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Wide field array calibration dependence on the stability of measured dose distributions
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Image of FIG. 1.
FIG. 1.

WF calibration reproducibility on LINACs with beam symmetry variations of (a) ±0.15% (Elekta LINAC) and (b) ±0.05% (Varian LINAC).

Image of FIG. 2.
FIG. 2.

Oblique view of the panel’s arrays and electronics. The panel’s -axis is parallel to the long axis of the device.

Image of FIG. 3.
FIG. 3.

(a) The perturbation that was applied to the hypothetical calibration measurements. (b) The effects of perturbations applied, separately, to each calibration measurement.

Image of FIG. 4.
FIG. 4.

The percentage error between ten consecutive measurements and their means for (a) a LINAC that produces ±1.6% calibration reproducibility, (b) a LINAC that produces ±0.5% calibration reproducibility, and (c) the same machine as used in (a) but with the beam continuously on. The spikes in the center detector of (b) were due to the preirradiation effect of ionization chambers and do not contribute significantly to calibration errors.

Image of FIG. 5.
FIG. 5.

Calibration reproducibility using a continuous beam during measurements and on an Elekta LINAC; no additional side-scatter was used.

Image of FIG. 6.
FIG. 6.

The effect of additional side-scatter on (a) beam measurements and (b) array calibrations. The measurements and calibrations were performed on a Varian LINAC.

Image of FIG. 7.
FIG. 7.

The agreement between calibration factors obtained with side-scatter and either a continuous beam (Elekta) or a standard on/off delivery (Varian).

Image of FIG. 8.
FIG. 8.

The calibration accuracy was evaluated for four measurement combinations. These included the presence (w/ss) or absence (n/ss) of additional side-scatter in the measurement (meas) and/or calibration (cal).

Image of FIG. 9.
FIG. 9.

The calibration accuracy expressed as the ratio between water tank measurements and panel measurements. The panel calibrations were performed using a continuous radiation source in the (a) presence of and (b) absence of additional side-scatter.


Generic image for table

The short term reproducibility of WF calibrations performed on the Elekta using either the standard protocol or the continuous beam (with and without additional ss).


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Wide field array calibration dependence on the stability of measured dose distributions