Penumbral width measurement by various diode detectors
Beddar et al. studied the effect of scanning direction and the structure of diode for beam profile measurement for 1, 2 and 3 cm circular cone diameter of Stereotactic radiosurgery 6 MV photon beams using a p-type Si photon diode (PFD), and a p-type Si electron diode (EFD). In this study, there are three scanning directions for measurement. For the direction one, the diodes were set parallel with the central axis and perpendicular to the scan direction. For the direction two and three, the diodes were set perpendicular with the central axis and parallel to the scan direction but scanned in an opposite direction. The result presented that beam profiles from direction one using both diodes were symmetry profiles for all field sizes and beam profiles from direction two and three using both diode were not symmetry profiles for all field sizes. Because all parts of diodes faced to the radiation equally between left and right half profiles, that made the direction one’s beam profile symmetry. However, according to the direction two and three, less part of diodes faced to the radiation at one half beam profile and most part of diodes faced to the radiation at the other half beam profile, those created asymmetry of beam profiles. As expected, all field sizes, the penumbral width from direction two and three were less than that of the direction one because the amount of the detector’s size faced to the radiation of direction two and three were less than that of the direction one. They commented further that there was not only the diode’s size affected to the penumbral width but also the material of the diode. Because its material was made of higher density compared to water, the secondary electron range was shorter, forming less penumbral width.
การวัดความกว้าง penumbral โดยเครื่องตรวจจับต่าง ๆ ของไดโอดBeddar et al. studied the effect of scanning direction and the structure of diode for beam profile measurement for 1, 2 and 3 cm circular cone diameter of Stereotactic radiosurgery 6 MV photon beams using a p-type Si photon diode (PFD), and a p-type Si electron diode (EFD). In this study, there are three scanning directions for measurement. For the direction one, the diodes were set parallel with the central axis and perpendicular to the scan direction. For the direction two and three, the diodes were set perpendicular with the central axis and parallel to the scan direction but scanned in an opposite direction. The result presented that beam profiles from direction one using both diodes were symmetry profiles for all field sizes and beam profiles from direction two and three using both diode were not symmetry profiles for all field sizes. Because all parts of diodes faced to the radiation equally between left and right half profiles, that made the direction one’s beam profile symmetry. However, according to the direction two and three, less part of diodes faced to the radiation at one half beam profile and most part of diodes faced to the radiation at the other half beam profile, those created asymmetry of beam profiles. As expected, all field sizes, the penumbral width from direction two and three were less than that of the direction one because the amount of the detector’s size faced to the radiation of direction two and three were less than that of the direction one. They commented further that there was not only the diode’s size affected to the penumbral width but also the material of the diode. Because its material was made of higher density compared to water, the secondary electron range was shorter, forming less penumbral width.
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