An investigation of a new amorphous silicon electronic portal imaging device for transit dosimetry

• Published in: Medical physics (Lancaster) 2002-10, Vol.29 (10), p.2262-2268
• Main Authors: Grein, Ellen E., Lee, Richard, Luchka, Kurt
• Format: Article
• Language: English
• Subjects: amorphous semiconductors; biomedical electronics; biomedical imaging; dosimetry; Electromagnetic radiation detectors; Field size; Image guided radiation therapy; Models, Statistical; Particle beam detectors; Phantoms, Imaging; Photons; Quality assurance equipment; Radiation Oncology - instrumentation; radiation therapy; Radiation therapy equipment; Radiometry - instrumentation; Radiometry - methods; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted; Radiotherapy sources; Radiotherapy, High-Energy; Silicon; Thin film devices; Transmission measurement; Verification
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.1508108

The relationship between the pixel value and exit dose was investigated for a new commercially available amorphous silicon electronic portal imaging device. The pixel to dose mapping function was established to be linear for detector distances between 116.5 cm to 150 cm from the source, radiation field sizes from 5×5  cm 2 to 20×20  cm 2 and beam energies of 6 to 18 MV. Coefficients in the mapping function were found to be dependent on beam energy and field size. Open and wedged field profiles measured with the device showed agreement to a maximum of 5% and 8%, respectively, as compared to film. A comparison of relative transmission measurements between the EPID and ion chamber indicate a maximum deviation of 6% and 2% at 6 and 18 MV, respectively, for an attenuator thickness of 21 cm and SDD⩾130 cm. It was found that accuracies of better than 1% could be obtained if detector position and field size specific fitting parameters were used to generate unique mapping functions for each configuration.