ABSTRACT
This chapter discusses the use of electronic portal imaging devices (EPIDs) for delivered dose verification. The most common clinical use of EPID is for patient imaging prior to treatment delivery, with the imager retracted during beam delivery. The motivation for in-treatment delivered dose estimation is to detect discrepancies between the dose distribution that is prescribed or planned, and the dose distribution that is actually delivered in the presence of intrafraction deformations. Various methods of delivered dose verification using the EPID have been developed, but each shares two key required components. These components are a method of estimating target and/or tissue motion based on EPID images and a method of incorporating the estimated motion into calculations of the delivered dose. Several methods for calculating delivered dose distributions based on motion tracked in EPID images have been presented in the literature. Recently, motion-model based methods of treatment verification have been developed that are capable of accounting for 3D deformations during treatment.
