Imaging Dose in Radiation Therapy

This chapter presents a variety of measurement and reviews calculation techniques for characterizing the radiation dose from x-ray imaging systems used in radiation therapy (RT). The electronic portal imaging device is probably the most basic of the systems and can be used to locate and track anatomy with little or no additional radiation dose to the patient. The established and standardized method for measuring fan beam computed tomography dose, since 1981, has been to measure the computed tomography dose index. For radiotherapy, the risk of concomitant imaging needs to be considered in the context of the existing risk of secondary cancer induction from radiotherapy treatment. The model has to be calibrated for absolute dose calculation, and dose profiles obtained in reference conditions must be validated against experimental measurements. The primary risk of radiation exposure from radiotherapy, including any concomitant imaging but excluding the risks of treatment failure and comorbidities, is the induction of a secondary primary malignancy.