Exploratory Analysis on Local Control of Stereotactic Radiotherapy for Lung Metastases from Colorectal Cancer

To identify the high-risk factors that affect the local control of colorectal cancer (CRC) patients with lung metastases treated with stereotactic body radiotherapy (SBRT). Patients with lung metastases of CRC undergoing SBRT at our center were included in this retrospective review. Local control (LC) according to treatment was calculated using the Kaplan-Meier method and compared using the Log-rank test, and the relationship between oncology parameters, prescribed dose and local recurrence was assessed. A total of 53 patients with 105 lesions confined to lung and treated from 2012 to 2018 were involved in this retrospective review. The median biologic effective dose (BED) was 100Gy (range, 75-131.2Gy), and the median period from SBRT to the first radiology evaluation was 1.8 month (range, 0.5-8.0 month), while 27 lesions achieved complete response (CR). The second/third radiology examination (with the median period of 5.3 month, ranging from 1.9-12.5 month) showed that 51 lesions achieved CR. At last, 10 lesions suffered local relapse after SBRT, and 9 of them occurred within 8 months post SBRT. The median follow-up time for all patients was 14 months (range, 5-63 months), and 1-year local control was 90.4%. Univariate analyses showed BED (≥100 Gy Vs. < 100 Gy, 96.3% vs 80.6%; P=0.003), volume of GTV (≥1.5cc Vs. < 1.5cc, 100% vs. 82.7%; P=0.011), and max diameter of the tumor (≥10mm Vs. < 10mm, 100% vs. 84.5%; P=0.006) could influence the 1-year local control. During the last follow-up, 4 patients suffered Grade 2 radiation pneumonitis, and no Grade 3-4 toxicity was observed. SBRT provides favorable local control in CRC patients with lung metastases, and radiology examinations nearly 5 months after radiotherapy might predict the final local effect of SBRT. BED ≥ 100 Gy or small size tumor may be associated with local control although further research was needed.