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Poster — Thur Eve — 06: Radiochromic Film Densitometry with Vista15 Optical Cone Beam CT Scanner
Author(s) -
Babic S,
Jordan K
Publication year - 2010
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 - 10.1118/1.3476111
Subject(s) - scanner , optics , dosimetry , calibration , materials science , densitometry , ghosting , shadow (psychology) , physics , nuclear medicine , medicine , psychology , quantum mechanics , psychotherapist
Purpose: To examine the performance of a scatter corrected commercial optical cone beam CT scanner, Vista15™, adapted for radiochromic film dosimetry. Methods: A slotted film mask adjacent to the EBT2 film was used to generate alternating open and dark areas. Three images were acquired with the mask centered along the optical axis and offset +/−0.7cm. The masked transmission images were processed by first forming composite images from the open and shadow areas of the three image sets. The composite shadow image was subtracted from the corresponding open image to create a “glare‐free image”. Net optical density (OD) images were generated by calculating −log 10 (corrected post/corrected pre image). The calibration dose response in EBT2 film using multiple 4MV photon fields and a single 12MeV electron field was measured. Results: In the corrected data, net OD increased and the buildup region mirrored actual 12MeV dose deposition in water. This trend was also observed in the multiple 4MV photon field calibration data. From comparing the two calibration techniques, a discrepancy in net OD of up to 4% was observed. This suggests that EBT2 film users should have a consistent method for calibrating the dose response. Conclusions: The emission spectrum of Vista15™ designed for readout of radiochromic gels and plastics overlaps the absorption peak in EBT2 films, thus, making this scanner convenient and economical for both planar and 3D dosimetry. A method for veiling glare correction is promising but a more complex multiple grid approach will be needed in order to achieve quantitative densitometry.