Cyberknife ® stereotactic radiation therapy for stage I lung cancer and pulmonary metastases: evaluation of local control at 24 months.

Background: CyberKnife® stereotactic radiotherapy allows for minimally invasive treatment with satisfactory results in patients with inoperable primary or metastatic lung cancer. The objective of this study was to identify factors influencing the probability of local control.

Methods: Ninety-five patients (100 lung tumors) treated between January and December 2013 at our department by SBRT (stereotactic body radiation therapy) using CyberKnife® were included in the study. There were 71 stage T1 or T2 primary tumors and 29 secondary tumors. The tracking methods were as follow: fiducial markers with Synchrony® in 50 cases (gold seeds in 35, coils in 15 cases), spine with 4D-CT and Xsight® Spine in 43 cases, and direct viewing by Xsight® Lung in 7 cases. The methods were allocated according to the characteristics of each target.

Results: With a median follow-up of 24 months, the probability of local control at 24 months was 88%. The probability of local control differed according to the size of the target (92% for tumors ≤35 mm and 54% for tumors >35 mm: P=0.013) and according to the distance of the fiducial markers in relation to the target (95% when <50 mm and 69% when ≥50 mm: P=0.011).

Conclusions: The best results were obtained with small lesions. With Synchrony® , the distance of the target relative to the fiducial markers should be less than 50 mm. Gold seeds are recommended, although coils may be used instead of gold seeds. The number of fiducial markers did not have a significant impact on the probability of local control. With an appropriate tracking method, stereotactic radiotherapy is an efficient treatment for stage I lung cancer and lung oligometastases.