ABSTRACT
Advanced radiation therapy (RT), such as intensity-modulated radiation therapy (IMRT) (Purdy, 1996; Burman et al., 1997; Webb, 1998; Boyer and Yu, 1999) and intensity-modulated rotational therapy, including volumetric modulated arc therapy (VMAT) and RapidArc (Lagerwaard et al., 2008), has been widely accepted as the standard treatment strategy for many treatment sites in the field of radiation oncology because of the ability to provide quality conformal dose distributions. Advanced RT treatment techniques offer better sparing for the surrounding normal tissues than conventional treatment methods and, therefore, lead to less normal tissue complications (Salama et al., 2006; Studer et al., 2008; Zelefsky et al., 2008) and the possibility for dose escalation to the treatment target (Al-Mamgani et al., 2009). To provide a conformal dose distribution, advanced RT treatment techniques require a more complex treatment planning process utilizing computers in the plan optimization and a more complex beam delivery system, which may utilize a multileaf collimator (MLC) with complex leaf motion sequences. For intensity modulation purposes, the radiation field is created with a number of small beamlets with a typical size of 10 × 10 or 5 × 5 mm2 delivered through many small, irregular, and asymmetric MLC fields, which obscure the relationship between the accelerator monitor unit (MU) setting and the radiation dose received by the patient. When on-line images or other localization and tracking systems are used for treatment guidance and intervention, the beam delivery may become even more complex. Furthermore, patient anatomy heterogeneity, organ motion, and deformation may add additional uncertainties to the actual dose distribution received by
the patient. Overall, potential errors associated with advanced RT include dose calculation inaccuracies, plan transfer errors, beam delivery errors, and target localization uncertainties due to patient setup errors and organ motion during the treatment. Considering the serious consequences of these errors, a comprehensive quality assurance (QA) should be performed before and/ or during the patient treatment.
