Stereotactic Intracranial Ablative Radiation Therapy For Brain Metastases With A Mono-Isocenter No-Coplanar Dedicated System: A Preliminary Dosimetric And Clinical Report

Brain metastases (BMs), the most common intracranial tumors in adults, affect approximately 20–40% of cancer patients. The focal irradiation approach for BMs, including Stereotactic Radiotherapy (SFRT) or Radiosurgery (SRS) is emerging as a large utilized treatment option, also for multiple BMs. Aim of the present study is to evaluate safety and effectiveness of SRS/SFRT for BMs, using a new mono-isocenter technique with multiple non-coplanar arcs. Patients aged >18 years with a diagnosis of BMs with a diameter < 3 cm, a life expectancy more than 3 months, and Karnosky Performance Status (KPS) ≥ 70 were eligible for SFRT/SRS with mono-isocenter technique with multiple non-coplanar arcs. Gross Tumor Volume (GTV) was delineated by the fusion between Magnetic Resonance Imaging (MRI) and Computed Tomography. A Planning Target Volume (PTV) was obtained from GTV by adding a 2-mm isotropic margin. The prescribed dose (Dp) ranged between 15-27 Gy in 1-3 fractions, based on dimension and anatomical location of BMs. For each patient, a mono-isocenter volumetric modulated arc therapy plan was generated with 5 non-coplanar 180°-arcs (couch at 0°, ±45°, ±90°). Corticosteroids were administered for all patients during SFRT/SRS. From August 2017 to December 2017, 48 patients with 210 BMs were irradiated with mono-isocenter technique with multiple non-coplanar arcs SRS/SRT. The median number of BMs for each patient was 5 (range 1-21). With a median follow-up time of 3 months (range 2-6 months), 153 out 210 BMs were here analysed. From a clinical point of view, 99.3% of BMs (152 out 153 lesions) were controlled at first MRI evaluation (60 days after treatment): 21 BMs, 13.7%, had a complete response; 88BMs, 57.5%, a partial response, 43BMs, 28.1% a stable disease, while only 1 lesion progressed at first follow-up (0.7%). At 5 months from treatment, 29/153 BMs were evaluated: only 1 lesion progressed (3.5%), while 13.8% showed a complete response, 75.8% a partial response and 6.9% a stable disease. No correlation was found between disease response and RT dose (single fraction vs 3 fraction, p=0.2) No acute toxicity, in terms of nausea or vomiting or headache, were registered during treatment. Ten patients out 30 showed intracranial progression. In terms of dosimetric findings, the mean average value of BMs PTV was 8.6 cc (range 0.5-27.9 cc); the mean dose to the brain-minus-PTV was 2.78 Gy and the V12 (volume of brain that received 12Gy) was 19.9 cc. The total treatment time for each session was 13 minutes. The present data showed that a mono-isocenter technique with multiple non-coplanar arcs is safe for BMs patients. Preliminary data showed 99% of disease control at 3 months. The clinical role of SFRT/SRS for multiple BM (more than 4) remains controversial and should be explored in randomized trial.