Early tumor response on 1-month CT as a predictor of 2-year local control following SBRT in pulmonary oligometastases: A multicenter retrospective study.

e20047 Background: Stereotactic body radiation therapy (SBRT) is a standard treatment for pulmonary oligometastases due to its high efficacy and low toxicity. Early tumor response on CT imaging may provide valuable prognostic insights. This study investigates the predictive value of early CT imaging features at 1-month follow-up for 2-year local control. Methods: This multicenter retrospective study analyzed 246 pulmonary oligometastatic lesions treated with SBRT between May 2018 and December 2022 across five centers: the Qingchun, Yuhang, and Zhijiang centers of the First Affiliated Hospital of Zhejiang University, and the Linhai and Enze centers of Taizhou Hospital. Early tumor response was assessed at 1-month follow-up CT and classified as favorable (partial/complete response) or unfavorable (stable/progressive disease) based on RECIST criteria. Predictors of local control were analyzed using Chi-square tests, and Kaplan-Meier (KM) estimates were used to calculate 2-year local control rates. Results: Of the 246 nodules, 216 achieved local control at 2 years, while 30 experienced recurrence. Significant predictors of local control included tumor size (≤20 mm, P < 0.001), higher BED10 (≥100 Gy, P = 0.022), and favorable early tumor response (P = 0.001). The KM-estimated 2-year local control rates were 95.0% for lesions with favorable early response and 81.1% for those with unfavorable response. Conclusions: Early tumor response observed at 1-month follow-up CT is a strong predictor of 2-year local control in pulmonary oligometastases treated with SBRT. Incorporating early imaging evaluations into follow-up protocols may enable timely intervention and improve patient outcomes. This study has been supported by the National Natural Science Foundation of China (82171890).