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Purpose: Recent advances in automated treatment planning demonstrated improved plan quality and best practice reducing routine planning workload. In this study, a not yet commercially available fully-automated lexicographic optimisation planning, called mCycle (Elekta AB, Stockholm), was validated for intracranial stereotactic radiosurgery (SRS). Material and methods: Twenty-one single-lesion SRS treatment plans (21 Gy/1 fx) delivered between November 2019 and December 2021 were retrospectively selected and re-planned by mCycle (Monaco 5.59.13). Constraints and objectives were sequentially optimized by multi-criterial optimization (MCO) according to an a-priori assigned priority list, a so-called Wish List (WL). Four patient sets were used to achieve a robust WL. All plans were optimized with 2 coplanar 140°-arcs and calculated with the Monte Carlo algorithm (1 mm-dose grid, 0.5%-statistical uncertainty). The main criteria for planning approval was a brain volume receiving more than 12 Gy less than 10 cm³ (V12Gy < 10 cm3 ). A target coverage as high as possible was requested, with at least the 80% of the prescription dose covering the 99% of the PTV. Manual plans (MP) and mCycle plans (mCP) were compared in terms of dose-volume constraints and monitor units (MUs). Statistical significance was assessed performing the Wilcoxon Mann Whitney test with Bonferroni correction for multiple tests (alpha=0.05). Plan deliverability was verified by pretreatment QA. Results: The 21 mCP re-planning took only 5 working days. Dose statistic comparison is reported in Table 1. Plan comparison showed a statistically significant increase in target dose coverage, both for CTVs and PTVs, without significantly increasing the near-maximum doses. The PTV Paddick’s conformity index (CI) was equally improved and the brain V12Gy in mCP was comparable to the one in MP. Other organs at risk (OARs) were never significantly interested by clinically relevant doses. These results were obtained with a lower median number of MU (-11.6%) even if this difference was not statistically significant and plans registered a comparable gamma analysis (local 2%/2mm). Conclusions: The novel mCycle autoplanning produced high-quality clinically acceptable radiosurgery plans with coplanar arcs significantly reducing the overall planning time: the planning of one MP and one mCP took about 1 working day and 2 hours, respectively. While the OAR sparing was comparable between MP and mCP, the target coverage was significantly increased, reducing the MU number and preserving the plan deliverability. The validation showed the mCycle capability to generate high-quality deliverable plans according to institutional-specific planning protocols. [ABSTRACT FROM AUTHOR]