Cyberknife

Three platforms were used: Cyberknife™, Varian Trilogy™, and Truebeam™ STX (11 (link)). Cyberknife™ uses a compact 6-MV linear accelerator mounted on a computer-controlled robotic arm with six rotation axes that permit the use of 1200 treatment positions, of which 80–120 are usually necessary to treat most lesions. Throughout the treatment delivery, two orthogonally positioned diagnostic x-ray cameras provide images of the patient’s anatomy. Bony landmarks or implanted fiducial markers were used to compare the patient’s planning CT to allow for continuous adjustment (intra-fraction correction) based on the patient’s positioning (12 (link)). For Varian Trilogy™ and Truebeam™ STX, a cone-beam CT was acquired and pre-treatment shifts were made to match the planning scan after immobilization of the patient and isocentric set-up. Via beam modulation and occasionally using RapidArc™ technology, dose is delivered both efficiently and conformally (13 (link), 14 (link)). For the 40 locally advanced or recurrent malignant skull base tumors (SBT) in our study, 26 were treated with Cyberknife™, 8 were treated with Varian Trilogy™, and 6 were treated with Truebeam™ STX.

RT-CT included one induction cycle with cisplatin 80 mg/m² at D1 and oral vinorelbine (Navelbine^®) 60 mg/m² at D1 and D8, followed by cisplatin 80 mg/m² at D22, D43 and D64 during irradiation and oral vinorelbine 40 mg/m² at D22, D29, D43, D50, D64, and D71. RT delivered 66 Gy from D22 in 33 fractions (2 Gy per session; 5 sessions per week) on mediastinal and hilar lymph node involvement without treating the peripheral tumor.
SBRT for primary peripheral tumor started within 3–4 weeks after the end of RT-CT and delivered 54 Gy in 3 fractions at D1, D3, and D5. SBRT was delivered either with a dedicated accelerator (Cyberknife^®, Vero^®) or a LINAC (VersaHD^® Elekta, TrueBeam^® Varian, Stockholm, Sweden. Patients treated with Cyberknife^® and Vero^® benefited from tumor tracking, which allowed to reduce the dose to healthy lungs and normal tissues. For the LINAC treatment, multiple (10 to 12) coplanar conformational small fields or VMAT^® (Volumetric Modulated Arc Therapy) were used. For tumor of the lower lobes, abdominal compression (Bodyframe^®) was used for reducing the amplitude of respiratory movements. In case of pulmonary or esophageal toxicity of grade ≥3 or tumor progression (>5 cm) preventing timely completion of SBRT, the patient discontinued the study.