Lung: SABR fractionation

Why C is correct

In the CHISEL trial, peripheral lesions were treated with SABR delivering 54 Gy in three fractions, and lesions closer to the chest wall received 48 Gy in four fractions. This peripheral tumour is well away from the chest wall, so 54 Gy in three fractions is the appropriate schedule. CHISEL showed this improved freedom from local treatment failure versus conventional radiotherapy.

And why the others are not

• A66 Gy in 33 fractions is conventionally fractionated radiotherapy, one of the CHISEL standard-arm regimens that gave inferior local control, not SABR.
• B60 Gy in 8 fractions is a risk-adapted schedule used for central tumours, not the CHISEL peripheral schedule asked about here.
• D45 Gy in 30 twice-daily fractions is the CONVERT thoracic regimen for limited-stage SCLC, not a SABR schedule for early NSCLC.
• E50 Gy in 20 fractions is a conventional/hypofractionated standard-arm regimen, not the CHISEL SABR peripheral schedule.

Source CHISEL (TROG 09.02) - SABR versus standard radiotherapy in stage 1 NSCLC — Ball D, Mai GT, Vinod S, et al. Stereotactic ablative radiotherapy versus standard radiotherapy in stage 1 non-small-cell lung cancer (TROG 09.02 CHISEL): a phase 3, open-label, randomised controlled trial. Lancet Oncol. 2019;20(4):494-503.