Measurement of patient setup errors using digitally reconstructed radiographs and electronic portal images

Three-dimensional conformal radiation therapy is the process by which high radiation doses are precisely focused to the target tumoral volumes while surrounding structures are treated with lower radiation doses. This process requires the use of tighter margins around the target tumoral volumes. In order to avoid misses resulting from the use of the tighter margins, frequent verification of patient positioning is essential. Comparison of digitally reconstructed radiographs (reference images) obtained by using a three-dimensional radiation planning system to the digital port images (treatment images) obtained by using an electronic portal imaging device is the best way to check the patient setup. This study presents the design and implementation of a method that makes such a comparison possible. Reference and treatment images have been presented on the same digital media without use of any analog processing. The designed tool was tested for clinical use on a patient and displacements in each axis were measured. The main advantages of the method are its accuracy, its low-cost as well as its time-saving property