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Statistical variability and confidence intervals for planar dose QA pass rates
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10.1118/1.3651695
/content/aapm/journal/medphys/38/11/10.1118/1.3651695
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/38/11/10.1118/1.3651695

Figures

Image of FIG. 1.
FIG. 1.

1 det/cm2 pass rate distributions for one H&N field, 100 low-density positional iterations, with: uniform grid and (c,2,2,L) in gray; uniform grid and (c,2,2,Gmax) in black; random grid and (c,2,2,Gmax) in horizontal stripes.

Image of FIG. 2.
FIG. 2.

2 det/cm2 pass rate distributions for the same H&N case as from Fig. 1 with: uniform grid and (c,2,2,L) in gray; uniform grid and (c,2,2,Gmax) in black; random grid and (c,2,2,L) in horizontal stripes.

Image of FIG. 3.
FIG. 3.

1 det/cm2 pass rate distributions for the same H&N case as from Figs. 1 and 2 with: uniform grid and (c,3,3,L) in gray; uniform grid and (c,3,3,Gmax) in black; random grid and (c,3,3,L) in horizontal stripes.

Image of FIG. 4.
FIG. 4.

A brain IMRT field as measured (left side) and compared (right side) via MAPCHECK at two different positions with respect to the delivered dose plane: (A) with the center of the MAPCHECK at the beam CAX; and (B) with the center of the MAPCHECK shifted 1.6 cm from CAX in the superior direction. Hot and cold spots are indicated by white and black marks, respectively, and the solid vertical line indicates the position of the dose profiles shown in Fig. 5.

Image of FIG. 5.
FIG. 5.

The co-located superior–inferior dose profiles illustrated in Fig. 4, with original diode positions indicated by round markers, shifted diode positions indicated by square markers, and hot and cold spots indicated by white and black marks, respectively.

Image of FIG. 6.
FIG. 6.

Pass rate distributions for the brain IMRT field referenced in Figs. 4 and 5, with (c,2,2,Gmax) analysis shown in gray and (c,3,3,Gmax) analysis shown in black. High density pass rates for these analyses were 83.1% and 95.6%, respectively.

Image of FIG. 7.
FIG. 7.

95% confidence interval coverage for the normal and Wilson methods, with HD pass rate varying from 75% to 95%, sample pass rates following a binomial distribution about the HD pass rate per iteration (1 000 000), and average samples sizes of 50, 250, 500, and 1000.

Tables

Generic image for table
TABLE I.

Pass rate (%) variation: %/DTA composite vs gamma analysis—Displayed percentages are calculated by subtracting the %/DTA composite pass rate from the gamma evaluation pass rate for each field, then finding the median, mean, minimum, maximum, and standard deviation of these differences. 95% confidence intervals about the median and respective p-values (5% significance level) are calculated via the Wilcoxon paired significance test (Ref. 22).

Generic image for table
TABLE II.

Pass rate (%) variation: Global vs local normalization—Displayed percentages are calculated by subtracting the locally normalized pass rate from the globally normalized pass rate for each field, then finding the median, mean, minimum, maximum, and standard deviation of these differences. 95% confidence intervals about the median and respective p-values (5% significance level) are calculated via the Wilcoxon paired significance test (Ref. 22).

Generic image for table
TABLE III.

Pass rate (%) variation: Global vs local normalization—Pass rate spread for the individual prostate field and H&N field with highest differences between global and local normalization (as shown in Table II).

Generic image for table
TABLE IV.

H&N low-density pass rate distributions: 10 H&N fields, sampled to 1 det/cm2 with 100 positional iterations, and analyzed with (c,2,2,L) criteria. For each field, the high density (HD) pass rate is displayed along with the average, minimum, maximum, and standard deviation of the distribution of low-density (LD) pass rates.

Generic image for table
TABLE V.

Confidence interval coverage: Percentage of iterations for which the HD pass rate fell within the 95% confidence intervals calculated with the binomial distribution [normal approximation, Eq. (5)].

Generic image for table
TABLE VI.

Confidence interval coverage: Percentage of iterations for which the HD pass rate fell within the 95% confidence intervals calculated with the binomial distribution [Wilson approximation, Eq. (6)].

Generic image for table
TABLE VII.

Fixed pass rate simulation summary: The coverage and width of normal approximation (CI N ) and Wilson (CI W ) confidence intervals (95%), with HD pass rate fixed at 75% (an atypically low value, possibly indicating error), 85% and 95% (roughly the average for 2%, 2 mm and 3%, 3 mm analysis, respectively), sample size selected by a Poisson distribution about the average sample size, and sample pass rate varied by the binomial distribution about the HD pass rate for each tier.

Generic image for table
TABLE VIII.

Random pass rate simulation summary: The coverage and width of normal approximation (CI N ) and Wilson (CI W ) confidence intervals (95%), with HD pass rate and sample size allowed to vary randomly between values typical for prostate and H&N cases. The low and high average sample sizes represent approximate average sample sizes for 1 det/cm2 and 2 det/cm2 grids, respectively.

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/content/aapm/journal/medphys/38/11/10.1118/1.3651695
2011-10-20
2014-04-18
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Statistical variability and confidence intervals for planar dose QA pass rates
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/38/11/10.1118/1.3651695
10.1118/1.3651695
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