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Measuring linac photon beam energy through EPID image analysis of physically wedged fields
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10.1118/1.4856075
/content/aapm/journal/medphys/41/2/10.1118/1.4856075
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/41/2/10.1118/1.4856075

Figures

Image of FIG. 1.
FIG. 1.

Crossbeam profile of a physically wedged field (solid line) fitted with a second order polynomial of the form 2 + 2 + (dashed line). The edges of the profile are ignored when applying the fit so as to minimize any skew that may be introduced.

Image of FIG. 2.
FIG. 2.

EPID image of a wedged field showing the ROI applied for sampling the wedge profile. The ROI was 1 pixel wide parallel to the wedge direction and 40 pixels in the perpendicular direction. The mean pixel value within the ROI was recorded as the ROI was moved along the wedge profile. For this reason, the ROI width in the wedge direction was deliberately narrow in order to reduce spread in the sampled pixel values due to the gradient of the wedge profile itself. The edges of the field were avoided to prevent skew in the profile due to penumbrae.

Image of FIG. 3.
FIG. 3.

from the polynomial fit of wedge profile as a function of beam energy (PDD measured in a water-tank) across the range corresponding to 6 MV nominal energy for LA06. Results are shown according to the month of the experimental session in which they were acquired. The combined data-set is fitted with a linear relation as shown (dashed line).

Image of FIG. 4.
FIG. 4.

Results for LA06 over a three month period. The dashed lines represent the window defined by local QA tolerances.

Image of FIG. 5.
FIG. 5.

from the polynomial fit of wedge profile as a function of beam energy (PDD measured in a water-tank) across the range corresponding to 6 MV nominal energy. Results are shown for two separate linacs (LA06; circles, LA04; triangles). Both data-sets are fitted with a linear relation (LA06; solid line, LA04; dashed line). The results for LA06 are the combined data-set of results shown in Fig. 3 .

Image of FIG. 6.
FIG. 6.

from the polynomial fit of wedge profile as a function of beam energy (PDD measured in a water-tank) across the range corresponding to 10 MV nominal energy. Results are shown for two separate linacs (LA06; circles, LA04; triangles). Both data-sets are fitted with a linear relation (LA06; solid line, LA04; dashed line).

Tables

Generic image for table
TABLE I.

Results of EPID image analysis and water-tank measurements for four other linacs in the SJIO fleet. In each case, the PDD returned using the LA06 fit has been calculated along with the difference to the water-tank measured value.

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/content/aapm/journal/medphys/41/2/10.1118/1.4856075
2014-01-13
2014-04-18
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Measuring linac photon beam energy through EPID image analysis of physically wedged fields
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/41/2/10.1118/1.4856075
10.1118/1.4856075
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