Clinical Outcomes of CyberKnife Radiosurgery for Early Stage Lung Cancer: Low Chest Wall Toxicity Rates Associated with Tracking

Purpose/Objective(s): To report the efficacy and toxicity of CyberKnife stereotactic body radiotherapy (SBRT) for early stage non-small cell lung cancer (NSCLC) in patients treated at the University of North Carolina.Material/Methods: The records of patients with medically inoperable early stage NSCLC treated using the CyberKnife system with Synchrony fiducial tracking were retrospectively reviewed. The actuarial local control, distant metastasis-free survival, overall survival, and toxicity rates were calculated.Results: 52 consecutive patients treated between 9/2007 and 8/2011 for primary (n = 43) or recurrent (n = 9) early stage NSCLC were included. The median follow up was 19.2 months (range 3.6 - 44.6), and all living patients had at least 6 months of follow up. Mean age of the cohort was 71 years (range 42 - 87). Twenty patients were male and 32 were female. Mean maximum tumor dimension was 2.5 cm (range 0.8 - 4.8 cm) and 67% received 48 Gy in 4 fractions (mean prescription dose was 4950 cGy in 3.8 fractions [range 24 - 60 Gy]). Mean distance from GTV to the chest wall was 1.5 cm (14 lesions were 0-0.5 cm, 10 were 0.6-1.0 cm, 12 were 1.1 - 2.0 cm, and 16 were > 2.0 cm away).Fiducial placement resulted in pneumothorax in 17 patients (32.7%), and 11 of those (64.7%) required a chest tube and/or hospitalization. The actuarial local control, distant metastasis-free survival, and overall survival were 93%, 70%, and 82% at 1 year and 89%, 61%, and 61% at 2 years, respectively. One patient (2% of all patients and 3% of those with tumors within 2 cm of the chest wall) developed a rib fracture 8 months following treatment (her tumor was located 0.7 cm from the chest wall), and 3 patients (5.8%) experienced chest wall pain. Five patients (9.6%) developed grade 2 radiation pneumonitis. No patient had grade ≥ 3 toxicity as a result of radiation treatment.Conclusion: CyberKnife SBRT resulted in a high rate of local control and low rate of toxicity, offering patients with early NSCLC an important, non-surgical curative option. However, morbidity from fiducial marker placement is an important consideration in a patient population with limited respiratory reserve, and newer fiducial-less technologies need to be developed and further studied as a potential solution. The low rate of rib fracture in this experience (2%) compared to the published literature using linac-based stereotactic systems (8%; Andolino, et al. 2011) may be attributable to the CyberKnife’s ability to track the tumor throughout the respiratory cycle, thereby decreasing the delivered dose to the adjacent ribs. Whether different delivery systems of SBRT result in different disease control or morbidity outcomes needs to be prospectively studied.

MSRO22-07

Clinical Outcomes of CyberKnife Radiosurgery for Early Stage Lung Cancer: Low Chest Wall Toxicity Rates Associated with Tracking