Dose optimisation during imaging in radiotherapy

The desire to increase the precision in radiotherapy delivery has led to the development of advanced imaging systems such as amorphous silicon (a-Si)-based electronic portal imaging, and kV and MV cone beam CT. These are used prior to the delivery of radiation to visualise the organ to be treated and to ensure that the patient setup and treatment delivery are accurate. However, little attention has been given to the dose received by adjacent normal tissues during these imaging procedures. Though these doses are very small compared to the dose delivered during radiotherapy, the involvement of normal tissues and the concern that these could increase the probability of stochastic effect, mainly the induction of secondary malignancy, cannot be ignored. This article reviews some work on the doses received during imaging in radiotherapy and the methods to optimise the same.