Relevance of biologically equivalent dose values in outcome evaluation of stereotactic radiotherapy for lung nodules.

Abstract

Different biologically equivalent dose (BED) values associated with stereotactic radiotherapy (SRT) of patients with primary and metastatic pulmonary nodules were studied. The BED values were calculated for tumoral tissue and low alpha/beta ratio, assuming that better local response could be obtained by using stereotactic high-BED treatment. Fifty-eight patients with T1-T3 N0 non-small-cell lung cancer and 46 patients with metastatic lung nodules were treated with SRT. The BED was calculated for alpha/beta ratios of 3 and 10. Overall survival (OS) was assessed according to Kaplan-Meier and appraised as a function of three BED levels: low (30-50 Gy), medium (50-70 Gy), and high (70-98 Gy; alpha/beta = 10). The OS rates for all 104 patients at 12, 24, and 36 months were 73%, 48.3%, and 35.8%, respectively. Local response greater than 50% for low, medium, and high BED values was observed in 54%, 47%, and 73%, respectively. In the high-BED treated group, OS rates at 12, 24, and 36 months (80.9%, 70%, and 53.6%, respectively) were significantly improved compared with low- (69%, 46.1%, and 30.7%, respectively) and medium-BED (67%, 28%, and 21%, respectively) treated patients. Results are also discussed in terms of BED calculated on alpha/beta 3 Gy characteristic of the microcapillary bed. No acute toxicity higher than Grade 1 was observed. Radioablation of pulmonary neoplastic nodules may be achieved with SRT delivered by using a high-dose fraction with high BED value.