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Statistical process control for radiotherapy quality assurance
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10.1118/1.2001209
/content/aapm/journal/medphys/32/9/10.1118/1.2001209
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/32/9/10.1118/1.2001209

Figures

Image of FIG. 1.
FIG. 1.

(a) The average chart for theoretical data from a normal distribution. The data are sampled from a normal distribution with mean and standard deviation and . Sixty subgroup averages are plotted based on a total of 240 values sampled from the normal distribution. The subgroup size was . The thick dashed lines are the process behavior limits and the thin dashed lines are the limits calculated by one standard deviation. Data with open circles indicate those points that were used to calculate the limits. (b) The range chart for theoretical data from a normal distribution. Each point represents the range of each subgroup that was plotted in Fig. 1(a). The open circles indicate the subgroup ranges that were used to calculate the process behavior limits indicated in the figure by a dashed line.

Image of FIG. 2.
FIG. 2.

(a) The average chart for theoretical data with known systematic variations. The data are sampled from a normal distribution with varying mean and standard deviation as shown in Table I. Sixty plotted values and a total of 240 values subgroup size . The thick dashed lines are the process behavior limits and the thin dashed lines are the limits calculated by one standard deviation. Data with open circles indicate those points that were used to calculate the limits. (b) The range chart for theoretical data with known systematic errors. The range of each subgroup in Fig. 2(a) is plotted. Data with open circles indicate those points that were used to calculate the limits.

Image of FIG. 3.
FIG. 3.

(a) The average chart for the clinical case. Subgroup size is used to verify the constancy of the flatness and symmetry. The thick dashed lines are the process behavior limits and the thin dashed lines are the limits calculated by one standard deviation. Data with open circles indicate those points that were used to calculate the limits. (b) The range chart of the four periphery ion chambers in the RBA-5 device. The range of each subgroup in Fig. 3(a) is plotted. Data with open circles indicate those points that were used to calculate the limits.

Image of FIG. 4.
FIG. 4.

(a) The average chart for the clinical case. Subgroup of size 1 is used to verify the constancy of central axis output. The thick dashed lines are the process behavior limits and the thin dashed lines are the limits calculated by one standard deviation. Data with open circles indicate those points that were used to calculate the limits. (b) The moving range chart of the central axis ion chambers in the RBA-5 device. Consecutive values in Fig. 4(a) are plotted as the range. Data with open circles indicate those points that were used to calculate the limits.

Image of FIG. 5.
FIG. 5.

(a) The average chart for the clinical case. Subgroup size is used to verify the constancy of the flatness and symmetry. The thick dashed lines are the process behavior limits and the thin dashed lines are the limits calculated by the standard deviation. The process behavior limits have been recalculated after a change in the process was detected as shown in Fig. 3(a). (b) The range chart of the four periphery ion chambers in the RBA-5 device. The range of each subgroup in Fig. 5(a) is plotted with new process behavior limits.

Image of FIG. 6.
FIG. 6.

(a) The average chart for the clinical case. Subgroup of size 1 is used to verify the constancy of central axis output. The thick dashed lines are the process behavior limits and the thin dashed lines are the limits calculated by the standard deviation. The process behavior limits have been recalculated after a change in the process was detected as shown in Fig. 3(a). (b) The moving range chart of the central axis ion chambers in the RBA-5 device. The range of each subgroup in Fig. 6(a) is plotted with new process behavior limits.

Image of FIG. 7.
FIG. 7.

This flow chart describes the interactive nature of SPC and the use of process behavior charts. It outlines the activity of identifying and removing systematic errors to reduce variation in the process of daily output and flatness/symmetry quality assurance.

Tables

Generic image for table
Generic image for table
TABLE I.

The mean and standard deviation of the normal distribution from which the data are sampled for our hypothetical cases. Each data point consists of four values (subgroup size ) sampled from the normal distribution for a total of 240 individual values sampled from the normal distribution.

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/content/aapm/journal/medphys/32/9/10.1118/1.2001209
2005-08-22
2014-04-17
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Statistical process control for radiotherapy quality assurance
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/32/9/10.1118/1.2001209
10.1118/1.2001209
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