Correlation of biologically effective dose and the tumor control in Stage I (<5 cm) non-small cell lung cancer with stereotactic ablative radiotherapy: a single institutional cohort study.

Backgrounds: Stereotactic ablative radiotherapy (SABR) is one of the newly developed innovative radiotherapy and of which optimal dose prescription needs to be standardized. We aimed to investigate the dose-response relationship for patients with SABR.

Methods: Fifty-three patients with Stage I non-small cell lung cancer patients, who underwent SABR between November 2006 and January 2015, were evaluated retrospectively. Thirteen patients (24.5%), who refused the surgery were included and 40 patients (75.5%) were medically inoperable at diagnosis. The median age was 74 years. The median SABR dose was 50 Gy in 3-8 fractions and the median biologically effective dose (BED;α/β = 10) was 105.6 Gy (range: 60-160.53 Gy).

Results: The median follow-up was 37.1 months. The 1 and 3 year local control rates were 91.7% and 85.1%. The 3 year overall and progression-free survival rate were 63.3% and 47.5%, respectively, and freedom from progression was 62.2%. Local control rate and 3-year overall survival according to tumor size was 100% and 79.4% in T1 tumors in a while 61.8% and 45% in T2a tumors. The 3-year local and regional control by BED10 was 79.4% and 69.4% in ≤100 Gy vs. 89.1% and 100% in >100 Gy (P = 0.526, 0.004). Dyspnea more than Grade 3 was reported in six (11.3%) patients and Grade 1 chest pain was shown in five (9.4%) patients.

Conclusions: The excellent regional control was conferred with a prescription of more than BED10 of 100 Gy, which also might be needed to achieve better local tumor control in T2a patients with tolerable lung function.