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ABSTRACT: Dose distributions in water of Model 6702 I-125 seeds have been measured to a distance of 9 cm from the seed center as a function of angle about the seed axis. A silicon diode and electrometer were used in the measurement. Two empirical models have been fitted to the data. The data have also been compared with Monte Carlo calculations.
International Journal of Radiation OncologyBiologyPhysics 06/1987; 13(5):795-9. · 4.11 Impact Factor
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ABSTRACT: The per cent ionisation curves for the 4 MV photon beam from a Clinac 4 exhibit pronounced enhancement with field size in the build-up region. The source and nature of this increase is investigated by analysing the radiation components of the 4 MV photon beam with a 0.23 T magnetic field. The build-up ionisation curves were measured at 86 cm SSD with a parallel-plate ionisation chamber embedded in a polystyrene phantom. The surface ionisation increases from 18% to 32% as the field size is increased from 4.3 cm X 4.3 cm to 9.7 cm X 32.3 cm. With the electromagnet placed beside the treatment head, the field size dependence reduces to 16% to 24%. This and similar results at 113.2 cm SSD, clearly demonstrate that electrons from the Clinac 4 treatment head are responsible for approximately half the observed increase in the surface ionisation with field size.
Physics in Medicine and Biology 07/1983; 28(6):659-65. · 2.83 Impact Factor
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ABSTRACT: Radiation fluence distribution around 192Ir and 198Au seeds of the type used for brachytherapy application was measured using a NaI crystal connected to a multi-channel analyzer. The radiation fluence, determined as a function of the angle between the seed axis and the direction of detection, is anisotropic with the fluence along the seed axis amounting to 78% of that perpendicular to the seed axis for seeds of both isotopes. The region of fluence reduction is broader for 198Au seeds, extending from 0-45 degrees; for 192Ir the decrease in fluence is evident for angles of 0-20 degrees. Integration of the angular distribution over 4 pi geometry indicated the effective activity of the implants to be 4% and 1% less than the nominal activity for the 198Au and 192Ir seeds, respectively, based on calibration measurements perpendicular to the seed axis.
Radiology 04/1983; 146(3):791-2. · 5.73 Impact Factor
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ABSTRACT: Radiation-therapy dosimetry surveys employing thermoluminescence dosimeters (TLDs) are now being considered for high-energy electron beams. Using a system of individually calibrated pressed LiF TLDs in a water and a polystyrene phantom, we established that the distortions of depth-dose distributions in non-conducting materials previously observed at high absorbed doses and high dose rates were not detectable in the present geometry at doses and dose rates as much as 40 times higher than those employed in radiation therapy. The system was then used to measure TLD response in water and in polystyrene in the nominal electron-energy range from 7 to 18 MeV. In the water phantom, the well-known trend for TLD response to decrease with increasing electron energy was observed. In the polystyrene phantom, TLD response was found to be independent of electron energy.
The International Journal of Applied Radiation and Isotopes 12/1982; 33(11):1007-13.
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International Journal of Radiation OncologyBiologyPhysics 06/1981; 7(5):665-9. · 4.11 Impact Factor
