Familial Nasopharyngeal Carcinoma 6

Advances in the Technology of Radiation Therapy for Nasopharyngeal Carcinoma 205Fig. 16.4. Continuedtion, SIB-IMRT enables an escalated dose to be deliveredper daily fraction, with as much as 2.12–2.4 Gyfor GTV, conventional dose (1.8–2.0 Gy) to the CTV,and lower dose to nontarget tissues. Such dosingregimen has the advantage of compressing the treatmentduration, which may further increase the biologicaleffectiveness to the tumor while sparing thenormal tissues and organs. The SIB technique inIMRT is a more popular technique in clinical practicefor the treatment of head and neck cancers.A number of IMRT delivery systems are available(Xia et al. 2001). The two commonly used systemsinclude segmental (also called “step-and-shoot”)and dynamic IMRT systems. The multileaf collimator(MLC) is the most common hardware used inIMRT delivery. Segmental mode MLC is used in the