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

Sung Joon Kim; Seoung Jun Lee; In Kyu Park; Jeong Eun Lee; Shin Hyung Park; Ki Ho Seol; Jae Chul Kim

doi:10.14316/pmp.2013.24.1.41

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Kim, Lee, Park, Lee, Park, Seol, and Kim: The Influence of Volume Effect in 2D-array Ion Chamber on the Measurement of IMRT Dose Distribution

Original Article

Progress in Medical Physics 2013;24(1):41-47.

Published online: 20 March 2013

DOI: https://doi.org/10.14316/pmp.2013.24.1.41

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

Sung Joon Kim^∗,^‡, Seoung Jun Lee^∗,^‡, In Kyu Park^∗,^†, Jeong Eun Lee^∗,^†, Shin Hyung Park^∗,^†, Ki Ho Seol^∗,^†, Jae Chul Kim^∗,^†,

^∗Department of Radiation Oncology, Kyungpook National University Hospital, Korea

^†Kyungpook National University School of Medicine, Daegu, Korea

^‡Department of Physics, College of Science, Yeungnam University, Gyongsan, Korea

책임저자：김재철, (700-721) 대구시 중구 삼덕동 2가 50 경북대학교 의학전문대학원 방사선종양학교실 Tel: 053)200-5352, Fax: 053)426-3303 E-mail: jckim@knu.ac.kr

Received 3 September 2012 Accepted 28 February 2013

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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.

Keywords: IMRT, Matrix phantom, Beam image system, Film, Volume effect

References

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Fig. 1.

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

Fig. 2.

Design of PTVs and normal tissues in the virtual phantom.

Fig. 3.

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

Fig. 4.

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

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.

Fig. 6.

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

Fig. 7.

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

Fig. 8.

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

Table 1.

PTVs with square field side.

Square field side (cm)	PTV (volume, unit: cm³)
1.5	PTV 1 (1.1)
3	PTV 2 (2.6)
5	PTV 3 (31.9)
7	PTV 4 (130)
10	PTV 5 (350)

Table 2.

Characteristics of detectors used this study.

Detector	Manufacturer	Model	Volume (cm³) number of chamber	Effective area (cm²)	Analysis program
Matrix phantom	IBA	I'mRT Matrix	0.08, 1,020	24.4×24.4	Omnipro-I'mRT
BIS	IBA	BIS 710	–	24×24	Omnipro-I'mRT
Film	Kodark	EDR2	–	25×30	Omnipro-I'mRT

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