(Dr. Nolan Hertel, advisor)

"High Precision Dosimetry Using Electronic Portal Imaging Devices"

Abstract

Radiation therapy seeks to identify a tumor volume, deliver a prescribed radiation dose to that tumor volume, and minimize the dose given to the surrounding healthy tissue.  Complex, three-dimensional treatment planning using computed tomography (CT) images is now available for precise dose prescription.  The use of intensity modulated (IM) fields can deliver highly conformal dose distributions.

Electronic portal imaging devices (EPIDs) use a small portion of the daily treatment dose to produce a digital on-line image during treatment. Although these images are currently being used for patient setup verification, none have been used to measure the exact dose received by the patient over the entire course of the treatment.

The proposed research seeks to determine the suitability of an amorphous silicon EPID for high precision dosimetry.  Clinical treatment setups will be modeled using a Monte Carlo transport code and the patient dose will be calculated from the photon fluence that is transmitted through the patient.  The theoretical models will be verified through experimentation with the amorphous silicon device.  The same experiments will be repeated using a more conventional scanning liquid ion chamber (SLIC) EPID in order to compare its suitability for dosimetry with that of the newer technology.  The dosimetric response functions derived from the computer models and from empirical measurements will be used to develop a protocol for the use of EPIDs as devices that can measure absolute dose.