Evaluation of an amorphous silicon electronic portal imaging device for use in radiation therapy dosimetry

Regan Estcourt Sibbald
The objective of external beam radiation therapy is to deliver a high dose of sterilizing radiation to a diseased tumor site while minimizing the dose to as much of the surrounding normal tissue as possible. This is often accomplished by directing one or more megavoltage xray treatment portals at the diseased area from different directions. In theory, this principle maximizes the dose to the target site while minimizing the dose to surrounding healthy tissue. The efficacy of a course of
more » ... a course of radiation therapy may however be compromised by several factors. Geometric factors related to the accuracy to which the beam delivery system can reproduce the desired treatment set-up may cause deviations from the desired results. Patient set-up uncertainties are another factor and are related to the alignment of skin markings with respect to the underlying target structures within the body. In addition, a presumably fixed target may be geometrically shifted due to its proximity to neighboring organs or the patient may simply move during treatment thereby shifting the treatment portal with respect to the intended target. All of these factors contribute to a sub-optimal treatment outcome and possibly an increase in the normal tissue complication probability (NTCP). On-line electronic portal imaging devices (EPIDs) have been developed to monitor and help correct the inaccuracies encountered in radiation therapy. EPIDs were developed for verification of geometric accuracy, as they are capable of producing near real-time 2D projection images of the target volume during a radiotherapy treatment. However, it has also become apparent that in addition to geometric verification, EPIDs can provide valuable dosimetric information, indicating points of interest in terms of over and under dosage. In this thesis, the dosimetric characteristics of the amorphous silicon EPID are investigated. First, the EPIDs ability to accurately and reproducibly measure dose as a function of fluence rate is investigated. EPID pixel intensi [...]
doi:10.14288/1.0092046 fatcat:qunvb7n6xne5hedymwqghmsse4