Original article Linac-based radiosurgery for multiple brain metastases: Comparison between two mono-isocenter techniques with multiple non-coplanar arcs Ruggero Ruggieri a,⇑ , Stefania Naccarato a , Rosario Mazzola a , Francesco Ricchetti a , Stefanie Corradini b , Alba Fiorentino a , Filippo Alongi a,c a Department of Radiation Oncology, IRCCS ‘Sacro Cuore don Calabria’, Negrar (VR), Italy; b Department of Radiation Oncology, University Hospital, LMU Munich, Germany; c University of Brescia, Italy article info Article history: Received 5 July 2018 Received in revised form 20 November 2018 Accepted 22 November 2018 Keywords: SRS VMAT Brain metastases HyperArc MultipleBrainMets abstract Background and purpose: Three mono-isocenter techniques with multiple non-coplanar arcs are nowa- days clinically available for linac-based stereotactic radiosurgery (SRS) of multiple brain metastases (BM): HyperArc (HA), Multiple Brain Mets (MBM), and Monaco-HDRS. Two of them, HA and MBM, are here compared in terms of plan-quality, and dosimetric consistency between planning and delivering. Materials and methods: For 20 patients with multiple BM (2–10), treated by mono-isocenter volumetric modulated arc therapy (VMAT) HA plans, mono-isocenter MBM dynamic conformal arc plans were gen- erated. Prescription dose (Dp) was 18–25 Gy, for single-fraction, and 21–27 Gy, for three-fractions. Mean overall Planning Target Volume (PTV), expanded by 2 mm from each lesion, was 9.6 cm 3 (0.5–27.9 cm 3 ). Dose normalization of 100%Dp at 98%PTV was adopted. Plan-quality was compared by the Paddick con- formity (CI) and gradient (GI) index, for the target, mean dose and V 12 volume, for the healthy brain, and number of monitor units (MU). Further, verification dosimetry by radiochromic films was performed for each plan, thus comparing also, by c-analysis, the consistency between in-phantom computed and mea- sured dose distributions. Results: CI significantly improved for HA plans, changing on average from 0.75 (MBM) to 0.94 (HA) (p < .001). No significant differences between HA and MBM plans were computed for GI (p = .216), and for mean dose (p = .436) and V 12 (p = .062) to the healthy brain; although V 12 increased on average from 23.7 cm 3 (HA) to 37.3 cm 3 (MBM). No significant difference resulted for MU (p = .107), whereas c (1 mm, 3%) and c (2 mm, 2%) passing-rates significantly improved for HA plans (p = .006; p = .023). Conclusions: HA plans assured a higher CI, while no significant difference resulted for any of the other planning metrics. Although on average slightly higher for HA plans, the dosimetric consistency between planned and delivered was satisfactory from both techniques. Hence, our judgement of near equal plan- quality from HA and MBM SRS-techniques. Ó 2018 Elsevier B.V. All rights reserved. Radiotherapy and Oncology xxx (2018) xxx–xxx Brain metastases BM are the most common intracranial tumors in adults: about 20–40% of cancer patients will develop BM in their oncological history [1]. In the past, patients with multiple BM were typically treated by whole-brain radiotherapy (WBRT). Radio- surgery, both as single-fraction (SRS) and as 3–5 fractions (FSRT) stereotactic radiotherapy, has also gained importance in this treat- ment setting [2], given the increased risk of detriment in neurocog- nitive functions for patients undergoing WBRT [3,4], without any improvement in overall survival (OS) as compared to SRS/FSRT [5,6]. Although SRS is now widely used for patients with 4 BM [5,7], Yamamoto et al. [8] have shown similar OS for patients with 5–10 BM when compared to patients with 2–4 BM, thus suggesting that the use of SRS/FSRT may be appropriate even in patients with up to 10 BM [9]. Such a clinical framework created the need for a technical solution which, while reproducing for multiple BM simi- lar dose-gradient steepness and target dose conformity to single- lesion SRS, could be performed within 20 min at the treatment machine. For linacs, a mono-isocentric approach by multiple non- coplanar arcs was then proposed. Treatment time was shortened enough, because the use of one isocenter involves one IGRT ses- sion, but the use of large fields, to cover many distinct lesions, also posed optimization problems for the kinetics of the leaves of the https://doi.org/10.1016/j.radonc.2018.11.014 0167-8140/Ó 2018 Elsevier B.V. All rights reserved. ⇑ Corresponding author at: IRCCS ‘Sacro cuore don Calabria’, Via don A. Sempreboni 5, 37024 Negrar, VR, Italy. E-mail address: ruggero.ruggieri@sacrocuore.it (R. Ruggieri). Radiotherapy and Oncology 132 (2019) 70–78 Contents lists available at ScienceDirect Radiotherapy and Oncology journal homepage: www.thegreenjournal.com