ABSTRACT
This chapter focuses on external beam radiotherapy. It is also important to note that many modern radiotherapy delivery techniques rely on imaging for target localization and treatment planning. The chapter considers image guidance in the context of its impact on dosimetry. For obvious reasons, many of the improvements in dose delivery make dosimetry more difficult. Small fields are not only used for stereotactic applications but also an integral part of intensity-modulated radiotherapy. Large fields are obviously important for half or total body irradiation (TBI). Increasing complexity of delivery often comes at the expense of more monitor units delivered in smaller fields or field segments. Therefore, it is attractive to increase dose rate to ensure that patient treatment times are not prolonged. Radiation must be delivered to the target using distinct pathways. In many clinical scenarios, it is advantageous to use many pathways to keep the dose to normal structures as low as possible in individual paths.
