To determine lung dosimetric constraints that correlate with radiation pneumonitis in non-small-cell lung cancer patients treated with three-dimensional radiation therapy and concurrent chemotherapy.

Between June 2002 and December 2006, 97 patients with locally advanced non-small-cell lung cancer were treated with concomitant radiochemotherapy. All patients underwent complete three-dimensional treatment planning (including dose-volume histograms), and patients were treated only if the percentage of total lung volume exceeding 20 Gy (V(20)) and 30 Gy (V(30)), and mean lung dose (MLD) had not exceeded the constraints of 31%, 18%, and 20 Gy, respectively. The total and ipsilateral lung dose-volume histogram parameters, planning target volume, and total dose delivered were analyzed and correlated with pneumonitis incidence.

If dose constraints to the total lung were respected, the most statistically significant factors predicting pneumonitis were the percentage of ipsilateral lung volume exceeding 20 Gy (V(20)ipsi), percentage of ipsilateral lung volume exceeding 30 Gy (V(30)ipsi), and planning target volume. These parameters divided the patients into low- and high-risk groups: if V(20)ipsi was 52% or lower, the risk of pneumonitis was 9%, and if V(20)ipsi was greater than 52%, the risk of pneumonitis was 46%; if V(30)ipsi was 39% or lower, the risk of pneumonitis was 8%, and if V(30)ipsi was greater than 39%, the risk of pneumonitis was 38%. Actuarial curves of the development of pneumonitis of Grade 2 or higher stratified by V(20)ipsi and V(30)ipsi were created.

The correlation between pneumonitis and dosimetric constraints has been validated. Adding V(20)ipsi and V(30)ipsi to the classical total lung constraints could reduce pulmonary toxicity in concurrent chemoradiation treatment. V(20)ipsi and V(30)ipsi are important if the V(20) to the total lung, V(30) to the total lung, and mean lung dose have not exceeded the constraints of 31%, 18%, and 20 Gy, respectively.