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. 2023 Apr-Jun;48(2):120-128.
doi: 10.4103/jmp.jmp_82_22. Epub 2023 Jun 29.

Multiple Brain Metastases Radiosurgery with CyberKnife Device: Dosimetric Comparison between Fixed/Iris and Multileaf Collimator Plans

Anna Ianiro  1 , Erminia Infusino  1 , Marco D'Andrea  1 , Laura Marucci  2 , Alessia Farneti  2 , Francesca Sperati  3 , Bartolomeo Cassano  1 , Sara Ungania  1 , Antonella Soriani  1
Affiliations

Multiple Brain Metastases Radiosurgery with CyberKnife Device: Dosimetric Comparison between Fixed/Iris and Multileaf Collimator Plans

Anna Ianiro et al. J Med Phys. 2023 Apr-Jun.

Abstract

Purpose: In our institution, stereotactic radiosurgery of multiple brain metastases is performed with the CyberKnife® (CK) device, using fixed/Iris collimators. In this study, nineteen fixed/Iris plans were recalculated with the multileaf collimator (MLC), to assess if it is possible to produce plans with comparable dosimetric overall quality.

Materials and methods: For consistent comparisons, MLC plans were re-optimized and re-normalized in order to achieve the same minimum dose for the total planning target volume (PTVtot). Conformation number (CN), homogeneity index (HI) and dose gradient index (DGI) metrics were evaluated. The dose to the brain was evaluated as the volume receiving 12 Gy (V12) and as the integral dose (ID). The normal tissue complication probability (NTCP) for brain radionecrosis was calculated as a function of V12.

Results: The reoptimized plans were reviewed by the radiation oncologist and were found clinically acceptable according to the The American Association of Physicists in Medicine (AAPM) Task Group-101 protocol. However, fixed/Iris plans provided significantly higher CN (+8.6%), HI (+2.2%), and DGI (+44.0%) values, and significantly lower ID values (-35.9%). For PTVtot less than the median value of 2.58cc, fixed/Iris plans provided significantly lower NTCP values. On the other side, MLC plans provided significantly lower treatment times (-18.4%), number of monitor units (-33.3%), beams (-46.0%) and nodes (-21.3%).

Conclusions: CK-MLC plans for the stereotactic treatment of brain multi metastases could provide an important advantage in terms of treatment duration. However, to contain the increased risk for brain radionecrosis, it could be useful to calculate MLC plans only for patients with large PTVtot.

Keywords: Brain radiosurgery; CyberKnife®; dosimetric comparison.

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Conflict of interest statement

There are no conflicts of interest.

Figures

Figure 1
Figure 1
Spearman’s correlation heatmaps obtained for (a) fixed plans and for (b) MLC plans. MLC: Multileaf collimator
Figure 2
Figure 2
Correlation between (a) the treatment time and the number of lesion, and (b) the number of MUs and the number of lesion, for both datasets. MUs: Monitor units
Figure 3
Figure 3
Correlation between (a) V12 and PTVtot and between (b) V12 and DGI, for both datasets. DGI: Dose gradient index, PTVtot: Total planning target volume, DGI: Dose gradient index
Figure 4
Figure 4
Dose distribution comparison between (a) MLC and (b) fixed/Iris plans, for a representative patient; (c) DVH comparison between fixed/iris (solid line) and MLC (dashed line) plans for the same patient. MLC: Multileaf collimator, DVH: Dose Volume Histogram
Figure 5
Figure 5
BEV comparison between (a) MLC and (b) fixed/Iris plans, from a similar node. The margin around the same metastasis is highlighted by a cyan rectangle for MLC and by a green circle for fixed/Iris collimator. MLC: Multileaf collimator, BEV: Beam Eye View
See this image and copyright information in PMC

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