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

Anna Ianiro; Erminia Infusino; Marco D'Andrea; Laura Marucci; Alessia Farneti; Francesca Sperati; Bartolomeo Cassano; Sara Ungania; Antonella Soriani

doi:10.4103/jmp.jmp_82_22

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

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

Authors

Anna Ianiro¹, Erminia Infusino¹, Marco D'Andrea¹, Laura Marucci², Alessia Farneti², Francesca Sperati³, Bartolomeo Cassano¹, Sara Ungania¹, Antonella Soriani¹

Affiliations

¹ Department of Medical Physics, IRCCS Regina Elena National Cancer Institute - IFO, Rome, Italy.
² Department of Radiation Oncology, IRCCS Regina Elena National Cancer Institute - IFO, Rome, Italy.
³ Department of Biostatistics and Bioinformatics, Clinical Trial Center, IRCCS San Gallicano Dermatological Institute - IFO, Rome, Italy.

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 (PTV_tot). 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 PTV_tot 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 PTV_tot.

Keywords: Brain radiosurgery; CyberKnife®; dosimetric comparison.