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Original Article

Korean Journal of Medical Physics 2014; 25(3): 185-192

Published online September 30, 2014

Copyright © Korean Society of Medical Physics.

Analysis of Output Constancy Checks Using Process Control Techniques in Linear Accelerators

Se An Oh*, Ji Woon Yea*, Sang Won Kim*, Rena Lee, Sung Kyu Kim*

*Department of Radiation Oncology, Yeungnam University Medical Center, Department of Radiation Oncology, Yeungnam University College of Medicine, Daegu, Department of Radiation Oncology, School of Medicine, Ewha Womans University, Seoul, Korea

Received: April 29, 2014; Revised: September 1, 2014; Accepted: September 4, 2014

Abstract

The purpose of this study is to evaluate the results for the quality assurance through a statistical analysis on the output characteristics of linear accelerators belonging to Yeungnam University Medical Center by using the Shewhart-type chart, Exponentially weighted moving average chart (EWMA) chart, and process capability indices Cp and Cpk. To achieve this, we used the output values measured using respective treatment devices (21EX, 21EX-S, and Novalis Tx) by medical physicists every month from September, 2012 to April, 2014. The output characteristics of treatment devices followed the IAEA TRS-398 guidelines, and the measurements included photon beams of 6 MV, 10 MV, and 15 MV and electron beams of 4 MeV, 6 MeV, 9 MeV, 12 MeV, 16MeV, and 20 MeV. The statistical analysis was done for the output characteristics measured, and was corrected every month. The width of control limit of weighting factors and measurement values were calculated as ?= 0.10 and L=2.703, respectively; and the process capability indices Cp and Cpk were greater than or equal to 1 for all energies of the linear accelerators (21EX, 21EX-S, and Novalis Tx). Measured values of output doses with drastic and minor changes were found through the Shewhart-type chart and EWMA chart, respectively. The process capability indices Cp and Cpk of the treatment devices in our institution were, respectively, 2.384 and 2.136 for 21EX, 1.917 and 1.682 for 21EX-S, and 2.895 and 2.473 for Novalis Tx, proving that Novalis Tx has the most stable and accurate output characteristics.

KeywordsOutput characteristics, Linear accelerator, Quality assurance, Process capability, Processability

Korean Society of Medical Physics

Vol.34 No.4
December 2023

pISSN 2508-4445
eISSN 2508-4453
Formerly ISSN 1226-5829

Frequency: Quarterly

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