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Radiation Oncology
Published in: Radiation Oncology 1/2018

Open Access 01-12-2018 | Research

Development of a PMMA phantom as a practical alternative for quality control of gamma knife® dosimetry

Authors: Jae Pil Chung, Young Min Seong, Tae Yeon Kim, Yona Choi, Tae Hoon Kim, Hyun Joon Choi, Chul Hee Min, Hamza Benmakhlouf, Kook Jin Chun, Hyun-Tai Chung

Published in: Radiation Oncology | Issue 1/2018

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Abstract

Background

To measure the absorbed dose rate to water and penumbra of a Gamma Knife® (GK) using a polymethyl metacrylate (PMMA) phantom.

Methods

A multi-purpose PMMA phantom was developed to measure the absorbed dose rate to water and the dose distribution of a GK. The phantom consists of a hemispherical outer phantom, one exchangeable cylindrical chamber-hosting inner phantom, and two film-hosting inner phantoms. The radius of the phantom was determined considering the electron density of the PMMA such that it corresponds to 8 g/cm2 water depth, which is the reference depth of the absorbed dose measurement of GK. The absorbed dose rate to water was measured with a PTW TN31010 chamber, and the dose distributions were measured with radiochromic films at the calibration center of a patient positioning system of a GK Perfexion. A spherical water-filled phantom with the same water equivalent depth was constructed as a reference phantom. The dose rate to water and dose distributions at the center of a circular field delimited by a 16-mm collimator were measured with the PMMA phantom at six GK Perfexion sites.

Results

The radius of the PMMA phantom was determined to be 6.93 cm, corresponding to equivalent water depth of 8 g/cm2. The absorbed dose rate to water was measured with the PMMA phantom, the spherical water-filled phantom and a commercial solid water phantom. The measured dose rate with the PMMA phantom was 1.2% and 1.8% higher than those measured with the spherical water-filled phantom and the solid water phantom, respectively. These differences can be explained by the scattered photon contribution of PMMA off incoming 60Co gamma-rays to the dose rate. The average full width half maximum and penumbra values measured with the PMMA phantom showed reasonable agreement with two calculated values, one at the center of the PMMA phantom (LGP6.93) and other at the center of a water sphere with a radius of 8 cm (LGP8.0) given by Leksell Gamma Plan using the TMR10 algorithm.

Conclusions

A PMMA phantom constructed in this study to measure the absorbed dose rates to water and dose distributions of a GK represents an acceptable and practical alternative for GK dosimetry considering its cost-effectiveness and ease of handling.
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Metadata
Title
Development of a PMMA phantom as a practical alternative for quality control of gamma knife® dosimetry
Authors
Jae Pil Chung
Young Min Seong
Tae Yeon Kim
Yona Choi
Tae Hoon Kim
Hyun Joon Choi
Chul Hee Min
Hamza Benmakhlouf
Kook Jin Chun
Hyun-Tai Chung
Publication date
01-12-2018
Publisher
BioMed Central
Published in
Radiation Oncology / Issue 1/2018
Electronic ISSN: 1748-717X
DOI
https://doi.org/10.1186/s13014-018-1117-8

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