Radiotherapy treatments for nasopharyngeal carcinoma (NPC) are common in the South China Region such as Hong Kong. The target volumes of NPC are usually of complex shape and surrounded by quite a number of critical normal organs. Besides, it is always located near small volumes of heterogeneous media such as air cavities and bony structures. When compared to other treatment sites, producing intensity modulated radiotherapy plans for NPC cases is relatively demanding. Accurate calculation of photon dose distribution for intensity modulated NPC plans by most current commercially available model-based algorithms can also be a problem due to the presence of heterogeneous media. Recently, volumetric-modulated arc radiotherapy (VMAT) has been developed and implemented for clinical use. A newly developed grid-based Boltzmann equation solver, Acuros XB (AXB), has been implemented in a commercial treatment planning system for accurate dose calculation. Some new features and options recently implemented in the commercial optimization algorithms would also affect the plan quality. It is worthy to assess the dosimetric impact of these advanced technologies for NPC treatment. The main objectives of this research study are to (1) assess the impact of using VMAT instead of conventional static field intensity modulated radiation therapy (IMRT) for NPC treatments, (2) verify and compare the dose calculation accuracy between a commonly used model based dose calculation algorithm, Anisotropic Analytical Algorithm (AAA) and AXB in NPC cases, (3) assess the clinical impact of using AXB instead of AAA, and (4) to assess the performance of some new features and options of optimization algorithms for the planning of NPC cases using intensity modulated radiotherapy techniques. The first few chapters of this thesis mainly cover topics on the useful background information and knowledge related to the research work. Chapter 1 gives an introduction of intensity modulated radiotherapy treatment techniques for NPC. Chapter 2 presents some background information about radiation dosimetry for photon beams. Chapter 3 gives a review on the commercially available dose calculation algorithms for external photon beam radiotherapy. Chapter 4 describes the evaluation methods to assess plan quality. Chapters 5 to 8 present the research work. Chapter 5 reports the comparison results between the use of VMAT and IMRT in NPC cases. Chapters 6 and 7 report the verification results of dose accuracy of AAA and AXB near heterogeneous media for IMRT and VMAT, and the dosimetric impact due to the conversion of dose calculations from AAA to AXB in NPC. Chapter 8 presents the effect of the different optimization options and methods for intensity modulated planning in NPC. Finally a summary and the potential of future work are presented in chapter 9. The dosimetric comparison results between IMRT and VMAT are useful for those who want to switch from IMRT to VMAT for NPC treatments. Both IMRT and VMAT are found to produce highly conformal plans with high dose gradient, which must be accomplished with accurate calculation of dose distributions. The information regarding the accuracy of the existing commonly used model based algorithm, AAA, and the newly developed algorithm, AXB, is also very useful for those who need to choose between AAA and AXB for photon dose calculation. The information on patient dose changes gained from using the more accurate AXB for NPC can be used to associate the local control of tumors with radiation dose. The study on the effect of new features and options in optimization algorithms is also a good piece of information for planners’ consideration when applied in NPC planning.