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Possibility of using cylindrical ionization chambers for percent depth-dose measurements in clinical electron beams
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10.1118/1.3608903
/content/aapm/journal/medphys/38/8/10.1118/1.3608903
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/38/8/10.1118/1.3608903

Figures

Image of FIG. 1.
FIG. 1.

Simplified schematic geometries used to calculate P cav and PQ for a cylindrical chamber and a parallel-plate chamber: (a) the dose to water, Dw , (b) the dose to LDW in the cylindrical chamber, D LDW,cyl, (c) the dose to LDW in the parallel-plate chamber, D LDW,PP, (d) the dose to LDW in the PTW30013 chamber, D LDW,PTW30013, (e) the dose to LDW in the NACP-02 chamber, D LDW,NACP-02, and (f) the dose to LDW in the Roos chamber, D LDW,ROOS. The dose scoring regions for the parallel-plate chambers are shown by the dotted lines, excluding the guard width region. Physical characteristics of the cylindrical chamber and the parallel-plate chamber are shown in Tables II and III. The EPOM for the cylindrical chamber is taken to be the shift upstream of 0.5r. For the parallel-plate chamber, the EPOM is set at the center of the front surface of the air cavity. The EPOM The size of a water phantom is 30 × 30 × 30 cm3.

Image of FIG. 2.
FIG. 2.

Calculated P cav values as a function of depth for the cylindrical chamber cavity and the parallel-plate chamber cavity at 6, 9, 15, and 18 MeV. The EPOM for the cylindrical chamber is shifted upstream by 0.5r. For parallel-plate chamber, the EPOM is set at the front surface of the air cavity. Also shown are the P cav values given by Verhaegen et al. (Ref. 20) and the EPOM is set at the front surface of the air cavity.

Image of FIG. 3.
FIG. 3.

Calculated PQ values as a function of depth for PTW30013, NACP-02, and Roos chambers at 6, 9, 15, and 18 MeV. The EPOM for the PTW30013 chamber is shifted upstream by 1.5 mm. For NACP-02 and Roos, the EPOM is placed at 0.6 mm and 1.0 mm below the surface of the front window respectively. Also shown are the PQ values given by Verhaegen et al. (Ref. 20) and the EPOM is placed at 0.6 mm below the surface of the front window.

Image of FIG. 4.
FIG. 4.

Calculated P wall values as a function of depth for PTW30013, NACP-02, and Roos chambers in 6, 9, 15, and 18 MeV. The EPOM for the PTW30013 chamber was shifted upstream by 1.5 mm. For NACP-02 and Roos, the EPOM was placed 0.6 and 1.0 mm below the surface of the front window respectively. Also shown are P wall values given by Verhaegen et al. (Ref. 20). They used the EPOM of 0.6 mm.

Image of FIG. 5.
FIG. 5.

Calculated percent depth-ionization curves for PTW30013, NACP-02, Roos chambers, and water at 6, 9, and, 18 MeV.

Tables

Generic image for table
TABLE I.

Characteristics of clinical electron beams from the Varian Clinac linear accelerator. The reference depth d ref is obtained from 0.6R 50-0.1 (cm).

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TABLE II.

Physical characteristics of a PTW Farmer-type chamber.

Generic image for table
TABLE III.

Physical characteristics of parallel-plate chambers.

Generic image for table
TABLE IV.

The variation in P cav values for cylindrical chambers of 6 mm, 4 mm and 2 diameters with 20 mm length and parallel-plate chambers at depths from the surface to R 50.

Generic image for table
TABLE V.

The variation in P Q values for PTW30013, NACP-02, and Roos chambers at depths from the surface to R 50.

Generic image for table
TABLE VI.

The shift to match PDI curves of PTW30013, NACP-02, and Roos chambers for water. Minus indicates an upstream side compared to water.

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/content/aapm/journal/medphys/38/8/10.1118/1.3608903
2011-07-25
2014-04-25
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Possibility of using cylindrical ionization chambers for percent depth-dose measurements in clinical electron beams
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/38/8/10.1118/1.3608903
10.1118/1.3608903
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