Dynamic multileaf collimation and intensity modulated radiotherapy (IMRT) produce dose distributions that are superior to conventional radiotherapy planning and may be exploited in a number of anatomic sites and clinical circumstances. In this chapter we report on techniques which combine the spatial accuracy of stereotactic positioning with the dose delivery capabilities of IMRT to treat small critically located targets. To date, the majority of studies demonstrating improvement in dose distribution with IMRT have been for broad field sizes using relatively large multileaf collimation systems, generally with leaves 1.0 cm in width. The recent introduction of micro-multileaf collimator systems have allowed the advantages of IMRT to be further extended to small intra- and extra-cranial targets. The dosimetric advantages seen with IMRT coupled with high precision localization systems have allowed the clinician to explore dose escalation and hypofractionation as ameans to improve both tumor control and patient convenience.
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