DOSIMETRY AND CLINICAL IMPLEMENTATION OF DYNAMIC WEDGE

Purpose: Wedge-shaped isodoses are desired in a number of clinical sit uations. Physical wedge filters have provided nominal angled isodoses with dosimetric consequences of beam hardening, increased peripheral d osing, nonidealized gradients at deep depths, along with the practical consequences of filter handling and placement problems. Dynamic wedgi ng uses a combination of a moving jaw and changing dose rate to achiev e angled isodoses, The clinical implementation of dynamic wedge and an accompanying quality assurance program are discussed in detail. Metho ds and Materials: The accelerator at our facility has two photon energ ies (6 MV and 18 MV), currently with dynamic wedge angles of 15 degree s, 30 degrees, 45 degrees and 60 degrees, The segmented treatment tabl es (STT) that drive the jaw in concert with a changing dose rate are u nique for field sizes ranging from 4.0 cm to 20.0 cm in 0.5 cm steps, resulting in 256 STTs. Transmission wedge factors were measured for ea ch STT with an ion chamber, Isodose profiles were accumulated with fil m after dose conversion, For treatment-planning purposes, d(max) ortho gonal dose profiles were measured for open and dynamic fields, Physica l filters were assigned empirically via the ratio of open and wedge pr ofiles. Results: A nonlinear relationship with wedge factor and field size was found, The factors were found to be independent of the statio nary field setting or second order blocking. Dynamic wedging provided more consistent gradients across the field compared with physical filt ers, Percent depth doses were found to be closer to open field, The cr eated physical filters provided planned isodoses that closely resemble d measured isodoses, Comparative isodose plans show improvement with d ynamic wedging. Conclusions: Dynamic wedging has practical and dosimet ric advantages over physical filters, Table collisions with physical f ilters are alleviated. Treatment planning has been solved with an empi rical solution. Dynamic wedge is a positive replacement for physical f ilters, and a first step for commercial introduction of dynamic confor mal therapy.