Validity of universal wedge equation over the range of 60Cobalt to 25 MV photon beam energies.
OBJECTIVE
Evaluating the validity of the universal wedge equation over the range of 60Cobalt (60CO) to 25 MV photon beam energies.


METHODS
The universal wedge equation relates the beam weight of the wedged field to the effective wedge angle produced by combining the wedged field to the nonwedged field and is expressed as tan (theta) = B tan (theta w), where B is the normalized weight imposed on the wedged field, theta w is the maximum wedge angle of the wedge filter, and theta is the effective wedge angle. The isodose distributions from 60Co to 25 MV photon beam energies were used. For each photon energy, the isodose distributions of wedged and nonwedged fields were combined in different proportions. The effective wedge angle was determined from each resultant isodose distribution.


RESULTS
The relationship between the weight of wedged field and the effective wedge angle was found to be nonlinear for wedge filters with maximum wedge angle greater than 30 degrees. The universal wedge equation predicts the effective wedge angle to within 2 degrees compared to the measured value.
Saw
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CB
Division of Radiation Oncology, West Virginia University School of Medicine, Morgantown 26506.
Pawlicki
T
T
Wu
A
A
Ayyangar
K M
KM
D003037:Cobalt Radioisotopes / Q000627:therapeutic use*; D006801:Humans; D017785:Photons; D011879:Radiotherapy Dosage
D003037:Cobalt Radioisotopes