ABSTRACT
IMRT delivery can be classied as static beam IMRT, in which the radiation source is xed during beam delivery, and rotational IMRT, in which the radiation source moves around the patient during delivery. Modulation of photon beam intensity is most commonly implemented through multileaf collimators (MLC) (Seco et al. 2001), which include (2D) eld-shaping MLC and (1D) binary MLC (bMLC) (Yang et al. 1997; Balog et al. 1999; Sarkar et al. 2007). Both eld-shaping MLC and bMLC can be used as static beam delivery or rotational beam delivery. Static beam IMRT includes step-and-shoot, dMLC-based, and topotherapy
(TomoDirectSM) delivery mode; the former two use 2D MLC, while the third uses bMLC. Rotational IMRT includes intensitymodulated arc therapy (Yu et al. 2002; Yu 1997) and helical tomotherapy (TomoHelicalSM) (Mackie et al. 1995; Mackie et al. 1993); the former uses 2D MLC and the latter uses bMLC.