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The DosiMap, a new 2D scintillating dosimeter for IMRT quality assurance: Characterization of two Čerenkov discrimination methods
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10.1118/1.2897966
/content/aapm/journal/medphys/35/5/10.1118/1.2897966
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/35/5/10.1118/1.2897966

Figures

Image of FIG. 1.
FIG. 1.

The device is composed of a plastic scintillator placed inside a polystyrene phantom whose geometry can be adapted to the orientation of the irradiation beam [(a) and (b)]. In order to absorb the Čerenkov radiation produced behind the scintillator, its back side is black-painted. A gelatin filter prevents the Čerenkov light to produce additional scintillation and a chessboard pattern allows the discrimination of the Čerenkov radiation. The CCD camera is kept away from the irradiation beam by using a mirror.

Image of FIG. 2.
FIG. 2.

UPS-974R scintillation and Čerenkov emission spectra, and the “Fire” gelatin filter transmission spectrum.

Image of FIG. 3.
FIG. 3.

A vertical (or horizontal) cut of the image modulated by the chessboard is closer to a sinusoidal signal than a crenel one.

Image of FIG. 4.
FIG. 4.

The chessboard can be unfolded with two orthogonal sinusoidal filters.

Image of FIG. 5.
FIG. 5.

For the subtractive discrimination method, the calibration of the DosiMap is obtained by irradiating with a homogenous field delivered by a vertical beam. (Note that for the clarity of the figure only the scintillator and the film are depicted but the other components—black paint, gelatin filter, and chessboard—are still present.)

Image of FIG. 6.
FIG. 6.

Transmission spectra of the optical filters compared to the emission spectra of the scintillation and the Čerenkov radiation (dotted lines).

Image of FIG. 7.
FIG. 7.

For the colorimetric calibration method, two irradiations are required. The first one, which is similar to the subtractive discrimination calibration, generates a lot of scintillation and Čerenkov light. The second irradiation is performed with a homogenous field delivered by a horizontal beam, which generates Čerenkov radiation but very little scintillation. (Note that for the clarity of the figure only the scintillator and the film are depicted.)

Image of FIG. 8.
FIG. 8.

Dose distribution measurement for a homogenous field delivered by a horizontal beam.

Image of FIG. 9.
FIG. 9.

Dose distribution measurement for a field modulated by a wedged filter and delivered by a vertical beam.

Image of FIG. 10.
FIG. 10.

Dose distribution measured by the DosiMap using the subtractive discrimination method for a homogenous field delivered by a horizontal beam. This distribution directly includes a depth dose measurement ( axis) and a dose profile at a depth of 2.5 cm ( axis).

Image of FIG. 11.
FIG. 11.

Comparison of the relative depth dose distributions measured with a dosimetric film, an ionization chamber, and the DosiMap using the different Čerenkov discrimination methods.

Image of FIG. 12.
FIG. 12.

Comparison of the dose profile at a depth of 2.5 cm measured with a dosimetric film, an ionization chamber, and the DosiMap using the different Čerenkov discrimination methods.

Image of FIG. 13.
FIG. 13.

Relative discrepancy (in ) between the dosimetric film and the DosiMap on the depth dose distribution, using the three Čerenkov discrimination methods.

Image of FIG. 14.
FIG. 14.

Dose distributions measured at a depth of 2.8 cm with a reference dosimetric film and the DosiMap (using the three Čerenkov discrimination methods) for a field, modulated by a wedged filter and delivered by a vertical beam.

Image of FIG. 15.
FIG. 15.

Horizontal cut of the dose distribution measured with the reference dosimetric film and the DosiMap using the three Čerenkov discrimination methods.

Image of FIG. 16.
FIG. 16.

Dose distributions measured at a depth of 5.2 cm with a reference dosimetric film and the DosiMap (using two of the Čerenkov discrimination methods: SD and GCD) for an IMRT field delivered by a vertical beam.

Image of FIG. 17.
FIG. 17.

Comparison between the film and the DosiMap measurements on a horizontal cut of the dose distribution.

Image of FIG. 18.
FIG. 18.

Comparison between the film and the DosiMap measurements on a vertical cut of the dose distribution.

Image of FIG. 19.
FIG. 19.

Spectra of the Čerenkov light attenuated by 0, 1, 12.5, and 24 cm of polystyrene. These spectra were deduced from the experimental transmission spectrum of 10 cm of polystyrene, measured with a calibrated tungsten light and a BTC111E Fiber Coupled TE Cooled CCD Spectrometer (produced by BWTEK), and the theoretical Čerenkov spectrum. It appears that polystyrene strongly absorbs in the lowest part of the visible spectrum.

Tables

Generic image for table
TABLE I.

Accuracy and precision calculated for each discrimination method on the depth dose profile.

Generic image for table
TABLE II.

Absolute discrepancies between the DosiMap and the ionization chamber in low dose regions.

Generic image for table
TABLE III.

Average gamma index and percentage of pixels satisfying the gamma criteria for doses higher than of the maximal dose.

Generic image for table
TABLE IV.

Mean standard deviation of the absolute and relative discrepancies between the film and the DosiMap (calculated on the dose profile between 10 and 15 cm) and gamma index analysis (for dose regions higher than of the maximal dose).

Generic image for table
TABLE V.

Average gamma index and percentage of pixels satisfying the gamma criteria for doses higher than of the maximal dose.

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/content/aapm/journal/medphys/35/5/10.1118/1.2897966
2008-04-07
2014-04-19
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: The DosiMap, a new 2D scintillating dosimeter for IMRT quality assurance: Characterization of two Čerenkov discrimination methods
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/35/5/10.1118/1.2897966
10.1118/1.2897966
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