Single-Isocenter Volumetric Modulated Arc Therapy vs. CyberKnife M6 for the Stereotactic Radiosurgery of Multiple Brain Metastases

Rami A El Shafie; Eric Tonndorf-Martini; Daniela Schmitt; Aylin Celik; Dorothea Weber; Kristin Lang; Laila König; Simon Höne; Tobias Forster; Bastian von Nettelbladt; Sebastian Adeberg; Jürgen Debus; Stefan Rieken; Denise Bernhardt

doi:10.3389/fonc.2020.00568

Single-Isocenter Volumetric Modulated Arc Therapy vs. CyberKnife M6 for the Stereotactic Radiosurgery of Multiple Brain Metastases

Front Oncol. 2020 May 8:10:568. doi: 10.3389/fonc.2020.00568. eCollection 2020.

Authors

Rami A El Shafie^{1

2}, Eric Tonndorf-Martini^{1

2}, Daniela Schmitt^{1

2}, Aylin Celik^{1

2}, Dorothea Weber³, Kristin Lang^{1

2}, Laila König^{1

2}, Simon Höne^{1

2}, Tobias Forster^{1

2}, Bastian von Nettelbladt^{1

2}, Sebastian Adeberg^{1

2}, Jürgen Debus^{1

2

4

5}, Stefan Rieken^{1

2

6}, Denise Bernhardt^{1

2}

Affiliations

¹ Department of Radiation Oncology, Heidelberg University Hospital, Heidelberg, Germany.
² National Center for Radiation Oncology (NCRO), Heidelberg Institute for Radiation Oncology (HIRO), Heidelberg, Germany.
³ Institute of Medical Biometry and Informatics (IMBI), Heidelberg University Hospital, Heidelberg, Germany.
⁴ Clinical Cooperation Unit Radiation Oncology (E050), German Cancer Research Center (DKFZ), Heidelberg, Germany.
⁵ Deutsches Konsortium für Translationale Krebsforschung (DKTK), Partner Site Heidelberg, German Cancer Research Center (DKFZ), Heidelberg, Germany.
⁶ Department of Radiation Oncology, University Medical Center Göttingen, Göttingen, Germany.

Abstract

Introduction: Stereotactic radiosurgery (SRS) is becoming more frequently used for patients with multiple brain metastases (BMs). Single-isocenter volumetric modulated arc therapy (SI-VMAT) is an emerging alternative to dedicated systems such as CyberKnife (CK). We present a dosimetric comparison between CyberKnife M6 and SI-VMAT, planned at RayStation V8B, for the simultaneous SRS of five or more BM. Patients and Methods: Twenty treatment plans of CK-based single-session SRS to ≥5 brain metastases were replanned using SI-VMAT for delivery at an Elekta VersaHD linear accelerator. Prescription dose was 20 or 18 Gy, conformally enclosing at least 98% of the total planning target volume (PTV), with PTV margin-width adapted to the respective SRS technique. Comparatively analyzed quality metrics included dose distribution to the healthy brain (HB), including different isodose volumes, conformity, and gradient indices. Estimated treatment time was also compared. Results: Median HB isodose volumes for 3, 5, 8, 10, and 12 Gy were consistently smaller for CK-SRS compared to SI-VMAT (p < 0.001). Dose falloff outside the target volume, as expressed by the gradient indices GI_high and GI_low, was consistently steeper for CK-SRS compared to SI-VMAT (p < 0.001). CK-SRS achieved a median GI_high of 3.1 [interquartile range (IQR), 2.9-1.3] vs. 5.0 (IQR 4.3-5.5) for SI-VMAT (p < 0.001). For GI_low, the results were 3.0 (IQR, 2.9-3.1) for CK-SRS vs. 5.6 (IQR, 4.3-5.5) for SI-VMAT (p < 0.001). The median conformity index (CI) was 1.2 (IQR, 1.1-1.2) for CK-SRS vs. 1.5 (IQR, 1.4-1.7) for SI-VMAT (p < 0.001). Estimated treatment time was shorter for SI-VMAT, yielding a median of 13.7 min (IQR, 13.5-14.0) compared to 130 min (IQR, 114.5-154.5) for CK-SRS (p < 0.001). Conclusion: SI-VMAT offers enhanced treatment efficiency in cases with multiple BM, as compared to CyberKnife, but requires compromise regarding conformity and integral dose to the healthy brain. Additionally, delivery at a conventional linear accelerator (linac) may require a larger PTV margin to account for delivery and setup errors. Further evaluations are warranted to determine whether the detected dosimetric differences are clinically relevant. SI-VMAT could be a reasonable alternative to a dedicated radiosurgery system for selected patients with multiple BM.

Keywords: linear accelerator; multiple brain metastases; palliative; radiosurgery; radiotherapy; robotic radiosurgery; stereotactic; whole-brain radiotherapy.