Individualized Stereotactic Ablative Radiotherapy for Lung Tumors The iSABR Phase 2 Nonrandomized Controlled Trial

IMPORTANCE Stereotactic ablative radiotherapy (SABR) is used for treating lung tumors but can cause toxic effects, including life-threatening damage to central structures. Retrospective data suggested that small tumors up to 10 cm3 in volume can be well controlled with a biologically effective dose less than 100 Gy. OBJECTIVE To assess whether individualizing lung SABR dose and fractionation by tumor size, location, and histological characteristicsmay be associated with local tumor control. DESIGN, SETTING, AND PARTICIPANTS This nonrandomized controlled trial (the iSABR trial, so named for individualized SABR) was a phase 2 multicenter trial enrolling participants from November 15, 2011, to December 5, 2018, at academic medical centers in the US and Japan. Data were analyzed from December 9, 2020, toMay 10, 2023. Patients were enrolled in 3 groups according to cancer type: initial diagnosis of non-small cell lung cancer (NSCLC) with an American Joint Committee on Cancer 7th edition T1-3N0M0 tumor (group 1), a T1-3N0M0 new primary NSCLC with a history of prior NSCLC or multiple NSCLCs (group 2), or lungmetastases from NSCLC or another solid tumor (group 3). INTERVENTION Up to 4 tumors were treated with once-daily SABR. The dose ranged from 25 Gy in 1 fraction for peripheral tumors with a volume of 0 to 10 cm3 to 60 Gy in 8 fractions for central tumors with a volume greater than 30 cm3. MAIN OUTCOME Per-group freedom from local recurrence (same-lobe recurrence) at 1 year, with censoring at time of distant recurrence, death, or loss to follow-up. RESULTS In total, 217 unique patients (median [IQR] age, 72 [64-80] years; 129 [59%] male; 150 [69%] current or former smokers) were enrolled (some multiple times). There were 240 treatment courses: 79 in group 1, 82 in group 2, and 79 in group 3. A total of 285 tumors (211 [74%] peripheral and 74 [26%] central) were treated. The most common dose was 25 Gy in 1 fraction (158 tumors). The median (range) follow-up period was 33 (2-109) months, and the median overall survival was 59 (95% CI, 49-82) months. Freedom from local recurrence at 1 year was 97%(90% CI, 91%-99%) for group 1, 94%(90% CI, 87%-97%) for group 2, and 96%(90% CI, 89%-98%) for group 3. Freedom from local recurrence at 5 years ranged from 83% to 93% in the 3 groups. The proportion of patients with grade 3 to 5 toxic effects was low, at 5%(including a single patient [1%] with grade 5 toxic effects). CONCLUSIONS AND RELEVANCE The results of this nonrandomized controlled trial suggest that individualized SABR (iSABR) used to treat lung tumors may allow minimization of treatment dose and is associated with excellent local control. Individualized dosing should be considered for use in future trials.

Automated summary

Stereotactic ablative radiotherapy (SABR) can be individualized based on tumor size, location, and histological characteristics to achieve excellent local control for lung tumors. This nonrandomized controlled trial suggests that individualized SABR may allow minimization of treatment dose and reduce toxic effects.