Beam characteristics of kilovoltage radiotherapy unit.
OBJECTIVE
To present the beam characteristics of the Siemens II orthovoltage x-ray therapy machine.


METHODS
x-ray beam qualities with the tube operating between 100 and 300 kV were determined. The field flatness, central axis depth dose, and relative output factors were measured for several applicator sizes for rectangular cones at 40 cm, and for circular cones at 30 cm focal skin distance (FSD).


RESULTS
The central axis depth doses were selectively compared with values presented in the literature and found to agree to within -/+3 % shallow depths for two energy ranges. The field edges had 85-95 % isodose line. Relative output factors of all the available cones were different.


CONCLUSIONS
The beam quality for all the stations should be determined and relative output factors should be measured for all the available cones.
Bilge
H
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University of Istanbul, Institute of Oncology, Department of Medical Physics, Istanbul, Turkey.