Compatibility of Varian 2100C gated operations with enhanced dynamic wedgeand IMRT dose delivery

An enhanced dynamic wedge (EDW) is one of the latest technical innovations frequently used in the radiotherapy department. Its usage is enthusiastical ly supported by radiation therapists. Intensity modulated radiotherapy (IMR T) is the other, which has become popular within the past several years. It s usage is not as straightforward as the EDW. However, its ability to furth er increase dose conformity to the target and to spare the surrounding norm al tissues has been evidenced. Both of these treatment modalities demand so phisticated software, which controls precision motion and speed of jaws or multileaf collimators as well as dose rate. This paper deals with the quest ion of how accurately the EDW profiles and IMRT dose distributions be maint ained when the additional constraint of linear accelerator gating is invoke d. For this, square pulses mimicking breathing were used in gated and nonga ted modes for film dosimetry and ion chamber measurements using the Varian 2100C linear accelerator. The results show no observable difference between gated and nongated EDW profiles and IMRT dose distribution regardless of t he machine repetition rate. Also studied in this paper an the "fuzzy" dose distributions caused by realistic finite gate window settings. (C) 2000 Ame rican Association of Physicists in Medicine. [S0094-2405(00)02108-8].