Individualized Stereotactic Ablative Radiotherapy (iSABR) for Lung Tumors

Individualized Stereotactic ablative radiotherapy (iSABR) used for managing lung tumours allows minimization of treatment dose and is tied to excellent local control, according to an Original Investigation published on September 14, 2023, in JAMA Oncology.

This study, “Individualized Stereotactic Ablative Radiotherapy for Lung Tumors: The iSABR Phase 2 Nonrandomized Controlled Trial”, is led by lead author Dr. Michael F. Gensheimer, MD, and co-author Harriet Gee, MD, PhD, and colleagues.

SABR is used for the management of lung tumors. However, it has toxic effects and can cause life-threatening damage to central structures. Based on insights from retrospective data, researchers say that small tumors up to 10 cm³ in volume are well controlled with a biologically effective dose of less than 100 Gy.

Is there an association between individualizing dose and fractionation of SABR by tumor size, location, histological characteristics, and local control in lung tumor management?

This was studied in the present nonrandomized controlled trial in which participants were enrolled from November 15, 2011, to December 5, 2018, at academic medical centres in the US and Japan.

Study Groups

• Group 1: Initial non–small cell lung cancer (NSCLC) diagnosis with an American Joint Committee on Cancer 7th edition T1-3N0M0 tumor.
• Group 2: T1-3N0M0 new primary NSCLC with a history of prior NSCLC or multiple NSCLCs.
• Group 3: Lung metastases.

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.

The primary outcome was per-group freedom from local recurrence at one year, with censoring at the time of distant recurrence, death, or loss to follow-up.

Key Findings

• The study had 217 unique patients with a median age of 72 years, including 59% male. These were followed up for 33 months.
• 69% were current or former smokers.
• The treatment courses in groups 1, 2, and 3 were 79, 82, and 79, respectively. [Total 240]
• Two hundred-eleven peripheral tumors and 74 central tumors, constituting 74% each, were treated with 285 tumors.
• 25 Gy in 1 fraction was the most common dose.
• The median overall survival was 59 months.
• Freedom from local recurrence at one year for groups 1, 2, and 3 was 97%, 94%, and 96%, respectively.
• In the three groups, freedom from local recurrence at five years was in the range of 83% to 93%.
• 5% of patients presented with grade 3 to 5 toxic effects. This proportion was low.
• A single patient had a grade 5 toxic effect.
• An individualized dosing regimen, including doses lower than those routinely administered, presents with excellent tumor control.

Based on the results from this study, iSABR allows the minimization of treatment doses for managing lung tumors and has excellent local control.

For further investigations and future trials, consideration should be given to individualized dosing.

Further Reading

Gensheimer MF, Gee H, Shirato H, et al. Individualized Stereotactic Ablative Radiotherapy for Lung Tumors: The iSABR Phase 2 Nonrandomized Controlled Trial. JAMA Oncol. Published online September 14, 2023. doi:10.1001/jamaoncol.2023.3495