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Statistical analysis on 2D array of ion chamber performance

Published online by Cambridge University Press:  12 January 2015

Akbar Anvari ,
Seyed Mahmoud Reza Aghamiri ,
Seyed Rabie Mahdavi  and
Parham Alaei
Akbar Anvari*
Affiliation:
Department of Radiation Medicine Engineering, Shahid Beheshti University, Tehran, Iran
Seyed Mahmoud Reza Aghamiri
Affiliation:
Department of Radiation Medicine Engineering, Shahid Beheshti University, Tehran, Iran
Seyed Rabie Mahdavi
Affiliation:
Department of Medical Physics, Iran University of Medical Sciences, Tehran, Iran
Parham Alaei
Affiliation:
Department of Radiation Oncology, University of Minnesota, Minneapolis, Minnesota, USA
*
Correspondence to: Akbar Anvari, Department of Radiation Medicine Engineering, Shahid Beheshti University, Tehran 19839-63113, Iran. Tel.: +98 21 29902541. E-mail: [email protected]
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Abstract

Purpose

In this work, dosimetric properties of the PTW Octavius detector in and out of the irradiation field have been evaluated. The 2D array of ion chambers has the potential to simplify the linear accelerator QA and pre-treatment verification.

Materials and methods

The evaluation was performed using customised written codes in Matlab and SPSS software for statistical analysis.

Results

Experiments indicate that the reproducibility and stability of the measurements were excellent; the detector showed the same signal with a maximum deviation of <0·5% in the short and long term. Comparisons of the ion chamber with the detector showed the same results with a maximum deviation of ~0·1%. As the detector response is linear with the dose, it can be used for the measurement at regions of high-dose gradient effectively. Logarithmic regression y=0·127 ln(x)+0·729 for detector signal and field size changes yielded a coefficient of determination of 0·997. The dose value decreases with increase in source-to-surface distance, which was modelled using a binomial regression with a coefficient of determination of 0·998 that agrees with the ionisation chamber measurement within 1%.

Conclusion

On the basis of the measurements and comparisons performed, this system is a reliable and accurate dosimeter for quality assurance in radiotherapy.

Keywords

ion chamber arraylinear acceleratorOctavius detector 729quality assurance
Type
Original Articles
Information
Journal of Radiotherapy in Practice , Volume 14 , Issue 2 , June 2015 , pp. 194 - 201
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Copyright
© Cambridge University Press 2015 

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