Investigation of pixel scale calibration on the Elekta iView electronic portal imager

Abstract

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Variation in Elekta iView electronic portal imager pixel scale factor with gantry angle, and impact on multi‐leaf collimator quality assurance

“…This variation in distance is the major contributor to the variation in PSF. [ 7 ] The PSF was observed to vary by a maximum range of 0.0018 mm/pixel for L1 and L3, and 0.0022 mm/pixel for L2, respectively. This corresponded with maximum variations of 8.7‐, 7.3‐, and 6.7‐mm variations in the IPD for L1, L2, and L3, respectively.…”

“…The functioning of this software and validation against the Elekta BLD calibration workflow have been described previously. [ 7 ] The IHS returns the PSF, which allows the conversion of a measurement made in pixels to a physical distance at the linac isocenter. The PSF determined with the gantry at 0° is henceforth referred to as the nominal PSF.…”

“…It has been shown that the largest contribution to the variation in PSF between Elekta Agility linacs is derived from variations in the SPD. [ 7 ] During rotation, the linac gantry head and EPID will flex due to rotational mechanics and the SPD may vary as a result, potentially introducing changes in the PSF. [ 2,6 ]…”

“…This is achieved via a multiplicative application of a pixel scale factor (PSF). [7] The PSF is derived by placing a calibration plate of known dimensions at isocenter, acquiring an image for gantry 0 • , and relating the number of measured pixels to the known plate dimensions. For images exported to external software applications, the PSF may be entered manually as a software parameter or extracted from the image DICOM header information.…”

“…It has been shown that the largest contribution to the variation in PSF between Elekta Agility linacs is derived from variations in the SPD. [7] During rotation, the linac gantry head and EPID will flex due to rotational mechanics and the SPD may vary as a result, potentially introducing changes in the PSF. [2,6] This work aimed to investigate the variation in PSF with respect to gantry angle, and the effect on MLC QA results completed at different gantry angles.…”