Fabrication of high aspect-ratio polymer microstructures for large-area electronic portal x-ray imagers
Megavoltage x-ray imaging performed during radiotherapy is the method of choice for geometric verification of patient localization and dose delivery. Presently, such imaging is increasingly performed using electronic portal imaging devices (EPIDs) based on indirect detection active matrix flat panel imagers (AMFPIs). These devices use a scintillating phosphor screen in order to convert incident x-rays into optical photons, which are then detected by the underlying active matrix photodiode array. The use of a continuous phosphor introduces a trade-off between x-ray quantum efficiency and spatial resolution, which limits current devices to use only ~2% of the incident x-rays. In order to circumvent this trade-off, we have proposed the concept of 'segmented phosphor screens', comprising a two dimensional matrix of optically-isolated cell structures filled with scintillating phosphor. In this work we describe the fabrication of millimeter-thick segmented phosphor screens using the MEMS (micro-electro-mechanical-system) polymer SU-8. This method is capable of being extended to large-area substrates.
Daniel, J. H. ; Sawant, A.; Teepe, M. R. ; Shih, C. ; Street, R. A. ; Antonuk, L. E. High aspect-ratio polymer microstructures for large-area electronic portal x-ray imagers. Sensors and Actuators A. 2007 November 10; 140 (2): 185-193.