ABSTRACT
Optical imaging has established itself in this era of imageguided radiation therapy as an accurate imaging technique for patient setup and monitoring (Meeks et al. 2005). Some optical systems reconstruct the three-dimensional (3D) coordinates of markers xed to the patient (Baroni et al. 2006; Liebler et al. 2009), whereas others reconstruct the complete 3D surface of the patient without the need for markers (Smith et al. 2003; Djajaputra and Li 2005). e main advantage of optical imaging is that it constitutes a nonionizing imaging technique and may therefore be applied daily, for example, before and aer correcting the setup of the patient without concern for any additional imaging dose to the patient. Optical imaging, when available in real time, is also useful for continuously monitoring the patient for intrafractional movement. is provides useful information to interrupt the radiation beam when motion thresholds are exceeded. e fact that optical imaging does not require additional radiation may make it a very appealing option for breast and pediatric radiotherapy treatments. Among all optical imaging techniques, surface imaging is the only one that provides 3D surface information of the patient. Surface imaging is achieved by means of stereo cameras. A pair of cameras separated by some specied distance is triggered at the same time, acquiring two dierent images that mimic human vision. ese two pictures can be combined to obtain 3D information of the object imaged, in this case, the patient. ere have been several studies on different commercially available systems (Djajaputra and Li 2005; Bert et al. 2005). In this chapter, we will focus on the AlignRT system (VisionRT Ltd., London, UK).
