Author/Editor		Méndez Carot, Ignasi; Šljivić, Željko; Hudej, Rihard; Jenko, Aljaša; Casar, Božidar
Title		Grid patterns, spatial inter-scan variations and scanning reading repeatability in radiochromic film dosimetry
Type		članek
Vol. and No.		Letnik 32, št. 9
Publication year		2016
Volume		str. 1072-1081
ISSN		1120-1797 - Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics (AIFB)
Language		eng
Abstract		When comparing different scans of the same radiochromic film, several patterns can be observed. These patterns are caused by different sources of uncertainty, which affect the repeatability of the scanner. The purpose of this work was to study these uncertainties. Methods The variance of the scanner noise, as a function of the pixel position, was studied for different resolutions. The inter-scan variability of the scanner response was analyzed taking into account spatial discrepancies. Finally, the distance between the position of the same point in different scans was examined. Results The variance of noise follows periodical patterns in both axes, causing the grid patterns. These patterns were identified for resolutions of 50, 72 and 96 dpi, but not for 150 dpi. Specially recognizable is the sinusoidal shape with a period of 8.5 mm that is produced with 72 dpi. Inter-scan variations of the response caused systematic relative dose deviations larger than 1% in 5% of the red channel images, 9% of the green and 51% of the blue. No systematic deviation larger than 1% was found after applying response corrections. The initial positioning and the speed of the scanner lamp vary between scans. Conclusions Three new sources of uncertainty, which influence radiochromic film dosimetry with flatbed scanners, have been identified and analyzed in this work: grid patterns, spatial inter-scan variations and scanning reading repeatability. A novel correction method is proposed, which mitigates spatial inter-scan variations caused by deviations in the autocalibration of the individual Charge Coupled Device detectors.
Keywords		radiokromski film dozimetrija optični čitalniki obsevanje radiochromic film dosimetry flatbed scanners