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Does the γ dose distribution comparison technique default to the distance to agreement test in clinical dose distributions?
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10.1118/1.4811141
/content/aapm/journal/medphys/40/7/10.1118/1.4811141
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/40/7/10.1118/1.4811141

Figures

Image of FIG. 1.
FIG. 1.

Example of three γ evaluations; Zero (1), moderate (2), and steep (3) dose gradients. The angle that the γ vector makes to the dose axis is θ. For steep dose gradients, the value of θ is assumed to be sufficiently close to 90° that the evaluation is essentially entirely along the distance axis (e.g., equivalent to the distance-to-agreement test).

Image of FIG. 2.
FIG. 2.

Examples of the γ vector for two different sets of dose difference and distance to agreement (DTA) criteria. The evaluated dose distribution gradient is 1% mm in both cases. In case 1, the dose and DTA criteria are 3% and 2 mm, respectively, while in case 2, the dose and DTA criteria are 2% and 3 mm, respectively. θ are 34° and 56° for cases 1 and 2, respectively.

Image of FIG. 3.
FIG. 3.

Example showing that the γ evaluation vector is always normal to the evaluated distribution and, therefore, the γ angle θ is a function only of the evaluated dose renormalized dose gradient.

Image of FIG. 4.
FIG. 4.

Typical (a) prostate and (b) PTV histograms showing the relationship between dose and normalized dose gradient (as described by sinθ). These angles were based on α = 1%/mm, corresponding to 3%, 3 mm dose difference and distance to agreement criteria, respectively.

Image of FIG. 5.
FIG. 5.

Example dose and gradient histogram of the rectum for a prostate cancer treatment plan. (a) These angles were based on α = 1%/mm, corresponding to 3%, 3 mm dose difference and distance to agreement criteria, respectively. (b) These angles were based on α = 1.5%/mm, corresponding to 3%, 2 mm dose difference and distance to agreement criteria, respectively. (c) These angles were based on α = 0.67%/mm, corresponding to 2%, 3 mm dose difference and distance to agreement criteria, respectively.

Image of FIG. 6.
FIG. 6.

Histogram of the maximum sinθ, based on α = 1%/mm, for the rectum for prostate cancer patients.

Image of FIG. 7.
FIG. 7.

Relative frequency, presented proportional to the marker area, of dose difference and DTA criteria for published studies that used the γ dose distribution comparison technique. The most common set of criteria were 3% and 3 mm, but dose differences as large as 20% (off scale) and DTA agreements as large as 7 mm were also used. The smallest value of α was 0.17%/ mm, although most comparisons employed α ⩾ 1%/mm.

Image of FIG. 8.
FIG. 8.

sinθ as a function of α. For example, for a comparison where sinθ = 0.95 with α = 1%/mm, representing the cases studied in this paper, the same comparison would have sinθ = 0.82 if α = 0.5%/mm.

Tables

Generic image for table
TABLE I.

Characteristics of the dose distributions used in the evaluation.

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/content/aapm/journal/medphys/40/7/10.1118/1.4811141
2013-06-18
2014-04-24
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Does the γ dose distribution comparison technique default to the distance to agreement test in clinical dose distributions?
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/40/7/10.1118/1.4811141
10.1118/1.4811141
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