Adding Ipsilateral V20 and V30 to Conventional Dosimetric Constraints Predicts Radiation Pneumonitis in Stage IIIA-B NSCLC Treated With Combined-Modality Therapy

Purpose: 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. Methods and Materials: 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 (V₂₀) and 30 Gy (V₃₀), 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. Results: 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 (V₂₀ipsi), percentage of ipsilateral lung volume exceeding 30 Gy (V₃₀ipsi), and planning target volume. These parameters divided the patients into low- and high-risk groups: if V₂₀ipsi was 52% or lower, the risk of pneumonitis was 9%, and if V₂₀ipsi was greater than 52%, the risk of pneumonitis was 46%; if V₃₀ipsi was 39% or lower, the risk of pneumonitis was 8%, and if V₃₀ipsi was greater than 39%, the risk of pneumonitis was 38%. Actuarial curves of the development of pneumonitis of Grade 2 or higher stratified by V₂₀ipsi and V₃₀ipsi were created. Conclusions: The correlation between pneumonitis and dosimetric constraints has been validated. Adding V₂₀ipsi and V₃₀ipsi to the classical total lung constraints could reduce pulmonary toxicity in concurrent chemoradiation treatment. V₂₀ipsi and V₃₀ipsi are important if the V₂₀ to the total lung, V₃₀ to the total lung, and mean lung dose have not exceeded the constraints of 31%, 18%, and 20 Gy, respectively.