Calculation of enhanced dynamic wedge factors for symmetric and asymmetric photon fields.

A method is introduced to calculate wedge factors for an enhanced dynamic wedge (EDW). An analytic formula has been derived that allows the determination of wedge factors at the center of symmetric and asymmetric photon fields. The formalism is an extension of the "MU fraction approximation," which holds that the dynamic wedge factor is equal to the fraction of MU delivered to the point of calculation. Extensive data are presented, comparing measured enhanced dynamic wedge factors with the current method and the MU fraction model for both symmetric and asymmetric fields. For both 6 and 18 MV photons, the current method demonstrates improved results: Agreement to within 1% is obtained in all symmetric fields and within 2% for all asymmetric fields compared with discrepancies of up to 4% obtained with the MU fraction model.