Impact of 3D Conformal Radiotherapy on Lung Function of Patients with Lung Cancer: A Prospective Study

<b><i>Background:</i></b> The development of three-dimensional conformal radiotherapy (3D-RT) has enabled the restriction of the dose to normal lung, limiting radiation-induced lung injury. <b><i>Objectives:</i></b> This study was designed to describe the time course of lung function until 7.5 months after 3D-RT in patients with lung cancer, and assess the relationship between lung function changes and dose-volume histogram (DVH) analysis or computed tomography scan changes. Radiation doses were optimized according to recent guidelines. <b><i>Methods:</i></b> Sixty-five lung cancer patients treated with 3D-RT agreed to participate in this prospective, hospital-based study. Lung volumes, forced expiratory volume in 1 s (FEV₁) and diffusing capacity of the lung for carbon monoxide (DL<smlcap>CO</smlcap>) were measured before radiotherapy (RT), 10 weeks, 4 and 7.5 months after the beginning of 3D-RT. <b><i>Results:</i></b> Eleven lung cancer patients (17%) developed grade 2-3 respiratory symptoms after RT. At 7.5 months, vital capacity (VC) was 96 ± 2%, total lung capacity (TLC) 95 ± 2%, FEV₁ 93 ± 2% and DL<smlcap>CO</smlcap> 90 ± 2% of the initial value. Only 15% of patients showed pulmonary function reduction >20%. Patients with FEV₁ or DL<smlcap>CO</smlcap> <60% before RT did not show significant changes after RT. There were weak correlations between reduction of VC, TLC, FEV₁ or DL<smlcap>CO</smlcap> and radiation dosimetric parameters and between reduction of VC or FEV₁ and radiation-induced pneumonitis images. <b><i>Conclusions:</i></b> In lung cancer, the reduction of lung function within 7.5 months after 3D-RT was small and correlated, albeit weakly, with DVH parameters. Patients with initially impaired lung function showed tiny changes in spirometry and DL<smlcap>CO</smlcap> values.