Correlation of dosimetric factors and radiation pneumonitis for non-small-cell lung cancer patients in a recently completed dose escalation study

Purpose: To determine dosimetric factors for lung, lung subregions, and heart that correlate with radiation pneumonitis (Radiation Therapy Oncology Group Grade 3 or more) in the 78 evaluable patients from a Phase I dose escalation study (1991-2003) of three-dimensional conformal radiation therapy (3D-CRT) of non-small-cell lung cancer. Methods and Materials: There were 10 <Grade 3 pneumonitis cases within 6 months after treatment. Dose-volume factors analyzed for univariate correlation with <Grade 3 pneumonitis were mean dose (MD), effective uniform dose (d_eff), normal tissue complication probability (NTCP), parallel model f_dam and V _D for 5 ≤ D ≤ 60 Gy for whole, ipsilateral, contralateral, upper and lower halves of the lungs and heart D₀₅, and mean and maximum doses. Results: The most significant variables (0.005 < p < 0.006) were ipsilateral lung V_D for D <20 Gy. Also significant (p < 0.05) for ipsilateral lung were V_D for D <50 Gy, MD, f _dam and d_eff; for total lung V_D (D <50 Gy), MD, f_dam, d_eff and NTCP; for lower lung V_D (D <60 Gy), MD, f_dam and d_eff. All variables for upper and contralateral lung were insignificant, as were heart variables. Conclusions: Previously reported correlations between severe pneumonitis and whole lung V₁₃ and with other dose-volume factors of total lung and lower lung are confirmed. The most significant correlations were for (V₀₅-V ₁₃) in ipsilateral lung.