Comparison of ghosting effects for three commercial a - Si EPIDs

• Published in: Medical physics (Lancaster) 2006-07, Vol.33 (7), p.2448-2451
• Main Authors: McDermott, L. N., Nijsten, S. M. J. J. G., Sonke, J.-J., Partridge, M., van Herk, M., Mijnheer, B. J.
• Format: Article
• Language: English
• Subjects: amorphous semiconductors; amorphous silicon; BEAMS; biomedical equipment; Calibration; Digital image processing; DOSE RATES; dose response; DOSIMETRY; Elastic moduli; EPID dosimetry; Equipment Design; ghosting; Humans; Image guided radiation therapy; image lag; IMAGE PROCESSING; Image Processing, Computer-Assisted - methods; Image sensors; Linear accelerators; Medical imaging; Particle beam detectors; Phantoms, Imaging; Photodiodes; radiation therapy; Radiation therapy equipment; Radiographic Image Interpretation, Computer-Assisted; RADIOLOGY AND NUCLEAR MEDICINE; Radiometry - methods; RADIOTHERAPY; Radiotherapy Dosage; Record and verify systems and applications; Reproducibility of Results; SEMICONDUCTOR MATERIALS; SIGNALS; SILICON; Silicon - chemistry; Software; Time Factors; Verification
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.2207318

Many studies have reported dosimetric characteristics of amorphous silicon electronic portal imaging devices (EPIDs). Some studies ascribed a non-linear signal to gain ghosting and image lag. Other reports, however, state the effect is negligible. This study compares the signal-to-monitor unit (MU) ratio for three different brands of EPID systems. The signal was measured for a wide range of monitor units (5–1000), dose-rates, and beam energies. All EPIDs exhibited a relative under-response for beams of few MUs; giving 4 to 10% lower signal-to-MU ratios relative to that of 1000 MUs . This under-response is consistent with ghosting effects due to charge trapping.