CyberKnife(®) stereotactic radiation therapy for stage I lung cancer and pulmonary oligometastases: is fiducial implantation still relevant?—a cohort study

BACKGROUND: Few studies have investigated whether there is a difference in local control or overall survival rates following treatment with robotic stereotactic body radiation therapy (SBRT) with or without prior fiducial marker implantation. Our study aimed to investigate this in patients with primary or secondary lung tumors. METHODS: A retrospective study was conducted at the Institut de Cancérologie de Lorraine of patients treated for primary lung cancer or pulmonary oligometastases with SBRT from January 2013 to July 2016. We included patients at least 18 years old who had stage I non-small cell lung cancer (NSCLC) or lung metastases and a follow-up of at least 1 month. RESULTS: A total of 294 patients were included. Tumors included 122 lung metastases, 89 stage I NSCLC, and 83 non-histologically confirmed lung lesions. The tracking methods were Synchrony(®) in 191 cases (119 gold seeds and 72 coils) and Xsight(®) Spine with 4D computed tomography in 103 cases. Median follow-up was 31.6 months [interquartile range (IQR), 18.1–50.2 months]. The two- and five-year probability of local control were respectively 92.22% [95% confidence interval (CI): 0.89–0.95] and 85.35% (95% CI: 0.79–0.99). The two- and five-year probability of overall survival were respectively 87.46% and 72.77% (P=0.586). Local control rates did not significantly differ between techniques at 2 and 5 years (P=0.685) (gold seeds, coils or Xsight(®) Spine) within tumors grouped by location, gross tumor volume (GTV) (respectively P=0.9, P=0.7, and P=0.4), planning target volume (PTV) (respectively P=0.4, P=0.9, and P=0.7), or PTV/GTV ratio (respectively P=0.6, P=0.6, and P=0.5). Metastasis-free survival and Overall survival rates did not significantly differ between techniques at 2 and 5 years (P=0.664 and P=0.586, respectively). There were no grade 4 or 5 toxicities and only one grade 3 pneumonitis and one grade 3 pneumothorax. CONCLUSIONS: Fiducial-less SBRT using Xsight(®) Spine is a safe alternative to Synchrony(®) using gold seeds or coils, with comparable local control and overall survival rates and a similar toxicity profile.