Image-Guided Robotic Stereotactic Radiation Therapy with Fiducial-Free Tumor Tracking for Lung Cancer

PURPOSE Stereotactic body radiation therapy (SBRT) for early-stage lung cancer can be achieved with several methods: respiratory gating, body frame, or real-time target and motion tracking. Two target tracking methods are currently available with the CyberKnife® System: the first one, fiducial tracking, requires the use of radio-opaque markers implanted near or inside the tumor, while the other, Xsight® Lung Tracking System, (XLTS) is fiducial-free. With XLTS, targeting is synchronized directly with target motion, which occurs due to respiration. While the former method (fiducial tracking) is well documented, the clinical relevance of the latter (tracking without fiducials) has never been well described to this date. PATIENTS AND METHODS A study was performed at our department for each patient treated for lung cancer with CyberKnife using XLTS. Selection criteria were: primary or recurring T1 or T2 stage non-small-cell lung cancer (NSCLC) with 15-60 mm tumor size. Initial staging included CT-Scan and FDG-PET. RESULTS Fifty-one patients not amenable to surgery were treated with XLTS. Median follow-up was 15 months (range, 5-30 months). Median tumor size was 24 mm (range, 15-60 mm). Median total dose was 60 Gy (36-60 Gy) in three fractions. Actuarial overall survival was 85.5% (95% CI = 74.5-96%) at 1 year and 79.4% (95% CI = 64-94.8%) at 2 years. Actuarial local control rate was 92% (95% CI = 84-99%) at one 1 year and 86% (95% CI = 75-97%) at 2 years. CONCLUSION Local control and overall survival rates were similar to previous reports that used fiducials for tumor tracking. Toxicity was lower than most studies since tumor tracking did not require fiducial implantion. This fiducial-free method for respiratory motion tracking is a valid option for the most fragile patients.