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

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).El Shafie et al. SI-VMAT vs. CyberKnife for Multiple BMConclusion: 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.

Radiosurgery for Five to Fifteen Brain Metastases: A Single Centre Experience and a Review of the Literature

“…SI-VMAT plans can be optimized to improve dosimetric parameters at the expense of number of arcs and MUs ( 50 ). A series of SI-VMAT plans for more than five brain metastases generated with 5mm MLCs reported comparatively poor GIs of 5.0 -5.6 ( 51 ). According to Ohira et al, optimization of the collimator angle ( 52 ) can achieve better sparing of healthy brain, although additional jaw tracking did not yield a benefit ( 53 ).…”

Radiosurgery for multiple brain metastases using volumetric modulated arc therapy: a single institutional series

“…The gradient dose outside the target was steeper for CK (p < 0.001). Estimated treatment time was shorter for VMAT (13.7 minutes) than for CK (130 minutes) (p < 0.001) [28]. LINAC, GK, and CK were dosimetrically compared in 10 patients with two or more large lesions (median: 18.31 cm 3 ).…”

Development of a 3D printed phantom for commissioning and quality assurance of multiple brain targets stereotactic radiosurgery

“…The single plan technique (SPT) for brain multiple targets (MBT) stereotactic radiosurgery (SRS) is becoming widely used due to its time-saving benefits in planning and delivery [ 1 – 5 ]. This technique involves a high dose prescription and tight target margins which requires comprehensive and stringent quality assurance (QA) measures.…”