It has been shown that IMRT optimization using purely biological parameters would result in highly inhomogeneous target dose distributions with an undesirable amount of hot spots. To improve the target dose homogeneity and conformity, some investigators have proposed to combine the use of physical dose parameters with biological based models for optimization. For example, Wu et al. proposed the use of the generalized EUD optimization followed by an DV-based optimization using a gradient technique to fine-tune the dose volume histogram, while Das et al. proposed to incorporate biological optimization after DV constrained optimization. The Eclipse System is one of the commercially available treatment planning systems that allows the users to perform BBTP using biological related cost functions together with some physical constraints for SCH772984 fluence optimization. Most of the previous evaluation studies on BBTP were performed using in-house developed TPS systems. Evaluation using two other commercial system, the MONACO and PINNACLE systems have been reported for various diseases. However, different planning systems provide different approaches of biological related optimization models. Extensive experiences for using the Eclipse System for BBTP have not been reported. The performance of a commercially available fluence optimization algorithm should be thoroughly tested before it can be used extensively for clinical cases. The main objective of our investigation was to assess the performance of the current commercially available BBTP optimization approach installed in the Eclipse system as compared to its conventional dose/dose volume based approach using NPC. Delivering a curative dose to the tumor while sparing the surrounding critical organs for NPC is one of the most challenging tasks for IMRT planning. The tumor is usually located near a relatively larger number of critical normal organs when compared to other diseases. These include the brain stem, spinal cord, parotid and the optic structures. Target dose homogeneity is also difficult to maintain in a NPC IMRT plan as there is a lot of tissue inhomogeneity inside the planning target volume, including air, bone and soft tissues. In addition, the planning also involves the prescription of multiple dose levels simultaneously to different target volumes. Planning for this disease would be a good demonstration on the performance of the system. Most plan evaluations of previous studies for biologically based IMRT optimization methods were performed using conventional physical dose quantities, while both biological indices and physical parameters were employed in the current study for plan quality evaluation. For NPC cases, the plan complexity level varies with the staging of the disease. The target volumes of advanced cases are usually larger and thus closer to its surrounding critical organs, representing a more difficult planning task. The estimation of TCP values also varies with staging.