ABSTRACT
Compensator-based intensity modulation is a well-accepted approach for intensity-modulated radiotherapy (IMRT) treatment delivery on any linac or Co-60 unit. First implemented in the early 1990s at a few academic institutions such as the University of North Carolina (Chang et al. 2004), compensator-IMRT is currently used by more than 250 clinics in the United States. e widespread use of this approach is promoted by commercial companies such as .decimal Inc. (Sanford, FL) that oer convenient mail-order services for IMRT compensators. ere are a number of dierent compensator-based IMRT techniques described in the literature (Chang et al. 2004; Chang 2006; Sasaki and Obata 2007; Nakagawa et al. 2007; Nakagawa, Fukuhara, and Kawakami 2005; Xu, Al-Ghazi, and Molloi 2004; O’Daniel et al. 2004; Yoda and Aoki 2003). Despite their dierences, all share the same basic dissimilarity with multileaf collimator (MLC)-based IMRT techniques in intensity modulation generation (Williams 2003). Compensator-IMRT converts the open-eld uniform photon uence map to the intended intensity-modulated map via a custom-made compensator as shown in Figure 93.1 that is oen manually placed in the wedge or block holder of the treatment machine. MLC-IMRT techniques rely on the accelerator’s built-in MLC to sequentially deliver dierent eld segments, which form the intended intensity-modulated map during treatment delivery (Figure 93.2). e fundamental dierence in intensity modulation formation between compensator-based and MLC-based IMRT delivery approaches dictates the major dierences in their commissioning and patient-specic QA procedures.
