- Poor pulmonary function precluding radical radiation therapy (Adequate pulmonary reserve for radical radiation therapy. Pulmonary function tests should have forced expiratory volume in 1 second (FEV1) > 1.0 liter or > 40% predicted, diffusing capacity of the lung for carbon monoxide (DLCO) > 45% and/or predicted contralateral FEV1 > 800 cc based on quantitative ventilation perfusion lung scan).