Dose-volume factors contributing to the incidence of radiation pneumonitis in non-small-cell lung cancer patients treated with three-dimensional conformal radiation therapy

Purpose: To analyze acute lung toxicity data of non-small-cell lung cancer patients treated with three-dimensional conformal radiation therapy in terms of dosimetric variables, location of dose within subvolumes of the lungs, and models of normal-tissue complication probability (NTCP). Methods and Materials: Dose distributions of 49 non-small-cell lung cancer patients treated in a dose escalation protocol between 1992 and 1999 were analyzed (dose range: 57.6-81 Gy). Nine patients had RTOG Grade 3 or higher acute lung toxicity. Correlation with dosimetric and physical variables, as well as Lyman and parallel NTCP models, was assessed. Lungs were evaluated as a single structure, as superior and inferior halves (to assess significance of dose to upper and lower lungs), and as ipsilateral and contralateral lungs. Results: For the whole lung, Grade 3 or higher pneumonitis was significantly correlated (p ≤ 0.05) with mean dose and Lyman and parallel model indices (d_eff and f_dam). It was significantly correlated with these indices and with V20 for the ipsilateral lung and with mean dose and d_eff for the inferior half of the lungs. Dosimetric and NTCP model quantities for the superior half of the lungs and contralateral lung were not significantly correlated (p > 0.5 for superior lung indices, and >0.1 for contralateral lung indices studied). Conclusions: For these patients, commonly used dosimetric and NTCP models are significantly correlated with ≥ Grade 3 pneumonitis. Equivalently strong correlations are found in the lower portion of the lungs and the ipsilateral lung, but not in the upper portion or contralateral lung.