A preliminary goal of radiation therapy is to deliver radiation doses that conform to targets, while minimizing dose to surrounding normal tissue. Intensity-modulated radiation therapy (IMRT) delivered with a multileaf collimator (MLC) is a promising resource to achieve conformal therapy. A medical linear accelerator (linac) equipped with an IMRT system can increase dose to the target and decrease dose to normal tissue. These capabilities may be significantly enhanced with dose optimization techniques. IMRT integrates rapidly evolving imaging, computer, optimization, and treatment delivery technologies. Resulting systems fundamentally distinguish themselves from prior technology. Thus, new quality assurance (QA) procedures are needed.