.

Cadmium Radioisotopes↗

PubMed1998

Calculation of microplanar beam dose profiles in a tissue/lung/tissue phantom.

Recent advances in synchrotron generated x-ray beams with a high fluence rate permit investigation of the application of an array of closely spaced, parallel or converging microplanar beams in radiotherapy. The proposed technique takes advantage of the hypothesized repair mechanism of capillary cells between alternate microbeam zones, which regenerates the lethally irradiated endothelial cells. The lateral and depth doses of 100 keV microplanar beams are investigated for different beam dimensions and spacings in a tissue, lung and tissue/lung/tissue phantom. The EGS4 Monte Carlo code is used to calculate dose profiles at different depths and bundles of beams (up to 20 x 20 cm square cross section). The maximum dose on the beam axis (peak) and the minimum interbeam dose (valley) are compared at different depths, bundles, heights, widths and beam spacings.

Animals↗

PubMed1996

Measurements and Monte Carlo simulations of the fluence and dose characteristics of microplanar photon beams.

The lateral absorbed dose, depth dose and photon fluence in a water phantom of a single microplanar beam is investigated using the Monte Carlo method. To validate the calculated axial and scattered photon fluence, an experiment is carried out using a NaI(TI) detector and 20 mCi Cd-109 source at energies of 22 keV and 88 keV. A 150 microns collimator is used to produce the microplanar beam, and the integrated scattered photon fluence is measured over 2.5 microns increments. The axial (depth) photon fluence is in good agreement with the calculated results. The scattered (lateral) photon fluence results agree to within two standard deviations.

Cadmium Radioisotopes↗