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SU‐DD‐A2‐03: 2‐D Lag and Ghosting Corrections for Dynamic IMRT Verification Using An EPID
Author(s) -
Steciw S,
Warkentin B,
Rathee S,
Fallone B
Publication year - 2007
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2760347
Subject(s) - ghosting , lag , nuclear medicine , image guided radiation therapy , dosimetry , dynamic range , signal (programming language) , computer science , physics , optics , mathematics , medical imaging , artificial intelligence , medicine , computer network , programming language
Purpose: To measure and correct the two dimensional lag and ghosting effects of an a‐Si EPID for dynamic MLC delivery in IMRT verification. Method and Materials: Varians aS500 EPID was used to acquire portal images at an SID of 105 cm with 2 cm solid‐water build‐up. Each image was averaged over 8 frames acquired in ‘continuous acquisition’ mode with Varis Portal Vision's service monitor (IAS3) to construct lag and signal‐to‐MU curves. To quantify lag, images were acquired post‐irradiation by inhibiting the M‐holdoff‐In signal, for a range of MUs. The resulting lag and signal‐to‐MU curves were used to calculate cumulative lag and cumulative dose‐response curves. Both these cumulative curves were used to correct the 2‐D lag and ghosting effects of the EPID images. Results: We found that the 2D effects of lag and ghosting can be corrected by measuring and then applying lag and signal‐to‐MU curves. This technique provides a maximum correction of approximately 1% for dynamic head‐and‐neck IMRT deliveries. Conclusion: Two‐dimensional lag and ghosting effects of the aS500 EPID can be measured and corrected. This approach can be of particular importance for the EPID IMRT verification of MLC dynamic deliveries.