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Estimation of optimal margin for intrafraction movements during frameless brain radiosurgery
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Image of FIG. 1.
FIG. 1.

(a) An example for intrafraction movement during a CyberKnife treatment. Statistical distributions for (b) mean positions and (c) standard deviations for the intrafraction movements. In (b) and (c), the probabilities are normalized to 262 radiosurgery fractions.

Image of FIG. 2.
FIG. 2.

Minimum dose on the 1.5-cm spherical pCTV (circles) as a function of the effective radial displacement for (a) systematic- and (b) random-error models generated by random-number generation method. In each figure, the minimum-, mean-, and maximum-dose curves for planned dose are superimposed as a function of radial displacement.

Image of FIG. 3.
FIG. 3.

Minimum pCTV doses (dots) with the effective radial displacement of actual patients' intrafraction movements for spherical targets with radii of (a) 1.0, (b) 1.5, and (c) 2.0 cm, respectively, for ellipsoidal targets with their longest axes along (d) SI and (e) LR axes, respectively, and for (f) arbitrary-shaped target. In each figure, the radial dose-gradient curves for each planned dose distribution are superimposed.

Image of FIG. 4.
FIG. 4.

(a) Population distributions of effective displacements and (b) time dependency in overall average of mean deviations (open circles) and standard deviations (error bars) in 262 radiosurgery fractions. In (a), the probabilities is normalized to 262 radiosurgery fractions. In (b), “tot” denoted in horizontal axis means no cut-off time setting in analysis of intrafraction movements.

Image of FIG. 5.
FIG. 5.

Axial (left) and sagittal (right) planes of three-dimensional population map for intra-fraction movements. The brighter (darker) color represents the higher (lower) probabilities for the intra-fraction movements. The optimal ellipsoid geometries at given confidence levels are indicated by white lines in each plane.

Image of FIG. 6.
FIG. 6.

Dose variations in outside the target volume induced by intrafraction movements are plotted as a function of the distance from the target boundary for the (a) 1 and (b) 2-cm-radius spheres. The filled boxes indicate the average planned dose for 50 sampling points around the target volume. The upper and lower bounds of error bar show the tenth percentiles from the top and bottom of the resultant dose population after applying the intrafraction movements, respectively.


Generic image for table

Optimal margins for intrafraction movements during frameless radiosurgery at various threshold elapsed times and confidence levels.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Estimation of optimal margin for intrafraction movements during frameless brain radiosurgery