MULTIPLE MACHINE IMPLEMENTATION OF ENHANCED DYNAMIC WEDGE

Purpose: After acquiring 4 years of experience with Dynamic Wedge, a s oftware-driven one-dimensional (1D) compensation system, we implemente d a new software version called Enhanced Dynamic Wedge (EDW), The EDW allows larger (30 cm) and asymmetric field sizes and additional angles for wedged fields, We implemented this software on four similar dual- energy accelerators that also possess upper and lower physical wedge s ets, Our goal was to implement EDW with one common wedge factor (WF) t able and one set of treatment-planning files. Methods and Materials: W e measured WFs with an ionization chamber and isodose profiles with bo th film and a diode array. We used a calculation scheme that requires only entry of the wedge angle and fixed jaw value, Filters for compute rized treatment planning were configured for each wedge angle, We also examined to what degree the multileaf collimation (MLC) orientation, which is orthogonal to the EDW direction, was compromised for specific treatment sites, As a comparative test, we examined the dosimetric co nsistency for the 8 sets of physical wedges on the four machines, Fina lly, we updated our DW quality assurance program for EDW. Results: The measured EDW WF was common for all four machines to within +/- 1.5% a nd the calculation scheme held to within 1.5%. The EDW isodoses were c onsistent among the machines as measured by film and diode array, The treatment-planning filters provided computed isodose profiles that wer e nearly identical to measured profiles, Regarding MLC orientation, we found that the collimator angle needed for EDW did not compromise iso dose distributions, as apparent in measured isodoses and calculated do se-volume histograms, The consistency of the physical wedges did not f are as well, Two of the lower wedge sets had Wfs and profiles differen t (>3%) from the other wedge sets. Conclusions: We have successfully i mplemented EDW on four machines using only one WF table and one set of treatment-planning filters, The EDW provides for improved treatment t echniques for particular sites due to the large field sizes and additi onal angles available, Daily treatment efficiency has increased becaus e of the remote capability provided by EDW. (C) 1998 Elsevier Science Inc.