Purpose:This study aimed to determine the optimal fractions scheme(FS)in small peripheral non-small cell lung cancer(NSCLC)patients undergoing stereotactic body radiotherapy(SBRT)by comparing the therapeutic ratio(TR).Materials and Methods:CT simulation data for 16 patients diagnosed with primary NSCLC or metastatic tumor with a single peripheral lesion ≤ 3 cm were used in this study.Volumetricmodulated arc therapy(VMAT)plans were designed based on ten different FS of 1×25 Gy,1×30 Gy,1×34 Gy,3×15 Gy,3×18 Gy,3×20 Gy,4×12 Gy,5×12 Gy,6×10 Gy and 10×7 Gy,respectively.Five different radiobiological models were employed to predict the tumor control probability(TCP).Three other models were utilized to estimate the normal tissue complication probability(NTCP)to the lung and the modified equivalent uniform dose(mEUD)value to the chest wall(CW).Results:The radiobiological models revealed that TCP improved with increasing tumor biologically effective dose(BED).We also determined that larger number of fractions was associated with reduced toxicities to the lung and CW for equivalent tumor BED.We concluded that the 10×7 Gy regimen was the optimal dose schedule because it achieved the highest TR.