EVALUATION OF 2 DOSE-VOLUME HISTOGRAM REDUCTION MODELS FOR THE PREDICTION OF RADIATION PNEUMONITIS

Purpose: To evaluate the similarities between the mean lung dose and t wo dose-volume histogram (DVH) reduction techniques of 3D dose distrib utions of the lung. Patients and methods: DVHs of the lungs were calcu lated from 3D dose distributions of patients treated for malignant lym phoma (44), breast cancer (42) and lung cancer (20). With a DVH reduct ion technique, a DVH is summarized by the equivalent uniform dose (EUD ), a quantity which is directly related to the normal tissue complicat ion probability (NTCP), Two DVH reduction techniques were used. The fi rst was based on an empirical model proposed by Kutcher et al. (Kutche r, G.J., Burman, C., Brewster, M.S., Goitein, M. and Mohan, R. Histogr am reduction method for calculating complication probabilities for thr ee-dimensional treatment planning evaluations. Int. J. Radiat. Oncol. Biol. Phys. 21: 137-146, 1991), which needs a volume exponent n. Sever al values for n were tested. The second technique was based on a radio biological model, the parallel functional subunit model developed by N iemierko et al. (Niemierko, A. and Goitein, M. Modeling of normal tiss ue response to radiation: the critical volume model. Int. J. Radiat. O ncol. Biol. Phys. 25: 135-145, 1993) and Jackson et al. (Jackson, A., Kutcher, G.J. and Yorke, E.D. Probability of radiation-induced complic ations for normal tissues with parallel architecture subject to non-un iform irradiation. Med. Phys. 20: 613-625, 1993): for which a local do se-effect relation needed to be specified. This relation was obtained from an analysis of perfusion and ventilation SPECT data. Results: It can be shown analytically that the two DVH reduction techniques are id entical, if the local dose-effect relation obeys a power-law relations hip in the clinical dose range. Local dose-effect relations based on p erfusion and ventilation SPECT data can indeed be fitted with a power- law relationship in the range 0-80 Gy, from which values of n = 0.8-0. 9 were deduced. These correspond to the commonly used value of n = 0.8 7 for lung tissue and yielded EUDn=0.87 values which were almost ident ical to the mean lung doses. For other n values, for which no experime ntal data are present, differences exist between EUD and mean dose val ues. Six patients with malignant lymphoma (6/44) and none of the breas t cancer patients (0/42) developed radiation pneumonitis. These cases occurred only at high values for the mean lung dose. Conclusion: The t wo DVH reduction techniques are identical for lung and are very simila r to mean dose calculations. The two techniques are also relatively si milar for other model parameter values. (C) 1998 Elsevier Science Irel and Ltd. All rights reserved.