P164] Dosimetric comparison between CyberKnife and VMAT treatment plans for radiosurgery

Abstract

Purpose Two advanced modalities for radiosurgery treatment in selected patients with brain lesions are CyberKnife (CK) and volumetric arc therapy (VMAT) through a TrueBeam Linac. We aim to evaluate and compare multiple radiosurgery metrics between both modalities to establish the benefits when treating with each one. Methods 13 patients having single brain lesions were used to create plans on each system, which were performed according to their usual methodologies, meaning stronger maximum dose restriction for VMAT. The comparison was performed by means of Pearson and Wilcoxon tests of various representative parameters distributions, such as: Conformity Index, Paddick Conformity Index, Homogeneity Index, Gradient Index, tissue volume receiving more than 12 and 10 Gy, beam-on time (BOT), Monitor Units (MU), as well as the V10%, V25%, V50% and V80% isodose volumes. Also, maximum and mean doses were taken for several organs at risk (OARs). Results Being both systems set to have the same coverage, the tumor volume received significantly more dose in CK plans, which agrees with the better homogeneity achieved in VMAT plans (μ ± σ = 1.25 ± 0.06 (CK) vs. 1.09 ± 0.03 (VMAT), p Both systems showed comparable results in terms of conformity (p = 0.388). Maximum dose for skin was significantly smaller for CK (μ ± σ = 5.0 ± 2.6 (CK) vs. 6.6 ± 3.4 (VMAT) Gy, p CK showed significantly steeper gradients (μ ± σ = 4.3 ± 1.1 (CK) vs. 5.8 ± 2.3 (VMAT) cc, p = 0.002), significantly more MU (μ ± σ = 22,177 ± 11,295 (CK) vs 3405 ± 1093 (VMAT), p Regarding dose spread, V10% indicated no significant difference, unlike V20%, V50% and V80% that showed progressively smaller values for CK (50%, 35% and 19% respectively, p The mean volume of brain receiving 12 Gy achieved better results for CK (μ ± σ = 6.5 ± 11.6 (CK) vs. 10.1 ± 18.5 (VMAT) cc, p Conclusions Considering different planning methodologies, preliminary results show that in general equivalent quality can be achieved using both modalities, with the distinctive feature that in cases OARs are adjacent to the target, CK would be a better option since steeper gradients can be achieved. On the other hand, VMAT could benefit from the reduced MUs and BOT. Further studies are being held where the methodology used for CK is performed for VMAT, regarding optimization objectives and beam geometry, expecting to improve gradient when planning with VMAT.