2381 - Real-World Outcomes of Single-Fraction Stereotactic Ablative Radiotherapy (SF-SABR) for Oligo-Persistent, Progressive, or Recurrent Primary and Metastatic Lung Tumors

Purpose/Objective(s): SF-SABR has shown robust local control (LC) and acceptable safety in trials for early-stage primary lung cancer and lung oligo-metastases. In clinical practice, its logistical advantages have extended its use to more advanced cases. We performed a multi-site, single-institution retrospective study to validate the efficacy and safety of SF-SABR in a broader patient(pt) cohort.

Materials/Methods: Pts with oligo-persistent, oligo-progressive, or oligo-recurrent primary and metastatic lung tumors treated with SF-SABR at two institutional sites from 2021/1 to 2024/7 were retrospectively identified. SF-SABR was delivered at a median dose of 30 Gy (range, 24–34 Gy). Local failure (LF) and regional failure (RF) were analyzed using competing risk models (with death as a competing event) and overall survival (OS) by the Kaplan–Meier method. Toxicities were graded per CTCAE v4.0. Gray’s test was used to compare subgroups, and uni- and multivariable logistic regression were used to assess toxicity predictors.

Results: 126 pts with 157 tumors were analyzed, with a median follow-up of 18.9 months(mos) (range, 1.6-48). Median age was 68 years (range, 36-94), with 55% female and 27% had smoking history. Oncogenic mutations were found in 83%. The most common primary site was lung (n=111, 70% EGFR-mutated). 60% had concomitant targeted therapy. 19% had multiple lesions. 62% were treated for metastatic disease. Median tumor size was 1.6 cm (range, 0.4–3.7), while 84% were peripheral and 61% received 30 Gy. At analysis, 19 pts (20 tumors) had LF and 20 pts had died. The cumulative incidence of LF was 5.6% (95% CI: 1.2-10%) at 12 mos and 19.6% (95% CI: 11-28.2%) at 24 mos; RF was 43.8% (95% CI: 34.7-52.9%) at 12 mos and 68.5% (95% CI: 59.1-78%) at 24 mos; OS was 90.3% (95% CI: 85-96%) at 12 mos and 83.2% (95% CI: 75.6-91.5%) at 24 mos. Grade 2 or higher pulmonary toxicity occurred in 19 pts (15%), with 3 grade 5 events. All 3 pts had concomitant conditions deemed unrelated to SF-SABR (2 pneumonia, 1 pulmonary embolism). Subgroup analyses showed no significant LF differences by tumor size, dose, location, systemic therapy, primary site, smoking status, or target number. Among lung pts with EGFR data, those with mutations trended toward higher LF (p = 0.16). Univariable logistic regression showed that multiple targets was associated with higher odds ratio (OR) of grade 2 or higher lung toxicity (OR = 21.8, p = 0.038); this association was attenuated in multivariable analysis (OR = 2.43, p = 0.15).

Conclusion: SF-SABR provides favorable LC, OS, and toxicity outcomes in a real-world pt cohort. A trend toward inferior LC in EGFR-mutated lung cancer and greater toxicity in pts with multiple targets warrants further investigation. These results support the broader application of SF-SABR for oligo-persistent, progressive, or recurrent lung tumors.