Prog Med Phys.  2013 Mar;24(1):41-47.

The Influence of Volume Effect in 2D-array Ion Chamber on the Measurement of IMRT Dose Distribution

• Kim SJ
• Lee SJ
• Park IK
• Lee JE
• Park SH
• Seol KH
• Kim JC

Abstract

We evaluated the influence of volume effect on the measurement of IMRT dose distribution by comparing a 2D-array ion chamber and other dosimeters. Matrix phantom which is a 2D-array ion chamber having volume effect was compared with beam image system and film for the measurement of dose distribution. Five intensity-modulated radiation therapy plans were created using five fields in thevirtual phantom. The measured dose distribution was compared with the calculated one by radiation treatment planning system and analysis program. We evaluated the conformity of dose distribution by calculating correlation coefficients and gamma values. The highest error rate of 1.3% was associated with matrix phantom in which volume effect in small field sizes was substantial.

Keyword

IMRT; Matrix phantom; Beam image system; Film; Volume effect

Figure

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  Fig. 1. Schematic overview of the various steps in the IMRT dose distribution measurement.

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  Fig. 2. Design of PTVs and normal tissues in the virtual phantom.

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  Fig. 3. Setup for measurement of dose distribution. (a) Matrix phantom. (b) BIS. (c) Film.

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  Fig. 4. Matrix phantom: 1,020 parallel plate chambers are on the matrix plate, spacing 0.762 mm internal.

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  Fig. 5. Beam image system operated by the principle of scintillation consists of the following components: 1 mm brass alloy, 0.8 mm scintillator, mirror, ccd camera etc.

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  Fig. 6. The calculated correlation coefficient by analysis program with three different detectors in changeable side of square field.

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  Fig. 7. Error rates with film-matrix phantom and film-BIS.

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  Fig. 8. The calculated gamma value by analysis program with Matrix phantom and BIS in changeable side of square field.

Reference

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