Density resolutionary optimization of real time radiotherapy portal imagings / 中华放射肿瘤学杂志

ABSTRACT

Objective Electronic portal imaging devices (EPIDs) are widely used as a replacement of portal films for patient position verification, but the image quality is not always optimal. Because of very low density resolution, the portal imaging is difficult to be used clinically. In this study, several transforming models and the optimization exposure or acquisition conditions were studied for optimization portal imaging, which based on DicomRT platform built by ourselves. Methods 6 MV X-ray from Varian 21EX linac was used to generate portal images by Portal Vision aSiS00 amorphous silicon detector image acquisition system. The density resolution study was based on the number of the lines which could be seen in the image of a special Las Vegas image quality test board. The optimization calculating models were focused on equalization after stretch transforming discrete wavelet transform (DWT) and Butterworth high pass filters. The calculation was performed in Matlab language. Results The optimal numbers of MU, average frames and reset number were 4 - 5,3 - 4 and 2 - 3, respectively. The density resolution of optimized imaging via equalization after stretch transforming, DWT and Butterworth high pass filter transforming was markedly improved. The bone structure could be definitely distinguished. The number of lines distinguished in Las Vegas image via equalization after stretch transforming, DWT and Betterworth high pass filter transforming was 3, 4 and 5, respectivly. Conclusions The proposed transforming systems, including DWT edge detection and Butterworth high pass filter transform, are suitable for improving density resolving power of MV X-ray portal image.