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Objective: To increase the quality of life of patients with multiple brain metastases, stereotactic radiosurgery (SRS)/ stereotactic radiotherapy (SRT) is increasingly used. Here we report our experience with robotic SRS/SRT concomitanly delivered to multiple (≥5) brain metastasis.

Methods: From March 2018 to December 2020 a total of 269 brain metastases in 24 pts (13 females and 11 males) were treated with a single treatment plan SRS/SRT in our institution. Primary site of tumors was lung in ten pts, breast in six pts, melanoma in four pts, kidney in one patient, two patients had lung and breast cancer and another one had lung and prostate cancer. Five pts previously underwent Whole Brain Radiotherapy (WBRT). Gross target volume (GTV) and organs at risk (OAR) were defined on fused computer tomography (CT) and contrast-enhanced T1-weighted MRI images. Planning target volume (PTV) was defined adding a 1 mm margin to GTV. All fractions were delivered in consecutive days. All pts received preventive steroid therapy; median dose was 4 mg/day (2-16 mg). Toxicity was scored in accordance with the CTCAE scale v.4.0. Patients were followed-up with contrast-enhanced MRI every 3 months.

Results: Patient's median age was 51.6 (29-84) years and median Karnofsky Performance Score (KPS) was 90% (70-100). Median number of brain metastasis was 8 (6-46). The median of the sum of the GTV volumes per patient was 6 cm3 (0.49-22.33 cm3), and the median of the sum of the PTV volumes 9.84 cm3 (1.54-33.18 cm3). Median prescribed dose was 32.5 (21-37.5) Gy, at a median isodose of 78% (65%- 89%), in a median number of 5 (1-5) fractions. Median estimated treatment delivery time was 74 (38-143) minutes, but the actual treatment time was reduced by about a third. Acute toxicity was observed in 3 patients and was limited to grade 1 neurological events represented by dizziness and paresthesia.

With a median follow up of 5 months (0.49-15.7 months), one patient developed symptomatic radionecrosis controlled with corticosteroids. Fourteen pts presented local control and four patients had progression/pseudoprogression of the lesions. Four pts had intracranial progression due to new lesions. Six pts were unavailable for follow up: 3 pts were dead for systemic progression, 1 patient died with heart failure two weeks after the treatment and 2 pts were lost to follow-up. At the last follow up, 11 pts were dead, 5 with systemic progression, 5 with intracranial progression and 1 with heart failure.

Conclusions: In our experience, concomitant robotic SRS/SRT for patients with multiple brain metastases is feasible with low toxicity and the possibility to repeat it as salvage treatment, but intracranial progression remains the main prognostic factor.