Radiosurgery of multiple brain metastases with single-isocenter dynamic conformal arcs (SIDCA)

Purpose: To propose single-isocenter dynamic conformal arcs (SIDCA), a novel technique for radiosurgery of multiple brain metastases, and to compare SIDCA with volumetric modulated arc therapy (VMAT) and multiple-isocenter dynamic conformal arcs (MIDCA) for plan quality.

Methods and materials: SIDCA, MIDCA, and VMAT plans were created on 6 patients with 3-5 metastases. Plans were evaluated using Radiation Therapy Oncology Group conformity index (RCI), Paddick conformity index (PCI), gradient index (GI), volumes that received more than 100% (V(100%)), 50% (V(50%)), 25% (V(25%)) and 10% (V(10%)) of prescription dose, total monitor units (MUs), and delivery time (DT).

Results: SIDCA achieved conformal plans (RCI = 1.38 ± 0.12, PCI = 0.72 ± 0.06) with steep dose fall-off (GI = 3.97 ± 0.51). MIDCA plans had comparable plan quality and MUs as SIDCA, but 52% longer DT. The VMAT plans had better conformity (RCI = 1.15 ± 0.09, p < 0.01 and PCI = 0.86 ± 0.06, p < 0.01) than SIDCA, worse GI (4.34 ± 0.46, p < 0.01), higher V(25%) (p = 0.05) and V(10%) (p = 0.02), 49% less MUs and 46% shorter DT.

Conclusions: All three techniques achieved conformal plans with steep dose fall-off from targets. SIDCA plans had similar plan quality as MIDCA but more efficient to delivery. SIDCA plans had lower peripheral dose spread than VMAT; VMAT plans had better conformity and faster delivery time than SIDCA.