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An improved MLC segmentation algorithm and software for step-and-shoot IMRT delivery without tongue-and-groove error
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10.1118/1.2188823
/content/aapm/journal/medphys/33/5/10.1118/1.2188823
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/33/5/10.1118/1.2188823

Figures

Image of FIG. 1.
FIG. 1.

(a) A schematic drawing of a multileaf collimator (MLC), where the shaded rectangles represent the MLC leaves which can move up and down (as indicated by the arrows) to form an MLC aperture, and the unshaded rectangles represent the backup diaphragms (or collimator jaws) that form a bounding box of the MLC aperture shaped by the MLC leaves. (b) An intensity map (IM).

Image of FIG. 2.
FIG. 2.

(a) Illustrating the tongue-and-groove (TG) feature of the MLC. (b) When the side of leaf B is at the field boundary, there is an underdose due to the protrusion of the tongue into the field. (c) The underdose areas of the tongue-and-groove feature on an MLC aperture shape.

Image of FIG. 3.
FIG. 3.

Illustrating the tongue-and-groove error. (a) and (b) Two MLC apertures (the shaded rectangles represent MLC leaves). (c) When delivering the two MLC apertures in (a) and (b) (one by one), the groove side of leaf B and the tongue side of leaf C are both used for field shaping, causing a tongue-and-groove error in the area between the leaves B and C. (d) Illustrating a “dip” in the combined fluence profile, which causes underdose in the final dose distribution where the tongue-and-groove error occurs.

Image of FIG. 4.
FIG. 4.

Comparisons of dose profiles perpendicular to the leaf motion direction for each individual beam. The vertical axis is for the absolute dose, and the horizontal axis indicates positions along the MLC leaf motion direction. The profiles on the left are from the plans and the profiles on the right are from the SLS plans. The tongue-and-groove errors in the SLS plans are indicated by the dark colored arrows.

Image of FIG. 5.
FIG. 5.

Comparisons of normalized dose distributions on the coronal plane, (a) The plan isodose lines: 90%, 85%, 75%, 60%, and 45%. (b) The SLS plan isodose lines: 90%, 85%, 75%, 60%, and 45%.

Image of FIG. 6.
FIG. 6.

The tradeoff curves between the number of segments and tongue-and-groove error. (a) A pancreatic case intensity map of size and a maximum intensity level of 5. (b) A prostate case intensity map of size and a maximum intensity level of 5.

Image of FIG. 7.
FIG. 7.

The tradeoff curves between the number of segments and tongue-and-groove error. (a) A pancreatic case intensity map of size and a maximum intensity level of 5. (b) A prostate case intensity map of size and a maximum intensity level of 5.

Image of FIG. 8.
FIG. 8.

Illustrating the tongue error and groove error as functions defined on the axis. (a) An MLC aperture. (b) The tongue error and groove error of the MLC leaf pair caused by the delivery of the MLC aperture in (a).

Image of FIG. 9.
FIG. 9.

Illustrating the relation between the tongue-and-groove and tongue-or-groove errors. (a) A set of two MLC apertures. (b) The groove error of the leaf pair and the tongue error of the leaf pair . (c) The tongue-and-groove error function and tongue-or-groove error function of the two MLC apertures in (a) (the tongue-and-groove error is twice the size of the intersection of the tongue error and groove error, as shown in Sec. ???). (d) The matrices of the two MLC apertures in (a) (assuming that the MLC apertures are both of a unit level). (e) The dose distribution created by the MLC apertures in (a). (f) The absolute differences between the two columns of the dose distribution in (e). (g) , which is the function corresponding to the absolute differences in (f).

Tables

Generic image for table
TABLE I.

A tradeoff table computed by our new algorithm for tongue-or-groove error, in which denotes the maximum intensity level, # denotes the number of segments, denotes the amount of tongue-or-groove error (in %), and denotes the estimated treatment time (in minutes), on an Elekta SL20 series linear accelerator (the estimations are based on typical intersegment delays on the Elekta SL20 MLC systems).

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/content/aapm/journal/medphys/33/5/10.1118/1.2188823
2006-04-12
2014-04-20
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: An improved MLC segmentation algorithm and software for step-and-shoot IMRT delivery without tongue-and-groove error
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/33/5/10.1118/1.2188823
10.1118/1.2188823
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