Dosimetric Characteristics of Dynamic Wedge Techinique

Keum, Ki Chang; Chu, Seong Sil; Kim, Gwi Eon; Oh, Young Taek

Abstract

PURPOSE: The wedge filter is the most commonly used beam modifying device during radiation therapy. Recently dynamic wedge technique is available through the computer controlled asymmetric collimator, independent jaw. But dosimetric characteristics of dynamic wedge technique is not well know. Therefore we evluate dosimetric characteristics of dynamic wedge compared to conventional fixed wedge.
MATERIALS AND METHODS
We evaluated dosimetric characteristics of dynamic wedge and fixed wedge by ion chamber, film dosimetry and TLD in phantoms such as water, polystyrene and average breast phantom. Six MV x-ray was used in 15X15 cm field with 15,30 and 45 degree wedge of dynamic/fixed wedge system. Dosimetric characteristics are interpreted by wellhofer Dosimetrie system WP700/WP700i and contralateral breast dose(CBD) with tangential technique was confirmed by TLD.
RESULTS
1) Percent depth dose through the dynamic wedge technique in tissue equivalent phantom was similar to open field irradiation and there was no beam hardening effect compared to fixed wedge technique. 2) Isodose line composing wedge angle of dynamic wedge is more straight than hard wedge. And dynamic wedge technique was able to make any wedge angle on any depth and field size. 3) The contralateral breast dose in primary breast irradiation was reduced by dynamic wedge technique compared to fixed wedge. When the dynamic wedge technique was applied, the scatter dose was similar to that of open field irradiation.
CONCLUSION
The dynamic wedge technique was superior to fixed wedge technique in dosimetric characteristics and may be more useful in the future.