Recent years have seen the development of sophisticated delivery technologies designed to enhance the efficacy of clinical radiotherapy through the escalation of tumor dose. Key among these is the use of intensity modulated x-ray beams now becoming widely available through innovations in multileaf collimator (MLC) technology. Yet the successful delivery of intensity modulated radiotherapy (IMRT) depends on additional factors beyond the techniques for radiation delivery. In particular, fundamental problems associated with the practical issues of patient positioning, setup reproducibility and organ motion have yet to be adequately addressed. Of particular interest are techniques designed to compensate for breathing motion associated with respiration, i.e., respiratory gating. In this work we have investigated an initial implementation of gated IMRT with regard to dosimetric issues. Dosimetry was compared for gated and non-gated irradiation conditions for the following field configurations: open rectangular fields, irregular fields, and wedged and arbitrarily modulated fields delivered by dynamic MLC.
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