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Consistency of absorbed dose to water measurements using 21 ion-chamber models following the AAPM TG51 and TG21 calibration protocols
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10.1118/1.2199598
/content/aapm/journal/medphys/33/6/10.1118/1.2199598
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/33/6/10.1118/1.2199598

Figures

Image of FIG. 1.
FIG. 1.

Sample data-capture. Data for the determination of and in a electron beam for three models of Farmer-type chambers. The upper curve shows the accumulated charge of the monitor chamber. The other plots are the accumulated charge of each sample chamber normalized to the monitor chamber. The indicated biases are the polarizing voltages on the thimble. The bias is cycled through full voltage, half voltage, reverse voltage, returning to the original full voltage. Each exposure represents . Note: In order to display all data simultaneously during data acquisition; an arbitrary normalization was additionally applied.

Image of FIG. 2.
FIG. 2.

Cylindrical-chamber results of TG21 output for (A) and (B) photon beams. The values are the measured output normalized to the monitor chamber(s). The shaded area represents the maximum-to-minimum distribution among the chambers.

Image of FIG. 3.
FIG. 3.

Cylindrical-chamber results of TG51 output for (A) and (B) photon beams. The outlier, as indicated is defined in the text.

Image of FIG. 4.
FIG. 4.

Plane-parallel chamber results of TG21 output for (A) and (B) photon beams, using “calib in beam” for PP chambers. All eight plane-parallel chambers were calibrated against chamber No. 1 in the electron beam. The cylindrical results are repeated here to emphasize the systematic difference in output obtained with the two chamber types.

Image of FIG. 5.
FIG. 5.

Plane-parallel chamber results of TG21 output for (A) and (B) photon beams. The plane-parallel chambers were calibrated by the ADCL in a beam. Again, the cylindrical results emphasize the systematic difference in output obtained with the two chambers types.

Image of FIG. 6.
FIG. 6.

Electron output using TG21 for both plane-parallel and cylidrical chambers at (A) and (B). The calibration of the plane-parallel chambers is based on cross calibration with chamber No. 1 in the electron beam.

Image of FIG. 7.
FIG. 7.

Electron output using TG51 for both plane-parallel and cylidrical chambers at (A) and (B). The calibration of the plane-parallel chambers is based on cross calibration with chamber No. 1 in the electron beam. The narrow shaded area over the plane-parallel data is artificial because it is based on comparison with chamber No. 1 alone. The actual spread for the plane-parallel chambers is the sum of the spreads over both cylindrical and plane-parallel chambers.

Image of FIG. 8.
FIG. 8.

Electron output using TG21 for both plane-parallel and cylindrical chambers at (A) and (B). The cylindrical chamber data are repeated from Fig. 6, to facilitate comparison with the plane-parallel results. The plane-parallel chambers are calibrated by the ADCL in a beam. The outlier (chamber No. 21), is outside the bounds of the figure.

Image of FIG. 9.
FIG. 9.

Electron output using TG51 for both plane-parallel and cylidrical chambers at (A) and (B). Again, the cylindrical chamber data are repeated from Fig. 7, to facilitate comparison with the plane-parallel results. The plane-parallel chambers are calibrated by the ADCL in a beam.

Tables

Generic image for table
TABLE I.

Chamber identification and specifications. The table also includes ADCL calibration coefficients, , and for each chamber.

Generic image for table
TABLE II.

Beam characteristics: Beam-energy specifier, measurement depth, and fractional depth-dose data for the four photon and electron beams used.

Generic image for table
TABLE III.

The values of and the product for the eight plane-parallel chambers using the two calibration techniques (ADCL calibration at and cross comparison with a cylindrical chamber in a high-energy electron beam). The ratios “ beam” emphasize discrepancies between the two techniques.

Generic image for table
TABLE IV.

Summary of results: The results in all of the figures are summarized. The spread represents maximum to minimum dispersion high-lighted by the shaded regions in the figures. The ratio, , represents the disagreement between the average plane-parallel and average cylindrical chamber results.d

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/content/aapm/journal/medphys/33/6/10.1118/1.2199598
2006-05-25
2014-04-23
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Consistency of absorbed dose to water measurements using 21 ion-chamber models following the AAPM TG51 and TG21 calibration protocols
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/33/6/10.1118/1.2199598
10.1118/1.2199598
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