Pulmonary oligometastases treated by stereotactic body radiation therapy (SBRT): a single institution’s experience

BACKGROUND: To investigate the effect of stereotactic body radiation therapy (SBRT) on pulmonary oligometastases and to analyze the clinical factors and dose parameters affecting local recurrence-free survival (LRFS) and overall survival (OS). METHODS: This study retrospectively enrolled a total of 84 patients (148 lesions) treated in our department from May 2015 to November 2018. Pulmonary oligometastases was defined as up to 5 metastatic lesions in the lung and with both the primary tumor and any extra-thoracic metastases being controlled. Patients receiving a BED(10) (biological effective dose, α/β =10) of SBRT ≥75 Gy and a dose/fraction ≥4 Gy were enrolled. The patient group consisted of 52 men (61.9%) and 32 women (38.1%), with a median age 56 years (range, 29–80 years). Median tumor diameter was 1.71cm (range, 1.2–5.0 cm). The BED(10) was 75–119 Gy in 4–15 fractions. Univariate and multivariate Cox regression analyses were performed on factors predicting the outcomes. RESULTS: All patients completed the treatment as planned, and the median follow-up time was 20.3 months. The median OS for the entire group was 34.3 months, with an actuarial 1-, 2-, 3- and 5-year OS of 74.7%, 59.4%, 49.7%, and 36.8%, respectively. Among the 148 lesions in the whole group, 19 (12.8%) lesions had local recurrence (LR). The median LRFS time for all patients was 56.9 months. The LRFS rate was 93.6%, 83.5%, 81.4%, and 76.6% at 1, 2, 3, and 5 years, respectively. No patient developed acute grade 3 or 4 toxicity. On univariate analysis, age ≥63 years old, primary site of colorectal cancer, BED(10) <85.2 Gy, pathological type of adenocarcinoma, planning target volume (PTV) min BED(10) <76.6 Gy, and gross tumor volume (GTV) ≥8.8 cc, were significantly associated with poorer LRFS. Multivariate analysis showed that age ≥63 years old, primary site of colorectal cancer, and PTV min BED(10) <76.6 Gy were significant risk factors affecting LRFS. CONCLUSIONS: SBRT is feasible for pulmonary oligometastasis with favorable local control and minimal toxicity. Multiple dose parameters, instead of a prescription dose only, in combination with clinical parameters, should be considered for optimal local control.