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EBT2 film as a depth-dose measurement tool for radiotherapy beams over a wide range of energies and modalities
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10.1118/1.3678989
/content/aapm/journal/medphys/39/2/10.1118/1.3678989
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/39/2/10.1118/1.3678989

Figures

Image of FIG. 1.
FIG. 1.

A full film was cut to 30 pieces of 4 × 4 cm. The pieces were chosen randomly (designated with red circles) for film uniformity investigation. Each piece was irradiated to 6 Gy using a 6 MV photon beam. Film pieces were read using a flat-bed scanner and the images were processed in red channel.

Image of FIG. 2.
FIG. 2.

(a) Shows the apparatus that is used for mounting a film for depth-dose irradiation in water. The stand is made of minimal amount of “solid water” strips. (b) A detachable plumb-line is used to set 2° tilt with respect to central axis of the beam. A 2° tilt of 28.5 cm long Plumb-line implies a 10-mm shift of the plumb. Level of water tank is adjusted to displace the plumb from its vertical position (circular mark) by 10 mm as shown by lines marked on the stand’s base. Prior to irradiation, the plumb-line attachment is gently removed. (c) A film (4.0 × 20.3 cm) is mounted in the stand, and placed inside the water tank. (d) Shows a small gap between film’s top-edge and its reflection is shown. Water is gently removed with a syringe until the gap gradually shrinks to zero. This ensures film’s top-edge matches exactly with the water surface. Subsequently, tank height is adjusted to achieve nominal SSD, and collimator jaws are set to the desired field side (i.e., 10 × 10 cm).

Image of FIG. 3.
FIG. 3.

(a) Template used to position 4 × 20.3 cm films for scanning on the flat-bed scanner. This ensures exact reproducible positioning of the film on the scanner-bed during back-ground reading and postexposure reading-sessions. The small notches at left and right ends in the cut-out provides scanning region beyond the film edges enabling identification of film edges. This helps to verify pixel-to-depth calibration and zero-depth position (water surface). (b) Illustrates the technique used to verify the depth-calibration. Pixel value at the spike in film OD readings at the film’s edge at water surface (not shown) is used to set depth to be zero, while spike at the film’s distal-edge is verified to reproduce depth equal to films geometric length (20.3 cm).

Image of FIG. 4.
FIG. 4.

Film-calibration curves are shown for the seven radiation-therapy beams used in this study. It is worth noting that all megavoltage photon and electron data are clustered in a central narrow band implying negligible energy dependence (1σ = ±4.5%). The dashed curves corresponding to proton and orthovoltage beams are away from the central band. The proton beam data are on left side of the cluster, while the orthovoltage (75 kVp nominal) data are on right side of the cluster.

Image of FIG. 5.
FIG. 5.

Comparison of percentage depth-dose data measured with EBT2 film and ion chamber (CC04) for 75 kVp beam. The film data were corrected (dashed-line) using a third order polynomial fitted to uncorrected (solid-line) data. At depth of 10 cm, a difference of 0.9% is noted between the film (uncorrected) and the ion-chamber data.

Image of FIG. 6.
FIG. 6.

Comparison of percentage depth-dose data measured with EBT2 film and BJR-25 data for 60Co beam. The data are normalized to depth of maximum dose at 0.5 cm. The maximum difference in percentage depth-dose of 0.3% at depth of 15 cm is detected.

Image of FIG. 7.
FIG. 7.

Comparison of percentage depth-dose data measured with EBT2 film and ion chamber (CC04) for an 18 MV photon beam. The data are normalized to depth of maximum dose at 3.0 cm. A maximum difference in percentage depth-dose of 1.6% at depth of 14 cm is detected.

Image of FIG. 8.
FIG. 8.

Comparison of percentage depth-dose data measured with EBT2 film and ion chamber (CC04) for a 7 MeV electron beam. The data are normalized to depth of maximum dose at 1.9 cm. The maximum difference in percentage depth-dose of 2.6% at depth of 0.1 cm is detected.

Image of FIG. 9.
FIG. 9.

Comparison of percentage depth-dose data measured with EBT2 film and ion chamber (CC04) for a 20 MeV electron beam. The data are normalized to depth of maximum dose at 2.6 cm. The maximum difference in percentage depth-dose of 1.4% at depth of 0.9 cm is detected.

Image of FIG. 10.
FIG. 10.

Comparison of percentage depth-dose data measured with EBT2 film and MLIC for a 126 (range of 11.6 cm) and a 152 (range of 16 cm) MeV proton beam. The data are normalized in plateau region at depth of 2 cm. The film data were corrected (dashed-line) using a third order polynomial fitted to uncorrected (open-circle) data.

Image of FIG. 11.
FIG. 11.

Shows the film OD nonuniformity of various pieces corresponding to Fig. 1. The percent deviations of each pieces are from relative average of OD of all pieces. The OD measured on the flat-bed scanner and analyzed in red channel. The nonuniformity of the OD is within 0.8% (1σ).

Tables

Generic image for table
TABLE I.

Characteristics of radiation sources employed in this investigation.

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/content/aapm/journal/medphys/39/2/10.1118/1.3678989
2012-01-26
2014-04-20
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: EBT2 film as a depth-dose measurement tool for radiotherapy beams over a wide range of energies and modalities
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/39/2/10.1118/1.3678989
10.1118/1.3678989
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