DOSE-VOLUME HISTOGRAM AND 3-D TREATMENT PLANNING EVALUATION OF PATIENTS WITH PNEUMONITIS

Purpose: Tolerance of normal lung to inhomogeneous irradiation of part ial volumes is not well understood. This retrospective study analyzes three-dimensional (3-D) dose distributions and dose-volume histograms for 63 patients who have had normal lung irradiated in two types of tr eatment situations. Methods and Materials: 3-D treatment plans were ex amined for 21 patients with Hodgkin's disease and 42 patients with non small-cell lung cancer. All patients were treated with conventional fr actionation, with a dose of 67 Gy (corrected) or higher for the lung c ancer patients. A normal tissue complication probability description a nd a dose-volume histogram reduction scheme were used to assess the da ta. Mean dose to lung was also calculated. Results: Five Hodgkin's dis ease patients and nine lung cancer patients developed pneumonitis. Dat a were analyzed for each individual independent lung and for the total lung tissue (lung as a paired organ). Comparisons of averages of mean lung dose and normal tissue complication probabilities show a differe nce between patients with and without complications. Averages of calcu lated normal tissue complication probabilities for groups of patients show that empirical model parameters correlate with actual complicatio n rates for the Hodgkin's patients, but not as well for the individual lungs of the lung cancer patients treated to larger volumes of normal lung and high doses. Conclusion: This retrospective study of the 3-D dose distributions for normal lung for two types of treatment situatio ns for patients with irradiated normal lung gives useful data for the characterization of the dose-volume relationship and the development o f pneumonitis. These data can be used to help set up a dose escalation protocol for the treatment of nonsmall-cell lung cancer.